tranning in " 220 kv GSS ALWAR "

“220 KV GRID SUBSTATION ALWAR”

A

SUMMER TRANNING REPORT

SUBMITTED

To

Rajasthan Technical University

In partial fulfillment  for the award of the Degree of

BACHELOR OF TECHNOLOGY

In

ELECTRICAL ENGINEERING

ACADEMIC SESSION 2011 – 2012

  Submitted To:                                                                    Submitted By:

  Mr. MANISH GUPTA                                                       SHAKTI SINGH

  LECTURER .                                                                    08ELDEE055

  ELECTRICAL DEPARTMENT                             ELECTRICAL

                                                                                             B.TECH 7^TH SEM  

                                                                                                                                         

          DEPARTMENT OF ELECTRICAL ENGINEERING

LAXMI DEVI INSTITUTE OF ENGINEERING & TECHNOLOGY

Alwar (Rajasthan)-301028

 ACKNOWLEDGMENT

I would like express my knowledgement for valuable cooperate rendered by Mr. N. K.  Garg (X En), Mr.  AlokSinha (A En) and Ms. HonnyChaudhary (J En), who prided me various facilities and lot of knowledge about GSS and its different parts during my training session I would like to express my thanks to staff members, technicians of GSS Alwar, who all co-operated me for setting the knowledge of various equipments and their operations And A very special thanks to Mr. AlokSinha Sir, who encouraged us in training session .

i would also like to thanks to mr.Mukesh Mathur(HOD) & mr.Kamal Arora(sr. lecturer) for their valuable cooperate.

           

 SHAKTI SINGH

 Electrical Engineering

 LIET, Alwar

                     

CONTENTS

      I.        ACKNOWLEDGEMENT                                                                                         I.  

    II.        CONTENTS                                                                                                  II.

   III.        LIST OF FIGURES                                                                                                  IV.

  IV.        ABUSTRACT                                                                                                 VI.

Chapter-1 INTRODUCTION                                                                                             1-3                      1.1 An Overview of R.S.E.B.                                                                      1

               1.2 An Overview of Grid Sub Stations                                                       3          

Chapter-2 gss  fOR  practical training                                                           4-8                       2.1 Constructional Features                                                                          5

                2.2  Single line diagram                                                                                     6

Chapter-3 Equipments used in G.S.S.                                                                   9-12  

Chapter-4 LIGHTNING ARRESTOR                                                                           13-17

               4.1 Introduction                                                                                       14

               4.2 Ratings of a LA.                                                                                           16

Chapter-5 CAPACITIVE  VOLTAGE  Transformer                                             17-18

Chapter-6 POTENTIAL  Transformer                                                                    19 Chapter-7 ISOLATOR                                                                                          20-22

Chapter-8 WAVE TRAP                                                                                           23-24

Chapter-9 CIRCUIT BREAKER                                                                                   25-35                     9.1Construction of  Air Blast Circuit Breaker                                              36

               9.2 Oil Circuit Breaker                                                                             28

               9.3  SF6 Circuit Breaker                                                                            30

               9.4  Vacum Circuit Breaker                                                                       34

Chapter-10 CURRENT TRANSFORMER                                                                   36-38

Chapter-11 bus bar SYSTEM                                                                                     39-40 Chapter-12 TRANSFORMER                                                                                        41-54                  12.1 Construction of a Transformer                                                                       41                        12.2 Working of a Transformer                                                                           43       

               12.3  Winding                                                                                             45

               12.4  Transformer oil                                                                                  46

               12.5 New ISI for  oil                                                                                    48

               12.6  Tapping & Tap changer                                                                     54                     

Chapter-13 Protection of transformers                                                  55-56    

               13.1 MERZ-PRICE protection                                                                            55

               13.2 FIRE protection                                                                                            56 Chapter-14  RELAY                                                                                                  57-59

               14.1  types of relay                                                                                      57

               14.2  Working of relay                                                                                 58

Chapter-15 INSULATOR                                                                                          60-61

Chapter-16 EARTHING                                                                                            62-63

Chapter-17 POWER LINE CARRIER COMMUNICATION                                      64-71

               17.1   EQUIPMENT USED                                                                         65

               17.2  BASIC PRINCIPLE                                                                            66

               17.3 COUPLING CAPACITOR                                                                   68

               17.4 ADVANTAGE & DISADVANTAGE                                                     69

Chapter-18  CONTROL ROOM                                                                                       72-74

Chapter-19  BATTERY ROOM                                                                                 75-76

Chapter-20  CAPACITOR BANK                                                                             77-78         

               DAILY DIARY                                                                                                        79-80

List of Figures

Fig.1.1  Graphical view of R.S.E.B.                                                                       2

Fig.2 1  220 KV g.s.S.ALWAR - A View                                                           4

Fig.2.2   SINGLE LINE DIAGRAM                                                                       7

Fig.4.1    LIGHTNING ARRESTER.                                                                             14

Fig 4.2 : L.A.in alwar g.s.s.                                                                                15

Fig.5.1    C.V.T. in ALWAR G.S.S.                                                                                   17

Fig. 6.1 Potential Transformer                                                                              19

Fig. 7.1: ISOLATOR                                                                                                  20

Fig.7.2: isolator in G.S.S. ALWAR                                                                     21

FIG. 8.1 LINE MATCHING FILTER & PROTECTIVE EQUIPMENTS                       24

Fig9.1 AIR BLAST CIRCUIT BREAKER              .                                                    26

Fig. 9.3 OIL CIRCUIT BREAKER                                                                              29

Fig. 9.6 SF6 CIRCUIT BREAKER                                                                             31

Fig. 9.7 VACUM CIRCUIT BREAKER                                                                       34

Fig 10.1 current transformer  single line diagam                                                       36

Fig. 10.2 CURRENT TRANSFORMER                                                                      37

Fig. 10.3 A set of Current transformer                                                                        38

Fig. 11.1 busbar                                                                                                         39

Fig. 12.1: An ideal transformer                                                                      41

Fig. 12.2 winding                                                                                                                   43

Fig. 12.3 220/132KV,100MVA,Power Transformer                                                    45

Fig. 12.5 TERMINAL ARRANGEMENT                                                                     50

Fig. 13.1: MERZ-PRICE PROTECTION RELAY                                                        55

Fig.14.1: BUCHHOLZ RELAY                                                                                    59

Fig.14.2: OVER CURRENT INDUCTION RELAY                                                      59

Fig 14.1 INSULATORS                                                                                              60

Fig16.1: Basic Power Line Carrier Terminal                                              65

Fig.16.3: wavev trap                                                                                             67

Fig.17.1:A panel of CONTROL ROOM                                                                 73

Fig.18.1 :a view of battery room                                                                    75

Fig.17.1:- CAPACITOR BANK                                                                                   77

ABSTRUCT

A substation is an assembly of apparatus, which transform the characteristics of electrical energy from one form to another say from one voltage level to another level. Hence a substation is an intermediate link between the generating station and the load units

there are four bus bars in 132 kv yard and five bus-bars in 220kv yard. the incoming feeders are connected to bus-bar through  lightingarrestors, capective voltage transformer ,line isolater, circuit breakers current-transformers,line isolater  etc.the bus-bars are to have an arrangement of auxilary bus.

In the 220KV GSS the income 220KV supply is stepped down to 132Kv with the help of transformers which is furthers supplied to different sub-station according to the load.220Kv G.S.S. has a loarge layout consisting of 3 Nos. of 100MVA transformers,with there voltage ratio respectively 220/132Kv in addition to these transformers.There are many other equipments are also installed in220 KV yards

At "GSS ALWAR" the separate control room switches and fuses. There are meters for reading purpose. A circuit concerning the panel is shown on the panel with standard co lour.provided for remote protection of 220KV switch yards transformer incoming feeder, outing feeders. Bus bar has their own control plant in their control rooms. The control panel carrier the appropriate relays. Necessary meters indicating lamp control

The training at grid substation was very helpful. It has improved my theoretical concepts of electrical power transmission and distribution. Protection of various apparatus was a great thing. Maintenance of transformer, circuit breaker, isolator, insulator, bus bar etc was observable.I had a chance to see the remote control of the equipments from control room itself, which was very interesting.

                                                                                                                               SHAKTI SINGH

                                                                                                                               08ELDEE055

                                                                                                                               ELECTRICALChapter-1

INTRODUCTION

1.1 AN OVERVIEW OF R.S.E.B.

“Rajasthan State Electricity Board” started working form 1 July, 1957. When India becomes independent its overall installed capacity was hardly 1900 mw. During first year plan (1951-1956) this capacity was only 2300 mw. The contribution of Rajasthan state was negligible during 1&2 year plans the emphases was on industrialization for that end it was considered to make the system of the country reliable. Therefore Rajasthan state electricity board came into existence in July 1957.

In 1957 RSEB (Rajasthan State Electric Board) is comes in to existance and it satisfactrily work from  1 july1957 at  that time energy level in Rajasthan is verylow . The 1^st survay for energy capacity in Rajasthan is held in 1989 at that time the total electric energy capacity of Rajasthan is 20116 MW.At that time the main aim of RSEB is to supply electricity to entire Rajasthan in the most economical way.

and the RSEB comes under northan zone.During the 1^st survey there are few GSS inRajasthan and the Alwar GSS is one of them. The Alwar GSS is 2km away from the  Railway station Alwar and located near the Govt. polytechnic college Alwar

The aim of RSEB is to supply electricity to entire Rajasthan state in the most economical way. Government of Rajasthan on 19th July 2000, issued a gazette notification unbundling Rajasthan State Electricity Board into Rajasthan RajyaVidyutUtpadan Nigam Ltd  (RRVUNL), the generation Company; Rajasthan RajyaVidyutPrasaran Nigam Ltd , (RRVPNL), the transmission Company and the three regional distribution companies namely Jaipur VidyutVitran Nigam Ltd , (JVVNL) Ajmer VidyutVitran Nigam Ltd  (AVVNL) and Jodhpur VidyutVitran Nigam Ltd  (JVVNL)

The Generation Company owns and operates the thermal power stations at Kota and Suratgarh, Gas based power station at Ramgarh, Hydel power station at Mahi and mini hydel stations in the State 

The Transmission Company operates all the 400KV, 220 KV, 132 KV and 66KV electricity lines and system in the State 

The three distribution Companies operate and maintain the electricity system below 66KV in the State in their respective areas 

Rajasthan State Electricity Board has been divided in five main parts are:-

-> Electricity production authority- RRVUNL

-> Electricity transmission authority-RRVPNL

-> Distribution authority for Jaipur-JVVNL

-> Distribution authority for Jodhpur-JVVNL

           -> Distribution authority for Ajmer- AVVNL

Fig.1.1: Graphical view of R.S.E.B.

Power obtain from these stations is transmitted all over Rajasthan with the help of grid stations. Depending on the purpose, substations may be classified as:-

1. Step up substation
2. Primary grid substation
3. Secondary substation
4. Distribution substation
5. Bulky supply and industrial substation
6. Mining substation
7. Mobile substation
8. Cinematograph substatio

Depending on constructional feature substation are classified as:-

1. Outdoor type
2. Indoor type
3. Basement or Underground type
4. Pole mounting open or kilos type

                                      

                                                                                                                                   

Chapter-2

Grid  Substation

 A substation is an assembly of apparatus, which transform the characteristics of electrical energy from one form to another say from one voltage level to another level. Hence a substation is an intermediate link between the generating station and

                                       2.1Side Views of GSS

For economic transmission the voltage should be high so it is necessary to step up the generated voltage for transmission and step down transmitted voltage for distribution. For this purpose substations are installed.

 The normal voltages for transmission are 400kv,220kv,132kv and for distribution 33kv,11kv etc.

2.2 CONSTRUCTIONAL FEATURES OF 220KV GSS ALWAR

In this substation the power is coming from five places namely

  1 Heerapura ( Jaipur)

  2. MIA (Badarpur )

  3.  Dousa

  4.  Bhiwadi

  5.  Khuskhera

Out going feeders are …

1.         220 KV Kotputli

2.         132 KV GSS Alwar

3.         132 KV Bharatpur

4.         132 KV LCAL

5.         132 KV Kishangarh Bass

6.         132 KV Mundawar

7.         132 KV M.I.A.

8.         132 KV Ramgarh

9.         132 KV Malakhera

10.       132 KV Bansur

In this substation there are two yards

1     220KV Yard.

132 KV Yard.

There are four bus bars in 132 KV yard and five bus-bars in 220KV yard  The incoming feeders are connected to bus-bar through circuit breakers, Isolators, lighting arrestors, current-transformers etc The bus-bars are to have an arrangement of auxiliary bus  So that when some repairing work is to be done an main bus the whole load can be transferred to the auxiliary bus through bus-coupler

In this 220KV GSS the incoming 220KV supply is stepped down to 132KV with the help of transformers which is further supplied to different sub-station according to the load

220KV G S S  has a large layout consisting of 3 Nos  of 100MVA transformers, 2nos  of 20/25MVA transformers and 1 X-mer of 40/50MVA and one X-mer of 16/20MVA having voltage ratio respectively 220/132, 132/11Kv in addition to these transformers

                                                                                                       Chapter-3

Equipments used in G.S.S.

3.1 Equipments used in 132 KV YARD IN 220 KV G.S.S.

S.No.	Name of Equipment	Specification	Qty.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17	132 KV P T 132 KV C T 132 KV Isolator 132/11 KV Transformer 132/33 KV Transformer 132 KV,ABCB 33 KV Isolators 33 KV O C B (Oil Circuit Breaker) 33 KV P T 33 KV C T 33 Bank Capacitor Station Service Transformer 11 KV O C B 11 KV P T D C Rectifier & Battery Charger L T  Panel Compressors	Make C G E Type V C M 138 Ratio- 132/110V Sr No -615259 Make BHEL Ratio 480/240/120 Sr No -1227 Make HIVELM Volts-220 Sr No 1052,1049, 1041,502,506,974,1074 Make NGEF Capacity-16/20MVA Ratio-132/11 KV Sr No -28000,30346 Yr of manafacture-1978 Currentrating-87 SA,105 A Make EMCO Capacity-16/20MVA Currentrating-10373/10856 Make HBB Type D C E  1633 1505576 Capacity-2500 KVA Make E M G Capacity-400A Make BHEL (i)Type HLC 36/1000    Capacity-400 A (ii)Type M E I 7377A Make SIMO Meters Ltd Sr No  HEO 700 Ratio-3X33000X110V (i)Make A E     Ratio-120/60/5/5                (ii)Make Merlih Gerigh    Ratio-120/60/5/5 (iii)Make-Crompton    Ratio-240/120/5/5 Make-Sprechers & scnich Capacity-800A,4190KVR Type-HPRC 307 F Sr no 69/21/7344051 Make-E E Capacity-100KVA Sr No -250/4 Make MEI Type: ACI Capacity-800A Sr No -68/025,67/262, 68/024,67/261,67/264, 70/85,70/067 Make A E Ratio-11000/11 OV Sr No -4124A Sr No -74877381/21 Type-CP Ratio-110/No DC output 115-118V/10A Make HIMD Rectifier Standard Cell type  T15 H Make Jyoti Sr No -205/66 Type- LTLT-5 550 V-34,4 Wire Make intesoll Rand Type-30 Size-3X11/4X2 3/4 Sr no 8100212,81oo198	1 1 9 3 1 2 2 3 1 2 2 2 1 1 7 1 1 1 2

Table 3.1 :Equipments used in 132 KV YARD

The switch house building of the G.S.S. has following parts:-

 1. Load Dispatch Unit(L.D.U.)

 2. Power Line Carrier Communication(P.L.C.C.)

 3. Battery Room

 4. Control Room

 5. Comopressor Room

                 

   DIFFERENT  EQUIPMENTS  USED  IN G.S.S.:

Some equipments are used in the G.S.S. for successful Operational Breaker & a half scheme two buses ,they are:

1     Lighting Arrester

2      CVT

3     Line isolator

4     Wave Trap

5      Circuit Breaker

6     Current Transformer

7      Bus Bars

8      Power Transformer

9      Static earthling system

10   Bushing

Chapter-4

LIGHTNING ARRESTOR

Lighting arrestor is a device, which protects the overhead lines and other electrical apparatus viz , transformer from overhead voltages and lighting  When the positively charged cloud produce negative charge on the overhead line by electrostatic induction then the negative charge is however presented right under the cloud and portion of the line away from the cloud becomes positively charged  This charge on the line does not flow 

Every instrument must be protected from the damage of lighting stroke. The three protection sin a substation is essential:-

• Protection for transmission line from direct strokes 

• Protections of power station or substation from direct strokes 

• Protection of electrical apparatus against traveling waves 

Effective protection of equipment against direct strokes requires a shield to prevent lighting from striking the electrical conductor together with adequate drainage facilities over insulated structure

Description

The Thyrite Alugard lightning arrester consists of a stack of one or more units connected in series depending on the voltage and the operating condition of the circuit Three single pole arresters are required for 3-phase installation. The arresters are single pole design and they are suitable for indoor and out-door service.

Each arrester unit consists essentrally of permanently sealed Porcelam housing equipped with pressure relief and containing a number of thyrite value-element dises and exclusive lumate gaps shunted by Thyrite resistors metal fitting cemented of the housing provide means for bolting arrester units into a stack.  Each arrester unit is shipped assembled. No charging or testing operation is required before placing them in service.

Installation Location :-

Install arrester electrically as close as possible to the appearatus being protected Line and ground connections should be short and direct  

grounding:-

The arrester ground should be connected to the apparatus grounds and the main station ground utilizing a reliable common ground network of low resistance. The efficient operation of the lightning arrester requires permanent low resistance grounds : Station class arresters should be provided with a ground of a value not exceeding five ohms.

Clearances:- These are given on the drawings. These are the maximum recommended. The term ‘clearance’ means the actual distance between any part of the arrester or disconnecting device at line potential, and any object at ground potential or other phase potential.

ARRESTER VOLTAGE:- The thyrite staion-class arrester is designed to limit the surge voltages to a safe value by discharging the surge current to ground; and to interrupt the small power frequency follow current before the first current zero.The arrester rating is a define limit of its ablity to interrupt power follow current. It is important, therefore, to assure that the system power frequency voltage from line to ground under any condition switching,fault,overvoltage,never exceeds the arrester’s rating.

LIGHTENING ARRESTER

It consist of a isolator in series and connected in such a way that long isolator is in upward and short isolator is in downward so that initially large potential up to earth is decreased to zero 

An ideal arrestor must therefore have the following properties:

1. It should be able to drain the surge energy from the line in a minimum time 
2. Should offer high resistance to the flow of power current 
3. Performance of the arresters should be such that no system disturbances are introduced by its operation 
4. Should be always in perfect from to perform the function assigned to it 
5. After allowing the surge to pass, it should close up so as not to permit power current to flow to ground 

Fig 4.2 : L.A.in alwar g.s.s.

WORKING:-

Lightning, is a form of visible discharge of electricity between rain clouds or between a rain cloud and the earth  The electric discharge is seen in the form of a brilliant arc, sometimes several kilometres long, stretching between the discharge points  How thunderclouds become charged is not fully understood, but most thunderclouds are negatively charged at the base and positively charged at the top  However formed, the negative charge at the base of the cloud induces a positive charge on the earth beneath it, which acts as the second plate of a huge capacitor 

When the electrical potential between two clouds or between a cloud and the earth reaches a sufficiently high value (about 10,000 V per cm or about 25,000 V per in), the air becomes ionized along a narrow path and a lightning flash results 

Many meteorologists believe that this is how a negative charge is carried to the ground and the total negative charge of the surface of the Earth is maintained 

The possibility of discharge is high on tall trees and buildings rather than to ground  Buildings are protected from lightning by metallic lightning rods extending to the ground from a point above the highest part of the roof  The conductor has a pointed edge on one side and the other side is connected to a long thick copper strip which runs down the building  The lower end of the strip is properly earthed  When lightning strikes it hits the rod and current flows down through the copper strip  These rods form a low-resistance path for the lightning discharge and prevent it from travelling through the structure itself

                                     

                                      Chapter-5

Capacitive voltage transformers(C.V.T.)

CVTs are special king of PTs using capacitors to step down the voltage. A capacitor voltage transformer (CVT), or capacitance coupled voltage transformer (CCVT) is a transformer used in power systems to step down extra high voltage signals and provide a low voltage signal, for measurement or to operate a protective relay  In its most basic form the device consists of three parts: two capacitors across which the transmission line signal is split, an inductive element to tune the device to the line frequency, and a transformer to isolate and further step down the voltage for the instrumentation or protective relay  The device has at least four terminals: a terminal for connection to the high voltage signal, a ground terminal, and two secondary terminals which connect to the instrumentation or protective relay  CVTs are typically single-phase devices used for measuring voltages in excess of one hundred kilovolts where the use of voltage transformers would be uneconomical  In practice, capacitor C₁ is often constructed as a stack of smaller capacitors connected in series  This provides a large voltage drop across C₁ and a relatively small voltage drop across C₂

The CVT is also useful in communication systems  CVTs in combination with wave traps are used for filtering high frequency communication signals from power frequency  This forms a carrier communication network throughout the transmission network

Fig.5.1 : Circuit diagram of a capacitor voltage transformer

Application:

1) Capacitve voltage transformer can be effectively as potential sources for measuring, metering protection, carrier communication and other vital functions of an electrical n/w

2) Capacitive voltage transformers are constructed      in single or multi-unit porcelain housing with their associated magnetic units.For EHV system.

3) In the case of EHV CVTs the multi-unit construction offers a number of advantages easy of transport and storing,Convenience in handling anderection etc.

Description:

1) The capacitive voltage transformer comprises of a capacitor  devider  with  its associated Electro-magnetic  unit.  The divider  provides an accurate proportioned  voltage,while the  magnetic  unittransformers this voltage,both in magnitude and toconvenient levels suitable for measuring phasemetering, protection etc. all W.S.I.capacitor unitshas metallic bellows to compensate the volumetric expansion of oil inside the porcelain.In the multiunit stack,all the potential point are electricallyelectrically tied and suitably shielded to overcomethe effects of corona, RIV etc.

2)  Capacitive voltage transformers are available for system voltage of 33kv to 420kv.

3)  Packing and transportation :

3.1All the capacitor units of capacitive voltage X-mer are securely packed in woolen crates. The  electro-magnetic unit form an integral part withthe capacitor unit is hermetically associated with the electromagnetic unit;the wooden crate for this is exclusive and is sized heavier taller than for the capacitor unit alone.

3.2 Each woolen crate is identified with the corresponding serial number of the unit .

3.3 Each capacitor unit has one nameplate designing the rating of the unit Positioin ofthe unit in the complete assembly is also indicated in the nameplate by a suffix T or M

Ratings of CVT:-

Make: W S  Insulators of India Limited

Intermediate voltage:                       22/ 3KV

Total output simultaneous:            500VA

Output maximum:                            1000VA at 50’C

Operating Voltage:                           400/ 3KV                    420/ 3KVmax

Voltage Factor:                                 1 5sec                       30sec

Chapter-6

POTENTIAL TRANSFORMER

Potential Transformer is designed for monitoring single-phase and three-phase power line voltages in power metering applications.

The primary terminals can be connected either in line-to-line or in line-to-neutral configuration. Fused transformer models are designated by a suffix of "F" for one fuse or "FF" for two fuses.

A Potential Transformer is a special type of transformer that allows meters to take readings from electrical service connections with higher voltage (potential) than the meter is normally capable of handling without at potential transformer.

6.1 Potential Transformer                   

Potential transformers are instrument transformers  They have a large number of primary turns and a few number of secondary turns  It is used to control the large value of voltage

Potential Transformer is designed for monitoring single-phase and three-phase power line voltages in power metering applications

The primary terminals can be connected either in line-to-line or in line-to-neutral configuration  Fused transformer models are designated by a suffix of "F" for one fuse or "FF" for two fuses

Chapter-7

            Isolator

7.1Isolator

An isolator switch is part of an electrical circuit and is most often found in industrial applications. They are commonly fitted to domestic extractor fans when used in bathrooms in the UK. The switch electrically isolates the circuit or circuits that are connected to it. Such a switch is not used normally as an instrument to turn on/off the circuit in the way that a light switch does. Either the switch isolates circuits that are continually powered or is a key element which enables an electrical engineer to safely work on the protected circuit.

Isolator switches may be fitted with the ability for the switch to padlock such that inadvertent operation is not possible (see:Lock and tag).In some designs the isolator switch has the additional ability to earth the isolated circuit thereby providing additional safety.Such an arrangement would apply to circuits which inter-connect power distribution systems where both end of the circuit need to be isolated.

The major difference between an isolator and a circuit breaker is that an isolator is an off-load device, whereas a circuit breaker is an on-load device.

When to carry out inspection or repair in the substation installation a disconnection switch is used called isolator. Its work is to disconnect the unit or section from all other line parts on installation in order to insure the complete safety of staff working. The isolator works at no load condition. They do not have any making or breaking capacity.

On fundamental basis the isolating switches can broadly divided into following categories: -

1.    Bus isolator

2.    Line isolator cum earthing switch

3.    Transformer isolating switch.

OPERATION: -

The operation of an isolator may be hand operated without using any supply or may be power operated which uses externally supplied energy switch which is in the form of electrical energy or energy stored in spring or counter weight.

In a horizontal break, center rotating double break isolator, 3 strokes are found. Poles are provided on each phase. The two strokes on side are fixed and center one is rotating. The center position can rotate about its vertical axis at an angle of 90. In closed position, the isolating stroke mounts on galvanized steel rolled frame. The three poles corresponding to 3 phases are connected by means of steel shaft.

Isolators are of two types -

1.    Single pole isolator

2.    Three pole isolator

                                       7.2Isolator

Construction of Isolator:  

Isolator for three-phase we provided in such a manner that for each phase one frame of isolator.These three isolator must be operated all together.In each frame,line is connected to terminal stud.Terminal stud is coupled with contact.Contact arm are supported by insulators. Contacts are made or broken by motor operated mechanism.When contact is to be open then both arms are rotated in opposite direction,so that contact is broken.same time earthing pole moves upward to make contact with a female contact situated adjoined to terminal stud.Hence,that terminal gets earthen.On this criteria isolator can be carried out manually but for quick operation motor is used. 

Rating of air break isolator:

Make: S&S Power switchgear Limited

(1)Motor operated mechanism

Make                                                  S&S

Motor voltage                                                415V ac

DC voltage                                       220V dc

(2) Air Break isolator

Rated voltage                                               420KV

Rated current                                                2000A

Rated short time current                 40kA/ 1sec

Rated impulse voltage                    1425kV

Rated nechanical term load           160 kg

Auxiliary voltage                              220 V dc

Chapter-8

          WAVE TRAP

To communicate between two G.S.S. we use power line ifself. Power line carrying

50Hz power supply also carries communication signals at high frequency.Wave Trap is a device used for this purpose. It traps the frequency of desired level for communication and sends it to P.L.C.C. department.    It is used to trap the communication signals & send PLCC room through CVT.  

Rejection filters are known as the line traps consisting of a parallel resonant circuit ( L and C in parallel) tuned to the carrier frequency are connected in series at each and of the protected line such a circuit offer high impedance to the flow of carrier frequency current thus preventing the dissipation. The carrier current used for PLC Communication have to be prevented from entering the power equipments such as attenuation or even complete loss of communication signals. For this purpose wave trap or line trap are used between transmission line and power station equipment to- 

Avoid carrier power dissipation in the power plant reduce cross talks with other PLC Circuits connected to the same power station.

 Ensure proper operating conditions and signal levels at the PLC transmit receive equipment irrespective of switching conditions of the power circuit and equipments in the stations.
   
Line Matching Filter & Protective Equipments

For matching the transmitter and receiver unit to coupling capacitor and power line matching filters are provided. These flitters normally have air corral transformers with capacitor assumed.

The matching transformer is insulated for 7-10 KV between the two windings and perform two functions. Firstly, it isolates the communication equipment from the power line. Secondly, it serves to match .

Figure-8.1 Line Matching Filter & Protective Equipments

Transmitter:-

The transmitter consists of an oscillator and a amplifier. The oscillator generates a frequency signal with in 50 to 500 HZ frequency bands the transmitter is provided so that it modulates the carrier with protective signal. The modulation process usually involves taking one half cycle of 50 HZ signal and using this to create block to carrier.    

Receivers :-

The receivers usually consist of and alternate matching transformer band pass filter and amplifier detector.

The amplifier detector converts a small incoming signal in to a signal capable of operating a relatively intensive carrier receiver relay. The transmitter and receiver at the two ends of protected each corresponds to local as far as transmitting. 

Chapter-9

CIRCUIT BREAKER

A circuit breaker is an automatically operated electrical switch designed to protect an electrical circuit from damage caused by overload or short circuit  Its basic function is to detect a fault condition and, by interrupting continuity, to immediately discontinue electrical flow  Unlike a fuse, which operates once and then has to be replaced, a circuit breaker can be reset (either manually or automatically) to resume normal operation  Circuit breakers are made in varying sizes, from small devices that protect an individual household appliance up to large switchgear designed to protect high voltage circuits feeding an entire city

In any circuit, carrying a large amount of current, if a contact is opened then normally a spark is produced due to fact that current traverses its path through air gap  Arcing is harmful as it can damage precious equipment media are provided between contacts

This is one of the important equipment in power system  It protects the system by isolating the faulty section while the healthy one is keep on working  Every system is susceptible to fault or damages while can be caused due to overloading, short-circuiting, earth fault etc  thus to protect the system and isolate the faulty section C B  are required  Apart from breaking and making contacts, a C B  should be capable of doing 

1. Continuously carry the maximum current at point of installation
2. Make and break the circuit under abnormal and normal condition 

   Close or open the faulty section only where fault exists

There are different arc quenching media:-

1)       Air blast

2)       Oil

3)       SF6 gas

4)       Vacuum

In 220 kV G S S , SF6 gas circuit breaker are used, as for greater capacity G S S , SF6 type breakers are very efficient

9.2 AIR BLAST CIRCUIT BREAKER

Figure 9.1 air blast circuit breaker

Air blast circuit breakers are normally only used at low voltage levels but are available with high current ratings up to 6000 A and short circuit ratings up to 100 kA at 500V.The air blast circuit breakers according to type of flow of blast of compressed air around the contacts are three namely (i)Axial(ii)Radial(iii)cross flow of blast air type.

Consuctruction & working:

The physical size of such units, which contain large arc chutes, quickly makes them uneconomic as voltages increase above 3.6kV. Their simplicity stems from the fact that they use ambient air as the arc quenching medium.

As the circuit breaker contacts open the arc is formed and encouraged by strong thermal convection effects and electromagnetic forces to stretch across splitter plates. The elongation assists cooling and deionization of the air/contact metallic vapour mixture. The long arc resistance also improves the arc power factor and therefore aids arc extinction at current zero as current and circuit breaker voltage are more in phase. Transient recovery voltage oscillations are also damped thus reducing overvoltages.

Arc products must be carefully vented away from the main contact area and out of the switchgear enclosure. As we know many MCB and MCCB low-voltage current limiting devices are only designed to have a limited ability to repeatedly interrupt short circuit currents. Care must therefore be taken when specifying such devices.Air circuit breaker with fully repeatable high short circuit capability as typically found in a primary substation auxiliary supply switchboard.

Advantages:-

• There is no risk of explosion and fire hazard.
• Due to less arc energy in it as compared to that in O.C.B. burning of contacts is less
• It requires less maintainance
• It provides facility of high speed reclosure

Disadvantages:-

• Compressor plant compressed air is required
• Air leaks at the fitting of the pipe line
• It is very sensitive to restriking voltage
• Current Choppin

9.2 Air Circuit Breaker

            OIL CIRCUIT BREAKER

Mineral oil has good dielectric strength and thermal conductive properties. Its insulation level is, however,dependent upon the level of impurities. Therefore regular checks on oil quality are necessary in order to ensure satisfactory circuit breaker or oil-immersed switch performance.Carbon deposits form in the oil(specially after heavy short circuit interrupting duties)as a result of decomposition under the arcing process.Oil oxygen instability, characterized by the formation of acids and sludge, must be minimized if cooling properties are to be maintained. Insulation strength is particularly dependent upon oil moisture content.The oil should be carefully dried and filtered before use.Oil has a coefficient of expansion of about 0.0008per°C and care must be taken to ensure correct equipment oil levels.

The oil can be moved into arc zone after the current reaches zero by the following actions.

(i)By the pressure cavsed by the natural head of the oil, (ii)by the pressure generated by the action of the arc itself (iii)by the pressure casused by external means.

Thus the oil circuit breakers may be classified as:

(i)Plain break oil circuit breakers.

(ii)self blast or self generated or arc control oil circuit oil circuit brekers.

(iii)externally generated pressure oil circuit breakers of foreed blast oil circuit breakers or impulse oil circuit breakers.

Oil,as an arc quenching medium,has the following advantages and dis-advantages.

ADVANTEGE:-

(i)arc energy is absorbed in decomposing of oil (ii)The gas formed,which is mainly hydrogen have a high diffusion rate and high head obsorption in changing from the diatomic to monotonic state and thus provides good coilling properties. (iii)Surrounding oil presents the coilling surface in close prorimity to the arc.(iv)The oil used such as transformer oil is a very good insulator and allows smaller cleaner between live conductors and earth components.(v)The oil has abilty to flow into the arc space after current is zero.

DISADVANTEGE:-

(i)There is a risk of formation of explosive mixture with air(ii)Oil is easily in flammable and may causes fire hazards(iii)Owingh to formation of carbon particles in the oil due to heat,the oil is to be kept clean and thus reguires periodical replacement.

9.3 Oil Circuit Breaker

9.4 Low-oil circuit breaker

SF6 BREAKER

The outstanding physical and chemical properties of SF6 gas makes it an ideal dielectric media for use in power switchgear.These properties of SF6 gas makes it an ideal dielectric media for use in power switchgear,these properties are included:

1)High dielectric strength

2)unique arc quenching ability

3)Excellent thermal stability

4)Good thermal conductivity

In addition, at normal temperature SF6 is chemically inert,inflammable,noncorrosive and non-condensable at low temperatures.

SF6 versus oil:

SF6 is not flammable and toxic like oil.It is easier to handle,maintain and repair equipment filled with SF6.

In case of breakdown of oil strong surges of pressure may occur due to sudden development of gaseous products.In case of breakdown of SF6,the only pressure rise will result from the thermal expansion of gas.

Figure 9.5 sf6 circuit breaker

SF6 versus air/gases:

SF6 has about times,the dielectric strength of N2.In addition SF6 has property that disassociated molecules recombined rapidly after the source of arcing is removed when superior arcing occurs. Excellent performance in operation confirms the high level of reliability and safety irrespective of environmental conditions.

9.6 SF6 Circuit Breaker

Rating of SF6 breaker:

Type: hydraulic operated: (1975)

Rated voltage:                                                                                  245kv

Rated impulse withstand voltage lightening Switching                     1050KV

Rated power frequency voltage                                                    520KVp

Rated frequency                                                                               50 Hz

Rated normal current                                                                                   2000 A

Rated short time current                                                                  40KA

Rated short circuit duration                                                                         1 sec

Breaking capacity symmetrical                                                      40 KA

Equivalent                                                                                         29000MVA

Asymmetrical                                                                                                49KA

Rated making current                                                                     100 Kamp

Rated pressure of hydraulic

 operating mechanism(guage):                                         250-350 bar

Rated pressure pf sf6 gas at 20c(gauge)                                 7.5 bar

Weigh of complete breaker:                                                           11700Kg

Weight of SF6                                                                                  76.5Kg

Rated closing coil voltage                                                  220Vdc

Rating of SF6 breaker:

Type: pneumatic operated

Make :ABB

Rated Voltage                                                                                   245KV

Rated normal current                                                                      2000KA

Rated lightning withstand impulse voltage:                                1425KV

Rated switching withstand impulse voltage:                  1050KV

Rated short circuit breaking current:                                            40KA

Rated short time withstand current andduration:                  40KA,3sec.       

Rated line charging ,breakering current:                        125A

Rated SF6 gas pressure at 20 c(abs.):                                        20.5bar

Closing and opening device supply voltage:                            220Vdc

Auxiliary circuit supply voltage:                                        240Vac

Rated air pressure:                                                             20.5bar

Rated frequency:                                                                 50Hz

Maximum weight:                                                                 3800Kg.

working of circuit breaker:

Intrrupter unit fixed contacts that are connected through a moving contact.Fixed contacts are of rod shape. There contacts are known as male contacts.

Inclosed position,fixed contacts are joined by a moving contact known as female contact.This female contact is of hollow cyclindrical shape. Main parts of female contacts are blast cylinder,contact tube and guide tube. In closed position female contact overlaps male contacts. Contact tube shorts two made contacts and current completes its path from one male contact to another through contact. Counteracting piston moves towards contact compressing the SF6 present in blast cylinder.

When it is required to open the contacts then piston is forced to move vertically download by hydraulic or pneumatic pressure.This piston pulls operating rod pulls blast cylinder using bell and crank mechanism.Contact tube moves away from contact.Counteracting piston moves towards contact compressing the SF6 present in blast cylinder.

When contact between male and female contacts is just going to break.Then counteracting piston reaches its extreme position performing maximum compression of SF6 gas .when arc is produced,SF6 at very high pressure quenches the arc.

In open position,blast cylinder reaches its extreme position reliving the SF6 to its normal pressure.Counter acting piston reaches its original position again. Contact tube lies entirely on male contact.

Vacuum Circuit Breaker

Vacuum interrupter tubes or ‘bottles’ with ceramic and metal casings are evacuated to pressures of some 10-6 to 10-9 bar to achieve high dielectric strength.The contact separation required at such low pressures is only some 0 to 20mm and low energy mechanisms may be used to operate the contacts through expandable bellows. Below figure shows a cut away view of such a device.The engineering technology required to make a reliable vacuum interrupter revolves around the contact design.Interruption of a short circuit current.

Figutre 9.7 vacum circuit breaker

9.8 High-voltage Vacuum circuit breaker

Advantages:-

è  Low maintenance

è  Vacuum ‘bottles

è  easy to replace

è  Complete isolation of the interrupter from atmosphere and contaminants

è  Absence of oil minimizes fire risk

Disadvantages:-

è  Limited availability

è  May be found for open terminal

è  Designs up to 72.5kV were used in conjunction with SF6 insulation system

è  Spare vacuum ‘bottle’ holding require

Chapter-10

CURRENT  TRANSFORMER

When current in a circuit is too high to directly apply to measuring instruments, a current transformer produces a reduced current accurately proportional to the current in the circuit, which can be conveniently connected to measuring and recording instruments  A current transformer also isolates the measuring instruments from what may be very high

Current transformer is a instrument transformer which is mainly used for measuring currents where very high currents are flowing.

According to the construction of the current transformer the primary winding of transformer is in series with high current carrying line & measuring instrument is connected to the secondary.

Figure 10.1 current transformer  single line diagam

10.2 CURRENT TRANSFORMER

The current Xmer is mounted one of the power transformer leads; it can be associated with an Lv or Hv lead; depending on voltage and current consideration. A section of the lead is demountable locally to enable the current transformer to removed, should the necessity arise, without disturbing the main connection.The secondary of CT is connected to the heating coil directly located under the main cover in the oil.On the larger Xers the various connections may be brought up to terminals in the main the cover for external linkage.

10.3 A set of Current transformer

Ratings of current transformer:

Make :            W.S.Insulators of India limited

Rated frequency :                50 Hz

High side voltage :              420 KV

Weight of oil :                                   750 Kg

Total weight :                                   2450 Kg

BIL :                                      630/1425 KV

CURRENT RATIO	2000-1000/1	2000-1000-500/1
Turns Ratio	2000-1000	2000-1000-500
Core No.	1&2	3  4&5  40   -  0.5  p.s.  10   -
Output(VA)	-
Accuracy Class	P.s.
ISF/ALF	-

                                                                                                                            

Chapter-11

             BUS BAR SYSTEM

the conductors used

(i)  For 400kV line       : Taran Tulla and Marculla conductor.

(ii) For 220kV line    : Zebra conductor is used composite of Aluminium strands and Steel wires.

(iii) For 132kV line      : Panther conductor is used composite of Aluminium strands and Steel wires.

The material used in these conductors is generally Aluminium Conductor Steel Reinforced (ACSR). The conductors run over the towers cross arms of sufficient height with the consideration to keep safe clearance of sagged conductors from ground level and from the objects (trees, buildings etc.) either side also.

Figutre 11.1 busbar

This bus bar arrangement is very useful for working purpose as every GSS. It is a conductor to which a number of  cut .Are connected in 220 KV GSS there are two bus running parallel to the each other, one is main and another is auxiliary bus is only for stand by, in case  of failure of one we can keep the supply continues.

If more loads are coming at the GSS then we can disconnect any feeder through circuit breaker which is connected to the bus bar. This remaining all the feeders will be in running position .if we want to work with any human damage. In this case all the feeders will be on conditions.

According to bus voltage the material is used .Al is used because of the property & features and it is cheap. 

PROPERTIES  COPPER   ALUMINIUM  1.    Electricity resistively at 20 c 0.017241,,0.00403  2.    Temp coff. Of resistively 0.00411,,,0.00403  3.     Softening tem. 200,180  4.    Thermal conductivity .932,.503  5.    Meting point 1083,57

Chapter-12

transformer

A transformer is a device that transfers electrical energy from one circuit to another through inductively coupled conductor -the transformer's coils  A varying current in the first or primary winding creates a varying magnetic flux in the transformer's core and thus a varying magnetic field through the secondary winding  This varying magnetic field induces a varying electro-motive force, or voltage in the secondary winding  This effect is called mutual induction

If a load is connected to the secondary, an electric current will flow in the secondary winding and electrical energy will be transferred from the primary circuit through the transformer to the load  In an ideal transformer, the induced voltage in the secondary winding (V_s) is in proportion to the primary voltage (V_p), and is given by the ratio of the number of turns in the secondary (N_s) to the number of turns in the primary (N_p) as follows:

By appropriate selection of the ratio of turns, a transformer thus allows an alternating current voltage to be "stepped up" by making N_s greater than N_p, or "stepped down" by making N_s less than N_p

Fig.12.1: An ideal transformer

Generally transformer is very costly (approximately 10 lakhs)  Its cost increases as its rating increase  Very high cost of transformers is due to three parts:-

1) CORE

2) WINDING

3) OIL

Now we describe the three major parts of transformer

CORE:-

Core is the main part of the transformer  It is subjected to magnetic flux  For efficient operation, it is essential that the core of transformer must be constructed from laminated magnetic material of low hysteresis loss and high permeability  Transformers for use at power or audio frequencies typically have cores made of high permeability silicon  The steel has permeability many times that of space and the core thus serves to greatly reduce the magnetizing current, and confine the flux to a path which closely couples the windings  Early transformer developers soon realized that cores constructed from solid iron resulted in prohibitive eddy-current losses, and their designs mitigated this effect with cores consisting of bundles of insulated iron wires  Later designs constructed the core by stacking layers of thin steel laminations, a principle that has remained in use  Each lamination is insulated from its neighbors by a thin non-conducting layer of insulation  The universal transformer equation indicates a minimum cross-sectional area for the core to avoid saturation

The effect of laminations is to confine eddy currents to highly elliptical paths that enclose little flux, and so reduce their magnitude  Thinner laminations reduce losses, but are more laborious and expensive to construct  Thin laminations are generally used on high frequency transformers, with some types of very thin steel laminations able to operate up to 10 kHz

A steel core's remanence means that it retains a static magnetic field when power is removed  When power is then reapplied, the residual field will cause a high inrushcrrent until the effect of the remaining magnetism is reduced, usually after a few cycles of the applied alternating current  Overcurrent protection devices such as fuses must be selected to allow this harmless inrush to passion transformers connected to long, overhead power transmission lines, induced currents due to geomagnetic disturbances during solar storms can cause saturation of the core and operation of transformer protection devices

WINDING:-

Figure 12.2 winding

Core type transformers use concentric type of winding  Each limb is wound with a group of coil consisting of both primary and secondary winding, which are concentric to each other  Low voltage winding is placed near to the core (which is at earth potential) and high voltage winding is placed outside, however L T  and H T  windings are inter-leaved to reduce the leakage reactance

            The type and arrangement used for winding in core type transformers depend upon many factors  Some of the factors are given below:

1.       current rating

2.       shot circuit strength

3.       temperature rise

4.       impedance

5.       surge voltage

6.       transportation facilities

The winding used for core type transformers are of following types

1.       Cylindrical type

2.       Helical type

3.       Double helical type

4.       Multi layer helical type

5.       Disc and continuous disc type

6.       Cross over type

7.       aluminum foil type

It is found that the magnetic properties of transformer sheet steel vary in accordance with the direction of the grain oriented by rolling, sheet are cut as far as possible along the grain which is the direction in which the material has a higher permeability  It must be made  In building the core, considerable pressure is used to minimize air gaps between the plates, which would constitute avoiding loosed of area and might contribute to noisy operation  The reduction of core sectional area due to presence of insulating material is of the order of 10%

Figure 12.3 220/132KV,100MVA,Power Transformer

The winding is layered type and used either rectangular or round conductors. In a cylindrical winding.using rectangular conductor, the conductors are wound on the flate side with three-layer side parallel to the core axis.The winding using rectangular conductors may be simultaneously wound from or more parallel conductors.

The layered winding may have conductors wound in one, two or more layers and is therefore accordingly called one, two or multi layer winding.       The windings using rectangular conductors are usually two layered because this case it is easier to secure the lead out ends. The windings designed foe haeavy currents are wound with a number of conductors connected in parallel located side by side in one layer. The parallel conductors have the same length and are locted in  the maganetic field or almost the same flux density and hence it is not necessary to make any transposition of conductors. A wedged shaped poacking is used at each of two entrance ends of winding in order to level it, the packing is made of press bar strips.

Cylindrical winding employing rectangular conductors are used mainly as L.V. winding up to 6.6 kva/kv ratings up to 600-750 volts however their use is up to 433 volts.

Cylindrical winding using circular conductors are multi layered.They are wound on a solid paper Bakelite cylinder.

Figure 12.4  transformer

TRANSFOMER OIL:

Oil in transformers construction, serves the double purpose of cooling and insulating. For use in transformer tank, oil has to fulfil certain specifications and must be carefully selected. All type of oils are good insulators. Animal oil are good insulator but the are too viscousn that thay tend to form fatty acids, which attack fibrous materials(e.g.cotton)and therefore are undesirable for transformers. Vegatable oils are opt to be inconsistent in quality and like animal oils, tend to form to form destructive fatty acids. Mineral oils are suitable for electric purpose; some have a bituminous and other have a paraffin base. The crude oil as tapped, is distilling producing a range of volatile spirits and oils ranging from the very light to the heavy paraffin wax or bitumen.In the choice of an oil for transformer Use, following characteristics have to be concern:

(1)       Viscosity:

It determines the rate of cooling and varies with the temperature. A high viscosity is an obvious disadvantage because of the sluggish flow through small aperture, which it entails.

(2) INSULATING PROPERTIES:

It is usually unnecessary to trouble about the insulating properties of oil. Since it is always sufficiently good. A more important matter is however, the reduction of the dielectric strength due to the presence of moisture,which must be avoided. A very small quantity of the water In iol greatly lowers its insulating power while the presence of dust and small fibers tends to paths of low resistivity

(3)FLASH POINT:

The temperature vapor above an oil surface ignites spontaneously is termed as the flash point. Flash point of iol, used in  transformer, is not to be less than about 160 degree for the reasons f safety.

(4)Fire point:

The oil must not contain any impurity such as sulphur and it’scompounds. Sulphur when presents, caused corrosion of metal parts and accelerates the production of degree.C

(6)SLUDGING:

This is the most important characteristic. Sluding means, the slow formationsemi solid hydrocarbons,sometime of an acidic nature.Which are deposited on winding and tank walls.The formation of sludge is due to heat and oxidation.In its turns. It makes the whole transformer hotter thus aggavating the trouble, which may proceed until the cooling ducts are blocked. Experiences shows that sludge is formed more quickly in the presence of bright cotter surface.

The chief remedy available is to use oil, which remains without sludge formation even it is heated in the presence of oxygen, and to employ expansion chambers to restrict the contact of hot oil with the surrounding air.Among the products of oxidation of transoformer oil are volatile, water soluble, organic acids and water.Thes in combination can attack and corrode iron and othe metals. The provision the breathers not only prevents the moisture produced by oxidation of the oil.

Conservators are desirable to avoid the condensationof the water soluble acids on the un under surface of the tank lid from which acidic drop leads may fall back into the oil

NEW ISI FOR TRANSFORMERN OIL

Transformer oil has been a product of up gradation in our country. The first specification, adopted by our country,was IS:335/1963.This was based on the Britich standard 148 through B.S. has now undergone changes in 1984 I.S. has been changed 3-4 times during the last three decades.The amendment made in july 1987 and feb.1988, make the transformer oil specification most crudical in comparison to other

world standard.The state electricity board now insists upon this specification for transformer oil while accepting new new transformers and tapping up running transformer.This specification is to ensure proper quality and performance in the field.

The elaboration covers eleven points listed here under.These underline the importance of various factors and their influence on the improvement of quality.

     1)   it is now mandatory for transformer oil  manufacturers to produce onlyIS:35/1983 with amendment no.one of 1987 and of 1988 quality transformer oil. Then we can apply the symbol of product guaranteed (ISI mark), on our transformer oil since all the electricity board insists for ISI marked quality.It is easy to get the instrument approve quickly without any expance, the use of non-ISI marked oil will result in the rejection of the transformer.

     2)    All transformers designs are based on the basic quality of transformer oil which is defined by IS:335/1983 with amenmet no.two of 1988. Therefore it is imperative that whether it is a distribution transformer or power transformer. The basic quality has to be met to achieve the desirable performance of the equipment;setting of lower quality shall jeopardize the performance of the equipment resulting in higher losses then the extra cost of better quality of oil.

     3)    ETDC 64 is an electromechanical development committee of bureau of Indian standard monitor and continuously upgrades the specification of products in our country, This is the committee of experts from the field of research institutes, transformer oil processors, transformer manufacturers, electricity utilities, railways and other associations.Tje body decides the best standards for an equipment to give best performance.The present standard is non recommended, accepted and released for adoption to achieve this goal surely. This will result in better functioning of the requirement for higher productivity.

    4)     Central power research institute has conducted a lot of equipment on indigenous paprffin commercial oil and imported hepatic oils. Indian oil corporation limited supplies special based oil for experimentation. An oil produced from this base oil was tested, as per ASTM aging test method no.D1934 for its electrical and dhemical aging. This method appears appendix in IS:335.The resistivity and power, factor after 96 hours of aging indicate the peramenters are fixed and only best quality oil pass through this test.

     5)    Dielectric strength:

The electric strength and water contains are specified as follows.

BDVWATER CONTENTSOIL ISI 35 30 KV     50PPM              50 kv

The transformer iol after filtration is expected to give minimum 60 kv break down voltage (BDV)

     6)    Dissolved gases: The analysis of gases that dissolved in oil can helf in obtaining

 valuable information about faults such as partial discharge, arcing, local overheating, core bolted failure ETC. A refined oil or an over refined oil will show the analysis harmful to the performance of the equipment.A balance of aromatics should be maintained to absorb the hydrogen etc. gases during operation.

    7)   power factor

The power factor has beenchanged as under;

OLD                is335              0.005(MAX) 90C

NEW               IS335              0.005(MAX) 90C

An accelerated aging test under simulative conditions for 164 hours is fine indication of the life of the iol. The sludge and acidity specified for transformer oil is revised IS:

OLD                IS335              ACIDITY                    0.4(MAX)

                                                SLUDGE                   0.1(MAX)

NEW               IS335              ACIDITY                    0.4(MAX)

                                                SLUDGE                   0.1(MAX)

8) STORAGE, IDENTIFICATION AND MISABILITY:

Since there is only one grade of oil,the storage handling, identification and misability of oil becomes very easy in the passing phas. A user had to separately store the products.The oils and possible tesultants consequences.

There are three tansformer 220 KV yard and four power transformer 132 KV yard in G.S.S. Alwar. There are following specification.

            Auto transformer      MVA- 25/50

          Vector symbol             Hv/LV-440

            Frequency                 - 50 Hz

                                                HV      LV

KV (No Load)                                    220     132

Amperes                                262.4437.4

Phases                                              3  -  3

Type of cooling         on/OB/of. On Rating

                                    50% OB’ Rating-70%

Temperature of oil 40 ‘C

Make                          - Crompton greaves Ltd(Bombay)

Sr No                          - 24062

Type                           - Star-Star(Y-Y)

                                     HV            LV

                                    900 KVO 550 KVP

TRANSFORMER- ACCESSORIES

12.5 TERMINAL ARRANGEMENT

The LV line end bushings are also mounted on the cover. The bushings are ratd for 36 KV and are of the solid porcelain type, confirming to be 3347 The line bushings have single gap arcing horns with fixed gaps.

The HV line and neutral bushings are also mounted on the cover.The line end bushing are rated for 145 Kv system voltage, and are outdoor oil filled condenser type bushings confirming to IEC- 137/IS:2099.

The paper is wound directly ob to the metallic central tube.single piece and brown glazed, are pressed on to the central tube by means of springs in the head.The space between the insulating core and the porcelain shells is filled with transformer oil. The oil expansion chamber, located in the head is hermetically sealed slight glass in the head permits the oil level to checked.

The bushings are provided with adjustable gap arcing horns. The hv neutral is connected to an outdoor type, solid porcelain bushing rated for 36kv peak system. The bushing confirms to Is:3347/part Vth/sec.2.But with arcing horns removed. The bushing is mounted directly on the tank cover.

Two terminals from tertiary winding are brough out at the tank cover by means of 12/175 Kv  solid porcelain type bushings confirming to IS:3347/part III, but without arcing horns.The two terminals, when shorted, complete the delta connection of the tertiary. A link arrangement is provided for this porpose. The terminals should be connected to earth under operating conditions.

Winding temperature indicator

Winding temperature indicator consists essentially of a current transformer and athermal unit comprising a heating coil and a thermometric device.The thermal unit, Which is designed to have a thermal performance similar to that of the win windings of the power Xer, is influenced by two factors:

(1) The temperature of the surrounding oil, and

(2) The current flowing throght the heater coil, which will raise the temperature of the unit above that of the surrounding oil.

The CT secondary current is dhosen to the max ‘hot spot’ winding gradient occurring in either Hv or Lv windings of the power transformer. Thus the thermal unit’s capable of simulating the hottest-spot temperature of the transformer windings under al conditions.

THERMAL DEVICE

The bulb of a capillary type dial thermometer is screwed into a blind pocket, which is fitted inside the heating coil. This type of pocket enables the dial thermometer to be removed from the transformer without having to lower the oil level.

The heating coil with its blind type pocket fitted Inside is supported independently under the cover of the transformer; hence it is always in the hottest oil. The dial thermometer is provided with one or more sets of contacts for alarm/ or trip circuit and at time for controlling cooking equipment when forced cooling is called for.

OIL TEMPERATURE INDICATOR

An oil temperature indicator has been provided for measuring the transformer top oil temperature.the heat sensitive device of the thermometer is placed in an oil pocket mounted at the transformer cover, the thermometer has two adjustable mercury contacts and a maximum reading pointer.The contact may be used to close circuit for alarm and tripping device. The mercury switches are accessible by removing the top cover of the instrument and are adsustable for different temperature ratings by lotation of the mount a repeater dial is for remote indication  of the oil temperature in the control room. The thermometer is housed in the marshalling box.

OIL SURGE REALY FOR OLTC GEAR

An oil- operated relay having one set of contracts is designed to trip the transformer hetween the oil conservator. The relay is designed to trip the transformer on the occurrence of violent oil surges arising out of any malfunction in the OLTC operation. The conservator for the OLTC gear is separate from the main transformer conservator forms the conscrvator forms the conservator for the OLTC The terminals from the relay are wired to the terminal block located in the marshalling box.

MARSHALLING BOX

The marshalling box is of sheet steel, weatherproof construction, mounted on the side of the transformer. It is provided with a hinged door and pad lock, and housed the following instrument and terminal block:-

(a) Win ding temperature indicator

(b) Oil tempreterature indicator

(c) Terminal block for alarm and contacts of   bucholz relay

(d) Terminal block for oil legel alarm and contacts of Magnetic oil level Gauge.

(f)  Heater with switch

(g)  Mangetic oil leel gauge

The oil level gauge is mounted on the flate end of the con servitor. The indicator reads the oil level inside the conservator and initiates an alarm by closing the mercury contacts swith when the oil level is below the predetermined minimum. The contacts from the oil level gauge are wired to the terminal block located in the marchalling box.

(h) Cooling equipment

The transformer having mixed cooling ONAF and ONAF is provided with detachable radiators foxed to the tank wall throght valves. The ONAF cooling equipment comprises of four 457 mm dia fans,each blowing 3600 cu.ft. of air per minute on the radiator element directed in such a way that the no longer effective they turn pink. At the bottom of the breather a cup containing the transformer oil is screwed this oil acts as a seal, preventing the crystals from obsorbing moisture except when breathing is taking place.

Cooling plant

Oil cooling is normally achieved by heat exchange to the surrounding air.Sometimes a water jacket acts as the secondary cooling medium. Fans may be mounted directly onto the radiators and it is customary to use a number of separate fans rather than one or two large fans. Oil pumps for OFAF cooling are mounted in the return pipe at the bottom of the radiators. The motors driving the pumps often use the transformer oil as their cooling medium.

With ODAF cooling, the oil-to-air coolers tend to be compact and use relatively large fan blowers. With this arrangement the cooling effectiveness is very dependent on proper operation of the fans and oil pumps since the small amount of

cooling surface area gives relatively poor cooling by natural convection alone.Water cooling(ODWF) has similar characteristics to the ODAF cooling described above and is sometimes found in power station situations where ample and well-maintained supplies of cooling water are available.Cooling effectiveness is dependent upon the flow of cooling water and therefore on proper operation of the water pumps. Natural cooling with the out-of-service water pumps is very limited. Operational experience has not always been good, with corrosion and leakage problems, and the complexity of water pumps, pipes, valves and flow monitoring equipment.The ODAF arrangement is probably favourable as a replacement for the ODWF designs. Double wall cooler pipes give added protection against water leakage.The inner tube carries the water and any leakage into the outer tube is detected and causes an alarm. This more secure arrangement is at the expense of slightly reduced heat transfer for a given pipe size.Normal practice with cooling plant is to duplicate systems so that a failure of one need not directly affect operation of the transformer.Two separate radiators or radiator banks and duplicate oil pumps may be specified. In the larger ODAF cooling designs there may be four independent unit coolers giving a degree of redundancy.The transformer may be rated for full output with three out of the four coolers in service.Dry type transformers will normally be naturally air-cooled (classification AN) or incorporate fans (classification AF).

TAPPINGS AND TAP CHANGER

The transformer has an on load tap changer to cater for a variation of +5% to -15% in the HV voltage in 14 equal steps of 1.43% each for a constant power output. The tappings from the HV tapping winding are connected to a 15 position ‘f66’KV crompton greaves make high-speed resistor transition on load tap-changer. The tap-changer may be either manually operated or motor driven.

The motor driving mechanism is also described in the leaflet and is arranged for the following types of control.

• Local electrical electrical independent
• Remote electrical electrical independent
• Remote electrical group parallel control

Tap changer is used to change the HV voltage. We use tap changer in HV side only because in HV side current is less hence it is easy to handle lower amount of current. Tap changers are of two types.

                        1)No Load Tap changer

                        2)On Load Tap changer

No Load Tap changer      In this type tap changer, we have to cut off load before changing the taps.These kinds of tap changer are used in small transformers only.

On Load Tap changer

In this type tap changer load remains connected to transformer while changing the taps.This kind of tap changer requires special construction.Tapping winding is placed over HV winding.Generally,tapping winding is divided in 6 parts by the combination of these 6 winding and HV winding 17 different tap positions are used.

Chapter-13

Protection of Transformers

13.1 MERZ-PRICE PROTECTION RELAY

            Merz Price voltage balance system for the protection of 3-phse line. Identical current transformers are placed in each phase at both ends of the line. The pair of CTs in each line is connected in series with a relay in such a way that under normal conditions, their secondary voltages are equal and in opposition i.e. they balance each other.

            Under healthy conditions, current entering the line at one-end is equal to that leaving it at the other end. Therefore equal and opposite voltages are induced in the secondary’s of the CTs at the two ends of the line. The result is that no current flows through the relays. When a fault occurs at point F on the line as shown in Fig 6. It will cause a greater current to flow through CT₁ than through CT₂. Consequently, their secondary voltages become unequal and circulating current flows through the pilot wires and relays. The circuit breakers at both ends of the line will trip out and the faulty line will be isolated.

           

Fig.13.1: MERZ-PRICE PROTECTION RELAY

13.2 FIRE PROTECTION

The fire protection of 220 KV GSS can be dividing into two parts.

         1. Emulsifier system

         2. Hydrant system

1.    Emulsifier system

            This fire protection system is used to protect the transformers in the yard by extinguish the fire. This system consists of water tanks. Jickey pumps, D.G. sets, air compressor and two pipelines having different colors one (red) is used to circulate the water and other (yellow) is for air. This network of pipelines covered all the area of transformer jockey pumps are used to maintain the pressure of water at 7 kg/cm2.

                        A quarterized solenoid plastic valve is used with yellow pipeline near the base of transformer. On being fired around the transformer this plastic valve contains alcohol, which expands and due to this valve will burst. A dilute valve is erected near the transformer, which consists of two gates these gates are blocked due to the pressure of air. A water line is connected to this valve whenever the air releases and pressure goes down the gate is opened and a stream of water having 7Kg-cm² pressure is flow through the pipe and a shower of water is started around the transformer to check the air to come inside and hence this way. It extinguishes the fire.

2.    Hydrant system

This protection system is used to protect the yard and office dep’t from fire. A network of this system covers 1250m areas of GSS.

            It consists of three types:-

1)       Halon system

2)       Fire alarm system

3)       Miscellaneous system

           

Chapter-14

RELAY

A relay is an electrically operated switch  Current flowing through the coil of the relay creates a magnetic field which attracts a lever and changes the switch contacts  The coil current can be on or off so relays have two switch positions and they are double throw (changeover) switches 

Relays allow one circuit to switch a second circuit which can be completely separate from the first  For example a low voltage battery circuit can use a relay to switch a 230V AC mains circuit  There is no electrical connection inside the relay between the two circuits, the link is magnetic and mechanical 

The coil of a relay passes a relatively large current, typically 30mA for a 12V relay, but it can be as much as 100mA for relays designed to operate from lower voltages  Most ICs (chips) cannot provide this current and a transistor is usually used to amplify the small IC current to the larger value required for the relay coil  The maximum output current for the popular 555 timer IC is 200mA so these devices can supply relay coils directly without amplification 

Relays are usually SPDT or DPDT but they can have many more sets of switch contacts, for example relays with 4 sets of changeover contacts are readily available  For further information about switch contacts and the terms used to describe them please see the page on switches 

Types of Relays

These are called normally opened, normally closed in GSS control room there is panel in which the relays are set and there are many types of relays 

1. Over voltage relays
2. Over current relays
3. I D M T  fault relay
4. Earth fault relay
5. Bucheloz’s relay
6. Differential relay

Over voltage relay: - This protection is required to avoid damage of system in case line becomes open circuited at one end  These fault would trip the local circuit breaker thus block the local and remote ends  This relay is operated i e , energized by CVT connected to lines 

Over Current RELAY: -This relay has the upper electromagnet of non-directional relay connected in series with lower non-directional electromagnet  When the fault current flow through relay current coil which produces flux in lower magnet of directional element  Thus the directional relay has the winding over the electromagnets of non-directional element and produces a flux in lower magnet and thus over current operates 

Earth fault relay: -when a conductor breaks due to some reason and it is earthen then earth fault occurs  The fault current is very high thus, there is need to of over current relay  This relay has minimum operating time 

Directional relay: - It allows flowing the current only in one direction then only this relay operates  It has a winding connected through the voltage coil of relay to lower magnet winding called current coil  Which is energized by C T  if fault occurs  This relay operates when v/I is less than theoretical value  The v/I is normally constant 

Differential relay: - This relay operates when phase difference of two electrical quantities exceeds the predetermined value  It has always two electrical quantities; hence in 400kv GSS for transformer differential relay is used 

Inverse time characteristics relay: - The relay using here having the inverse time characteristics having the time delays dependent upon current value  This characteristic is being available in relay of special design  There are:-

                          i.    Electromagnetic Induction type

                        ii.    Permanent magnetic moving coil type

                       iii.     Static type

Buchholz’s relay: - It is the protective device of the transformer  When any fault occurs in the transformer then it indicates about fault and we disconnect the transformer from the circuit  It is used in the power transformer  It is connected between the tank and conservator  It has two floats on which two mercury switch are attached  One float is used for the bell indication and other float is used for the tripping  In the normal position the relay is filled with the oil and contacts of the mercury switch are opened  When the earth fault occurs in the transformer then it increases the temperature of oil and oil flows into the conservator through relay  On the way it makes the contacts of the tripping circuit short  So in the we can say that this relay works as circuit breaker

Fig.14.1: BUCHHOLZ RELAY               Fig.14.2: OVER CURRENT INDUCTION RELAY

Chapter-15

INSULATORS

 In order to avoid current leakage to the Earth, through the supporting structure provide to the conductor of overhead transmission lines, insulators are used. The conductors are secured to the supporting structures by means of insulating feature, which do not allow current to flow through these support and hence finally to the earth . Bus support insulators are porcelain or fiberglass insulators that serve to the bus bar switches and other support structures and to prevent leakage current from flowing through the structure or to ground. These insulators are similar in function to other insulator used in substations and transmission poles and towers. 

An Insulator should have following characteristic:-

1. High Insulation resistance.
2. High mechanical strength
3. No internal impurity or crack  Disc

  Generally Porcelain or glass is used as material for insulators. Porcelain because of its low cost. is more common. 

Insulators can be classified in following ways :- 

Pin Type: - These are designed to be mounted on a pin, which in turn is installed on the cross arm of a pole. 

Figure-14.1 INSULATORS

Suspension Type:-These insulators hang from the cross arm, there by forming a string. 

 The centre post carries the moving contact assembled at the extremities the moving contact engages the fixed contacts are generally in the form of spring loaded finger contact.

The insulator consist of following parts - 

1. Contacts :- The contacts are rated for line current and designed to withstand electromagnetic strains and prevent charging at rated shortly time current the contact are made of electrolytic fixed in housing.

Figure 14.2  insulators

2. Switching blade:- The blade is made of electrolytic copper. 

3. Tandom pipe:-All three phases are opened or closed simultaneously with a tandem pipe this is dipped galvanized and provided with on or off insulators and pad locking. 

4. Motor operated:-This is meant rotary motion of the linear operating pipe for either of opening or closing for remote level local operation. Hand operation is also provides withdetectable handle that can be fitted and square.     

Chapter-16

EARTHING

 Earthing is the provision of a surface under the sub station, which has a uniform potential as nearly as zero or equal to Absolute Earth potential. The provision of an earthing system for an electric system is necessary by the following reason. 

1. In the event of over voltage on the system due to lighting discharge or other system fault. These parts of equipment which are normally dead as for as voltage, are concerned do not attain dangerously high potential.

2. In a three phase, circuit the neutral of the system is earthed in order to stabilize the potential of circuit with respect to earth

 The resistance of earthing system is depending on shape and material of earth electrode used.    

 the earthing is of two principal types  :-

1. Neutral Earthing
2. quipment Body Earthing

    Neutral Earthing:-

Neutral Earthing also known as System Neutral Earthing (or Grounding) means connecting the neutral point i.e. the star point of generator,transformer etc. to earth. In rotating machines, generator, transformer circuit etc., the neutral point is always connected to earth either directly or through a reactance. The neutral point is usually available at every voltage level from generator or transformer neutral. If neutral point is not available, then the most common method used is using a Zigzag transformer. Such a transformer has no secondary. Each phase of primary has two equal parts. There are 3 limbs and each limb has two winding, providing flux density under normal condition. Since the fluxes are opposite, the transformer takes very small magnetizing current under normal conditions. During fault, the circuit is primary side,

which provides very less impedance to the current. The grounding transformers are short time rating. Their size is almost one tenth as compared to power transformer. 

Electrical Earthing:-

electrical Earthing is different from neutral earthing. During fault condition, the metallic parts of an electrical installation which do not carry current under normal conditions, may attain high potential with respect to ground. As human body can tolerate only I=0.165A/T current for a given time t so to ensure safety we connect such metallic parts to earth by means of Earthing system ,which comprises of electrical conductor to send fault current to earth. The conductor used is generally in the form of rods, plates, pipes etc. 

Earthing system ensures safety in following ways :-

1. The potential of earthen body does not reach dangerously high value about earth, since it is connected to earth.
2.  Earth fault current flows through earthing and readily causes the operation of fuse or an earth relay.

Connection of Electrical Equipment to Substation:- 

S.NO.	Apparatus	Path to be connected
1.	Supporting of bus insulator	Base plate
2.	High voltage circuit breaker	Operating mechanism frame
3.	Isolator	Operating mechanism frame bed
4.	Potential transformer	Transformer tank LV
5.	Power transformer	Core tank

Merits of neutral Earthing:-

1. Arcing grounding is reduced.

2. Voltage of heating with respect to earth remains at harmless value they don't increase to root 3 times of normal value. 

3. Suitable neutral point.

4. The earth fault relaying is relatively simple useful amount of earth fault current is available to operate earth fault relay.

5. The over voltage due to lightening are discharged to earth. 

6. Improved service reliability due to limitation of arcing ground and improved of unnecessary fringing of CB.

At GSS the neutral point of power transformer is connected solidly to earth generally the earth connection are provided which leads reliability.

Chapter-17

 POWER LINE CARRIER COMMUNICATION

16.1  Introduction

Power line communication or power line carrier (PLC), also known as Power line Digital Subscriber Line (PDSL), mains communication, power line telecom (PLT), or power line networking (PLN), is a system for carrying data on a conductor also used for electric power transmission. Broadband over Power Lines (BPL) uses PLC by sending and receiving information bearing signals over power lines.

Electrical power is transmitted over high voltage transmission lines, distributed over medium voltage, and used inside buildings at lower voltages. Powerline communications can be applied at each stage. Most PLC technologies limit themselves to one set of wires (for example, premises wiring), but some can cross between two levels (for example, both the distribution network and premises wiring). Typically the transformer prevents propagating the signal so multiple PLC technologies are bridged to form very large networks.

All power line communications systems operate by impressing a modulated carrier signal on the wiring system. Different types of powerline communications use different frequency bands, depending on the signal transmission characteristics of the power wiring used. Since the power wiring system was originally intended for transmission of AC power, in conventional use, the power wire circuits have only a limited ability to carry higher frequencies. The propagation problem is a limiting factor for each type of power line communications. A new discovery called E-Line that allows a single power conductor on an overhead power line to operate as a waveguide to provide low attenuation propagation of RF through microwave energy lines while providing information rate of multiple Gbps is an exception to this limitation.

Data rates over a power line communication system vary widely. Low-frequency (about 100-200 kHz) carriers impressed on high-voltage transmission lines may carry one or two analog voice circuits, or telemetry and control circuits with an equivalent data rate of a few hundred bits per second; however, these circuits may be many miles long. Higher data rates generally imply shorter ranges; a local area network operating at millions of bits per second may only cover one floor of an office building, but eliminates installation of dedicated network cabling.

16.2  MAJOR SYSTEM COMPONENTS EQUIPMENT          

The major components of a PLC channel are shown in Figure. The problem associated with the PLC channel is the requirement to put the carrier signal onto the high voltage line without damaging the carrier equipment. Once the signal is on the power line it must be directed in the proper direction in order for it to be received at the remote line terminal.

Fig16.1: Basic Power Line Carrier Terminal

16.3 BASIC PRINCIPLE OF PLCC

In PLCC the higher mechanical strength and insulation level of high voltage power lines result in increased reliability of communication and lower attenuation over long distances.

 Since telephone communication system cannot be directly connected to the high voltage lines, suitably designed coupling devices have therefore to be employed. These usually consist of high voltage capacitors or capacitor with potential devices used in conjunction with suitable line matching units (LMU’s) for matching the impedance of line to that of the coaxial cable connecting the unit to the PLC transmit-receive equipment.

 Also the carrier currents used for communication have to be prevented from entering the power equipment used in G.S.S as this would result in high attenuation or even complete loss of communication signals when earthed at isolator.. Wave traps usually have one or more suitably designed capacitors connected in parallel with the choke coils so as to resonate at carrier frequencies and thus offers even high impedance to the flow of RF currents.

Fig 16.2. Power Line Carrier Communication

                                 

16.4  LINE TRAPS or WAVE TRAPS:-

The carrier energy on the transmission line must be directed toward the remote line terminal and not toward the station bus, and it must be isolated from bus impedance variations. This task is performed by the line trap. The line trap is usually a form of a parallel resonant circuit which is tuned to the carrier energy frequency. A parallel resonant circuit has high impedance at its tuned frequency, and it then causes most of the carrier energy to flow toward the remote line terminal. The coil of the line trap provides a low impedance path for the flow of the power frequency energy. Since the power flow is rather large at times, the coil used in a line trap must be large in terms of physical size.

Fig.16.3: wave trap

Once the carrier energy is on the power line, any control of the signal has been given over to nature until it reaches the other end. During the process of traveling to the other end the signal is attenuated, and also noise from the environment is added to the signal. At the receiving terminal the signal is decoupled from the power line in much the same way that it was coupled at the transmitting terminal. The signal is then sent to the receivers in the control house via the coaxial cable.

16.5 COUPLING CAPACITORS:-

The coupling capacitor is used as part of the tuning circuit. The coupling capacitor is the device which provides a low

impedance path for the carrier energy to the high voltage line and at the same time, it blocks the power frequency current by being a high impedance path at those frequencies. It can perform its function of dropping line voltage across its capacitance if the low voltage end is at ground potential. Since it is desirable to connect the line tuner output to this low voltage point a device must be used to provide a high impedance path to ground for the carrier signal and a low impedance path for the power frequency current. This device is an inductor and is called a drain coil. The coupling capacitor and drain coil circuit are shown in Figure.

Fig 16.4 Coupling Capacitor and Drain Coil Combination

                       

                       

 It is desirable to have the coupling capacitor value as large as possible in order to lower the loss of carrier energy and keep the bandwidth of the coupling system as wide as possible. However, due to the high voltage that must be handled and financial budget limitations, the coupling capacitor values are not as high as one might desire. Technology has enabled suppliers to continually increase the capacitance of the coupling capacitor for the same price thus improving performance.

16.6 DRAINAGE COILS:-

The drainage coil has a pondered iron core that serves to ground the power frequency charging to appear in the output of the unit. The coarse voltage arrester consists of an air gap, which sparks over at about 2 KV and protects the matching unit against line surges. The grounding switch is kept open during normal operation and is closed if anything is to be done on the communication equipment without interruption to power flow on the line. The matching transformer is isolated for 7 to 10 KV between the two winding and former two functions. Firstly it isolates the communication equipment for the power line. Secondly it serves to match the characteristic impedance of the power line 400-600 ohms to that of the co-axial vacuum arrester (which sparks) is over at about 250 V is provided for giving additional protection to the communication equipment.

                        The LMU which consists of the matching transformer and tuning capacitors indicated above is tailor-made to suit the individual requirements of the coupling equipment and is generally tuned to a wide band of carrier frequencies-(100-450 KHz typical).

16.7 ADVANTAGES & DISADVANTAGES OF PLCC

 ADVANTAGES

1. No separate wires are needed for communication purposes as the power lines themselves carry power as well as the communication signals. Hence the cost of constructing separate telephone lines is saved.
2. When compared with ordinary lines the power lines have appreciably higher mechanical strength. They would normally remain unaffected under the condition which might seriously damage telephone lines.

3.    Power lines usually provide the shortest route between the power stations.

4.    Power lines have large cross-sectional area resulting in very low resisntanc3 per unit length. Consequently the carrier signal suffers lesser attenuation than when travel on usual telephone lines of equal lengths.

 5. Power lines are well insulated to provide negligible leakage between conductors and ground even in adverse weather conditions.

     6. Largest spacing between conductors reduces capacitance which results in smaller attenuation at high frequencies. The large spacing also reduces the cross talk to a considerable extent.

DISADVANTAGES

1. Proper care has to be taken to guard carrier equipment and persons using them against high voltage and currents on the line.
2. Reflections are produced on spur lines connected to high voltage lines. This increases attenuation and create other problems.
3. High voltage lines have transformer connections, which attenuate carrier currents. Sub-station equipments adversely affect the carrier currents.
4. Noise introduced by power lines is much more than in case of telephone lines. This due to the noise generated by discharge across insulators, corona and switching processes.

16.8 Failure Scenarios

There are many ways in which the communication signal may have error introduced into it. Interference, cross chatter, some active devices, and some passive devices all introduce noise or attenuation into the signal. When error becomes significant the devices controlled by the unreliable signal may fail, become inoperative, or operate in an undesirable fashion.

1. Interference: Interference from nearby systems can cause signal degradation as the modem may not be able to determine a specific frequency among many signals in the same bandwidth.

2. Signal Attenuation by Active Devices: Devices such as relays, transistors, and rectifiers create noise in their respective systems, increasing the likelihood of signal degradation.

3. Signal Attenuation by Passive Devices: Transformers and DC-DC converters attenuate the input frequency signal almost completely. "Bypass" devices become necessary for the signal to be passed on to the receiving node. A bypass device may consist of three stages, a filter in series with a protection stage and coupler, placed in parallel with the passive device.

Chapter-17

Control room

 To remote control of power switch gear requires the provision of suitable control plates located at a suitable point remote from immediate vicinity of CB’s  and other equipments.

At "GSS ALWAR" the separate control room provided for remote protection of 220KV switch yards transformer incoming feeder, outing feeders. Bus bar has their own control plant in their control rooms. The control panel carrier the appropriate relays. Necessary meters indicating lamp control switches and fuses. There are meters for reading purpose. A circuit concerning the panel is shown on the panel with standard co lour.

On each panel a control switch is provided for remote operation of circuit breaker. There are two indicators which show that weather circuit breaker is closed or open. A control switch for each insulator is also provided. The position indicator of isolator is also done with the help of single lamp and indicator. The colour of signal lamps are as follows :- 

RED:- For circuit breaker or isolator is close option

Green - For circuit breaker is in open position.

Amber - Indicates abnormal condition requiring action.

In addition to used indication an alarm is also providing for indicating abnormal condition when any protective relay or tripping relay has operated. Its constants energies on auxiliary alarm. Relay which on operation completes the alarm belt circuit. 

Synchronizing:-

There is a hinged Synchronizing panel mounted at the end of control panel. Before coupling any incoming feeders to the bus bar. It just be Synchronized with switches. When the synchronous copy shows zero we close the circuit breaker. 

Synchronoscope is used to determine the correct instant of closing the switch which connect the new supply  to bus bar. The correct instant of synchronizing when bus bar incoming voltage. 

1.    Are in phase

2. Are equal in magnitude
3. Are in some phase sequence
4. Having same frequency
5. The voltage can be checked by voltmeter the function of synchronoscope is to indicate the difference in phase and frequency. 

Fig.17.1:A panel of CONTROL ROOM

Energy Meter: - These are fitted on different panel to record transmitted energy and recorded in energy hours. For this purpose MWH meter have been provided. 

Watt Meter: - This is mounted on each feeder panel to record import or export power.

Frequency Power: - Provided to each feeder to measure frequency which analog or digital. 

lt METER:-Provided on each panel or the purpose of indication of voltage. 

Ammeter:-These are used to indication the line current. 

MVAR Meter:-Provided for indicating power factor of import and export. 

Maximum Indicator DEMAND:-

Chief requirement of these indicators to record the minimum power factor taken by feeder during a particular period. This record the average power successive predetermined period.

Fig 17.2 control room

Chapter-18

BATTERY ROOM

There is a battery room which has 55 batteries of 2 volt each for 132KV section and 110 batteries for 220KV section. Therefore D.C. power available is for functioning of the control panels. A battery charger to charge the battery. 

1. Various parts of lead acid batteries:-

1. Plates
2. Separators
3. Electrolyte
4. Container
5. Terminal port
6. Vent plugs

Fig.18.1 :a view of battery room

Charging of batteries:-

Initial charging

It is the first charging given to batteries by which the   positive plates are converted to “lead peroxide”, where as  the –ve plates will converted to spongy lead. Also in a fully charged battery the electrolyte specific gravity will be at its highest venue or 1.2 and its terminal voltage will be 24  volts                      

Fig.18.2 :a view of battery room

Discharging:-    

 When a fully charged battery delivers its energy out by meeting a load the lead peroxide of the +ve plates slowly gets converted to lead sulphate and the spongy lead of the –ve plates also gets converted into lead sulphate during this time the specific gravity of the electrolyte also decreases the value around 1.00 and the terminal voltage also decreases from its initial to a lower value which may be around 1.85 or 1.8.

                            Chapter-17

Capacitor bank

Capacitor banks are used to improve the quality of the electrical supply and the efficient operation of the power system. Studies show that a flat voltage profile on the system can significantly reduce line losses. Capacitor banks are relatively inexpensive and can be easily installed anywhere on the network.

                                                   Fig.17.1:- CAPACITOR BANK

The capacitor unit is made up of individual capacitor elements, arranged in parallel/ series connected groups, within a steel enclosure. The internal discharge device is a resistor that reduces the unit residual voltage to 50V or less in 5 min. Capacitor units are available in a variety of voltage ratings (240 V to 24940V) and sizes (2.5 kvar to about 1000 kvar).

The capactor bank used for 33 kv   at alwar is

1     3 units of 2*5.4  MVAR

2     1 unit of  4.2 MVAR

3     1 unit of 2*2.1 MVAR

4     1 unit of 6.6 MVAR

The capactor bank used for 11  kv   at alwar is

                 1    1 unit of 4 MVAR   

Fig.17.2 : capacitor bank in g.s.s. alwar

            DAILY DIARY

On 13th june

I study about the all the incoming & out going feeder of the 220 kv gss

On 14th june

I went in to the yard and practically saw the feeders of 220kv side yard and the 132 kv yard

On 15th june

In the control room i saw the single line diagram of both yard and made in my diary

On 16th june

Saw the 100 MVA transformer(220/132)KV And (132/33)KV transformer

On 17th june

Study about the capacitor bank  ,RVT,SR

On 20th june

Saw the Bus arrangement in t he two yards

On 24th june

Study about the lightning arrester(LA),isolator ,circuit breakers

On 27th june

Saw the compressor room &saw the CT,Pt,CVT

On 28th june

Learn about the PLCC& PLCC room

On 30th june

Basic about  the  Control room

On 1th july

Battery room & transformer oil cleaning

On 4th july

About the conductor &insulator types of material used

On 5th july

 Maintenance  of the gss & fault analysis

On 6th july

Control pannels of transformer &out going feeders

On 8th july

Reays & other protecting devices

On 11th july

revision

On 12th july

Ask questions &take   feedback

On 13th july

Pursue certificate

            The training at grid substation was very helpful. It has improved my theoretical concepts of electrical power transmission and distribution. Protection of various apparatus was a great thing. Maintenance of transformer, circuit breaker, isolator, insulator, bus bar etc was observable.

 I had a chance to see the remote control of the equipments from control room itself, which was very interesting.