Practical Training Report
“ 220 K.V GRID SUBSTATION”
ALLAHABAD CANTT (U.P)
in partial fulfillment
for the award of the Degree of
Bachelor of Technology
Submitted To: Submitted By:
Mr.Deepak Sharma Srijan Tripathi
Head of Department 11EAYEE049
Department of Electrical Engineering
AryaCollege of Engineering &Research Centre, Jaipur
Rajasthan Technical University, Kota
ARYA COLLEGE OF ENGINEERING & RESEARCH CENTRE
SP-40, RIICO Industrial Area, Jaipur (Raj)-302022
Department of Electrical Engineering
This is to certify that the work, which is being presented in the Practical
Training Seminar report for practical training taken at 220kv G.S.S
ALLAHABAD CANTT(UP),10/06/2014 to10/07/2014 submitted by Mr
SRIJAN TRIPATHI a student of fourth year (VII Sem) B.Tech. in
Electrical Engineering as a partial fulfilment for the award of degree of
Bachelor of Technology is a record of student’s work carried out and
found satisfactory for submission.
Mr. Avdhesh Agrawal Mr. Deepak Sharma
PTS Coordinator Head of Department
I hereby declare that the work, which is being presented in the practical training seminar,
entitled “220 K.V GRID SUBSTATION ALLAHABAD CANTT (U.P)”in partial
fulfillment for the award of Degree of “Bachelor of Technology” in Electrical Engineering,
submitted to the Department of Electrical Engineering, Arya College of Engineering
&Research Centre, Rajasthan Technical University is a record of my own work carried under
the Guidance of Mr. A.K.Singh (G.S.S,).
I have not submitted the matter presented in this Report anywhere for the award of any other
(Signature of Candidate)
We wish to express our deep sense of gratitude to our Practical Training Guide
Mr.A.K.Singh & Mr. Chandra Mohan, 220kv Substation, UPPTCL, Cantt Allahabad.
For guiding me from the inception till the completion of the project. We sincerely
acknowledge him for giving his valuable guidance, support for literature survey, critical
reviews and comments for our Project.
We would like to first of all express our thanks toDr. Pooja Agarwal, Director of Arya
Main Campus,for providing us such a great infrastructure and environment for our overall
We express sincere thanks to Prof(Dr.)I C Sharma the Principal of ACERC, for his kind
cooperation and extendible support towards the completion of our project.
Words are inadequate in offering our thanks to Mr. Deepak Sharma, H.O.D of EE
Department, for consistent encouragement and support for shaping our project in the
We also express our deepest thanks to Mr. Avdesh Agarwal for his support in providing
technical requirement and fulfilling our various other requirements for making our project
We also like to express our thanks to all supporting EE faculty members who have been a
constant source of encouragement for successful completion of the project.
Also our warm thanks to Arya College of Engineering &Research Centre, who provided
us this opportunity to carryout, this prestigious Project and enhance our learning in various
Substation is situated nearby ALLAHABAD CANTT. It is 1km away from city, the
substation is equipped with various equipments and here are various arrangements for the
The equipments in the G.S.S. are listed previously.
At this substation following feeders are established.
220 KV Incoming Feeders
1. FATEHPUR LINE
132 KV Outgoing Feeders
1. REVA ROAD LINE
2. MANURI LINE
33 KV Outgoing Feeders
2. KANPUR ROAD
4. KARELI I
220 KV G.S.S CANTT is an outdoor type primary substation and distribution substation as
well it has not only step down station but also the distribution work.
LIST OF FIGURES
FIG 1.1 BASIC OUTLAY DIAGRAM OF 132 K V G.S.S F.C.I 1
FIG 1.2 SINGLE LINE DIAGRAM OF 132 K V G.S.S F.C.I 7
FIG 2.1 BASIC OPERATION OF A TRANSFORMER 9
FIG 2.2 LARGE POWER TRANSFORMER OF 132 K V G.S.S F.C.I 10
FIG 2.3 TRANSFORMER CORE 12
FIG 3.1 CT IN THE YARD 14
FIG 4.1 CVT 16
FIG 4.2 ELECTROMAGNETIC TYPE POTENTIAL TRANSFORMER 18
FIG 5.1 BUS-BAR 19
FIG 6.1 ISOLATORS 24
FIG 7.1 SF6 CIRCUIT BREAKER 29
FIG 8.1 LIGHTNING ARRESTORS ON SUB-STATION 33
FIG 9.1 BUS SUPPORT INSULATORS 35
FIG9.2 PIN TYPE INSULATOR 36
FIG 9.3 SUSPENSION TYPE INSULATOR 37
FIG 9.4 STRAIN TYPE INSULATOR 38
FIG 9.5 SHACKLE TYPE INSULATOR 38
FIG 10.1 SUB-STATION CONTROL PANEL 40
FIG 11.1 SUB-STATION RELAY PANEL 43
FIG 11.2 INTERNAL STRUCTURE OF THE BUCHHOLZ RELAY 45
FIG 12.1 POWER LINE CARRIER SCHEMATIC 49
FIG 12.2 POWER LINE CARRIER COMMUNICTION SYSTEM 50
FIG 12.3 POWER LINE CARRIER DEVICES IN CONTROL HOUSE 50
FIG 12.4 WAVE TRAP 51
FIG 12.5 COUPLING CAPACITOR AND DRAIN COIL COMBINATION 52
FIG 13.1 GROUND WIRES 56
FIG. 14.1 BATTERY ROOM 58
FIG. NO. FIGURE NAME PAGE NO.
TABLE TABLE NAME PAGE NO.
TABLE 1.1 SPECIFICATIONS OF PLANT TRANSFORMER 11
TABLE 4.2.3 RATING OF CVT 17
TABLE 6.3 RATING OF SOME ISOLATORS 25
TABLE 9.3 RATING OF AIR BREAK INSULATOR 38
S.NO. NAME FIGURE
1 TWO WINDING
2 THREE WINDING
3 AUTO TRANSFORMER
4 CURRENT TRANSFORMER
5 POTENTIAL TRANSFORMER
6 CIRCUIT BREAKER
8 LIGHTENING ARRESTER
CERTIFICATE FROM DEPARTMENT I
CERTIFICATE FROM COMPANY II
CANDIDATE’S DECLARATION III
FIGURE LIST VI
TABLE LIST VII
SYMBOLS LIST VIII
CHAPTER 1 INTRODUCTION 1-8
1.1 U.P.P.T.C.L 1
1.2 400 KV GRID SUBSTATION, G.S.S F.C.I 4
1.3 MAIN EQUIPMENTS HOUSED AT GSS 6
1.4 DETAILS OF ORGANIZATION SETUP 8
CHAPTER 2 POWER TRANSFORMER 9-12
2.1 DESCRIPTION OF PLANT TRANSFORMER 10
2.2 CORE 12
CHAPTER 3 CURRENT TRANSFORMER 13-15
3.1 BASIC FEATURE OF CURRENT TRANSFORMER 14
CHAPTER 4 POTENTIAL TRANSFORMER/CVT 16-18
4.1 CLASSIFICATION OF POTENTIAL TRANSFORMER 16
4.2 CAPACITIVE VOLTAGE TRANSFORMER 17
4.3 ELECTROMAGNETIC TYPE POTENTIAL
CHAPTER 5 BUS-BARS 19-22
5.1 BAR-BUS ARRANGEMENT MAY BE OF
FOLLOWING TYPESWHICH ARE BEING
ADOPTED BY U.P.P.T.C.L 20
5.2 BUS-BAR ARRANGEMENT DEPENDS UPON 20
5.3 DOUBLE BUS BAR / CONTENTS MAIN BUS-I WITH
MAIN BUS-II ARRANGEMENT 20
5.4 DOUBLE BUS-BAR ARRANGEMENTS/CONTAIN
MAIN US WITH AUXILIARY BUS
(OR TRANSFORMER BUS)21
5.5 DOUBLE BREAKER 21
5.6 MESH SCHEME 21
CHAPTER 6 ISOLATORS 23-25
6.1 INTRODUCTION 23
6.2 OPERATION 24
6.3 RATING OF SOME ISOLATORS 25
6.4 PARTS 25
CHAPTER 7 CIRCUIT BREAKERS 26-30
7.1 INTRODUCTION 26
7.2 FUNCTIONS OF CIRCUIT BREAKER 26
7.3 CIRCUIT BREAKER TYPES 27
CHAPTER 8 LIGHTNING ARRESTORS 31-34
8.1 INTRODUCTION 31
8.2 PRINCIPLE 31
8.3 CONSTRUCTION 32
8.4 THYRITE TYPE 33
CHAPTER 9 INSULATORS 35-39
9.1 BUS SUPPORT INSULATORS 35
9.2 TYPES OF INSULATORS 36
9.3 RATING OF AIR BREAK INSULATOR 39
CHAPTER 10 CONTROL ROOM 40-42
10.1 SYNCHRONIZING PANEL 41
10.2 SYNCHRONOSCOPE 41
10.3 ANNOUNCIATOR 41
10.4 ASURING INSTRUMENT USED 42
CHAPTER 11 RELAYS 43-47
11.1 POWER TRANSFORMER PROTECTION 44
11.2 BUCHHOLZ RELAY 45
11.3 OVER CURRENT AND EARTH FAULT PROTECTION 46
11.4 TRANSMISSION LINE PROTECTION 47
CHAPTER 12 POWER LINE CARRIER COMMUNICATION 49-54
12.1 BASIC PRINCIPLE OF PLCC 49
12.2 COMPONENT OF COUPLING ARRANGEMENT 50
12.3 ADVANTAGE AND DISADVANTAGE OF PLCC 53
12.4 PLCC SYSTEM IN RAJASTHAN 54
CHAPTER 13 EARTHING OF THE SYSTEM 55-57
13.1 PROCEDURE OF EARTHING 55
CHAPTER 14 BATTERY ROOM 58-59
14.1 BATTERY SYSTEM 58
SAFETY DEPARTMENT 62
DO’S & DON’TS 63
Uttar Pradesh Power Transmission Co-operation Limited a company under the Companies
Act, 1956 and registered with Registrar of Companies as "UTTAR PRADESH POWER
TRANSMISSION CO- OPERATION LIMITED" vide No. 17-016485 of 2000-2001 with its
Registered Office at VIDYUT BHAWAN, has been established on 19 July, 2000 by Govt. of
UTTAR PRADESH under the provisions of the UTTAR PRADESH Power Sector Reform act
1999 as the successor company of UPPTCL. The UPPTCL has granted UPPTCL a license for
transmission and bulk supply vide UPPTCL/Transmission and Bulk Supply License 4/2001
dated 30.4.2001 to function as Transmission and Bulk Supply Licensee in the State.
Figure 1.1 Basic outlay of GSS
Under the provision of the Electricity Act, 2003, UPPTCL has been declared as State
Transmission Utility (STU) by Govt. of UTTAR PRADESH. Section 39(1) of this act,
prohibits the STU to undertake business of trading of electricity, however UPPTCL continued
its function of transmission of bulk power from generating stations to inter-phase point of
Discoms from 1st April 2004. Now the Distribution Companies are directly contracting with
Generating Companies in accordance to the share allocated by the State Government. UTTAR
PRADESH Power Procurement Cell (UPPPC) has been established for purchase of power on
behalf of Discoms.
UPPTCL will be professionally managed utility supplying reliable and cost efficient
electricity to every citizen of the state through highly motivated employees and state of art
technologies, providing an economic return to our owners and maintaining leadership in the
country.UPPTCL provides the pathway for power within whole of UTTAR PRADESH.
UPPTCL owns, builds, maintains and operates the high-voltage electrical transmission system
that helps to keep the lights on, businesses running and communities strong. UPPTCL also
owns the shared generating projects as representative of erstwhile UPEB.
Our customers include electricity generators, distribution companies and open access
consumers who count on UPPTCL to deliver power from the location of generation to inter-
phase point of Discoms enabling them to supply where it's needed in the homes and
businesses they serve. Our aim is to provide reliable electric transmission service to these
customers. As a public utility whose infrastructure serves as the link in transporting electricity
to millions of electricity users, UPPTCL has following duties and responsibilities:
1. Intra state transmission of electricity through Intra-State Transmission System.
2. Planning and co-ordination relating to intra-state transmission with all concerned
agencies such as CTU, State Govt., generating companies, licensees, Regional Power
3. Ensuring development of an efficient, co-ordinate and economical system of intra-state
transmission of electricity from generating stations to Load Centers.
4. Non-discriminatory Open Access to its transmission system on payment of
5. Complying with the directions of RLDC and SLDC, operating SLDC until any other
authority is established by the State Govt.
Now UPPTCL is "An ISO 9001:2000 Certified Company" .UTTAR PRADESH POWER
TRANSMISSION CO-OPERATION LIMITED which will be the transmission Company and
three regional distribution companies namely Uttar PradeshVidyutVitaran Nigam Ltd.
The Transmission Company will own and operate all the 400kV, 220 kV, 132kV and
electricity lines and system in State and will also be responsible for procuring power.
The three Distribution Companies will operate and maintain the electricity system below 132
kV in the state and their respective areas.
Along these transmission lines secondary substation are created where voltage is further
stepped down to sub transmission and primary distribution voltage.
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 consumer.
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 400 kV, 220 kV,
132 kV and for distribution 33 kV, 11 kV etc.
Electricity boards are setup in all states of India which are responsible for:-
They also construct, install and maintain all the station made for these purpose. In UTTAR
PRADESH U.P.P.T.C.L is responsible for transmission and distribution of electrical power all
over UTTAR PRADESH. It has its own generating station and it’s also gets power from
various other stations also. Power obtain from these stations is transmitted all over UTTAR
PRADESH with the help of grid stations. Depending on the purpose, substations may be
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 substation
Depending on constructional feature substation is classified as:-
1. Outdoor type
2. Indoor type
3. Basement or Underground type
4. Pole mounting open or kilos type
The control room is equipped with protective relays, ammeters, voltmeters, energy meters and
frequency and power factor meters. D.C. supply is heart of GSS batteries are used for this
purpose. They have separate charging circuit also. For communication purpose P.L.C.C. is
used which has its various components.
1.2 220 KV GRID SUBSTATION, CANTT
The 220KVRewa road line is connected to main bus of 220KV. Now the transmission line
first parallel connected with lightning arrester to diverge surge, followed by CVT connected
parallel. CVT measures voltage and steeps down at 110V. A.C. for control panel, at the
location a wave trap is connected to carrier communication at higher frequencies. A current
transformer is connected in series with line which measure current and step down current at
ratio 800:1 for control panel.
Switchgear equipment is provided, which is the combination of a circuit breaker having an
isolator at each end. A transformer is connected to main bus though a bus coupler. The main
bus has total capability of 160 MVA for 33 KV, which is subdivided into two transformer
capacity of 80 MVA (40MVA+40MVA) parallel connected for 33KV and other two
transformer capacity of 80KV (40KV+40KV) are parallel connected for substation.
At both ends of transformer lightning arrester current transformer and switchgear equipment
provided. Transformer step downs voltage from 220KV to 132KV. The main bus is provided
with switchgear equipment & a current transformer. This gives way to six feeders transmitting
power . The main bus is connected to jack bus .This gives way to feeders transmitting power
to 11 feeders 0f 33KV.
220 KV INCOMING/ OUTGOING FEEDERS
1. REWAROAD LINE
132 KV OUTGOINGFEEDERS
1. REWAROAD LINE
2. MANURI LINE
33 KV OUTGOING FEEDERS
3. NEW MES
4. WESTEND -I
5. KANPUR ROAD
6. WESTEND- II
7. KARELI - II
8. KARELI - I
11. KASARI MASARI
220 KV G.S.S , is an outdoor type primary substation and distribution substation as well it has
not only step down station but also the distribution work.
The electrical work in a substation comprises of
1. Choice of bus bar arrangement layout.
2. Selection of rating of isolator.
3. Selection of rating of instrument transformer.
4. Selection of rating of circuit breaker.
5. Selection of lightning arrestor [LA].
6. Selection of rating of power transformer.
7. Selection of protective relaying scheme, control and relay boards.
8. Selection of voltage regulator equipment.
9. Design a layout of earthling grids and protection against lightening strokes.
1.3 MAIN EQUIPMENTS HOUSED AT G.S.S.
1. Power transformers.
3. Potential transformer.
4. Current transformer.
5. Lightening arresters.
6. Circuit breaker.
8. Bus coupler and Sectionalizer.
9. Power line communication equipment (PLCC).
1.4 DETAILS OF ORGANIZATION SETUP
GRID: - Grid is a technical word used for the interconnection of power received from more
than one place. It is a network of main power line for transmission of electricity.
DUTIES: - Following are the duties of U.P.P.T.C.L:-
1. Supply maximum demands and should be prepare to increase its future is asked for.
2. Provide the service line to customer, which must carry the consumer load safety.
3. The standard value of voltage (132 kV) should be maintained.
4. Not discriminate between consumers of the same category, i.e. the categories of
consumers may be domestic, industrial and bulk consumers etc.
Fig1.2:- Single Line Diagram Of 220 KV GSS , ALLAHABAD CANTT
A transformer makes use of Faraday's law and the ferromagnetic properties of an iron core to
efficiently raise or lower AC voltages. It of course cannot increase power so that if the voltage
is raised, the current is proportionally lowered and vice versa. Power transformer are called
autotransformer fitted with a on load tap changer [OLTC]
Figure 2.1:- Basic Operation of a Transformer
2.1 DESCRIPTION OF PLANT TRANSFORMER
The three transformers are oil immersed with rating of 100MVA auto. However a
synchronous loading of 100MVA at 0.8 power factor (lag) and 18 MVA 0.8 pf (lag) on the
tertiary can also be loaded to 20MVA loading with 100MVA 0.8 pf on LV without exceeding
the generated temperature rise.
The transformer is equipped with German Reign Hansen make on load voltage regulation to
facilitate HV variation. The transformer is simultaneous parallel operation. It is ensured that
the tertiary winding will operate also satisfactory with each other.
The transformer is also provided with a separate bank of radiation, fans, and associated
control equipments. The control equipments are housed in a tank mounted miscalling.
Figure 2.2:- Large Power Transformers
Table 2.1Specification of plant transformer
Continuous rating KVA 50000/70000/100000
Customer's order No. & date P.O. No. RSEB/SE/SSPC/E3A2/TN.2409/
EMCO/ NO. 2446 dated 10/11/95.
W.O. No. and Sr. No. HT-1362/11674
Frequency 50 Hz.
Normal voltage ratio at No Load 220/132/11 KV
Connections Star/Star (Auto)/Delta
Vector Group Y
Tapping’s on HV +10% to -15% of HV in 1.25% steps on HV
for HV variation.
Type of tap changer OLTC Type 3-x DI 500 star.
150/150-12233 W (HHE Make)
Details of CT HV WTICT, class 5, 10 VA/308.8/1.8A
LV WTICH, class 5,10 VA/437.4/1.8A
HV Protection CT, 600/1A, Class P5
LV Protection CT, 600/1A, Class P5
HV 245 kV/800 A, OIP Condenser
bushing with 600 BCT.
IV Bushing 145 kV/800 A O.I.P. Condenser
busing with 300 BCT 36 kV/2000 A Neutral
bushing Short stem type.
Total weight of transformer 128430 kg.
Weight/Quantity of oil 43430 kg/48800 Liters
Untankling weight 55000 kg.
Untanking height 9000 mm
Transport weight 68000 kg. (Without oil)
Magnetic circuit is a three limbed care type construction; each limp being interleaved with
miter joints with top and bottom yokes the winding surrender with three limbs. The lamination
are made from high grade cooled rolled grain oriented alloy steel. The insulation on
lamination is varnish.
The cooling ducts are provided parallel to the plane of laminations the yoke are clamped with
by means of clamping per sling plate.
They are clamped with bolts for lifting the core with 8 lighting blotters are provided insulated
from each other to withstand a pressure of 2 kV, 50 c/s AC for one minute.
Figure 2.3:- Transformer Core
Current transformer is used for monitoring the current for the purpose of measuring and
protection. They can be classified as dead tank inverter type. The dead tank current
transformer accommodates the secondary core inside the tank, which is at the ground
potential. The insulated primary passes through the porcelain and the tank and the terminals
into the top chamber. The primary used in such types of construction is of ‘U’ type. The
inserted secondary cores are insulated to the system voltage and hence inside the top chamber
which is at the line potential. Before commissioning of the current transformer the earthing of
the power terminal and base is essential, otherwise excessive high voltage appears at the
power factor terminals and leads to heavy spark. The secondary terminal of the core should be
short circuited and earthed which are not in use otherwise excessive high voltage will be
developed across the current transformer secondary. The current transformer should always be
in vertical position so that gas forming at the top does not enter the insulated part. The current
transformer actually steps down the current so that it can be measured by standard measuring
instrument. There are three current transformers in each feeder. The current transformers are
inserted into energy incoming and outgoing feeder from 220 kV systems for measurement.
The current transformer is used with its primary winding connected in series with the line
carrying the current to be measured and therefore the primary current is not determined by the
load on the secondary of the current transformer. The primary consists of a very few turns and
there is no appreciable voltage across it. The secondary consists of a very large number of
turns. The ammeter or wattmeter current coil is connected directly across the secondary
terminals thus a current transformer operates its secondary nearly under short circuit
conditions. The secondary circuit is connected to ground in many cases.
Instrument transformers perform two important functions: they serve to extend the range of
the measuring instrument, much as the shunt or the multiplier extends the range of the dc
ammeter. They also serve to isolate the measuring instrument from the high voltage power
line. The primary winding of the current line transformer is connected directly to the load
circuit, while the secondary is open circuited. The voltage across the open terminal can be
very high (because of the step up ratio) and could easily break down the insulation between
the secondary windings. The secondary winding of a current transformer should therefore
always be short circuited or connected to a relay coil.
3.1 BASIC FEATURE OF CURRENT TRANSFORMER
1. As you all know this is the device which provides the pre-decoded fraction of the
primary current passing through the line /bus main circuit. Such as primary current
60A, 75A, 100A, 120A, 150, 240A, 300A, 400A, to the secondary output of 1A to 5A.
Figure 3.1:- Current Transformer in Yard
2. Now a day mostly separate current transformers units are used instead of bushing
mounting CT’s on leveled structure they should be for oil level indication and the base
should be earthed properly. Care should be taken so that there should be no strain on
3. When connecting the jumpers. Mostly secondary connections are taken to junction
boxes where star delta formation is connected for three phases and final leads taken to
protection /metering scheme. There should be no chance of secondary circuit
remaining opens as it leads to extremely high voltages which ultimately damage the
4. Current transformers can be used to supply information for measuring power flows and
the electrical inputs for the operation of protective relays associated with the
transmission anddistribution circuits or for power transformers. These current
transformers have the primary winding connected in series with the conductor carrying
the current to be measured or controlled. The secondary winding is thus insulated from
the high voltage and can then be connected to low-voltage metering circuits.
5. Current transformers are also used for street lightning circuits. Street lightning requires
a constant current to prevent flickering lights and a current transformer is used to
provide that constant current. In this case the current transformer utilizes a moving
secondary coil to vary the output so that a constant current is obtained.
A potential transformer (P.T.) is used to transform high voltage of power line to a lower value,
which is in the range of an AC voltmeter or the potential coil of an AC voltmeter.
4.1 CLASSIFICATION OF POTENTIAL TRANSFORMER
1. Capacitive voltage transformer
2. Electro-Magnetic type
4.2 CAPACITIVE VOLTAGE TRANSFORMER
Capacitive voltage transformers are special kind of power transformers using capacitors to
step down the voltage.
Figure 4.1:- Current Voltage Transformer
The capacitive voltage transformer comprises of a capacitor divider with its associated
electromagnetic unit. The divider provides an accurate proportioned voltage, while the
magnetic unit transforms this voltage, in both magnitude and phase to convenient levels
suitable for measuring, metering, protection etc. All WSI capacitor units have metallic bellows
to compensate the volumetric expansion of oil inside. The porcelain in multi unit stack, all the
potential points are electrically tied and suitably shielded to overcome the effect of corona
RIV etc. Capacitive voltage transformers are available for system voltages of 33 kV to 420
1. Capacitive voltage transformers can be effectively as potential. Sources for measuring,
metering, protection, carrier communication and other vital functions of an electrical
2. CVT are constructed in single or multi unit porcelain housing with their associated
magnetic units. For EHV system cuts are always supplied in multi unit construction.
3. In case of EHV cuts the multi unit system has many advantages easy to transport and
storing, convenience in handling.
4.2.3 RATING OF CVT
Frequency 50 Hz
Capacitance C1 4880 Pf
Capacitance C2 44455 Pf
Equivalent Capacitance 4400+10% Pf
Insulation level 460/1050 Kv
Emu oil 95+10% Kg
Total weight 530+10% Kg
Total sim burden/class 300 VA/0.5
4.3 ELECTROMAGNETIC TYPE POTENTIAL TRANSFORMER
The electromagnetic potential transformers are used for the system voltages up to or below
132 kV, due to the economic aspects. The basic principle of these transformers is same as
power transformers. The high alternating voltages are reduced in a fixed proportion for the
measurement purpose with the help of electromagnetic type potential transformer. These are
extremely accurate ratio step down transformer. The windings are low power rating windings.
Primary winding consist of large number of turns while secondary has less number of turns
and usually rated for 110 V, irrespective of the primary voltage rating. The potential
transformer used larger core and conductor sizes compared to conventional power
Figure 4.2:-Electromagnetic Type Potential Transformer
If the bus-bars are of rigid type (Aluminum types) the structure heights are low and minimum
clearance is required. While in case of strain type of bus-bars suitable ACSR conductors are
strung/tensioned strain by tension insulator discs according to system voltages. In the widely
used strain type bus bars stringing tension is about 500-900 kg depending upon the size of
conductor used and tensioning is manual by means of rope pulleys or by pull lifts. It may also
with the help of tractors.
Here proper clearance would be achieved only if require tension is achieved. Loose bus bars
would affect the clearances when it swings while over tensioning may damage insulators.
Clamps or even affect the supporting structures in low temperature conditions.
The clamping should be proper, as loose clamp would spark under in full load condition
damaging the bus bars itself.
The bus bar is provided with lightening protection to safeguard the equipment against direct
stroke by providing aerial earth wire giving a protection at 30 degree i.e. height and earth wire
such that all the equipment and bus bar should be covered with in this 30 degree.
Figure 5.1:- Bus-Bar
5.1 BAR BUS ARRANGEMENT MAY BE OF FOLLOWING TYPES
WHICH ARE BEING ADOPTED BY U.P.P.T.C.L
1. Single bus bar arrangement.
2. Double bus bar arrangement.
a. Main bus with transformer bus.
b. Main bus-l with Main bus-ll.
3. Double bus bar arrangement with auxiliary bus.
5.2 BUS BAR ARRANGEMENT DEPENDS UPON
1. Interruption tolerable in the supply scheme.
2. Alternative supply arrangements in case of failure of Equipments.
5.2.1BUS BAR ARRANGEMENT
1. Single bus bar arrangement-This arrangement is simplest and cheapest. It suffers,
however, from major defects.
a. Maintenance without interruption is not possible.
b. Extension of the substation without a shutdown is not possible.
The equipment connections are very simple and hence the system is very convenient to
operate. This scheme is not very popular for 33 kV and above, except where the relative
importance of the substation is less or the position of the substation does not justify elaborate
schemes. The indoor 11 kV switchyards have quite often-single bus bar arrangement.
5.3 DOUBLE BUS BAR / CONTAINTS MAIN BUS-I WITH MAIN BUS-ll
This scheme has two bus bar so that-
1. Each load may be fed from either bus.
2. The load circuits may be divided in two separate groups if needed from operational
consideration. Two supplies from different sources can be put on each bus separately.
3. Either bus bar may be taken out from maintenance and cleaning of insulators.
This arrangement has been quite frequently adopted where the loads and continuity of supply
is necessary. In such a scheme a bus coupler breaker is mostly provided as it enables on load
change over from one bus to other.
The normal bus selection isolators cannot be used for breaking load currents. The arrangement
does not permit breaker maintenance without causing stoppage of supply.
5.4 DOUBLE BUS BAR ARRANGEMENTS/CONTAIN MAIN BUS WITH
AUXILIARY BUS (OR TRANSFER BUS)
The double bus bar arrangement provides facility to charge over to either bus to carry out
maintenance on the other but provide no facility to carry over breaker maintenance. The main
and transfer bus works the other way round. It provides facility for carrying out breaker
maintenance but does not permit bus maintenance. Wherever maintenance is required on any
breaker the circuit is changed over to the transfer bus and is controlled through bus coupler
5.5 DOUBLE BREAKER
This scheme is the modification of double bus bar scheme. In this arrangement the
maintenance of CB or isolator without an outage is possible, which is the main drawback of
double bus bar. This arrangement is costly so it varies for various generating stations.
1. It provides a double feed to each circuit i.e. opening of any breaker for maintenance
does not affect the supply to any circuit.
2. It provides breaker maintenance..
3. It is cheaper than the double bus bar or main bus scheme.
5.6.1 THE DISADVANTAGES OF THIS SCHEME ARE
1. If any breaker is to be taken under maintenance, then under this condition tripping of
any one circuit breaker may result in loss of supply to a no. of circuits.
2. Expansion of mesh is extremely difficult the scheme is limited to four or six circuits.
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. Theydo not have any making or breaking capacity.
Isolators are used to isolate the bus when it is not in working condition. If the bus is to be
Isolators are also called as disconnect switches or air break switches. Shut down then it is
isolated from the main bus. The moving and fixed contacts is done so that all the three phase
of the isolator close and open simultaneously and there is a full surface contact between
moving and fixed contacts. The adjustment of the tendon pipes, leveling of post isolator, stops
Holts in the fixed contacts etc. are done for smooth operation of isolator. Isolators are
provided at both ends of the bus. There are ten isolators provided at 400 kV substations.
Following type of isolator provided at 400 kV substations.
Following type of isolator are being used in R.S.E.B
a. Isolator without earth blades.
b. Isolator with earth blades.
c. Tendon isolator
On fundamental basis the isolating switches can broadly divided into following categories
1. Bus isolator
2. Line isolator cum earthing switch
4. Transformer isolating switch.
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
Figure 6.1:- Isolators
6.3 RATING OF SOME ISOLATOR
1. Air breaker isolator
Short time amperes 40 ka/sec
Auxiliary voltage 220 v dc
2. Air breaker isolator
Volt 420 Kv
Rated amps 2000 amp
Impulse voltage 1425 Kv
Auxiliary voltage 220 v dc
1. Contacts: Contacts are liberally rated and have been designed to with stand
electromagnetic stresses and preventing shattering at rated short time current. The
contact is made out of electrolytic copper, fixed in co housing.
2. Switch plans: All the three phases of switch are cleaned open or closed simultaneously
with provision of adjustable tendon pipe connected to towers provided at the center
Breakers are switching and current interrupting devices. Basically a Circuit breaker comprises
a set of fixed and movable contacts. The contacts can be separated by means of an operating
an arc. The arc is extinguished by a suitable medium such as dielectric oil vacuum, SF6 gas.
The circuit breakers play an important role in the design and performance of a power system,
in that these are the key pieces of apparatus protecting the system and thus ensure continuity
of supply from consideration of cost, the circuit breakers represent a major items, and are next
only to the generator and transformer, since their quantity is greater than that of
generators/transformer in a power system owing to the services required for control of
transmission lines, bus-bar etc. in addition to control of transformers and generator.
7.2FUNCTIONS OF CIRCUIT BREAKER
The Expected functions of a circuit breaker are: -
It must be capable of closing on to and carrying full load currents for long period of time.
Under proscribed condition,
1. It must open automatically to disconnect the load or some small overload.
2. It must successfully and rapidly interrupt the heavy current, which flow when a short
circuit has to be cleared from the system.
3. It must be capable of closing on to a circuit in which a fault exists and immediately re-
opening to clear the fault from system.
4. It must be capable of carrying current of short circuit magnitude until, and for such
time as, the fault is cleared by another breaker nearer to the pint of fault.
7.2.1CIRCUIT BREAKER TYPES
(i) Bulk oil Circuit Breaker.
(ii) Minimum oil Circuit Breaker.
(iii)Air blast Circuit Breakers.
(v) Vacuum Circuit Breakers.
7.3.1 (A) OIL CIRCUIT BREAKER
Circuit breaking in oil has been adopted since the early stages of circuit breakers manufacture.
The oil in oil-filled breakers serves the purpose of insulating the live parts from the earthed
ones and provides an excellent medium for arc interruption. Oil circuit breakers of the various
types are used in almost all voltage ranges and ratings. However, they are commonly used at
voltages below 115 kV leaving the higher voltages for air blast and SF6 breakers. The contacts
of an oil breaker are submerged in insulating oil, which helps to cool and extinguish the arc
that forms when the contacts are opened. Oil circuit breakers are classified into two main
types namely bulk oil circuit breakers and minimum oil circuit breakers. The methods of arc
control and interruption is different from one type to the other.
1. It absorbs the arc energy to decompose the oil into gases, which have excellent cooling
2. It acts as an insulator and permits smaller clearance between live conductors and
1. It’s inflammable and there is risk of fire.
2. It may form an expulsive mixture with air.
3. The arcing products remain in the oil and it reduces the quality of oil after several
4. This necessities periodic checking and replacement of oil.
(B) BULK OIL CIRCUIT BREAKER
Bulk oil circuit breakers are widely used in power systems from the lowest voltages up to 115
kV. However, they are still used in systems having voltages up to 230 kV.
The contacts of bulk oil breakers may be of the plain-break type, where the arc is freely
interrupted in oil, or enclosed within arc controllers. Plain-break circuit breakers consist
mainly of a large volume of oil contained in a metallic tank. Arc interruption depends on the
head of oil above the contacts and the speed of contact separation. The head of oil above the
arc should be sufficient to cool the gases, mainly hydrogen, produced by oil decomposition. A
small air cushion at the top of the oil together with the produced gases will increase the
pressure with a subsequent decrease of the arcing time.
7.3.2. MINIMUM OIL CIRCUIT BREAKER
Bulk oil circuit breakers have the disadvantage of using large quantity of oil. With frequent
breaking and making heavy currents the oil will deteriorate and may lead to circuit breaker
failure. This has led to the design of minimum oil circuit breakers working on the same
principles of arc control as those used in bulk oil breakers. In this type of breakers the
interrupter chamber is separated from the other parts and arcing is confined to a small volume
of oil. The lower chamber contains the operating mechanism and the upper one contains the
moving and fixed contacts together with the control device. Both chambers are made of an
insulating material such as porcelain. The oil in both chambers is completely separated from
each other. By this arrangement the amount of oil needed for arc interruption and the
clearances to earth are roused.
However, conditioning or changing the oil in the interrupter chamber is more frequent than in
the bulk oil breakers. This is due to carbonization and slugging from arcs interrupted chamber
is equipped with a discharge vent and silica gel breather to permit a small gas cushion on top
of the oil. Single break minimum oil breakers are available in the voltage range 13.8 to 34.5
7.3.3. SF6 CIRCUIT BREAKER
Sulphurhexafluoride has proved its-self as an excellent insulating and arc quenching medium.
The physical, chemical, and electrical properties of SF6 are more superior to many of the other
media. It has been extensively used during the last 30 years in circuit breakers, gas-insulated
switchgear (GIS), high voltage capacitors, bushings, and gas insulated transmission lines. In
SF6 breakers the contacts are surrounded by low pressure SF6 gas. At the moment the contacts
are opened, a small amount of gas is compressed and forced through the arc to extinguish it.
Figure 7.1:- SF6 Circuit Breaker
7.3.4. VACUUM CIRCUIT BREAKER
A vacuum circuit breaker is such kind of circuit breaker where the arc quenching takes place
in vacuum. The technology is suitable for mainly medium voltage application. For higher
voltage Vacuum technology has been developed but not commercially visible. The operation
of opening and closing of current carrying contacts and associated arc interruption take place
in a vacuum chamber in the breaker which is called vacuum interrupter. The vacuum
interrupter consists of a steel arc chamber in the centre symmetrically arranged ceramic
The material used for current carrying contacts plays an important role in the performance of
the vacuum circuit breaker. Cu Cr is the most ideal material to make VCB contacts. Vacuum
interrupter technology was first introduced in the year of 1960. But still it is a developing
technology. As time goes on, the size of the vacuum interrupter is being reducing from its
early 1960’s size due to different technical developments in this field of engineering. The
contact geometry is also improving with time, from butt contact of early days it gradually
changes to spiral shape, cup shape and axial magnetic field contact. The vacuum circuit
breaker is today recognized as most reliable current interruption technology for medium
voltage system. It requires minimum maintenance compared to other circuit breaker
Advantages of Vacuum Circuit Breakers:-
1. Very long lifetime of the contacts (This provides longer breaker life.)
2. Less maintenance required
3. Less moving parts in mechanism
4. Less force needed to separate the contacts (since the distance between them is shorter.)
5. Environment friendly. Since interruption takes place in vacuum medium,
VCBs do not require gas or liquid addition. This reduces the possibility of leakage of
gas (or any material) that can be harmful for environment.
The lightning arrester (or) the lightning conductor is a commonly used device which is used to
protection a substation is essential:
1. Protection for transmission line from direct strokes.
2. Protections of power station or substation from direct stroke.
3. Protection of electrical apparatus against traveling waves.
4. 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.
Lightning arrestor is a device, which protects the overhead lines and other electrical apparatus
viz., transformer from overhead voltages and lighting. When electrostatic induction then the
negative charge is however presented right under the cloud and portion of the line away from
the cloud becomes positively right under the charge on the line does not flow.
The positive charge on the far and flows to the earth through insulators, thus leaving the
negative charge on the line directly under the cloud. Now assume due to the direct discharge
occurring between this clouds and passing by negative charge cloud the charge in the cloud
becomes neutralized, then the charge on the line is no more bound charge and is free to travel
on both direction in the form of waves. These travelling waves will be of light magnitude and
have steep wave form, which can damage the unprotected equipment connected to the line.
These waves are passed to the earth through the lightning arrestors.
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.
The lightning arrestor protects the structure from damage by intercepting flashes of lightning
and transmitting their current to the ground. Since lightning strikes tend to strike the highest
object in the vicinity, the rod is placed at the apex of a tall structure. It is connected to the
ground by low-resistance cables. In the case of a building, the soil is used as the ground, and
on a ship, water is used. A lightning rod provides a cone of protection, which has a ground
radius approximately, equal to its height above the ground. Surges due to lightning are mostly
injected into the power system through long cross-country transmission lines. Substation
apparatus is always well shielded against direct lightning strokes. The protection of
transmission lines against direct strokes requires a shield to prevent lightning from striking the
electrical conductors .Terminal equipment at the substation is protected against by surge
diverters, also called surge arrester or lightning arresters.
Earthing screen and ground wires can well protect the electrical system against direct
lightning strokes but they fail to provide protection against travelling waves, which may reach
the terminal apparatus.
8.2.1 AN IDEAL ARRESTOR MUST THEREFORE HAVE THE FOLLOWING
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 form 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.
The apparatus consists of a long thick rod made up of copper which is a very good conductor
of electricity so that it can allow a large amount of charges to flow through it. This copper rod
passes through the walls of the building. The upper end of the rod is provided with a metal
plate having a number of sharp spikes which are visible at the top of the building while the
lower end is connected to a plate of copper which is deeply buried in the ground so that the
excess of charges is passed to the earth which is a good conductor of electricity and this
process is called "earthing".
The working of a lightning arrestor can be explained either with a positively charged cloud
commonly called "male cloud" or with a negatively charged cloud commonly called "female
cloud". Consider a negatively charged cloud which passes over the building with a lightning
arrestor. Due to the negative charge of the cloud, positive charges are induced to the sharp
spikes which are at the top of the building. Now, due to the principle of action of points,
leakage of the positive charges from the sharp spikes occurs so that the nearby atoms in the
space are ionized into positive and negative charges. Now, the positive charges in the sharp
spikes repel the newly formed positive ions and these ions try to neutralize the negative charge
of the cloud. If the negative charges are not completely neutralized, these charges due to the
attraction of the positive charges in the sharp spikes are passed through the copper rod to the
ground where they are earthed. Thus, the intensity of lightning can be reduced thus saving the
building from its destructive attack. A lightning conductor can save its surroundings for more
than half a kilometer from the attack of lightning.
8.4 THYRITE TYPE
Ground wire run over the tower provides an adequate protection against lightning and reduce
the induced electrostatic or electromagnetic voltage but such a shield is inadequate to protect
any traveling wave, which reaches the terminal of the electrical equipment, and such wave can
cause the following damage.
1. The high peak of the surge may cause a flashover in the internal wiring thus it may
spoil the insulation of the winding.
2. The steep wave font may cause internal flash over between their turns of transformer.
The stop wave front resulting into resonance and high voltage may cause internal or
external flashover causing building up the oscillator is the electrical operation.
Lightening arrestor are provided between the line and earth provided the protection against
traveling wave surge the thyrite lightening arrestor are provided at GSS.
This type of LA has a basic cell made of thirties, which is a particular type of clay, mixed with
carborendum. Thirties has a particular property of being insulator one voltage.
Fig 8.1:- Lightning Arrestors on Substations
This type of LA has a basic cell made of thirties, which is a particular type of clay, mixed with
carborendum. Thirties has a particular property of being insulator one voltage
At high voltage it will behave like a conducting material the electrical resistance of thyrite
depends upon the voltage each time the voltage is Made twice the resistance decrease in such
a manner as to allow an increased current of 12.5 times the change in current is independent of
rate of application voltage and its instantaneous value.
One upon each other and they are further placed in to a porcelain container with a suitable
arrangement of gap between them. These gaps serve as the purpose of preventing any current
flow during normal operating voltage in case of nay transients the gap.
9.1 BUS SUPPORT INSULATORS
These are porcelain or fiberglass insulators that serve to isolate 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 insulators used in substations and
transmission poles and towers. These insulators are generally made of glazed porcelain or
toughened glass. Poly come type insulator [solid core] are also being supplied in place of hast
insulators if available indigenously. The design of the insulator is such that the stress due to
contraction and expansion in any part of the insulator does not lead to any defect. It is
desirable not to allow porcelain to come in direct contact with a hard metal screw thread.
Figure 9.1:-Bus Support Insulators
9.2. TYPES OF INSULATORS
There are several types of insulators but the most commonly used are pin type, suspension
type, strain insulator and shackle insulator.
9.2.1. PIN TYPE INSULATOR
As the name suggests, the pin type insulator is secured to the cross-arm on the pole. There is a
groove on the upper end of the insulator for housing the conductor. The conductor passes
through this groove and is bound by the annealed wire of the same material as the conductor.
Pin type insulators are used for transmission and distribution of electric power at voltages up
to 33 kV. Beyond operating voltage of 33 kV, the pin type insulators become too bulky and
Figure 9.2:-Pin Type Image
9.2.2 SUSPENSION TYPE INSULTOR
For high voltages (>33 kV), it is a usual practice to use suspension type insulators shown in
Figure 9.3. Consists of a number of porcelain discs connected in series by metal links in the
form of a string. The conductor is suspended at the bottom end of this string while the other
end of the string is secured to the cross-arm of the tower. Each unit or disc is designed for low
voltage, say 11 kV. The number of discs in series would obviously depend upon the working
voltage. For instance, if the working voltage is 66 kV, then six discs in series will be provided
on the string.
Figure 9.3:-Suspension Type Image
9.2.3.STRAIN TYPE INSULTOR
When there is a dead end of the line or there is corner or sharp curve, the line is subjected to
greater tension. In order to relieve the line of excessive tension, strain insulators are used. For
low voltage lines (< 11 kV), shackle insulators are used as strain insulators. However, for high
voltage transmission lines, strain insulator consists of an assembly of suspension insulators as
shown in Figure 9.4. The discs of strain insulators are used in the vertical plane. When the
tension in lines is exceedingly high, at long river spans, two or more strings are used in
Figure 9.4:-Strain Type Insulator
9.2.4.SHACKLE TYPE INSULATOR
In early days, the shackle insulators were used as strain insulators. But now days, they are
frequently used for low voltage distribution lines. Such insulators can be used either in a
horizontal position or in a vertical position. They can be directly fixed to the pole with a bolt
or to the cross arm.
Figure 9.5:-Shackle Type Insulator
9.3 RATING OF AIR BREAK INSULATOR
Motor voltage 220 V DC
Rated voltage 420 Kv
Rated current 2000 A
Rated short time current 55 KA/3sec
Rated mechanism term load 1630 Kg
Control panels contain meters, control switches and recorders located in the control building,
also called a doghouse. These are used to control the substation equipment, to send power
from one circuit to another or to open or to shut down circuits when needed
Figure 10.1:- Substation Control Panel
10.1 SYNCHRONIZING PANEL
There is a hinged panel mounted on the end of a control board to take out new supply. On bus
bar we have the synchronies and fee the synchronoscope zero on this bus bar.
The voltage can be checked by voltmeter the function of synchronoscope is to indicate phase
and frequently voltage of bus bar and incoming feeder voltage of bus bar and incoming feeder
A synchronoscope is used to determine the correct instance of closing the switch with connect
the new supply to bus bar the correct instance of synchronizing is indicated when bus bar and
1. Are equal in magnitude
2. Are equal in phase
3. Have the same frequency.
4. The phase sequence is same.
The voltage can be checked by voltmeter the function of synchronoscope is to indicate phase
and frequently voltage of bus bar and incoming feeder voltage of bus bar and incoming feeder
In the control room the Announciator the most compact in which probable faults at different
feeders and different feeders and different zone have written to inform the bulb behind the
structure when some faults is announciator auxiliary relay. Relay’s first signal trip the circuit
breaker and signal goes to the auxiliary trip the relay, the relay send the signal to the
announciator which give alarm and bulb is lighting up in front of the type of fault occurred.
10.4 MEASURING INSTRUMENT USED
1. ENERGY METER: To measure the energy transmitted energy meters are fitted to the
panel to different feeders the energy transmitted is recorded after one hour regularly
for it MWH meter is provided.
2. WATTMETERS: Wattmeter’s are attached to each feeder to record the power
exported form GSS.
3. FREQUENCY METER: To measure the frequency at each feeder there is the
provision of analog or digital frequency meter.
4. VOLTMETER: It is provided to measure the phase-to-phase voltage. It is also
available in both the forms analog as well as digital.
5. KA METER: It is provided to measure the line current. It is also available in both the
forms analog as well as digital.
6. MAXIMUM DEMAND INDICATOR: These are also mounted on the control panel to
record the average power over successive predetermined period.
7. MVAR METER: It is to measure the reactive power of the circuit.
8. COSФ METERS: To indicate the power factor of the power being transferred or
imported. These meters are provided on various panels.
Every electrical equipment needs portion the house wiring is protected by the fuses. Modern
generators are protected by complex protective schemes. The choice of protection depends
upon several aspects such as type and rating of protective equipments.
The location of relay is very important the protective relay may protect the concerned
equipment from the abnormal operating condition develops in protective relaying of that
equipment sense the abnormal condition and initiates the alarm and close the trip circuit of CB
and isolate the equipment from the supply
The relays are compact self-contained device, which respond to an abnormal condition
whenever and abnormal condition is developed. The relay close their contacts thereby the trip
circuit of CB is closed current from the battery supply flows in the trip circuit [coil] of breaker
and breaker opens and the faulty part is disconnected from the supply.
Figure 11.1:- Substation Relay Panel
Besides relays and CB there are several components in relaying schemes these includes
potential transformer protective fine relay time delay relay auxiliary relay secondary circuit
and accessories each equipment is important in protection relaying in team work of their
The function of protection relaying scheme includes following.
1. To sound an alarm or close the trip coil of CB to disconnect the equipment in abnormal
condition, which includes overload under voltage temperature rise, unbalanced load
reserve power under frequency short circuit.
2. To disconnect the abnormally operating part to prevent subsequent fault as over load
protection of machine and prevent machine failure.
3. To disconnect the faulty part if a machine is connected immediately after a winding
fault only a few coil may need replacement.
4. To realize the effect of fault by disconnecting faulty part from healthy part causing
least disturbance to the healthy replacement.
5. To disconnect the faulty part quickly to improve the system stability service condition
and system performance.
The component of a substation which are provided with the protection schemes are:
1. Power transformer.
2. Transmission line feeder.
3. Bus bars.
4. Shunt capacitor banks.
11.1 POWER TRANSFORMER PROTECTION
A power transformer is subjected to following faults
1. Over load and external short circuit.
2. Terminal fault
3. Winding fault
4. Incipient fault.
Winding and oil temperature indicator with alarm and trip contacts are provided. As soon as
the temperature of winding and oil exceed the predetermined value of contacts are bridged
reaches the spot valve the transformer is tripped the different protection which are provided to
a power transformer are
1. Buchholz relay
2. Over current and earth fault
3. Differential protection
4. Frame leakage protection
11.2 BUCHHOLZ RELAY
This relay is used for the protection of the transformer and is based upon the principle of a gas
operated relay since any internal fault inside the transformer will evaporate the oil due top
intense heat generated by short circuit current and will generate gases. This type of relay can
be fitted only to the transformers, which are equipped with conservator tank and the main tank
i.e. in the transformer pipe connecting. The two relays consists of an oil cum tuner with the
two internal floats which operates and Accurate mercury switches, which are in turn
connected to external to the external alarm and to the tripping circuit.
Fig 11.2:- Internal Structure of Buchholz Relay
The relay is normally full of oil and floats remain engaged in seat due to buoyancy and floats
are made aluminum each one has a counter weight, which has mild steel coated with nickel.
The relay is also useful in indicating any loss of oil that a transformer may suffer because heat
loss of oil will cause oil level to drop the top float will indicate it by dropping and shorting the
alarm contact and if the oil level keeps on falling the lower float will affected and will close
the trip circuit of transformer.
The alarm circuit is made these by going a warning bell is advanced that a serious fault is
developing inside. The tank occurs the volume of gas generated is considerable which is
moving through the relay causes the gas surge flap valve to be defected. There by close the
mercury contact switch and energizing the trip coil of CB and isolate the transformer from the
supply sample for analysis if gas from the top valve.
11.3 OVER CURRENT AND EARTH FAULT PROTECTION
These protection schemes are provided against external short circuit and excessive load.
Commonly the over current and earth fault protection is provided on the front side of
transformer and is made to trip both HV and LV breaker these protections serve only as
backup protection both for transformer internal and external fault.
The over current relay has a single element for each phase and earth fault has a single element
the connection for restricted earth fault protection on one winding of transformer with a
similar scheme. For a star connected winding three lines current transformer is balanced
against a CT the neutral connection. In case of delta connected winding the three lines CT are
parallel and connected to across the earth fault relay some of them same in CT is used for over
current protection as well as earth fault protection.
11.3.1 FRAME LEAKAGE PROTECTION
This protection is known as tank protection. The transformer is lightly insulated from earth by
mounting it on a concrete plinth. The transformer tank is connected to earth fault relays. Earth
fault current due to insulation failure in any winding of the transformer will flow to
transformer energizes here two relay operates.
11.3.2 DIFFERENTIAL PROTECTION
For the differential protection, different relay is used. Different protection scheme compares
quality derived from the input and output current of the protected circuit in such a way that all
the healthy system and protection in operative while for fault condition the balance is
disturbed and the protection operated.
The protection has many advantage over other protection over other protections the flash over
at the bushing are not adequately covered by other protective scheme also unless it. Involves
ground the differential relay scheme delete such fault and also on the lead between the CB and
power transformer provided. The current transformer are separately mounted and not in the
transformer bushing. In case of every serve internal faults differential faults differential relay
operates faster than the buchholz’s relay this control the external damages.
The differential damage protection response to phase to phase faults with in the protection
zone. This generally comprises all equipments and connection between ct and all side of
transformer. It provides protection against turn to turn faults also. It operates on the principle
of the circulating current by comprising current in various winding through the media of CT’s
the ratio and connection of the CT’s on various winding shown that secondary current are
equal in magnitude and phase in normal condition.
11.4 TRANSMISSION LINE PROTECTION
The protection scheme for transmission lines is differential relaying.
11.4.1 DIFFERENTIAL RELAYING
In this type of relaying 6 point conductors would be required one for each phase CT and one
for neutral connection and two for the trip circuit but this scheme is costlier. A modified
scheme is applicable only on parallel feeder. In this scheme the secondary current from CT’s
on the two circuits at the same end is compared. Under normal condition, each line will carry
equal current. In the event of fault the balance is disturbed that is why relay trips the CB.
11.4.2 DIRECTION BACKUP RELAYS
These relays are used for the over current and earth fault of high voltage 132,220 kV sides.
This consists of main and backup scheme at standby. As carrier current protection of short
distance impedance, reactance and pilot relay for long short and very short distance
POWER LINE CARRIER COMMUNICATION
12.1 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 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 GSS as this would result in high attenuation or even complete loss
of communication signals when earthed at isolator. To prevent this loss, wave traps or line
traps are employed. These consist of suitably designed choke coils connected in series with
line, which offers negligible impedance to RF carrier current.
As electronics plays a vital role in the industrial growth, communication is also a backbone of
any power station, communication between various generating and receiving station is very
essential for proper operation of power system. This is more so in case of a large
interconnected system where a control lead dispatch station has to coordinate the working of
various units to see that the system is maintained in the optimum working condition, power
line communication is the most economical and reliable method of communication for
medium and long distance in power network.
Figure 12.1:- Power-Line Carrier Schematic
Figure 12.2:- Power Line Carrier Communication System
Fig12.3:- Power Line Carrier Device in Control House
12.2 COMPONENT OF COUPLING ARRANGEMENT
1. Wave Trap.
2. Coupling Capacitor.
3. Drainage coil.
4. Voltage arrestor.
5. Ground switch.
6. Matching transformer.
7. Tuning capacitor.
8. Vacuum arrestor.
12.2.1 WAVE TRAP
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 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.
Once the carrier energy 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 same way that it was coupled at the
transmitting terminal. The signal is then sent to the receivers in the control house via the
Fig 12.4:- WAVE TRAP
12.2.2 COUPLING CAPACITOR
The coupling capacitor is used as part of the tuning circuit. The capacitor is a device which
provides 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
for the carrier signal and low impedance path for the power frequency current. This device is
an inductor and it is called a drain coil. The coupling capacitor and drain coil circuit are
shown in diagram.
Fig 12.5:- Coupling Capacitor and Drain Coil Combination
12.2.3 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 units against line surge. The grounding
switch is kept open during normal operation and is closed if any thing is to be done on the
communication equipment without interruption to power flow on the line.
The LMU which consist 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 (100-450kHz typical).
12.3 ADVANTAGE AND DISADVANTAGE OF PLCC
1. No separate wires are needed for communication purpose as the power lines
themselves carry power as well as the communication signals. Hence the cost of
constructing separate telephone line 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 resistance 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
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 equipment adversely affected the carrier current.
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
EARTHING OF THE SYSTEM
The provision of an earthing system for an electric system is necessary by the following
1. In the event of over voltage on the system due to lightning discharge or other system
fault. These part 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
1. Shape and material of earth electrode used.
2. Depth in the soil
3. Specific resistance of soil surrounding in the neighborhood of system electrodes.
13.1 PROCEDURE OF EARTHING
Technical consideration the current carrying path should have enough capacity to deal with
more fault current. The resistance of earth and current path should be low enough to prevent
voltage rise between earth and neutral. Main earthling system must be separate from earthing
for lightning protection. The earth electrode must be drive ion to the ground to a sufficient
depth to as to obtain lower value of earth resistance. To sufficient lowered earth resistance a
number of electrodes are inserted in electrode must be drive ion to the ground to a sufficient
depth to as to obtain lower value of earth resistance. To sufficient lowered earth resistance a
number of electrodes are inserted in the earth to a depth they are connected together to form a
The resistance of earth should be for the mesh in generally inserted in the earth at 0.5m depth
the several point of mesh then connected to earth electrode or ground connection. The earth
electrode is metal plate copper is used for Earth plate.
13.1.1 GROUNDING OF LINE STRUCTURE
High voltage transmission lines are carried out on lattice structure, which are grounded with
one or more grounding rods driven vertically at the surface. When earth resistivity is high and
driven rod id not adequate the remedy is bury the wire in earth and connect it to the lower
footing. The wire may run parallel or at some angle to the time conductor is called as counter
Figure 13.1:- GROUND WIRE
13.1.2 OVERHEAD SHIELDING WIRE
These wires are supported on the top of substation structure each top is connected to earthing
system by galvanized iron earthing strips, cover entire switchyard.
13.1.3 NEUTRAL EARTHING
Neutral earthing of power transformer all power system operates with grounded neutral.
Grounding of neutral offers several advantages the neutral point of generator transformer is
connected to earth directly or through a reactance in some cases the neutral points is earthed
through is adjustable reactor of reactance matched with the line.
The earthing is one of the most important features of system design for switchgear protection
neutral grounding is important because:
1 The earth fault protection is based on the method of neutral earthing.
2 The neutral earthing is associated switch gear.
3 The neutral earthing is provided for the purpose of protection arcing ground
sunbalanced voltages with respect to protection from lightning and for improvement of
Merits of neutral 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 the normal value.
3 The life of insulation is long due to prevention of voltage surges or sustained over
4 Suitable neutral point.
5 The earth fault relaying is relatively simple useful amount of earth fault current is
available to operate earth fault relay.
6 The over voltage due to lightning are discharged to earth.
7 By employing resistance reactance in earth connection the earth fault can be
In a GSS, separate dc supply is maintained for signaling remote position control, alarm circuit
etc. Direct current can be obtained from 220volt 3 phase ac supply via rectifier and in event of
arc failure, from the fixed batteries, which are kept, charged in normal condition by rectifier
Figure 14.1:- Battery Room
A VRLA battery (valve-regulated lead–acid battery) is more commonly known as a sealed
battery a lead–acid rechargeable battery. Because of their construction, VRLA batteries do not
require regular addition of water to the cells, and vent less gas than flooded lead-acid batteries.
The reduced venting is an advantage since they can be used in confined or poorly ventilated
spaces. But sealing cells and preventing access to the electrolyte also has several considerable
disadvantages as discussed below.
VRLA batteries are commonly further classified as:
1 Absorbed glass mat (AGM) battery
2 Gel battery ("gel cell")
An absorbed glass mat battery has the electrolyte absorbed in a fiber-glass mat separator. Agel
cell has the electrolyte mixed with silica dust to form an immobilized gel.
While these batteries are often colloquially called sealed lead–acid batteries, they always
include a safety pressure relief valve. As opposed to vent (also called flooded) batteries, a
VRLA cannot spill its electrolyte if it is inverted. Because AGM VRLA batteries use much
less electrolyte (battery acid) than traditional lead–acid batteries, they are sometimes called an
The name "valve regulated" does not wholly describe the technology. This is really
"recombinant" batteries, which means that the oxygen evolved at the positive plates will
largely recombine with the hydrogen ready to evolve on the negative plates, creating water
and preventing water loss. The valve is a safety feature in case the rate of hydrogen evolution
becomes dangerously high. In flooded cells, the gases escape before they can recombine, so
water must be periodically add
I have successfully completed my summer training of 30 days in 220 KV GSS UPPTCL.,
CANTT,ALLAHABAD, and got immense knowledge regarding different power equipments
used in GSS.
The first phase of practical training has proved to be quite fruitful. It provided an opportunity
for encounter with such huge machines like power transformers etc.
It also provided an opportunity to learn technology used at proper place and time can save a
lot of labour.
But there are few factors that require special mention. Training is not a carried out in its trees
sprit. It is recommended that there should be some project specially meant for student where
the authorities should be insured.
However training has proved too is quite faithful. It has allowed as an opportunity to get an
exposure of the practical implementation to theoretical fundamentals.
Training at 220 K.V G.S.S CANTT,ALLAHABAD gives the insight of the real instruments
used. There are many instruments like transformer, CT, PT, CVT, LA, relay, PLCC, bus
bars, capacitor bank, insulator, isolators, control room, Battery room etc. What is the various
problem seen in substation while handling this instruments. There are various occasion when
relay operate and circuit breaker open, load shedding, shut down, which has been heard
To get insight of the substation, how things operate, how things manage all is learned there.
Practical training as a whole proved to be extremely informative and experience building and
the things learnt at it would definitely help a lot in snapping the future ahead a better way.
Safety is one of the fundamental needs of all living beings. Accident is an unwanted event and
held due to carelessness. So necessary precautions should be taken to avoid such accidents. In
order to get the best out of an ‘individual’, his physical safety is essential. The following are
two main reasons, which include the accidents:
1. UNWANTED CONDITIONS
In an accident occurred by the unwanted acts, the workers are directly responsible. These
types of accidents are held by improper acts, carelessness, shortcuts for completing work early
by keeping awareness, patience in doing work. The main reasons which motivate the accidents
in the form of unwanted acts are as follows:-
1. Use of machine or equipments without permission.
2. Filling and loading the materials improperly.
3. Keeping high speed of machine.
4. Maintaining, oiling and greasing the machine in running Conditions.
5. Standing in unsafe conditions.
6. Use of unsafe tool and safety equipments.
7. Lifting and keeping the material unsafe.
There are many safety rules for safety but main golden rules are as follows:
1. Comply with all safety rules and regulations.
2. Correct or report unsafe conditions immediately to supervisor.
3. Wear rotating safety equipments only when authority is given.
4. Use right tool for the right job and use it safely.
5. Keep the workplace clean
DO’S AND DON’TS
1. Smoking is not allowed in any part of the GSS boundary
2. Before starting of any job, make certain you have obtained the necessary work permit.
3. Whenever any dangerous condition is noted. It should be reported immediately to the
action supervisor and fire safety action.
4. Be a good housekeeper, keep your tools and surrounding cleaned your equipment in
5. Unnecessary running is not allowed in the GSS area.
6. In protective measure employees must not walk through of across any operating unit
unless their duties require them to do so.
7. Where walkways are provided use them instead of short cuts.
8. All stairways platforms and walkways must be kept clear of any obstructions at all
9. Make shift arrangement without prior approval and valid reason are prohibited
10. After completion / stopping of the work, all left over junk and tools are to be removing
to the proper place.
11. All condition that may affect the safety of the employees or equipment must be
reported at once.
12. Do attempt to operate any machine or equipment to which you are not assigned
13. Walking on the pipeline is prohibited.
14. On sounding of siren, rush security gate after stopping all your jobs, do jumps, if you
are caring out job at height.
1. Instruction manual of instrument transformer (TELK instrument transformer) provided
2. Instruction manual of Lighting Arresters (LAMCO’S metal oxide surge
arrestermorester) provided by U.P.P.T.C.L.
3. A Text-book of ELECTRICAL TECHNOLOGY ( AC and DE machines) by B.L.
4. A Text-book of POWER SYSTEM by V.K. Mehta
5. Electrical Power System by C. L. Wadhwa
6. B.R. Gupta / a Text Book of Electrical Technology Vol. II / Chapter 32/ Transformer/
Page No. 1116-1120.
7. Sunil S. Rao / Switch Gear Protection and Power Systems / Chapter 33/
8. Protection of Transformer/ Page No. 826-830.
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