1

VOCATIONAL TRAINING

Submitted By:

PRATEEK PAWARELECTRICAL ENGINEERINGMAHARANA PRATAP ENGG. COLLEGEKANPUR

Submitted To:

Mr. S.C JOSHISDO-TRANSPORT NAGERELECTRICTY RURAL DISTRIBUTION DIVISION (HALDWANI)

DISTRIBUTION & MAINTANCE

OF SUBSTATION

O

ACKNOWLEDGMENT

There are few moments in life when you really feel like expressing gratitude and

sincere thanks. I take this opportunity to express my deep gratitude to persons who

have helped me. It is well-established fact that behind every achievement lays an

unfathomable sea of gratitude of those who have extended their support and without

whom it would ever come into existence. To them I lay the words of gratitude.

First of all, I would like to thank for the mercy of Almighty that I could successfully

complete this project. I bow my head before him.

I would also like to thanks Gopal Singh Bagadwale support and for providing me with

the time and inspiration needed to detail out this project

SUMMER TRAINEE:

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CONTENTS

CHAPTER-1

Introduction

Objective of the study

Period of the study

Scope of the study

CHAPTER-2

Company profile

CHAPTER-3

Study of power substation

Transformer

Oil circuit breaker

Isolator

Feeder

Earthing

Bibliography

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INTRODUCTION

As a part of B.TECH program I had an opportunity to do summer training. I did

summer training in “uttarakhand power coperation Ltd.

I was supposed to make a project report on Distribution & Maintaiance of power

supply in U.P.C.L on Rural haldwani.

Various data is being collected through questionnaire from the various staff member

and the worker. I also collected data from company website and company manuals.

In the completion of this project I have made our best efforts to summarize the same

in the report so that our report act as understanding practical and knowledge imparting

detail for all readers .

OBJECTIVE OF THE STUDY:

Objective of the study is to know about the various equipment or machine which is

use by uttarakhand power coperation Ltd on the supply of power distribution for

different consumer and Domestic supply.

PERIOD OF THE STUDY.

The period of the study consist of one month from 14 July to 10 Aug .

SCOPE OF THE STUDY:

Scope of the study is as follows:

1. This research is useful for the company for the assessment of there customers.

2. This is report can be useful for the company for report preparation.

3. It is based on primary study hence can be passed to the higher authority by line

managers.

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COMPANY PROFILE:

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COMPANY HISTORY-:

UTTARAKHAND POWER COPERATION LTD

Uttaranchal, the 27th State of India was created on 9th November 2000 as the 10th

Himalayan State of the country blessed with the natural and mineral resources in

abundance and poised to be a 20000 MW HYDRO POWER HUB of India in the

future.

Uttarakhand Power Corporation Ltd (UPCL), formerly Uttaranchal Power

Corporation Ltd was incorporated under the Companies Act, 1956 on February 12,

2001 consequent upon the formation of the State of Uttarachal. UPCL, has been

entrusted to cater to the Transmission & Distribution Sectors inherited after the de

merger from UPPCL (erstwhile UPSEB) since 1st April 2001. The Electricity Act.

2003 mandated the separation of Transmission functions under Power Sector

Reforms. On 1st June 2004, the Power Transmission Corporation Limited (PTCUL)

was formed to maintain & operate 132 KV & above Transmission Lines &

substations in the State. Today UPCL, the State Power Distribution Utility of  the

Government of Uttaranchal (GoU) caters to the Sub –Transmission & Distribution

Secondary Substations & Distribution Lines 66 KV & below in the State.

UPCL - the Frontline State Power Distribution Utility & service provider of

QUALITY & RELIABLE POWER SUPPLY to over 1.08 million consumers of

electricity spread over the 13 Districts of Uttarakhand i.e Dehradun, Pauri, Tehri,

Haridwar, Pithoragarh, Almora, Nainital, Uttarkashi, Udhamsingh Nagar,

Rudraprayag, Chamoli, Bageshwar & Champawat. These electrical consumers are

categorized depending ont heir domestic, commercial, agricultural and industrial

loads. UPCL is also the first electrical utility in India to initiate women empowerment

by employing local women through Self Help Groups, as franchisees, for meter

reading, bill distribution and revenue collection.

UPCL looks forward to a committed participation from a Team of professionals

always striving for performance excellence with new innovative technologies to

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strengthen the Power Distribution Infrastructure of the STATE in Seamless

Integration with Generation & Transmission Utilities for the Socio – economic

development.. A comprehensive POWER EVACUATION PLAN is underway with

construction of new 33/11 KV Substations in the State.

With the Revenue Cycle Management for the optimal Metering, Billing & Collection

( MBC) efficiency the record Revenue Realization is targeted during 2007-08 .

During 2008-09 , the re-organisation of the Organisation Structure of UPCL is aimed

to provide better services to the Consumers of electricity which is the priority over the

dichotomy between POWER & ENERGY

PARTICULARS OF ORGANISATION-:

Pursuant to the reorganisation of Uttar Pradesh & creation of the State of

Uttaranchal, Uttaranchal Power Corporation Ltd. was incorporated under the

Companies Act, 1956 on 12.02.2001 to manage and operate the distribution

of power in the State of Uttaranchal. Uttaranchal Power Corporation Ltd caters

to the power distribution functions in the Uttaranchal.

The Head Quarter/Corporate office of the Corporation is situated at Urja

Bhawan, Kanwali Road, Dehradun. The Corporation is managed by the Board

of Directors having the maximum number of 12 and minimum number of 3

Directors. The Board of Directors meets frequently and at least once in every

quarter. The day to day management of the Corporation is looked after by the

Chairman & Managing Director who works under the control, supervision &

superintendence of Board of Directors. The Chairman & Managing Director is

assisted by the 3 whole time Directors, Secretary and other officers of the

Corporation

The Corporation is having two Zones viz Garhwal Zone and Kumaun Zone.

Garhwal Zone is having 5 Circle offices and 12 EDD Divisions, 4 Testing

Divisions, 1 store Division, 3 Civil Divisions, 1 Rural Electrification Division, 1

Electricity Secondary Works Division and 1 Electricity Workshop Division. and

Kumaun Zone is having 3 Circle offices, 10 EDD Divisions, 3 Testing

Divisions, 1 Store Division, 1 Civil Division, 1 Rural Electrification Division, 1

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Electricity Secondary Works Division and 1 Electricity Workshop Division.

FUNCTIONS-:

The main functions of UPCL are as follows:

1. To acquire, establish, construct, takeover, erect, operate, run, manage,

hire, maintain, enlarge, alter, renovate, modernize, work and use

electrical lines, sub-stations, including distribution centers, supply and

distribution of electricity.

2. To carry on the business of purchasing, selling, importing, exporting,

trading of power, including finalisation of tariff, billing and collection

thereof

3. To execute Power Purchase Agreement with generating companies.

Central and State generating stations, Regional Electricity Boards,

neighbouring states, Utilities, Companies, persons, societies & firms

including the independent power producers.

4. To undertake, for and on behalf of other erection, operation,

maintenance, management of extra-high voltage, high voltage, medium

voltage and low voltage, lines and associated sub-stations, equipment,

apparatus, cable and wires.

5. To execute agreement for sale of power to distribution companies,

institutions, bodies and other persons and to coordinate, aid and advise

on the activities of other companies and concerns, including subsidiaries,

associates and affiliates engaged in generation, transmission,

distribution, supply.

.

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DUTIES:

1. The Corporate office is responsible for making the policies,

administration, financial control, finalisation of tariff and controlling the

activities of the entire Corporation.

2. Zone office & Circle office are supervisioning and controlling the work

and functions of the Divisions under their control. The various Divisions

functioning under the Corporation are the main units responsible to

directly deal with consumers for supply & distribution of electricity

through the sub-divisions functioning under each Division.

The addresses of the office of the Forum are:

1. Consumers Grievances Redressal Forum,

C/o General Manager (Kumaon Zone),

Uttaranchal Power Corporation Ltd.

132 K.V. Sub-station Premises

Kathgodam,

Dist. Nainita

2. Consumers Grievances Redressal Forum,

C/o General Manager (Garhwal Zone)

Uttaranchal Power Corporation Ltd.

120, Haridwar Road,

Dehradun

Any person aggrieved by the non-redressal of his grievances in the Forum,

may make a representation for the redressal of his grievance to an authority to

be known as Ombudsman.

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Addresses of the office of Ombudsman is

Office of Ombudsman,

24 Vasant Vihar,

Phase-II,

Dehradun-248006

ADDRESSES OF THE HEAD OFFICES AND OTHER OFFICES

HEAD OFFICE

Uttaranchal Corporation Ltd.,

Urja Bhawan, Kanwali Road,

Power Dehradun

ZONE OFFICE (UPCL)

1. General Manager(Garhwal Zone)

Uttaranchal Power Corporation Ltd.

120, Haridwar Road,

Dehradun.

2. General Manager(Kumaon Zone),

Uttaranchal Power Corporation Ltd.

132 K.V. Sub-station Premises

Kathgodam,

Dist. Nainital

CIRCLE OFFICES (UPCL)

1. DGM, Electricity Distribution Circle(Urban), Uttaranchal Power

Corporation Ltd., Dehradun

2. DGM, Electricity Distribution Circle(Rural), Uttaranchal Power

Corporation Ltd. Dehradun

3. DGM, Electricity Distribution Circle, Uttaranchal Power Corporation Ltd.,

Roorkee

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4. DGM, Secondary Works Circle, Uttaranchal Power Corporation Ltd.,Dehradun

5. DGM, Secondary Works Circle, Uttaranchal Power Corporation Ltd.

Haldwani

6. DGM, Electricity Distribution Circle, Uttaranchal Power Corporation Ltd.,

Srinagar.

7. DGM, Electricity Distribution Circle, Uttaranchal Power Corporation Ltd.,

Ranikhet

8.Electricity Distribution Circle, Uttaranchal Power Corporation Ltd.,

Rudrpur

9. DGM lectricity Civil Circle, Uttaranchal Power Corporation Ltd.,

Dehradun

10. DGM, E. DGM, Electricity Distribution Circle, Uttaranchal Power Corporation

Ltd.,Haldwani.

.DIVISION OFFICES (UPCL)

1. Executive Engineer, Electricity Distribution Division (South), Uttaranchal

Power Corporation Ltd., Dehradun.

2. Executive Engineer, Electricity Distribution Division (North), Uttaranchal

Power Corporation Ltd., Dehradun.

3. Executive Engineer, Electricity Distribution Division (Rural), Uttaranchal

Power Corporation Ltd., Dehradun

4. Executive Engineer, Transmission Division-I, Uttaranchal Power

Corporation Ltd., Dehradun.

5. Executive Engineer, Secondary Works Division, Uttaranchal Power

Corporation Ltd. Dehradun.

6. Executive Engineer, Test(Rural), Uttaranchal Power Corporation Ltd.,

Dehradun

.7. Executive Engineer, Test(Urban), Uttaranchal Power Corporation Ltd.

Dehradun.

8. Executive Engineer, Workshop, Kaulagarh, Uttaranchal Power

Corporation Ltd, Dehradun

9. Executive Engineer, Electricity Workshop Division, Uttaranchal Power

Corporation Ltd., Dehradun

10. Executive Engineer, Store Division, Uttaranchal Power Corporation Ltd.

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Dehradun

11. Electricity Test Division, Uttaranchal Power Corporation Ltd. Haldwani.

12. Executive Engineer, Workshop, Uttaranchal Power Corporation Ltd.

Haldwani

13. Executive Engineer, Store Division, Uttaranchal Power Corporation Ltd.,

Haldwani

14. Executive Engineer, Secondary Works Division, Uttaranchal Power

Corporation Ltd., Haldwani.

15. Executive Engineer, Electricity Distribution Division, Uttaranchal Power

Corporation Ltd., Haldwani

16. Executive Engineer, Civil Division, Uttaranchal Power Corporation Ltd.

Srinagar

17. Executive Engineer, Electricity Distribution Division, Uttaranchal Power

Corporation Ltd. Srinagar

18. Executive Engineer, Electricity Test Division, Uttaranchal Power

Corporation Ltd. Srinagar.

19. Executive Engineer, Civil Cons. Division, Uttaranchal Power Corporation

Ltd. Roorkee.

20. Rudrapur lectricity Distribution Division, Uttaranchal Power

Corporation Ltd., Rishikesh.

21. Executive Engineer, E Executive Engineer, Electricity Distribution Division,

Uttaranchal PowerCorporation Ltd.,

22. Executive Engineer, Electricity Test Division 400 KV (Control),

Uttaranchal Power Corporation Ltd. Uttaranchal Power Corporation Ltd.

Rishikesh

23. Executive Engineer, Electricity Distribution Division, Uttaranchal Power

Corporation Ltd., Hardwar.

24. Executive Engineer, Electricity Distribution Division, Uttaranchal Power

Corporation Ltd., New Tehri

25. Executive Engineer, Electricity Distribution Division, Uttaranchal Power

Corporation Ltd., Uttarkashi.

26.Executive Engineer, Electricity Distribution Division, Uttaranchal

PowerCorporation Ltd., Rudrapur.

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VISION-:

To provide

Cost-effective,

Good quality,

24X7 power supply

At competitive rates

to all the consumers of the State of Uttarakhand.

MISSION-:

Uttaranchal Power Corporation Ltd. was created on the 1st April 2001 after the de-

merger from UPPCL (erstwhile UPSEB) catering to the Transmission & Distribution

Infrastructure in the Uttaranchal born on 9th November 2000 as the 27th State of

India & 10th Himalayan State of the country. Since then UPCL is engaged for

improving the power supply of Uttaranchal State with the following (MISSION) aims

& objectives :

To achieve 100% Rural Electrification Infrastructure for Electrification of

Villages & Hamlets by March 2009 and Rural Households by March 2012.

To provide 24x7 reliable, quality and un-interrupted supply to its

consumers. ? To provide POWER TO ALL on demand.

To provide POWER TO ALL on demand.

To strengthen the existing power network based on present advanced

technology with an objective to reduce T&D losses.

To provide power system network with minimal environmental impact.

To plan and provide strong power system to the state and its consumers at

an affordable cost.

To develop a professionally managed organization.

To generate additional revenue for the Corporation and State by

developing a strong, adequate, reliable and cohesive power network based

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on most techno-economical aspects to contribute towards the development

and prosperity of the State.

To improve social status of the people.

To reduce poverty of the people.

To provide employment in the rural sections by providing reliable supply.

To establish Consumer Care Centre, Central Call Centre etc. to provide

Quality Service to the Consumers.

To release Electricity Connection to the consumers under Talkal Sewa

within 24 hours for better service to them.

To contribute to the formation of a developed & progressive Uttaranchal

State.

DEVELOPMENT PLANS-:

ACTION PLAN FOR REDUCTION OF AT&C LOSSES

Uttarakhand Power Corporation Ltd. was incorporated in February 2001 and is the

State’s only Distribution Company serving a customer base of 12.04 lacs. The

Revenue Districts served by the Company are thirteen, out of which eight are in hills

and the remaining in the plains. The coverage and power consumption patterns differ

in the hills and plains – hills accounting for only about 10% of consumption (mainly

lighting & heating loads) and the plains for the remaining 90% again nearly 65% of

which is accounted for by Industries.

The existing Distribution infrastructure mainly comprises of the following:

1. 33/11 KV Substations – 260 Nos. (2170 MVA)

2. 33 KV lines – 3894 KMs.

3. 11 KV Substations- 41668 (2455 MVA)

4. 11 KV lines – 33047 KMs.

5. LT lines – 48201 KMs.

This network is proving inadequate to cater to the increasing demands (mainly due to

industrial growth and village electrification) and the requirements of better network

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availability, improved voltage and customer service. To enable achievement of these,

the secondary and distribution system requires strengthening. Main projects planned

(some underway) comprise of –

1. Renovation/reconductoring of lines,           

2. Capacity increase in power transformers and DTs,

3. Replacement of bare service lines with Aerial Bunch Conductors,

4. Replacement of LT system with HVDS and

5. Increasing capacitance loading of lines and substations through capacitors. 

A long-term plan is already under implementation through various schemes including

APDRP. Inspite of these schemes, it is seen that high levels of AT&C losses which

are the bane of the Discom, persist at a very high figure and it is the endeavor /target

of the Company to bring it to a more acceptable level.

UPCL has planned to implement following specific projects/initiatives to facilitate

reduction of AT&C losses and improve customer service & satisfaction.

The Company’s performance has to be analyzed on the basis of two major parameters,

namely,

1. Customer Service & Satisfaction and

2. Financial performance in terms of T&D/AT&C loss reduction and Collection

efficiency.

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NAINITAL -:

S.No Name of S/sExisting Capacity

(in MVA)Sub-Division

EDD Urban Haldwani1. 132 KV Kathgodam 1x7.5

Haldwani Town-I 2. Subhash Nagar 2x53. Golapar 2x54. HMT Ranibagh 2x55. Kaladhungi Chauraha 2x8 Haldwani Town-II

EDD Rural Haldwani6. Kamaluganja 2x5 Kamaluaganja7. Transport Nagar 2x5 Transport Nagar 8. Lal Kuan 2x5

Lal Kuan 9. Dholakhera 2x5

EDD Nainital 10. Sukhatal 2x5

Nainital11. Pines 1x512. Bhimtal 2x3

Bhimtal13. Padampuri 1x1.514. Sarghakhet 1x315. Mehragaon -16. Garampani 1x1+3x0.3

Bhawali17. Betalghat 1x1.518. 132 KV Mehragaon -

EDD Ramnagar19. Kaladhungi 1x3

Ramnagar Rural 20. Bailparaw 1x521. Kotabagh 1x322. Chilkiya 5+3

Ramnagar Town 23. Ramnagar 8+5

 

COMMERCIAL-:

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Since Uttarakhand Power Corporation is a commercial organization, it is absolutely

necessary to have correct recording of energy received and energy sold. For this

purpose provision has been made to install electronic meters at all S/s and all

industrial feeders as well as commercial consumers. Further, attempt has been made

to cover about 100% of L&F consumers under electronic metering. This arrangement

will block all possibilities of pilferage of energy or manipulation of consumption by

consumers on one hand and will enable the department to identify loss prone areas

and analyse the reasons of high losses. As the state of Uttarakhand covers mostly hilly

region in which villages are scattered and far-flung, electrification is not a profitable

preposition. It the norms of minimum 15% return on electrification are adhered to, a

very few villages will be covered. Since electricity is now a necessity and no longer a

luxury, all the people have to be provided with the benefits of electricity. Thus

electrification is an obligation on the Government for social upliftment of its people.

It is, therefore, strongly stressed that expenses being incurred in electrification work

must be such managed so that interest burden can be minimized along with maximum

support possible from the Govt. as no commercial organization can survive with

recurring losses by executing economically non-viable works, like rural

electrification.

Quality of Power Supply

Our performance standards are to provide quality power supply to our electricity

consumers who are regularly paying their electricity bills within the stipulated dates

as mentioned therein. The services shall only remain suspended during force majeure

conditions such as war, civil commotion, riot, flood, cyclone, lightning, earthquake or

other unforeseen circumstances such as strike, lockout, fire affecting the Corporation

and their activities.

We promise to act in response within 4 hours to a consumer's complaint regarding

higher/lower voltage and frequency of POWER SUPPLY beyond the tolerance limit

(as prescribed under Indian Electricity Rules) at the point of COMMENCEMENT OF

SUPPLY.

We promise to improve the QUALITY OF POWER SUPPLY within 15 days of

receiving the ORIGINAL COMPLAINT or furnish a written reply to the electricity

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consumer intimating them the reason for poor quality of power supply, if the same is

beyond our control. We promise to respond within 180 days in respect of the

complaint regarding low voltages arising due to inadequacy in the DISTRIBUTION

SYSTEM requiring UPGRADATION OF DISTRIBUTION TRANSFORMERS

(DTRs) AND ITS ASSOCIATED LINES OR INSTALLATION OF LT

CAPACITORS etc

Rajiv Gandhi Gramin Vidyutikaran Yojna (RGGVY)

VISION

POWER FOR ALL by 2012 and provide access to electricity to all the rural

households of Uttarakhand by March 2012

STRATEGY

1. The development of Village Electrification Infrastructure by means of

extension, up-gradation and strengthening of the Distribution Systems.

2. 100% Rural Electrification based on District-wise actual Survey of villages &

hamlets

3. Implementation of Franchisee-based system for Metering, Billing &

Collection.

RURAL ELECTRIFICATION – An Overview

1. 98.6% villages in Uttarakhand (erstwhile UTTARANCHAL) has been

electrified covering 15545 villages, as on 15th July 2010, with access to

electricity provided against a total of 15761 Revenue villages identified during

the Census 2001.

2. On 31 March, 2001, 79.7% villages of Uttarakhand were electrified, which

amounted to 12563 villages.

3. As on 15th July 2010, 216 villages remains to be electrified by UPCL and

UREDA. Under RGGVY, out of the remaining 10 un-electrified villages,

namely 4 villages in Tehri , 2 villages in Almora, 4 villages in Champawat

District of Uttarakhand.

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4. Out of the 653 villages electrified by UREDA up to March'2010 through

MHP/ Solar energy in the remote hinterland of the state, it may be noted that

514 villages electrified by Solar energy may be re-visited for connectivity by

GRID in future using other energy sources e.g. Bio-mass Gasifier, MHP, etc.

5. 13998 villages were electrified by March 2005 and 15541 villages were

electrified by March 2010 respectively.

6. RAJIV GANDHI GRAMEEN VIDYUTIKARAN YOJANA (RGGVY)

launched in April 2005 aims to achieve 100% electrification of villages and

provide access to electricity to all rural households by March 2012.

Action Plan for meeting RGGVY target

1. A time-bound ACTION PLAN for Rural Electrification for 2010-11 to

achieve 100% electrification by March 2012 with access to electricity to every

household being formulated through District–wise Survey of balance RE

Works, as per the REC Guidelines.

2. Expeditious energizing of villages and hamlets/ Toks by the Distribution Wing

under the Operations Directorate of UPCL has been facilitated with the use of

Project management charts -Line Charts, Connection Diagrams, etc.- by the

respective RGGVY Contractor duly-verified by the Projects Directorate, along

with the release of BPL connections simultaneously.

3. A comprehensive list of District-wise energized villages & its associated

hamlets/ Toks with their respective Village Code and Date of energizing for

which Village Electrification Infrastructure (VEI) is being re-conciled/

compiled, taking support from the Local District Authorities/ Gram

Panchayats.

4. Plan is underway to complete the balance District-wise works under RGGVY

by December 2010 and release of 21594 BPL connections by June 2011.

Note: The revised awarded cost of the scheme is Rs. 760.14 crores. The expenditure

incurred was Rs. 638.98 Crores by 15 July 2010. REC Ltd. New Delhi which is the

Nodal Agency for the implementation of the scheme has released Rs. 651.45 crores

for the Rural Electrification works under RGGVY.

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POWER DISTRIBUTION SUBSTATION

SUPPLY OF 8 MVA 33/11 KV,STEP DOWN

TRANSFORMERS

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VARIOUS STEPS INVOLVED IN DISTRIBUTION OF POWER SUBSTATION:-

POWER PLANT-:

Hydro power plant generated power of 250mw and supply to station where it

convert to 132kv and again transmitted to 33kv to substation where is further

converted .

SUBSTATION:-

In substation 33kv is supply to 33kv double feeder where three phase supply goes to

step down transformer where it convert to 11kv and going to main incoming feeder

where it connect to various feeder and supply to big consumer and domestic purpose.

33KV CONTROL AND RELAY PANEL FOR DOUB LE FEEDER-:

In this 33kv is direct feed to main panel ,which control the power in panel and direct

the power to step down transformer and control by the isolator and relay and various

power or fault is control by it.ammeter voltmeter and powe r factor correction.

STEP DOWN TRANSFORMER:-

In this 33kv is step down to 11kv and transfer to main incoming feeder and earthing

aur fault are control in transformer.

INCOMING FEEDER:-

Incoming feeder is used to supply to varios feeder which are connect for supply of

power to commercial and domestic purpose.

TRANSMISSION LINE-:

A transmission substation connects two or more transmission lines. The simplest case

is where all transmission lines have the same voltage. In such cases, the substation

contains high-voltage switches that allow lines to be connected or isolated for fault

clearance or maintenance.

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SINGLE LINE DIAGRAM OF 33/11KV SUBSTATION

SINGLE LINE DIAGRAM OF33/11KV SUBSTATION

22

TRANSFORMER:-

A transformer is a device that transfers electrical energy from one circuit to another

through inductively coupled conductors—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 electromotive force (EMF) 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 (VS) is in proportion to the primary voltage (VP), and is given by the ratio of

the number of turns in the secondary (NS) to the number of turns in the primary (NP)

as follows:

By appropriate selection of the ratio of turns, a transformer thus allows an

alternating current (AC) voltage to be "stepped up" by making NS greater than

NP, or "stepped down" by making NS less than NP.

In the vast majority of transformers, the windings are coils wound around a

ferromagnetic core, air-core transformers being a notable exception.

Transformers range in size from a thumbnail-sized coupling transformer hidden

inside a stage microphone to huge units weighing hundreds of tons used to

interconnect portions of power grids. All operate with the same basic principles,

although the range of designs is wide. While new technologies have eliminated the

need for transformers in some electronic circuits, transformers are still found in

nearly all electronic devices designed for household ("mains") voltage. Transformers

are essential for high voltage power transmission, which makes long distance

transmission economically practical.

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SPECIFICATION FOR 8MVA STEP DOWN TRANSFORMER

S.NO-SPECIFICATION RATING

1 Phases (HV) 3

2 Phases (LV) 3

3 Load loss 36 KW

4 Current(HV) 140 A

5 Current(LV) 420 A

6 No load loss 4.5

7 Type of cooling Onan

8 Vector group Dyn-11

9 Frequency 50 HZ

10 Impedence (Volts) 8.35%

11 Wt. of core & wdg 10200 kg

12 Wt. of tank & filter 4600 kg

13 Wt. of oil 3100 kg

14 Voltage 3000 KVA

HV 33000 Volts

LV (No load) 11000 Volts

15 Total weight 17900 kg

16 Vol. of oil 3600 LTR

17 Temp. rise in oil/ wdg 45/55 *c

FEEDER-:

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The minimum requirement of instrument transformers, metering and protections to

be provided.

for different type of feeders are listed below :

1.0 33kV Incoming Feeder

a) 3 - Protection Class (5P20) CTs (1-phase)

b) 3 – Metering Class CTs (Cl. 1.0) (1-phase)

c) 3 – Differential Class (Class PX) CTs (1-phase)

d) 3 – Two winding Potential Transformer (1-phase)

e) 1 – Multi-function Meter

f) 1 – Ammeter with selector switch

g) 1 – Voltmeter with selector switch

h) Two (2) pole IDMTL O/C relay with Instantaneous element (50/51) for phase

fault.

i) One (1) no. IDMT O/C relay with Instantaneous element (50N) for earth fault.

j) One 3-ph Differential Relay (87)

k) All auxiliary relays, Lockout relay, Transformer auxiliary relays, indicating lamps,

etc.

. Incoming feeder (From Transformer)

a) Three (3) no. measuring class current transformers.

b) Three (3) no. protection class current transformers for over current relays.

c) Three (3) no. PX class current transformers for differential protection for

33/11.5kV

transformer.

d) Three (3) no. three winding voltage transformer (1-phase), one winding with open

delta.

e) 1 – Multi-function Meter

f) 1 – Ammeter with selector switch

g) 1 – Voltmeter with selector switch

h) Two (2) pole directional o/c relays (67) for phase fault.

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i) One (1) no. directional o/c relay (67N) for earth fault.

j) One 1-ph Restricted E/F Relay (64)

k) Three (3) no. under voltage relays (27) of range 40-80% with timer and auxiliary

relay.

l) One (1) no. Frequency Relays (81).

m) One (1) no. Voltage relay for ground fault detection.

n) All auxiliary relays, Lockout relay, Transformer auxiliary relays, indicating lamps,

etc.

3.0 11kV Bus VT

a) Three (3) no. two winding voltage transformer.

b) Three (3) no. no volt relay (0 – 20%) with timer and auxiliary relay

4.0 11kV Line Feeder

a) Three (3) no. measuring class current transformers.

b) Three (3) no. protection class (class 5P20) current transformers for O/C Protection

relays.

c) Two (2) no. inverse time o/c relays (51) for phase fault.

d) One (1) no. inverse time o/c relay (51N) for earth fault .

e) One no. Multifunction Meter.

f) 1 – Ammeter with selector switch.

f) 1 – Ammeter with selector switch.

g) All auxiliary relays, Lockout relay, Transformer auxiliary relays, indicating lamps,

etc.

5.0 LV Transformer Feeder

a) Three (3) no. measuring class current transformers.

b) Three (3) no. protection class (class 5P20) current transformers for O/C

Protectionrelays.

c) Three (3) no. inverse time o/c relays with instantaneous element (50/51) for phase

fault.

d) One (1) no. inverse time o/c relay with instantaneous element (50N) for earth fault

.

26

e) One no. Multifunction Meter.

f) 1 – Ammeter with selector switch.

g) All auxiliary relays, Lockout relay, Transformer auxiliary relays, indicating

lamps,etc.

6.0 Capacitor Bank Feeder

a) Three (3) no. measuring class current transformers.

b) Three (3) no. protc) Two (2) no. inverse time o/c relays with instantaneous

element (50/51) for phase fault.

d) One (1) no. inverse time o/c relay with instantaneous element (50N) for earth fault

.

e) One no. Multifunction Meter.

f) 1 – Ammeter with selector switch.

g) One no Current Unbalance Relay for Neutral Displacement.

h) All auxiliary relays, Lockout relay, Transformer auxiliary relays, indicating lamps,

etc.

7.0 Apart from protection relays, each breaker shall be provided with antipumping

(94), trip

annunciation (30), trip supervision (74), lockout (86) and other auxiliary relays.

Lockout relay

shall be hand reset type.

8.0 All inverse time o/c relays shall be of 3 sec version. All definite time o/c relays

shall have

adjustable time range to be decided by the Bidder after application check.

9.0 Any other protection/relay not explicitly mentioned but necessary for satisfactory

and trouble-free

operation of the system are deemed included within the scope of supply

27

ELECTRICAL SUBSTATION-:

An electrical substation is a subsidiary station of an electricity generation, and

distribution system where voltage is transformed from high to low or the reverse

using transformers. Electric power may flow through several substations between

generating plant and consumer, and may be changed in voltage in several steps.

A substation that has a step-up transformer increases the voltage while decreasing the

current, while a step-down transformer decreases the voltage while increasing the

current for domestic and commercial distribution. The word substation comes from

the days before the distribution system became a grid. The first substations were

connected to only one power station where the generator was housed, and were

subsidiaries of that power station

.

28

CONTENTS

1 Elements of a substation

2 Transmission substation

3 Distribution substation

4 Collector substation

5 Stations with change of current type

6 Switching substation

7 Design

ELEMENTS OF A SUBSTATION-:

Substations generally have switching, protection and control equipment and one or

more transformers. In a large substation, circuit breakers are used to interrupt any

short-circuits or overload currents that may occur on the network. Smaller distribution

stations may use recloser circuit breakers or fuses for protection of distribution

circuits. Substations do not usually have generators, although a power plant may have

a substation nearby. Other devices such as power factor correction capacitors and

voltage regulators may also be located at a substation.

Substations may be on the surface in fenced enclosures, underground, or located in

special-purpose buildings. High-rise buildings may have several indoor substations.

Indoor substations are usually found in urban areas to reduce the noise from the

transformers, for reasons of appearance, or to protect switchgear from extreme

climate or pollution conditions.

Where a substation has a metallic fence, it must be properly grounded (UK: earthed)

to protect people from high voltages that may occur during a fault in the network.

Earth faults at a substation can cause a ground potential rise. Currents flowing in the

Earth's surface during a fault can cause metal objects to have a significantly different

voltage than the ground under a person's feet; this touch potential presents a hazard of

electrocution.

29

TRANSMISSION SUBSTATION-:

A transmission substation connects two or more transmission lines. The simplest

case is where all transmission lines have the same voltage. In such cases, the

substation contains high-voltage switches that allow lines to be connected or isolated

for fault clearance or maintenance. A transmission station may have transformers to

convert between two transmission voltages, voltage control devices such as

capacitors, reactors or static VAr compensator and equipment such as phase shifting

transformers to control power flow between two adjacent power systems.

Transmission substations can range from simple to complex. A small "switching

station" may be little more than a bus plus some circuit breakers. The largest

transmission substations can cover a large area (several acres/hectares) with multiple

voltage levels, many circuit breakers and a large amount of protection and control

equipment (voltage and current transformers, relays and SCADA systems). Modern

substations may be implemented using International Standards such as IEC61850.

DISTRIBUTION SUBSTATION-:

30

A distribution substation transfers power from the transmission system to the

distribution system of an area. It is uneconomical to directly connect electricity

consumers to the high-voltage main transmission network, unless they use large

amounts of power, so the distribution station reduces voltage to a value suitable for

local distribution.

The input for a distribution substation is typically at least two transmission or

subtransmission lines. Input voltage may be, for example, 115 kV, or whatever is

common in the area. The output is a number of feeders. Distribution voltages are

typically medium voltage, between 2.4 and 33 kV depending on the size of the area

served and the practices of the local utility.

The feeders will then run overhead, along streets (or under streets, in a city) and

eventually power the distribution transformers at or near the customer premises.

Besides changing the voltage, the job of the distribution substation is to isolate faults

in either the transmission or distribution systems. Distribution substations may also be

the points of voltage regulation, although on long distribution circuits (several

km/miles), voltage regulation equipment may also be installed along the line.

Complicated distribution substations can be found in the downtown areas of large

cities, with high-voltage switching, and switching and backup systems on the low-

voltage side. More typical distribution substations have a switch, one transformer, and

minimal facilitie on the low voltage side.

Stations with change of current type

Substations may be found in association with HVDC converter plants or, formerly,

where rotary converters changed frequency or interconnected non-synchronous

networks.

Switching substation

A switching substation is a substation which does not contain transformers and

operates only at a single voltage level. Switching substations are sometimes used as

collector and distribution stations. Sometimes they are used for switching the current

31

to back-up lines or for paralellizing circuits in case of failure. Example herefore are

the switching stations at HVDC Inga-Shaba.

Design

The main issues facing a power engineer are reliability and cost. A good design

attempts to strike a balance between these two, to achieve sufficient reliability without

excessive cost. The design should also allow easy expansion of the station, if required.

Selection of the location of a substation must consider many factors. Sufficient land

area is required for installation of equipment with necessary clearances for electrical

safety, and for access to maintain large apparatus such as transformers. Where land is

costly, such as in urban areas, gas insulated switchgear may save money overall. The

site must have room for expansion due to load growth or planned transmission

additions. Environmental effects of the substation must be considered, such as

drainage, noise and road traffic effects. Grounding (earthing) and ground potential

rise must be calculated to protect passers-by during a short-circuit in the transmission

system. And of course, the substation site must be reasonably central to the

distribution area to be served.

Layout

The first step in planning a substation layout is the preparation of a one-line diagram

which shows in simplified form the switching and protection arrangement required, as

well as the incoming supply lines and outgoing feeders or transmission lines. It is a

usual practice by many electrical utilities to prepare one-line diagrams with principal

elements (lines, switches, circuit breakers, transformers) arranged on the page

similarly to the way the apparatus would be laid out in the actual station.

Incoming lines will almost always have a disconnect switch and a circuit breaker. In

some cases, the lines will not have both; with either a switch or a circuit breaker being

all that is considered necessary. A disconnect switch is used to provide isolation, since

it cannot interrupt load current. A circuit breaker is used as a protection device to

interrupt fault currents automatically, and may be used to switch loads on and off.

When a large fault current flows through the circuit breaker, this may be detected

through the use of current transformers. The magnitude of the current transformer

32

outputs may be used to 'trip' the circuit breaker resulting in a disconnection of the load

supplied by the circuit break from the feeding point. This seeks to isolate the fault

point from the rest of the system, and allow the rest of the system to continue

operating with minimal impact. Both switches and circuit breakers may be operated

locally (within the substation) or remotely from a supervisory control center.

Once past the switching components, the lines of a given voltage connect to one or

more buses. These are sets of bus bars, usually in multiples of three, since three-phase

electrical power distribution is largely universal around the world.

The arrangement of switches, circuit breakers and buses used affects the cost and

reliability of the substation. For important substations a ring bus, double bus, or so-

called "breaker and a half" setup can be used, so that the failure of any one circuit

breaker does not interrupt power to branch circuits for more than a brief time, and so

that parts of the substation may be de-energized for maintenance and repairs.

Substations feeding only a single industrial load may have minimal switching

provisions, especially for small installations.

Once having established buses for the various voltage levels, transformers may be

connected between the voltage levels. These will again have a circuit breaker, much

like transmission lines, in case a transformer has a fault (commonly called a 'short

circuit').Along with this, a substation always has control circuitry needed to command

the various breakers to open in case of the failure of some component.

ELECTRICITY DISTRIBUTION-:

Electricity distribution is the final stage in the delivery (before retail) of electricity

to end users. A distribution system's network carries electricity from the transmission

system and delivers it to consumers. Typically, the network would include medium-

voltage (less than 50 kV) power lines, electrical substations and pole-mounted

transformers, low-voltage (less than 1 kV) distribution wiring and sometimes

electricity meters.

33

Modern distribution systems

Electric distribution substations transform power from transmission voltage to

the lower voltage used for local distribution to homes and businesses

The modern distribution system begins as the primary circuit leaves the sub-station

and ends as the secondary service enters the customer's meter socket. A variety of

methods, materials, and equipment are used among the various utility companies, but

the end result is similar. First, the energy leaves the sub-station in a primary circuit,

usually with all three phases.

The actual attachment to a building varies in different parts of the world.

Most areas provide three phase industrial service. There is no substitute for three-

phase service to run heavy industrial equipment. A ground is normally provided,

connected to conductive cases and other safety equipment, to keep current away from

equipment and people. Distribution voltages vary depending on customer need,

equipment and availability. Delivered voltage is usually constructed using stock

transformers, and either the voltage difference between phase and neutral or the

voltage difference from phase to phase.

In many areas, "delta" three phase service is common. Delta service has no distributed

neutral wire and is therefore less expensive. The three coils in the generator rotor are

in series, in a loop, with the connections made at the three joints between the coils.

Ground is provided as a low resistance earth ground, sometimes attached to a

34

synthetic ground made by a transformer in a substation. High frequency noise (like

that made by arc furnaces) can sometimes cause transients on a synthetic ground.

In North America and Latin America, three phase service is often a Y (wye) in which

the neutral is directly connected to the center of the generator rotor. Wye service

resists transients better than delta, since the distributed neutral provides a low-

resistance metallic return to the generator. Wye service is recognizable when a grid

has four wires, one of which is lightly insulated.

Many areas in the world use single phase 220 V or 230 V residential and light

industrial service. In this system, a high voltage distribution network supplies a few

substations per city, and the 230V power from each substation is directly distributed.

A hot wire and neutral are connected to the building from one phase of three phase

service..

Rural services normally try to minimize the number of poles and wires. Single-wire

earth return (SWER) is the least expensive, with one wire. It uses high voltages,

which in turn permit use of galvanized steel wire. The strong steel wire permits

inexpensive wide pole spacings. Other areas use high voltage split-phase or three

phase service at higher cost.

The least expensive network has the fewest transformers, poles and wires. Some

experts say[2] that this is three-phase delta for industrial, SWER for rural service, and

230 V single phase for residential and light industrial. The system of three-phase Wye

feeding split phase is flexible and somewhat more resistant to geomagnetic faults, but

more expensive.

Electricity meters use different equations for each distribution system.

HISTORY

In the early days of electricity distribution, direct current (DC) generators were

connected to loads at the same voltage. The generation, transmission and loads had to

be of the same voltage because there was no way of changing DC voltage levels, other

than inefficient motor-generator sets. Low DC voltages were used (on the order of

100 volts) since that was a practical voltage for incandescent lamps, which were the

35

primary electrical load. Low voltage also required less insulation for safe distribution

within buildings.

The losses in a cable are proportional to the square of the current, the length of the

cable, and the resistivity of the material, and are inversely proportional to cross-

sectional area. Early transmission networks used copper, which is one of the best

economically feasible conductors for this application. To reduce the current and

copper required for a given quantity of power transmitted would require a higher

transmission voltage, but no efficient method existed to change the voltage of DC

power circuits. To keep losses to an economically practical level the Edison DC

system needed thick cables and local generators. Early DC generating plants needed

to be within about 1.5 miles (2.4 km) of the farthest customer to avoid excessively

large and expensive conductors.

Introduction of alternating current

General layout of electricity networks

The adoption of alternating current (AC) for electricity generation following the War

of Currents dramatically changed the situation. Power transformers, installed at power

stations, could be used to raise the voltage from the generators, and transformers at

local substations could reduce voltage to supply loads. Increasing the voltage reduced

the current in the transmission and distribution lines and hence the size of conductors

and distribution losses. This made it more economical to distribute power over long

single wire earth return systems (SWER) are used to electrify remote rural areas.

While power electronics now allow for conversion between DC voltage levels, AC is

still used in distribution due to the economy, efficiency and reliability of transformers.

High-voltage DC is used for transmission of large blocks of power over long

distances, or for interconnecting adjacent AC networks, but not for distribution to

customers.

DISTRIBUTION NETWORK CONFIGURATIONS-:

36

Distribution networks are typically of two types, radial or interconnected. A radial

network leaves the station and passes through the network area with no normal

connection to any other supply. This is typical of long rural lines with isolated load

areas. An interconnected network is generally found in more urban areas and will

have multiple connections to other points of supply. These points of connection are

normally open but allow various configurations by the operating utility by closing and

opening switches. Operation of these switches may be by remote control from a

control centre or by a lineman. The benefit of the interconnected model is that in the

event of a fault or required maintenance a small area of network can be isolated and

the remainder kept on supply.

Within these networks there may be a mix of overhead line construction utilizing

traditional utility poles and wires and, increasingly, underground construction with

cables and indoor or cabinet substations. However, underground distribution is

significantly more expensive than overhead construction. In part to reduce this cost,

underground power lines are sometimes co-located with other utility lines in what are

called Common utility ducts. Distribution feeders emanating from a substation are

generally controlled by a circuit breaker which will open when a fault is detected.

Automatic Circuit Reclosers may be installed to further segregate the feeder thus

minimizing the impact of faults.

Long feeders experience voltage drop requiring capacitors or voltage regulators to be

installed.

Characteristics of the supply given to customers are generally mandated by contract

between the supplier and customer. Variables of the supply include:

AC or DC - Virtually all public electricity supplies are AC today. Users of

large amounts of DC power such as some electric railways, telephone

exchanges and industrial processes such as aluminium smelting usually either

operate their own or have adjacent dedicated generating equipment, or use

rectifiers to derive DC from the public AC supply

Voltage , including tolerance (usually +10 or -15 percentage)

Frequency , commonly 50 & 60 Hz, 16.6 Hz for some railways and, in a few

older industrial and mining locations, 25 Hz.[3]

37

Phase configuration (single phase, polyphatwo phasethree phase

Maximum demand (usually measured as the largest amount of power

delivered within a 15 or 30 minute period during a billing period)

Load Factor, expressed as a ratio of average load to peak load over a period of

time. Load factor indicates the degree of effective utilization of equipment

(and capital investment) of distribution line or system.

Power factor of connected load

Earthing arrangements - TT, TN-S, TN-C-S or TN-C

Prospective short circuit current

Maximum level and frequency of occurrenctransients, electricity.

CIRCUIT BREAKER-:

The Circuit Breakers are automatic Switches which can interruptfault currents. The

part of the Circuit Breakers connected in one phase is called the pole. A Circuit

Breaker suitable for three phase system is called a ‘triple-pole Circuit Breaker. Each

pole of the Circuit Breaker comprises one or more interrupter or arc-extinguishing

chambers.

The interrupters are mounted on support insulators. The interrupter encloses a set of

fixed and moving contact's The moving contacts can be drawn apart by means of the

operatin links of the operating mechanism. The operating mechanism of the Circuit

Breaker gives the necessary energy for opening and closing of contacts of the Circuit

Breakers.

The arc produced by the separation of current carrying contacts is interrupted by a

suitable medium and by adopting suitable techniques for arc extinction. The Circuit

Breaker can be classified on the basis of the arc extinction medium.

The Fault Clearing Process

During the normal operating condition the Circuit Breaker can be opened or closed by

a station operator for the purpose of Switching and maintenance.

38

During the abnormal or faulty conditions the relays sense the fault and close

the trip circuit of the Circuit Breaker. Thereafter the Circuit Breaker opens.

The Circuit Breaker has two working positions, open and closed.

These correspond to open Circuit Breaker contacts and closed Circuit Breaker

contacts respectively.

The operation of automatic opening and closing the contacts is achieved by means

of the operating mechanism of the Circuit Breaker.

As the relay contacts close, the trip circuit is closed and the operating mechanism of

the Circuit Breaker starts the opening operation.

The contacts of the Circuit Breaker open and an arc is draw between them.

The arc is extinguished at some natural current zero of a.c. wave. The process of

current interruption is completed when the arc is extinguished and the current reaches

final zero value. The fault is said to be cleared.

 

The process of fault clearing has the following sequence:

Fault Occurs. As the fault occurs, the fault impedance being low, the

currents increase and the relay gets actuated.The moving part of the relay

move because of the increase in the operating torque. The relay takes

some time to close its contacts.

Relay contacts close the trip circuit of the Circuit Breaker closes and trip coil

is energized.

The operating mechanism starts operating for the opening operation. The

Circuit Breaker contacts separate.

Arc is drawn between the breaker contacts. The arc is extinguished in the

Circuit Breaker by suitable techniques. The current reaches final zero as

the arc is extinguished and does not restrict again.

 

39

THE TRIP-CIRCUIT-:

The basic connections of the Circuit Breaker control for the opening operation

STANDARD RATINGS OF CIRCUIT BREAKERS AND THEIR SELECTION

 

The characteristics of a Circuit Breaker including its operating devices and

auxiliary equipment that are used to determine the rating are:

40

(a) Rated characteristics to be given for all Circuit Breakers.

1. Rated voltage.

2. Rated insulation level.

3. Rated frequency.

4. rated current.

5. Rated short Circuit Breaking current.

6. Rated transient recovery voltage for terminal faults.

7. Rated short circuit making current.

8. Rated operating sequence.

9. Rated short time current.

(b) Rated characteristics to be given in the Specific cases given below:

Rated characteristics for short line faults for three pole Circuit Breakers rated

at 72.5 kV and above, more than 12.5 kA rated short circuit breaking current

and designed for direct connection to overhead transmission lines.

Rated line charging breaking current, for three pole Circuit Breakers rated at

72.5 kV and above and intended for Switching over- head transmission lines.

Rated supply voltage of closing and opening devices, where applicable.

Rated supply frequency of closing and opening devices, where applicable.

Rated pressure of compressed gas supply for operation andInterruption, where

applicable.

 

41

THE TYPE OF THE CIRCUIT BREAKER-:

The type of the Circuit Breaker is usually identified according to the medium of arc

extinction. The classification of the Circuit Breakers based on the medium of arc

extinction is as follows:

(1) Air break' Circuit Breaker. (Miniature Circuit Breaker).

(2) Oil Circuit Breaker (tank type of bulk oil)

(3) Minimum oil Circuit Breaker.

(4) Air blast Circuit Breaker.

(5) Vacuum Circuit Breaker.

(6) Sulphur hexafluoride Circuit Breaker. (Single pressure or

      Double Pressure).

42

Small Oil Volume Breaker-:

As the system voltages and fault levels increased the Bulk Oil Breakers required huge

quantities of insulating oil and became unwieldy in size and weight.

 This added enormously to the cost of a power system.  Simultaneously improvements

were made in the technique  of ceramics.

 The function of oil as insulating medium in the Bulk Oil Breakers was transferred to

the porcelain containers.

 Only a small quantity of oil was used to perform its functions as arc quenching

medium. This led to the development  of small oil volume or low oil content breakers

in the continent of Europe.

 Like the Bulk Oil Breakers these have also since then passed through many stages of

development with varying designs of the arcing chambers.

Today the small oil volume breakers are available for voltages up to 36 kV and the

fault levels associated therewith.Contrary to the operation of the impulse type Circuit

43

Type Medium Voltage, Breaking Capacity

1 – Air break Circuit

Breaker

Air at atmospheric

pressure

(430 – 600) V– (5-15)MVA

(3.6-12) KV -  500 MVA

2 – Miniature CB. Air at atmospheric

pressure

(430-600 ) V

3 – Tank Type oil CB. Dielectric oil (3.6 – 12) KV

4 – Minimum Oil CB. Dielectric oil (3.6 - 145 )KV

5 – Air Blast CB. Compressed Air

(20 – 40 ) bar

245 KV, 35000 MVA

up to 1100 KV, 50000 MVA

6 – SF6 CB. SF6 Gas 12 KV, 1000 MVA

36 KV , 2000 MVA

145 KV, 7500 MVA

245 KV , 10000 MVA

7 – Vacuum  CB. Vacuum 36 KV, 750 MVA

8 – H.V.DC CB. Vacuum , SF6 Gas 500 KV DC

Breaker, such as air blast Circuit Breaker, in which arc extinction and dielectric

recovery are affected by means of an external quenching medium, the process of arc

extinction in  the small oil volume Circuit

Breaker is of internal thermo- dynamic origin.

 During the tripping operation an arc strikes

in oil between the moving contact and the

fixed contact's.  This arc is elongated

vertically in the explosion pot until the

distance traveled is sufficient to withstand

the voltage between contacts.

 The increase in internal pressure due to

the Splitting up  and vaporization of oil by

the arc creates a rapid movement of the

extinguishing medium round the arc

This self-quenching effect causes a

rapid cooling of the ionized column along

its whole

 Length due to partition of the

explosion pot and the dielectric recovery is

sufficiently rapid.

 To prevent the arc restricting after a

natural Passage Through zero. The electric arc itself has, therefore,Supplied the

necessary energy for its own extinction. There are now numerous manufacturers of

small oil volume breakers.

 However, to illustrate the principles of working, the sectional view of working

portion of 170 kV 3500 MVA.

BREAKERS OF-:

M/s Delle France have been shown in Fig. (4) the most important part of the breaker

is its extinguishing chamber.

 This takes the form of an insulating cylinder containing oil, in the axis of which

44

moves the contact rod and within

 which breaking occurs.

 The arcing chamber is supported at its base by a casing enclosing a mechanism

whose function is to

 move the contact rod  According to the impulses given by the control mechanism. In

the on position, the current flows from

 the Upper current terminal (1) to the contact fingers, (2) Follows the movable contact

rod (7) and reaches the current terminal (10)

 across the lower contact fingers (8). At the beginning of the stroke and before

breaking, the contact rod strongly pulled down. Wards by the tripping springs, starts a

high speed opening motion. Then, an arc strikes between the contact rod tips (6) and

the stationaryArcing ring (3) protecting the upper contact fingers.

 At this moment gases escape without hindrance towards top of the apparatus.

 The contact rod rapidly reaches a very high linear speed; it moves the arc downwards

and forces it to enter the explosion pot (5) where it is maintained rectilinear and is

elongated in a direction opposite  to the   release of gases towards fresh oil. Since the

arc is as short as possible the arc voltage is minimized and the energy dissipated is

reduced.  

  Still, since the gases can no longer develop freely, they generate a considerable

pressure in the explosion pot (5), thus producing a violent upward  axial blast of oil

vapor, exhausting the highly ionized gaseous mass.

 The optimum distance is thus obtained, the jet of oil causes the dielectric strength to

be rapidly increased, and at the following current zero, the arc is impeded from

restricting and the breaking is thus achieved.

 The explosion pot (5) is intended to withstand high pressures.  It is partitioned into

several components by means of discs whose function is to retain a certain quantity of

fresh oil while the first break is proceeding; this allows a second break to occur with

complete safety at the full short circuit current. The low oil content Circuit Breakers

require separate current Transformers of wound type. Still at all  voltages from 33 kV

and above the costs of these breakers inclusive of current Transformers compete

favorably with that of the Bulk Oil Breaker.

33kV Isolator-:

45

Isolators shall be panel mounted, triple pole, single throw, air insulated, load-break

type.All other details of the panels will be identical to that circuit breaker panels.

Isolators shall be mechanically & electrically (wherever possible) interlocked with

circuit breakers in order to avoid operation of Isolators when the CB is closed.

Each breaker will be provided with suitable cable side earthing truck or built-in

earthing arrangement.

Current Transformer-:

1 Current transformers shall be cast resin type. All secondary connections shall be

brought out toterminal blocks where wye or delta connection will be made. The CT

secondary shall be rated for-:

1A (for relays) and 5A (for metering).

2 Accuracy class of the Current Transformers shall be :

a) Class PX for differential relaying.

b) Class 5P20 for other relaying

c) Class 1.0 and ISF <5 for metering.

3 Other particulars of the CTs viz. ratio, burden, knee point voltage, excitation current

and secondary resistance shall be as shown in SLD.

Voltage Transformer-:

Voltage Transformers shall be cast-resin, drawout type and shall have an accuracy

class of-:

1.0.Voltage Transformer mounted on breaker carriage is not acceptable.

2 High voltage windings of voltage transformer shall be protected by current limiting

fuses. Thevoltage transformer and fuses shall be completely disconnected and visibly

grounded in fullydraw-out position.

46

3 On low voltage sides, MCBs will be provided to prevent overload.

Relays-:

1 Main power circuit Relays shall be static/digital/numeric type, of drawout design

with built-in testingfacilities, having provision for remote communications. Small

auxiliary relays may be electromechanicalin non-drawout execution and mounted

within the cubicle.

.2 Relays shall be rated for operation on 110V secondary voltage and 1A secondary

current. Numberand rating of relay contacts shall be as required.

.3 The Bidder shall furnish, install & co-ordinate all relays to suit the requirements of

protection, interlock and bus transfer schemes.

4 The protection equipment offered shall have proven field experience and similar site

condition as stated .

EARTHING-:

Earthing is done to prevent from shock or short ckt fault occur in the system .

All the non-current carrying metal parts of the electrical installation and mechanical

equipments shall be earthed properly. The cables armour and sheath, electric panel

boards,lighting fixtures, ceiling and exhaust fan and all other parts made of metal

shall be bonded together and connected by means of specified earthing system. An

earth continuity conductorshall be installed with all the feeders and circuits and shall

be connected from the earth barof the panel boards to the conduit system, earth stud of

the switch box, lighting fixture, earthpin of the socket outlets and to any metallic wall

plates used. All the enclosures of motors shall be also connected to the earthing

system.

TYPE OF EARTHING STATION-:

47

PLATE EARTHING STATIONS

1.The Equipment neutral earthing shall be with copper plate earthing station and

equipment body earthing shall be with hot dip galvanised iron earthing station.

2. The plate electrode shall be 600 x 600 x 3.25 mm copper plate for neutral earthing

and shallbe of hot dip galvanised iron plate having dimensions 600 x 600 x 6.3 mm

thick for body earthing.

3.The earthing station shall be as shown on the drawing.

4. The earth resistance shall be maintained with suitable soil treatment as shown in the

drawing.

5. The resistance of each earth station should not exceed 1 ohm.

6. The earth lead shall be connected to the earth plate through Hot Dip G.I. bolts.

7. The earthing conductors shall be of copper strip in case of copper earthing and hot

dip galvanised iron strip in case of G.I. earthing.

8. G.I. pipe with funnel of approved quality shall be used for watering the earthing

electrodes stations.

9. The block masonry chamber with chequered plate shall be provided for housing the

funneland the pipe for watering the earthing electrodes / stations.

10. The hardware and other consumables for earthing installation shall be of

copper/brass in

case of copper earthing and shall be hot dip galvanised iron material in case of G.I.

earthing.

11. Test link test pit cover through chequered plate.

PIPE ELECTRODE EARTH STATION -:

1. The earth station shall be as shown on the drawing and shall be used for equipment

earth grid and or street light pole earthing.

2. The earth electrode shall be 3 M long 50 mm dia class "B", Galvanised steel pipe.

3. The earth resistance shall be maintained with a suitable soil treatment as shown on

the drawing.

4. The resistance of each earth station should not exceed 1 ohm.

5.The earth lead shall be fixed to the pipe with a nut and safety set screws. The clamp

shall be permanently accessible.

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6.The earthing grid and the earthing conductor shall be hot dip Galvanised iron strips

of the size as shown.

7.G.I. pipe with funnel of approved quality shall be used for watering the earth

electrode station.

8.The block masonry chamber with chequered plate shall be provided for housing the

above referred funnel and pipe.

9.The hardware and other consumables for earthing installation shall be hot dip

Galvanised iron material.

BIBLOGRAPHY-:

www.wikimedia.com

www.upcl.com

www.google.com

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