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AC Supply

System

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Importance of Elect System for Auxiliary

Classification of Auxiliaries

Choice of Voltage for Aux

Aux. Power supply system

Emergency AC Supply

Presentation outline

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Auxiliary Power Supply System

The purpose of an Electrical system is to generate and supply electrical energy .

The system should be designed and managed to deliver power with Reliability and Economy.

As these two requirements are quite opposed a balance is required to have an optimum design of Auxiliary power

supply system

The auxiliaries have Ratings range from a few watts to few Mega Watts & Located over a large area

Work under varied Operating Conditions

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Auxiliary Power Supply System

Failure of Auxiliaries can cause Outage of Power Plant

Auxiliaries need Reliable Power Supply

System designed to cater to this need

Loads segregated on the basis of

Rating (to decide Voltage)

Location (to decide the

Feeding Point)

Change-over schemes & Alternate Power Supply arrangement

to ensure Reliability

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Elements of Aux. Power System

More than 95% of the auxiliaries are driven by Motors

Different Voltage levels are interconnected through

Transformers

Miscellaneous Elements

Incomers

Ties

Diesel Generators

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Auxiliary Power Supply

Voltage Rating of Motors Decided based on kW Rating Rating 160kW 415V (LV), Contactor > 160kW & 200kW 415V (LV), Breaker > 200kW & 1500kW 3.3kV (MV), Breaker > 1500kW 11kV (MV), Breaker Frequent Start / Stop Operations (Coal Conveyor Motors)

MV Vacuum Contactor

List of Boards / Feeding Points arrived at based on Location of Load Centers / Systems

Quantity & Rating of Transformers calculated based on Load & Operational Requirements

Rating of Board Calculated based on the Operating Load & Transformer Rating

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MV Switchgears System Parameters

Nominal System voltage 6.6kV 11kV 3.3kV

Highest System voltage 7.2 kV 12kV 3.6kV

Rated Frequency 50Hz 50Hz 50Hz

Number of phases/ poles Three Three Three

System Neutral Earthing Earthed through Resistance of 6.35 to Limit E/F Current to 300A

One minute power frequency

withstand voltage 20kV 28kV 10kV

Impulse withstand voltage 60kV (peak) 75kV (peak) 40kV (peak)

Maximum System Fault Level 40kA (rms)

Short time rating of Eqpt. 40kA (rms) for 1 second

Dynamic withstand rating 100kA (peak)

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LV Switchgears System Parameters

Nominal System voltage 415V, 10%

Rated Frequency 50Hz

Number of phases Three

System Neutral Earthing Solidly Earthed

Maximum System Fault Level 45kA (rms)

Short time rating of Eqpt. 45kA (rms) for 1 second

Dynamic withstand rating 105kA (peak)

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Auxiliary Power Supply System

Sizing of Unit & Station transformer

Start up source short circuit power

Feeding offsite areas loads

Rating of the Switchgear

Loads

Power Supply arrangement

6.6& 0.415kV System

11 & 3.3 & 0.415kV System

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Auxiliary Power Supply

INTRODUCTION

Commonly used voltage level up to 200 MW unit size- 6.6kV, 415V

Initially same voltage level (6.6 kv, 415v) were adopted

for 500 MW unit size as well.

With 500 MW unit, quantitative and qualitative change

in auxiliaries took place.

However no significant change in SWGR available in

market.

Need for optimizing and cost effective solution

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Aux. Supply system(500MW)

Grid Voltage- Normally 400kV for most of the200, 500MW units in India except few deviations

Any Intermediate Voltage Available-to provide reliable start-up power source and to meet initial

commissioning activities as well as to supply bulk

loads(CW system, make-up water etc.) away from

the main plants.Generally used Intermediate voltage

levels are 220kV, 132kV, 33kV

Nature of Auxiliaries i.e. ratings, basic characteristics and location

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Auxiliary Power Supply-

500MW

Selection of voltage levels to be adopted for 500MW and above unit size.

a) 6.6 KV and 415 V system

b) 11& 3.3 kV system

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HT/LT Supply System- Without

GCB

G

UAT-A Dyn1

UAT-B 16.5 KV

6.6 KV Ynd11

GT

Ynyn0

Station TRF-1

UNIT SWGR--A UNIT SWGR--B

Stn. SWGR-SA SB

UST

A

ESP TRF-A

S/Serv.

Trf.-B

UST-B ESP TRF-B

USS-A USS-B 415 V Unit EMG SWGR

X

From DG SWGR

X Blr MCC

Turb MCC

BFP ID Fan

Air Compr

Trf

X X

X

Stn Serv

Trf-A DMP Serv

Trf

1)SWYD

Serv

Trf-1

2)Ash

Handl T/F

1600KVA

6.6 KV

B.C.

N.O.

TMCC

Fdr to

Clarif

Water

SWGR

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220 KV TRANSFER BUS

220 KV BUS I

220 KV BUS II

C.B.

G.T.

UAT-A

GENERATOR

UAT-B

1A 1B

ST

SA SB

Elect. Layout With GCB (220 KV BUS

SYSTEM)

ISOLATOR

GCB

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Transformer feeder Details

To PMCC

MCC/PCCMedium Voltage

Magnetic Contactor

SFU CB

To ACDB

Motor Feeder

Unit Service Transformer

To PMCC

Magnetic Contactor

SFU

To ACDB

Motor Feeder

Dyn11

C.B.

415 V

6.6 KV

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X X

X X

X X X X

DG-1 DG-3

DG-2

DG SWGR-1 DG SWGR-2

UNIT EMER

SWGR-1 UNIT EMER

SWGR-2

UNIT EMER

SWGR-3

UNIT EMER

SWGR-4

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1A 1B 2A 2B 3A 3B 4A 4B

USS-1 USS-2 USS-3 USS-4

UES-1 UES-2 UES-3 UES-4

DG SWGR-1 DG SWGR-2

DG-3 DG-1 DG-2

EMERGENCY SWGR. SYSTEM

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EMCC

(1) AOP-1 (2) Em. Lighting Trf.

(3) TVDC Reserve Supply (4) UPS Ch.

(5) Scanner Air Fan (6) BVDC Reserve Supply

(7) AC Seal Oil Pump (8) Air Heater Lub Oil Panel

(9) Jacking Oil Pump (10) Stator Water Pump-B

(11) Barring Gear (12) +26 v DC ATRS Ch. B

(13) -26V DC ATRS Ch.B (14) 26V DC FSSS Ch. B

(15) 26V DC DDC Ch. A

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From Unit SWGR A Normally

(1) BFP-1C (2) BFP-1A

(3) PA Fan-1A (4) ID Fan -1A

(5) UST-1A (6) ESP T/F -1A

(7) FD Fan -1A (8) Coal Mill- 1A, C, E

(9) CEP-1A,C (10) ACW Booster Pump-1A

(11) Bus V.T.

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USS A

(1) Unit Em. SWGR (2) Boiler MCC

(3) BVDC A (4) Turb. MCC A

(5) 220V Dc Ch. A (6) +24 DC ATRS Ch. A

(7) -24V DC ATRS Ch.A (8) Turb ACDB A

(9) +24 V DDCMIS Ch. B (10) Gen Control Panel

(11) Boiler ACDB A a) Grav. Feeder A,B, C,D,E,F

b) S/B MCC Feeder-1

c) INC From USS B

(12) MOT Centrifuge

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USS B

(1) UPS Ch. (2) +24V FSSS Ch.

(3) TVDC (4) Boiler MCC B

(5) Turb MCC B (6) Turb ACDS B

(7) Boiler ACDB B

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THANK YOU