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AC SupplySystem
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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 andsupply electrical energy .
The system should be designed and managed to deliverpower with Reliability and Economy.
As these two requirements are quite opposed a balanceis required to have an optimum design of Auxiliary powersupply system
The auxiliaries have Ratings range from a few watts to
few Mega Watts & Located over a large areaWork 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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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 onLocation of Load Centers / Systems
Quantity & Rating of Transformers calculated based on
Load & Operational Requirements Rating of Board Calculated based onthe Operating Load &
Transformer Rating
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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 toLimit E/F Current to 300A
One minute power frequencywithstand 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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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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Sizing of Unit & Station transformer
Start up 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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Commonly used voltage level up to 200 MW unitsize- 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. (11 kv Switchgear)
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Grid Voltage- Normally 400kV for most of the200,500MW units in India except few deviations
Any Intermediate Voltage Available-to providereliable start-up power source and to meet initialcommissioning activities as well as to supply bulk
loads(CW system, make-up water etc.) away fromthe main plants.Generally used Intermediate voltagelevels are 220kV, 132kV, 33kV
Nature of Auxiliaries i.e. ratings, basic
characteristics and location
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G
UAT-A Dyn1
UAT-B16.5 KV
6.6 KV Ynd11
GT
Ynyn0
Station TRF-1
UNIT SWGR--AUNIT SWGR--B
Stn. SWGR-SA SB
UST
A
ESP TRF-AS/Serv.Trf.-B
UST-B ESP TRF-B
USS-A USS-B 415 V Unit EMG SWGR
X
From DG SWGR
XBlr MCC
Turb MCC
BFPID Fan
Air Compr
Trf
X X
X
Stn Serv
Trf-ADMP Serv
Trf
1)SWYServ
Trf-1
2)Ash
Handl T/
1600KV
6.6 KV
B.C.
N.O.
TMCC
Fdr to
Clarif
Water
SWGR
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Transformer feeder Details
To PMCC
MCC/PCCMediumVoltage
MagneticContactor
SFUCB
To ACDB
Motor Feeder
Unit ServiceTransformer
To PMCC
MagneticContactor
SFU
To ACDB
Motor Feeder
Dyn11
C.B.
415 V
6.6 KV
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X X
X X
X XX X
DG-1DG-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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(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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(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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(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,Fb) S/B MCC Feeder-1
c) INC From USS B
(12) MOT Centrifuge
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(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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