The document discusses the AC supply system for auxiliary loads in a coal power plant. It describes the various auxiliary systems that require power supply like coal handling, boiler, turbine, cooling water etc. It discusses the classification of auxiliaries based on rating and location to decide the suitable voltage levels. The key voltage levels used are 6.6kV, 3.3kV and 415V. The document also provides details of the switchgear parameters, transformer feeders and motor feeder protection settings. Single line diagrams of various auxiliary systems at different voltage levels are presented.
3. Auxilliary supply for coal power station
• Coal transfer from Track
hopper/wagon tippler to
bunker
• Coal crusher
• Coal mills and feeders and
PA fan
• FD fan APH
• Flue gas path
• ESP and ID Fan
• DM water path from BFP
to Boiler Drum
• Circulating water path
• Lub oil system of TG
• Seal oil system
• Equipment cooling water
system
• Stator water cooling system
• Hydrogen system
• DM water system
• Raw water system
• Ash handling plant
• Liquid fuel unloading station
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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 6.35Ω 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
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/
1600KVA
6.6 KV
B.C.
N.O.
TMCC
Fdr to
Clarif
Water
SWGR
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Transformer feeder Details
To PMCC
MCC/PCCM
edium
Voltage
Magnetic
Contactor
SFUCB
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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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 (digital distribution control)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 (monitoring information system)Ch. ‘B’
10 GRP
(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
23. 1B1A SA 2A 2B SB 3A 3B SC 4A 4B SD
GT-1
UAT-1A
UAT-1B
ST-1 GT-2
UAT-2A
UAT-2B
UAT-3A
UAT-3B
GT-3
ST-2
GT-4
UAT-4A
UAT-4B
GA DRAWING OF GT ST ,UAT AND 6.6 KB BUSES
G
4
G
3
G
2G
1
24. SA SC 1A 3A 2A 4A SB SD SA SC SB SD
DM PLANT SWGR AIR COMP SWGR-1 AIR COMP SWGR-2
SOFTENING SWGR FOPH SWGR WORK SHOP SWGR
SB SD SB SD
AMMIN SWGR SWYD SWGR
GA DRAWING OF OFF-SITE ELECTRICAL SYSTEM
25. SA 1A 1B SB 2A 2B SC 3A 3B SD 4A 4B
SSS-1 USS-1 ESP-1 SSS-2 USS-2 ESP-2 SSS-3 USS-3 ESP-3 SSS-4 USS-4 ESP-4
UES-1 UES-2 UES-3 UES-4
DG-1 DG-3 DG-2
GA DRAWING OF 6.6 KV/415 VOLTS SYSTEMS
LO MCC-1 LOMCC-2 LOMCC-3
LOMCC-4