The document discusses the auxiliary power supply system for a power plant. It outlines the importance of a reliable auxiliary power system and describes how loads are segregated based on their rating and location. The key elements of an auxiliary power system include motors that drive over 95% of auxiliaries, transformers that step voltages up and down, and emergency diesel generators. The document also discusses voltage levels used for motors based on their kW rating, lists of feeding points, sizing of unit and station transformers, and examples of 6.6kV and 11kV/3.3kV auxiliary power supply systems.

1. August 14, 2014 1
AC Supply
System
http://studygalaxy.com/

2. August 14, 2014 2
•Importance of Elect System for Auxiliary
•Classification of Auxiliaries
•Choice of Voltage for Aux
• Aux. Power supply system
•Emergency AC Supply
Presentation outline

3. August 14, 2014 3
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

4. August 14, 2014 4
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

5. August 14, 2014 5
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

6. August 14, 2014 6
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

7. August 14, 2014 7
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)

8. August 14, 2014 8
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)

9. August 14, 2014 9
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

10. August 14, 2014 10
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

11. August 14, 2014 11
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

12. August 14, 2014 12
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

13. August 14, 2014 13
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/F
1600KVA
6.6 KV
B.C.
N.O.
TMCC
Fdr to
Clarif
Water
SWGR

14. August 14, 2014 14
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

15. August 14, 2014 15
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

16. August 14, 2014 16
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

17. August 14, 2014 17
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.

18. August 14, 2014 18
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

19. August 14, 2014 19
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’

20. August 14, 2014 20
THANK YOU