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August 14, 2014 1
AC Supply System
http://studygalaxy.com/
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
August 14, 2014 3
Auxil iary 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
August 14, 2014 4
Auxil iary 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
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
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
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 EarthingEarthed 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)
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)
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
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
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
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
August 14, 2014 13
HT/LT Supply SystemG
UAT-A Dyn1 UAT-B
16.5 KV
6.6 KV Ynd11 GT
Ynyn0 Station TRF-1
UNIT SWGR--AUNIT SWGR--B
Stn. SWGR-SA SB
UST‘A’
ESP TRF-A
S/Serv.
Trf.-BUST-B ESP TRF-B
USS-A USS-B 415 V Unit EMG SWGR
X
From DG SWGR
XBlr MCCTurb MCC
BFPID Fan
Air Compr Trf
X X
X
Stn Serv Trf-A
DMP Serv Trf
1)SWYDServTrf-12)AshHandl T/F1600KVA
6.6 KV
B.C.
N.O.
TMCC
Fdr toClarifWater SWGR
August 14, 2014 14
Transformer feeder Details
To PMCC
MCC/PCCMedium Voltage
Magnetic Contactor
SFUCB
To ACDB
Motor Feeder
Unit Service Transformer
To PMCC
Magnetic Contactor
SFU
To ACDB
Motor Feeder
Dyn11C.B.
415 V
6.6 KV
August 14, 2014 15
X X
X X
X XX X
DG-1 DG-3 DG-2
DG SWGR-1 DG SWGR-2
UNIT EMERSWGR-1 UNIT EMER
SWGR-2
UNIT EMERSWGR-3
UNIT EMERSWGR-4
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
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.
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
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’
August 14, 2014 20
THANK YOU