Station Protections
Transcript of Station Protections
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STATION PROTECTION
ENGINEERING
Knowledge Management System
ELECTRICAL
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STATION PROTECTIONS
By
NTPC
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Specifications for Bus bar protection
OPERATING TIME OF 15 MS AT 5 TIMES SET VALUE
INCLUDE CT SUPERVISION
INDIVIDUAL TRIP RELAYS(DUPLICATED) FOR EACH FEEDER
TRANSIENT FREE OPERATION
DC SUPPLY SUPERVISION
IN /OUT SWITCH FOR EACH ZONE
MODERN NUMEIRCAL BUSBAR PROTECTIONS AREAVAILABLE IN CENTRALISED AND DECENTRALISED FORM
IN DUPLICATED BUS BAR SCHEME, PREFERABLY ONESCHEME SHALL BE LOW IMPEDANCE BASED AND SECONDSHALL BE HIGH IMPEDANCE BASED
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Bus bar prot scheme design
R1
R2
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LOGI C OF MAI N AND TRANSFER BUS SYSTEM
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Bus section protection
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Designed stability level Shall correspond to swgr ratingeven if the available SC level is less
Settings
Vs = If(Rct+2 Rl)
Vk not less than 2 x Vs
Effective current settingIr = Is+ n, Ie
Is= relay circuit current setting
Ie= Magnetising curent
N= No of CTs in parallel
I pry = Ir X turns ratio
CT
Matching CT ratio to avoid spill current duringhealthy state
Less Rct/ less Ie/high CT ratio
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BUS BAR PROTN (contd)
Supvn of CT circuit Detected by using a 3 phase rectifier relay to
effect the summation of the bus wire voltages andshort the pilot wire from the affected phase
Routing of CT connection
Looped at the yard itself to ensure minimum loopresistance and thus a minimum setting voltageand a minimum Vk for a given stability limit
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LOW IMP BUS BAR
PROTECTION Use biased differential PRINCIPLE.
Stability for through fault achieved by restraining quantities proportional tothe feeder current.
Less stringent CT parameters
CT wires directly to the relay
More stability for spill current
CT mismatch (typ of the order of 1:5 ) can be accommodated. More suitable for numerical integrated protection systems
AS THE CTs CAN BE SHARED FOR MANY FUNCTIONS.
BUILT IN LBB FUNCTION IS ACCEPTED IN BUS BAR PROTN.
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Use of bias
Compensate for small ratio mismatch AC switching of feeder current through isolator
contacts are avoided and switching is done on thesec side of aux CTs forming part of therelay.Alternatively in static / numerical relays,thebus bar replica is made inside the relay through
isolator contacts and the logic is done by thesame.
Aux CT takes care of ratio mismatch of CTs
A current operated auxiliary relay is used todetect any unbalance sec current for supervisionof the CT ckts. Current setting of the supvn relay
must be less than that of main diff relay and morethan the lowest loaded feeder
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Setting criteria
Main diff relay is set above the highestloaded feeder.
Must be more than 30% of the min fault
level.
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Numerical bus bar protections
Centralized: all functions in a centre unit Decentralized : Peripheral units attached to
each bay and a central unit forrelay logic.
Have many zones of protection in the samerelay
Many added functions like LBB, Feeder back upprotection
Event logging Dist recording
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ISLANDING SCHEMES
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Islanding scheme
n DEPENDS ON TYPE OF GENERATING SYSTEM
n GRID CONNECTED GENERATING STATIONS
GENERATOR IS CONNECTED TO THE GRID THROUGHEHV TRANSMISSION LINES.
CAPTIVE GENERATING STATION
DEDICATED GENERATOR(S) SUPPLIES POWER TO APARTICULAR UTILITY/ESTABLISHMENT.
NOT CONNECTED TO THE GRID.
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TYPE OF ISLANDING SCHEMES.
FOR GRID CONNECTED GENERATORS
CRITERIA:
UNDER FREQUENCY AND/OR RATE OF
CHANGE OF FREQUENCY
ACTION:
STAGGERED TRIPPING OF GRID LINES ATPREDTERMINED LOGIC AT THE PRE DECIDEDSEQUENCE.
CONCERN: VERY DYNAMIC SYSTEM CONDITIONS
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ISLANDING SCHEME FOR GRIDCONNECTED GENERATORS.
KEY FEATURES INTEGRATED SCHEME FOR THE WHOLE PLANT
FREQUENCY BASED
TRIGGERING BASED ON THRESHOLD AND RATE OFCHANGE OF FREQUENCY
U/F RELAYS CONNECTED TO BUS CVT
BASED ON 2 OUT OF 3 LOGIC
INDIVIDUAL TRIP RELAYS FOR EACH FEEDER
STAGGERED TRIPPING SCHEME TO BE ENGINERED INCOORDINATION WITH RESPECTIVE GRID AGENCYDEPENDING ON THE SYSTEM CONDITIONS AND THEPOWER NUMBER OF THE CONNECTED GRID.
SUCCESS CHANCE MORE IF RADIAL LOAD IS AVAILABLE.
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CVT SUPPLY FOR U/FRELAYS CONNECTED TO THE SELECTED
BUS CVT SUPPLY
OR
DISTRIBUTED AMONG THE 2 BUS CVTS
{2 ON ONE BUS CVT (ON 2 CORES) & 1 ON OTHER BUS CVT}
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TYPICAL SWYD SLD
1
381F
2
3
281F
10
11
4
181F
6
5
7
8
12 13
14
15
481F581F 681F
19
9 16
R2 R2
18
17
20
21
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TYPICAL ISLANDING LOGIC
FOR SELECTED BUS CVT
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TYPICAL ISLANDING LOGICFOR NON SELECTED BUS CVT SUPPLY
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ISLANDING FOR CAPTIVE
GENERATING PLANTS. FEATURES
BASED ON LOAD GENERATION BALANCE.
SCADA BASED DYNAMIC LOGIC
ADAPTIVE TO SYSTEM CHANGES
PRIORITY GROUPS ARE SET FOR ISLANDING
TRIPPING SEQUENCE IS DECIDED BY THE SOFTWAREBASED ON THE PRIORITY AND THE DYNAMIC LOADGENERATION BALANCE.
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THANK YOU
FOR
YOUR TIME