bus-bars form a link between the incoming and outgoing circuits at the generating stations or sub...
TRANSCRIPT
BUS-BARS FORM A LINK BETWEEN THE INCOMING AND OUTGOING
CIRCUITS AT THE GENERATING STATIONS OR SUB STATIONS. IF A FAULT
DEVELOPS IN THIS PART OF THE POWER SYSTEM, CONSIDERABLE
DAMAGE AND DISRUPTION OF SUPPLY WILL OCCUR. TO REDUCE THE
EFFECT OF FAULT, VARIOUS BUS-BAR ARRANGEMENTS ARE EMPLOYED.
STILL PROPER PROTECTION SCHEME HAS TO BE ADOPTED TO
IMPROVE THE RELIABILITY OF SUPPLY. ALTHOUGH, THE VARIOUS
SCHEMES HAVE BEEN DEVELOPED FOR THE PROTECTION OF BUS-BARS
BUT THE MOST COMMON SCHEME IS DIFFERENTIAL PROTECTION
THE SCHEMATIC DIAGRAM OF CURRENT DIFFERENTIAL PROTECTION
SCHEME EMPLOYED FOR THE PROTECTION OF SUB- STATION BUS-BARS IS
SHOWN IN PREVIOUS SLIDE.
THE SECONDARY'S OF ALL THE CT’S CONNECTED IN INCOMING &
OUTGOING FEEDERS ARE CONNECTED IN PARALLEL AS BEFORE. THE CTS
DESIGNED IN SUCH A WAY THAT UNDER NORMAL CONDITION , THE EMF’S
INDUCED IN SECONDARY’S OF THE CT’S PLACED ON OUTGOING FEEDER.
THEN NO CURRENT FLOWS THROUGH THE OPERATING COIL OF THE RELAY
WHICH IS CONNECTED ACROSS THE CONNECTING WIRES.
OPEARTION
UNDER NORMAL CONDITIONAL OR EXTERNAL FAULT CONDITIONS, THE SUM
OF THE CURRENT ENTERING THE BUS BAR IS EQUAL TO THE SUM OF CURRENT
LEAVING IT. THEREFORE, NO CURRENT FLOWS THROUGH THE OPERATING COIL.
HOWEVER, WHEN FAULTS OCCURS WITHIN THE PROTECTED ZONE ( BUS- BAR),
THE CURRENT ENTERING THE BUS-BAR WILL NO LONGER BE EQUAL TO THOSE
LEAVING IT. THUS, A DIFFERENTIAL CURRENT FLOWS THROUGH THE OPERATING
COIL OF THE RELAY WHICH CLOSES THE TRIP CIRCUIT.
HIGH BUS FAULT CURRENTS DUE TO LARGE NUMBER OF CIRCUITS CONNECTED:
CT SATURATION OFTEN BECOMES A PROBLEM AS CTS MAY NOT BE
SUFFICIENTLY RATED FOR WORST FAULT CONDITION CASE
LARGE DYNAMIC FORCES ASSOCIATED WITH BUS FAULTS REQUIRE FAST
CLEARING TIMES IN ORDER TO REDUCE EQUIPMENT DAMAGE
FALSE TRIP BY BUS PROTECTION MAY CREATE SERIOUS PROBLEMS:
SERVICE INTERRUPTION TO A LARGE NUMBER OF CIRCUITS
SYSTEM-WIDE STABILITY PROBLEMS
WITH BOTH DEPENDABILITY AND SECURITY IMPORTANT, PREFERENCE IS ALWAYS
GIVEN TO SECURITY.
INTERLOCKING SCHEMES
OVER-CURRENT (“UNRESTRAINED” OR “UNBIASED”) DIFFERENTIAL
OVER-CURRENT PERCENT (“RESTRAINED” OR “BIASED”)
DIFFERENTIAL
LINEAR COUPLERS
HIGH-IMPEDANCE BUS DIFFERENTIAL SCHEMES
LOW-IMPEDANCE BUS DIFFERENTIAL SCHEMES
BLOCKING SCHEME TYPICALLY USED.
SHORT COORDINATION TIME
REQUIRED .
CARE MUST BE TAKEN WITH
POSSIBLE SATURATION OF FEEDER CTS.
BLOCKING SIGNAL COULD BE SENT
OVER COMMUNICATIONS PORTS.
TECHNIQUE IS LIMITED TO SIMPLE
ONE-INCOMER DISTRIBUTION BUSES.
50
50 50 50 50 50
BL
OC
K
DIFFERENTIAL SIGNAL FORMED BY
SUMMATION OF ALL CURRENTS
FEEDING BUS.
CT RATIO MATCHING MAY BE
REQUIRED.
ON EXTERNAL FAULTS, SATURATED
CTS YIELD SPURIOUS DIFFERENTIAL
CURRENT.
TIME DELAY USED TO COPE WITH
CT SATURATION.
51
ZC = 2 – 20 - typical coil impedance
(5V per 1000Amps => 0.005 @ 60Hz )
59
If = 8000 A
40 V 10 V 10 V 0 V 20 V
2000 A
2000 A 4000 A
0 A
0 VExternal
Fault
ESEC= IPRIM*XM - SECONDARY VOLTAGE ON RELAY TERMINALS
IR= IPRIM*XM /(ZR+ZC) – MINIMUM OPERATING CURRENT
WHERE,
IPRIM – PRIMARY CURRENT IN EACH CIRCUIT
XM–LINER COUPLER MUTUAL REACTANCE (5V PER 1000AMPS => 0.005
@ 60HZ ),
ZR – RELAY TAP IMPEDANCE
ZC – SUM OF ALL LINEAR COUPLER SELF IMPEDANCES
59
If = 8000 A
0 A
0 V 10 V 10 V 0 V 20 V
40 V
2000 A
2000 A
4000 A
0 A
Internal BusFault
FAST, SECURE AND PROVEN.
REQUIRE DEDICATED AIR GAP CTS, WHICH MAY NOT BE USED FOR ANY
OTHER PROTECTION.
CANNOT BE EASILY APPLIED TO RECONFIGURABLE BUSES.
THE SCHEME USES A SIMPLE VOLTAGE DETECTOR – IT DOES NOT
PROVIDE BENEFITS OF A MICROPROCESSOR-BASED RELAY .
(E.G. OSCILLOGRAPHY, BREAKER FAILURE PROTECTION, OTHER
FUNCTIONS)
OPERATING SIGNAL CREATED BY CONNECTING ALL CT SECONDARY'S IN PARALLEL.CTS MUST ALL HAVE SAME RATIO.MUST HAVE DEDICATED CTSOVERVOLTAGE ELEMENT OPERATES ON VOLTAGE DEVELOPED ACROSS RESISTOR CONNECTED IN SECONDARY CIRCUIT.REQUIRES VARISTORS OR AC SHORTING RELAYS TO LIMIT ENERGY DURING FAULTS.ACCURACY DEPENDENT ON SECONDARY CIRCUIT RESISTANCE.USUALLY REQUIRES LARGER CT CABLES TO REDUCE ERRORS HIGHER COST
CANNOT EASILY BE APPLIED TO
RECONFIGURABLE BUSES AND OFFERS
NO ADVANCED FUNCTIONALITY
59
PERCENT CHARACTERISTIC USED
TO COPE WITH CT SATURATION AND
OTHER ERRORS.
RESTRAINING SIGNAL CAN BE
FORMED IN A NUMBER OF WAYS.
NO DEDICATED CTS NEEDED.
USED FOR PROTECTION OF RE-
CONFIGURABLE BUSES POSSIBLE.
5187
nDIF IIII ...21
nRES IIII ...21 nRES IIII ...,,,max 21
INDIVIDUAL CURRENTS SAMPLED BY PROTECTION AND SUMMATED
DIGITALLY.
CT RATIO MATCHING DONE INTERNALLY (NO AUXILIARY CTS).
DEDICATED CTS NOT NECESSARY.
ADDITIONAL ALGORITHMS IMPROVE SECURITY OF PERCENT
DIFFERENTIAL CHARACTERISTIC DURING CT SATURATION.
DYNAMIC BUS REPLICA ALLOWS APPLICATION TO RECONFIGURABLE
BUSES.
DONE DIGITALLY WITH LOGIC TO ADD/REMOVE CURRENT INPUTS
FROM DIFFERENTIAL COMPUTATION.
SWITCHING OF CT SECONDARY CIRCUITS NOT REQUIRED.
LOW SECONDARY BURDENS.
ADDITIONAL FUNCTIONALITY AVAILABLE.
DIGITAL OSCILLOGRAPHY AND MONITORING OF EACH CIRCUIT
CONNECTED TO BUS ZONE.
TIME-STAMPED EVENT RECORDING.
BREAKER FAILURE PROTECTION.
IMPROVE THE MAIN DIFFERENTIAL ALGORITHM OPERATION.
A) BETTER FILTERING B) FASTER RESPONSE
C) BETTER RESTRAINT TECHNIQUES D)SWITCHING TRANSIENT BLOCKING
PROVIDE DYNAMIC BUS REPLICA FOR RECONFIGURABLE BUS BARS.
DEPENDABLY DETECT CT SATURATION IN A FAST AND RELIABLE MANNER,
ESPECIALLY FOR EXTERNAL FAULTS.
IMPLEMENT ADDITIONAL SECURITY TO THE MAIN DIFFERENTIAL
ALGORITHM TO PREVENT INCORRECT OPERATION.
EXTERNAL FAULTS WITH CT SATURATION.
CT SECONDARY CIRCUIT TROUBLE (E.G. SHORT CIRCUITS).
DATA ACQUISITION UNITS (DAUS)
INSTALLED IN BAYS.
CPU PROCESSES ALL DATA FROM
DAUS.
COMMUNICATIONS BETWEEN DAUS
AND CPU OVER FIBRE USING
PROPRIETARY PROTOCOL.
SAMPLING SYNCHRONISATION
BETWEEN DAUS IS REQUIRED.
PERCEIVED LESS RELIABLE.
DIFFICULT TO APPLY IN RETROFIT
APP.
5 2
DA U
5 2
DA U
5 2
DA U
CU
co pp er
f i be r
ALL CURRENTS APPLIED TO A
SINGLE CENTRAL PROCESSOR
NO COMMUNICATIONS,
EXTERNAL SAMPLING
SYNCHRONISATION NECESSARY
PERCEIVED MORE RELIABLE (LESS
HARDWARE NEEDED)
WELL SUITED TO BOTH NEW AND
RETROFIT APPLICATIONS.
52 52 52
CU
co pp er
THE CHANCES OF FAULTS OCCURING ON THE FEEDER (TRANSMISSION
LINE) IS MUCH MORE DUE TO THEIR GREAT LENGTH AND EXPOSURE TO
THE ATMOSPHERIC CONDITIONS. THEREFORE, VARIOUS PROTECTION
SCHEMES HAVE BEEN DEVELOPED WHICH MAY BE CLASSIFIED AS:
A) TIME-GRADED OVER CURRENT PROTECTION
B) DIFFERENTIAL PROTECTION
C) DISTANCE PROTECTION
IN TIME GRADED OVER CURRENT PROTECTION SCHEME, THE TIME
SETTING OF RELAY IS SO GRADED THAT IN THE EVENT OF FAULT, THE
SMALLEST POSSIBLE SECTION OF THE SYSTEM POSSIBLE SECTION OF THE
SYSTEM IS ISOLATED. THIS SCHEME IS APPLIED FOR THE PROTECTION OF
(A) RADIAL FEEDERS
(B) PARALLEL FEEDERS
(C) RING MAINS
• THE TIME-GRADED PROTECTION FEEDER IS OBTAINED BY EMPLOYING
INVERSE DEFINITE MINIMUM TIME LAG RELAYS. THE RELAYS ARE SO SET
THAT THE MINIMUM TIME OF OPERATION DECREASE FROM THE POWER
STATION TO THE REMOTE SUB-STATION AS SHOWN IN FIG. IN NEXT
SLIDE.
• THE OPERATING TIME OF INVERSE DEFINITE MINIMUM TIME LAG
RELAYS IS INVERSELY PROPRTIONAL TO THE OPERATING CURRENT, BUT
IS NEVER LESS THAN THE MINIMUM DEFINITE FOR WHICH IT IS SET.
IF A FAULT OCCURS BETWEEN STATION E AND F, IT WILL BE CLEARED IN
0.1 SECOND BY THE RELAY AND CIRCUIT BREAKER OF SUBSTATION E
BECAUSE ALL OTHER RELAYS HAVE HIGHER OPERATING TIME. IF THE
RELAY AT SUB STATION E FAILS TO TRIP, THE RELAY AT D WILL OPERATE
AFTER A TIME DELAY OF 0.5 SECONDS I.E. AFTER 0.6 SECONDS FROM THE
OCCURRENCE OF FAULT.
WHERE CONTINUITY OF SUPPLY IS ABSOLUTELY NECESSARY, TWO
FEEDERS ARE RUN IN PARALLEL. IF A FAULT OCCURS ON ONE FEEDER, THE
SUPPLY CAN BE MAINTAINED FROM THE OTHER FEEDER, DISCONNECTING
THE FAULTY FEEDER. FOLLOWING FIG. SHOWS THE SYSTEM WHERE TWO
FEEDERS ARE CONNECTED IN PARALLEL BETWEEN GENERATING STATION &
SUB-STATION.
AT THE GENERATING STATION, NON-DIRECTIONAL OVER CURRENT
RELAYS ARE CONNECTED WHEREAS DIRECTIONAL OVER CURRENT
INSTANTANEOUS RELAYS ARE CONNECTED AT SUB-STATION END.
IF AN EARTH FAULT OCCURS ON FEEDERS AT POINT F AS SHOWN IN FIG.
THE FAULT IS FED;
(A) DIRECTLY FROM FEEDER 2 VIA RELAY B.
(B) FROM FEEDER I VIA A , P AND SUB-STATION Q AS SHOWN IN FIG. BY THE
DOTTED ARROWS.
THIS CLEARLY SHOWS THAT DIRECTIONAL RELAY P CARRIES THE CURRENT IN
NORMAL DIRECTION WHERE AS DIRECTIONAL RELAY Q CARRIES THE
CURRENT IN REVERSE DIRECTION MOMENTARILY. THIS OPEARATES THE
RELAY Q INTANTANEOUSLY. THE RELAY B HAVING INVERSE TIME
CHARACTERISTICS ALSO OPERATES BECAUSE OF HEAVY FLOW OF CURRENT .
THE SYSTEM IN WHICH VARIOUS POWER STATIONS OR SUB-STATIONS
ARE INTER-CONNECTED BY THE NUMBER OF FEEDERS FORMING A CLOSED
CIRCUIT IS CALLED A RING- MAIN SYSTEM.
IN THIS SYSTEM OF PROTECTION, NON-DIRECTIONAL OVER CURRENT
RELAYS HAVING INVERSE TIME CHARACTERISTIC ARE EMPLOYED. WHEREAS
DIRECTIONAL OR REVERSE POWER ARE EMPLOYED ON BOTH THE SIDES OF
EACH SUBSTATION. THE MINIMUM DEFINITE TIME OF ALL THE RELAY ARE
SET PROPERLY AS SHOWN IN FIG.
WHENEVER THE FAULT OCCURS ON ANY OF THE SECTION ONLY
CORRESPONDING RELAYS WILL OPERATE WITHOUT DISTURBING THE
OTHER RELAYS OF THE NETWORK, THUS, THE FAULTY SECTION IS ISOLATED
AND SUPPLY IS MAINTAIN.
THE TRANSLATION SCHEME IS BASICALLY A VOLTAGE BALANCE
DIFFERENTIAL PROTECTION SCHEME. BUT IN THIS SCHEME, VOLTAGES
INDUCED IN THE SECONDARY WINDINGS WOUND ON THE RELAY
MAGNETS IS COMPARED IN PLACE OF SECONDARY VOLTAGES OF THE
LINE CURRENT TRANSFORMERS.
THE SCHEMATIC DIAGRAM OF A TRANLEY SCHEME FOR THE
PROTECTION OF 3-PHASE FEEDER IS SHOWN IN FIG . ON NEXT SLIDE.
THE RELAYS USED IN THE SCHEME ARE ESSENTIALLY OVERCURRENT
INDUCTION TYPE RELAYS.
THE CENTRAL LIMB OF THE UPPER MAGNET (U.M.) CARRIES A WINDING
(A OR A’) WHICH IS ENERGISED BY THE SUM OF SECONDARY CURRENTS OF
CT’S PLACED ON FEEDER TO BE PROTECTED.
THE CENTRAL LIMBS OF UPPER MAGNET ALSO CARRIES A
SECONDARY WINDING (B OR B’) WHICH IS CONNECTED IN SERIES WITH
THE OPERATING WINDING (C OR C’) PLACED ON THE LOWER MAGNETS
(L.M). IN BETWEEN THE TWO MAGNETS, AN ALUMINIUM DISC D IS
PLACED WHICH IS FREE TO ROTATE. SPINDLE OF DISC CARRIES MOVING
CONTACT WHICH CLOSES TRIP CIRCUIT UNDER FAULT CONDITIONS.
• UNDER NORMAL CONDITIONS, THE CURRENTS AT TWO ENDS OF THE
FEEDER ARE EQUAL SO THAT THE SECONDARY CURRENT IN BOTH SETS
OF CT’S ARE EQUAL. CONSEQUENTLY, THE E.M.F’S INDUCED IN THE
SECONDARY WINDINGS C AND C’ ARE EQUAL AND OPPOSITE AND NO
CURRENT FLOWS THROUGH THE CLOSED CIRCUITED SECONDARIES.
HOWEVER, WHEN FAULT OCCURS ON FEEDER SYSTEM SAY AT POINT F
THE VOLTAGE INDUCED IN C AND C’ WILL NO LONGER REMAIN EQUAL.
THEREFORE, CURRENT FLOWS THROUGH THIS WINDING AND TORQUE
IS DEVEOLPED IN THE DISC.