Siemens SIPROTEC 7SJ531 - Page 63

-ETHOD OF OPERATION3*
6

#
' #
&IGURE  SHOWS A FAULT CURVE WHEN THE VOLTAGE
TRANSFORMERS ARE CONNECTED AT THE OUTGOING FEED
ER SIDE (ERE THE CURRENT CRITERION ## ) IS USED FOR
RESET OF THE PICK
UP AFTER OPENING OF THE CIRCUIT
BREAKER 4HE START
UP CRITERION IS ALSO ACTIVE IN THIS
EXAMPLE
7ITH A VOLTAGE DECREASE BELOW THE PICK
UP THRESH
OLD TRIPPING IS EFFECTED AFTER THE TIME DELAY 4
5
7ITH THE OPENING OF THE CIRCUIT BREAKER THE VOLTAGE
DROPS TO ZERO WHILE THE UNDERVOLTAGE PICK
UP PER
SISTS 4HE CURRENT ALSO DROPS TO ZERO AND AS SOON AS
IT FALLS BELOW THE RELEASE THRESHOLD ## ) CAUSES
RESET OF THE CURRENT CRITERION "Y THE !.$
LOGIC OF
THE VOLTAGE AND CURRENT CRITERION ALSO THE PROTECTION
PICK
UP RESETS SO THAT RECLOSING IS POSSIBLE AFTER
THE MINIMUM COMMAND TIME HAS EXPIRED
7HEN THE CIRCUIT BREAKER IS CLOSED THEN THE CURRENT
CRITERION ## ) IS DELAYED FOR A SHORT TIME )F THE VOLT
AGE CRITERION RESETS DURING THIS TIME 4
##
  MS THE PROTECTION DOES NOT PICK UP 4HIS EN
SURES THAT BREAKER CLOSING UNDER NO
FAULT CONDITION
DOES NOT PROVOKE CREATION OF A FAULT EVENT 4HIS
MEANS ON THE OTHER HAND THAT BREAKER CLOSING ONTO
AN UNDERVOLTAGE CONDITION BRINGS THE THEN REQUIRED
PROTECTION PICK
UP NOT BEFORE THE CURRENT CRITERION S
TIME DELAY 4
## IS EXPIRED
&IGURE  SHOWS THE LOGIC DIAGRAM OF THE UNDERVOL
TAGE PROTECTION
4 ##
MS
5
N
T
)
RMS
T
)
N
5
3# )
T
T
4 5
4
3#
 MIN COMMAND DURATION
## )
T
T
#URRENT CRITERION FULFILLED
0ICK UP WITHOUT DELAY
4 42)0
0ICK UP 5 WITHOUT CURRENT CRITERION
5
RMS
T
4RIP
COMMAND
#,/3%
COMMAND
0ICK
UP
5
$ROP OFF
5
2ESET THRESHOLD
0ICK
UP THRESHOLD
4HRESHOLD FOR
START
UP CRITERION
4HRESHOLD FOR
CURRENT CRITERION
#URRENT CRITERION FULFILLED
4RIP
0ICK
UP
5 RESET
5 3#
&IGURE  4YPICAL FAULT SEQUENCE WITH VOLTAGE TRANSFORMERS INSTALLED AT THE FEEDER SIDE CURRENT AND
START
UP CRITERION EFFECTIVE
www . ElectricalPartManuals . com