-ETHOD OF OPERATION
3*
6
# ' #
)N THE
VOLTAGE PATH
THERE ARE THREE INPUT CONVER
TERS 4HE SUM OF THE PHASE TO PHASE VOLTAGES IS
ALWAYS MONITORED SINCE THESE ARE NOT AFFECTED BY
EARTH FAULTS )F THE PHASE TO EARTH VOLTAGES ARE
CONNECTED THE PHASE TO PHASE VOLTAGES ARE
CALCULATED IN THE RELAY FROM THOSE ! FAULT IN THE
VOLTAGE CIRCUITS WILL BE RECOGNIZED WHEN
\U
, ,
U
, ,
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\ 6
#OMMAND OUTPUT CHANNELS
4HE COMMAND RELAYS FOR TRIPPING AND CLOSING ARE
CONTROLLED BY TWO COMMAND AND ONE ADDITIONAL
RELEASE CHANNELS !S LONG AS NO PICK UP CONDI
TION EXISTS THE PROCESSOR MAKES A CYCLIC CHECK OF
THESE COMMAND OUTPUT CHANNELS FOR AVAILABILITY
BY EXCITING EACH CHANNEL ONE AFTER THE OTHER AND
CHECKING FOR CHANGE IN THE OUTPUT SIGNAL LEVEL
#HANGE OF THE FEED BACK SIGNAL TO LOW LEVEL INDI
CATES A FAULT IN ONE OF THE CONTROL CHANNELS OR IN THE
RELAY COIL 3UCH A CONDITION LEADS AUTOMATICALLY TO
ALARM AND BLOCKING OF THE COMMAND OUTPUT
-EMORY MODULES
4HE MEMORY MODULES ARE PERIODICALLY CHECKED
FOR FAULT BY
C
7RITING A DATA BIT PATTERN FOR THE WORKING
MEMORY 2!- AND READING IT
C
&ORMATION OF THE MODULUS FOR THE PROGRAM
MEMORY %02/- AND COMPARISON OF IT WITH A
REFERENCE PROGRAM MODULUS STORED THERE
C
&ORMATION OF THE MODULUS OF THE VALUES STORED
IN THE PARAMETER STORE %%02/- THEN COM
PARING IT WITH THE NEWLY DETERMINED MODULUS AF
TER EACH PARAMETER ASSIGNMENT PROCESS
3OFTWARE MONITORING
&OR CONTINUOUS MONITORING OF THE PROGRAM SE
QUENCES A WATCHDOG TIMER IS PROVIDED WHICH WILL RE
SET THE PROCESSOR IN THE EVENT OF PROCESSOR FAILURE OR
IF A PROGRAM FALLS OUT OF STEP &URTHER INTERNAL PLAUSI
BILITY CHECKS ENSURE THAT ANY FAULT IN PROCESSING OF
THE PROGRAMS CAUSED BY INTERFERENCE WILL BE RECOG
NIZED 3UCH FAULTS LEAD TO RESET AND RESTART OF THE PRO
CESSOR SYSTEM
)F SUCH A FAULT IS NOT ELIMINATED BY RESTARTING FURTHER
RESTARTS ARE INITIATED )F THE FAULT IS STILL PRESENT AFTER
THREE RESTART ATTEMPTS THE PROTECTIVE SYSTEM WILL
SWITCH ITSELF OUT OF SERVICE AND INDICATE THIS CONDITION
BY DROP OFF OF THE AVAILABILITY RELAY THUS INDICATING
EQUIPMENT FAULT AND SIMULTANEOUSLY THE ,%$
"LOCKED COMES ON
-ONITORING OF EXTERNAL MEASURING
TRANSFORMER CIRCUITS
4O DETECT INTERRUPTIONS OR SHORT CIRCUITS IN THE EXTER
NAL MEASURING TRANSFORMER CIRCUITS OR FAULTS IN THE
CONNECTIONS AN IMPORTANT COMMISSIONING AID THE
MEASURED VALUES ARE CHECKED AT CYCLIC INTERVALS AS
LONG AS NO PICK UP CONDITION EXISTS
#URRENT SYMMETRY
)N HEALTHY OPERATION IT CAN BE EXPECTED THAT THE
CURRENTS WILL BE APPROXIMATELY SYMMETRICAL 4HE
FOLLOWING APPLIES
\ )
MIN
\ \ )
MAX
\ 39-&ACT)
IF
)
MAX
)
.
39-)THRES )
.
)
MAX
IS ALWAYS THE LARGEST OF THE THREE PHASE CUR
RENTS AND )
MIN
ALWAYS THE SMALLEST 4HE SYMMETRY
FACTOR 39-&ACT) REPRESENTS THE MAGNITUDE OF
ASYMMETRY OF THE PHASE CURRENTS AND THE THRESH
OLD 39-)THRES IS THE LOWER LIMIT OF THE PROCESSING
AREA OF THIS MONITORING FUNCTION SEE &IGURE
"OTH PARAMETERS CAN BE SET SEE 3ECTION
39-)THRES
3LOPE
39-&ACT)
)
MIN
)
.
)
MAX
)
.
&IGURE #URRENT SYMMETRY MONITORING
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