-ETHOD OF OPERATION
6+
6
# ' #
5
THE VOLTAGE MAGNITUDE DIFFERENCE
F
THE FREQUENCY DIFFERENCE
THE PHASE ANGLE DIFFERENCE
-ONITORING FUNCTIONS
4HE DEVICE INCORPORATES COMPREHENSIVE MONITORING
FUNCTIONS WHICH COVER BOTH HARDWARE AND SOFTWARE
(ARDWARE MONITORING
4HE COMPLETE HARDWARE IS MONITORED FOR FAULTS AND
INADMISSIBLE FUNCTIONS FROM THE MEASURED VALUE IN
PUTS TO THE OUTPUT RELAYS )N DETAIL THIS IS ACCOM
PLISHED BY MONITORING
!UXILIARY AND REFERENCE VOLTAGES
4HE PROCESSOR MONITORS THE OFFSET AND REFERENCE
VOLTAGE OF THE !$# ANALOGDIGITAL CONVERTER 4HE
PROTECTION IS BLOCKED AS SOON AS IMPERMISSIBLE
DEVIATIONS OCCUR 0ERMANENT FAULTS ARE ANNUN
CIATED
&AILURE OR SWITCH OFF OF THE AUXILIARY VOLTAGE AUTO
MATICALLY PUTS THE SYSTEM OUT OF OPERATION THIS
STATUS IS INDICATED BY A FAIL SAFE CONTACT 4RAN
SIENT DIPS IN SUPPLY VOLTAGE OF LESS THAN MS WILL
NOT DISTURB THE FUNCTION OF THE RELAY
#OMMAND OUTPUT CHANNELS
4HE COMMAND RELAYS FOR CLOSING ARE CONTROLLED BY
TWO COMMAND AND ONE ADDITIONAL RELEASE CHAN
NELS !S LONG AS NO PICK UP CONDITION EXISTS THE
CENTRAL PROCESSOR MAKES A CYCLIC CHECK OF THESE
COMMAND OUTPUT CHANNEL FOR AVAILABILITY BY EXCIT
ING EACH CHANNELS ONE AFTER THE OTHER AND CHECK
ING FOR CHANGE IN THE OUTPUT SIGNAL LEVEL #HANGE
OF THE FEED BACK SIGNAL TO LOW LEVEL INDICATES 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
)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
