-ETHOD OF OPERATION
3$
6
# ' #
0ILOT WIRE MONITORING
OPTIONAL
4HE PILOT WIRES BETWEEN THE TWO DIFFERENTIAL RELAYS AT
THE ENDS OF THE PROTECTED LINE FORM AN ESSENTIAL PART
OF THE SCHEME 4HEIR PROPER INSTALLATION AND CON
STANT INTEGRITY IS A PREREQUISITE FOR SATISFACTORY OPERA
TION ! FAILURE OF THE PILOT WIRES DISABLES THE PROTEC
TION FUNCTION 4HE PILOT WIRES WHICH ARE INSTALLED IN
THE GROUND ARE MECHANICALLY ENDANGERED TO A SIMI
LAR EXTEND AS THE ENERGY CABLE ITSELF &OR THIS REASON IT
IS ALWAYS RECOMMENDED THAT THE PILOT WIRES BE SU
PERVISED BY THE PILOT WIRE MONITORING OPTION
4HE PILOT WIRE MONITOR IS ARRANGED ON A SEPARATE
PRINTED CIRCUIT BOARD 0'! 4HIS PROCESSOR CONTROLLED
MONITOR MODULE CARRIES ALSO THE INTERTRIPPING AND
TRANSFER TRIP FUNCTIONS MODEL 3$
J JJJ
J
4HE PILOT WIRE MONITOR IS COMPOSED OF A TRANSMITTER
AND A RECEIVER FOR EACH DIRECTION IN THE RELAYS WHICH
ARE CONNECTED BY THE PILOT WIRES &IGURE )T OP
ERATES WITH A PULSED CODE WHICH IS MODULATED ON A
VOICE FREQUENCY SIGNAL OF (Z 4HE MONITORING
CODE IS TRANSMITTED ALTERNATELY BY ONE RELAY TO THE
OTHER AND VICE VERSA )N ORDER TO ENSURE A DEFINED
STARTUP OF THIS HANDSHAKE OPERATION ONE OF THE RE
LAYS MUST BE DECLARED AS MASTER AND THE OTHER AS
SLAVE 4HE MASTER DEVICE WILL ALWAYS START WITH
THE COMMUNICATION THE SLAVE DEVICE RESPONDS
!N INTERRUPTION OR SHORTCIRCUIT ON THE PILOT WIRES IS
DETECTED BY BOTH RELAYS 7HEN THE PILOT WIRES ARE IN
TERRUPTED THE DIFFERENTIAL PROTECTION CANNOT TRIP ANY
MORE SINCE NO DIFFERENTIAL CURRENT CAN BE PRESENT )F
THE PILOT WIRES ARE SHORTCIRCUITED A HIGH THROUGH
FAULT CURRENT EXTERNAL FAULT MAY CAUSE TRIPPING &OR
THIS REASON THE DIFFERENTIAL PROTECTION CAN BE BLOCKED
WHEN A PILOT WIRE FAULT IS DETECTED SELECTABLE 4HE
REMAINING PROTECTION FUNCTIONS
ESPECIALLY THE
OVERCURRENT TIME PROTECTION IF IT IS SET EFFECTIVE
WILL
CONTINUE THEIR OPERATION EVEN DURING PILOT WIRE FAULT
3INCE THE PILOT WIRE MONITOR IS A SLOW FUNCTION IT
CANNOT ALWAYS AVOID THAT THE RELAY TRIPS ON A THROUGH
FAULT CURRENT WHEN AN EXTERNAL FAULT OCCURS JUST AT
THAT MOMENT WHEN THE PILOT WIRES ARE SHORTCIRCUITED
"UT THIS IS EXTREMELY IMPROBABLE SINCE THERE IS NO CO
HERENCE BETWEEN A PILOT WIRE SHORTCIRCUIT AND AN
EX
TERNAL
POWER LINE FAULT
4HE PILOT WIRE MONITOR DOES NOT OPERATE AS LONG AS A
NETWORK FAULT IS PRESENT BECAUSE THE DIFFERENTIAL CUR
RENT TRANSMISSION WITH SYSTEM FREQUENCY HAS PRIORITY
NOW 4HE PILOT WIRE MONITOR IS ALSO INOPERATIVE AS
LONG AS A TRANSFER TRIP SIGNAL CF 3ECTION IS
TRANSMITTED BECAUSE ONLY ONE PILOT WIRE PAIR AND
ONLY ONE CARRIER FREQUENCY ARE AVAILABLE
)F THE RELAYS ARE USED FOR THE PROTECTION OF THREETER
MINAL LINES TEED LINES ANY PILOT WIRE DISTURBANCE IS
INDICATED AT ALL THREE ENDS ! PRECONDITION IS THAT THE
TWO RELAYS WHICH ARE INSTALLED IN ONE SUBSTATION IN
FORM EACH OTHER VIA BINARY OUTPUTS AND INPUTS REFER
TO 3ECTION FOR DETAILS
3TATION
3TATION
)
)
A
)
B
2
B
)
A
)
)
B
2
B
2
A
2
A
2
4
#
+
2
4
#
+
,EGEND
4
4RANSMITTER CURRENT SOURCE
2
2ECEIVER
#
+
#OUPLING CAPACITOR
&IGURE #OUPLING OF THE PILOT WIRE MONITORING CIRCUITS WITH DIFFERENTIAL PROTECTION USING TWO PILOT WIRES
Summary of Contents for 7SD502
Page 148: ... PPENDIX 3 6 PPENDIX ENERAL DIAGRAMS ONNECTION DIAGRAMS 4ABLES ...
Page 176: ... 3 6 ...