Siemens 7SD502, Instruction Manual

Page: 43 / 178

-ETHOD OF OPERATION 3$
6
# ' #
5SE ON THREETERMINAL LINES
)F THE DIFFERENTIAL PROTECTION SYSTEM IS USED ON LINES
WITH THREE TERMINALS TEED LINES IE WITH A BRANCH
POINT EACH LINE END MUST BE CONNECT WITH EACH LINE
END WITH A PAIR OF PILOT WIRES REFER TO &IGURE
%ACH PAIR OF PILOT WIRES CONNECTS TWO RELAYS 4HUS
TWO ADJACENT RELAYS ARE INSTALLED IN EACH SUBSTATION
FROM WHICH EACH COMMUNICATES WITH AN OPPOSITE
END RELAY AT ONE OF THE REMOTE ENDS
4HE ADJACENT RELAYS IN ONE SUBSTATION RECEIVE THE
SAME CURRENTS FROM THE POWER LINE SO THEY MUST BE
CONNECTED IN SERIES IN THE CURRENT PATHS 4HE MIXED
CURRENT OF RELAY OF SUBSTATION SHOULD BE DESIG
NATED WITH ) WHEREAS THE MIXED CURRENT OF RELAY
OF SUBSTATION SHOULD BE CALLED ) 4HEORETICALLY
BOTH CURRENTS ARE EQUAL 2ELAY IS CONNECTED VIA A
PAIR OF PILOT WIRES WITH RELAY OF THE SUBSTATION ETC
SO THAT A CYCLIC ARRANGEMENT RESULTS
!N ESSENTIAL FACTOR IS THAT THE ADJACENT RELAYS OF ONE
STATION RECEIVE THE CURRENTS OF BOTH OUTGOING PILOT
WIRES "ESIDES THE PILOT WIRE CURRENT OF THE CON
NECTED PILOT WIRES )
A
RELAY RECEIVES ALSO THE CUR
RENT OF THE PILOT WIRES TO THE THIRD LINE END )
A
3IMI
LARLY RELAY RECEIVES THE CURRENTS )
A
AND )
A
.OTE THAT THE FIGURE SHOWS THE CURRENT FLOW NOT THE
PHYSICAL ARRANGEMENT 4HE QUANTITIES WITH BELONG
TO RELAY THE QUANTITIES WITHOUT TO RELAY ! CON
NECTION EXAMPLE IS ILLUSTRATED IN !PPENDIX "
&IGURE "
%ACH OF THE RELAYS CAN CALCULATE THE CURRENT OF THE
OPPOSITE LINE END FROM THE CURRENT OF THE OWN PILOT
WIRES EG )
A
TO THE REMOTE END EG RELAY AND
THE CURRENT OF THE THIRD LINE END FROM THE CURRENT OF
THE PILOT WIRES TO THE THIRD END EG )
A
4HE TRIP COMMANDS OF THE TWO ADJACENT RELAYS OF A
SUBSTATION ARE CONNECTED IN PARALLEL
3TATION 3TATION
) )
A
)
A
)
)
A
) )
A
)
A
)
A
)
A
) )
A
)
)
A
)
A
)
A
)
)
A
3TATION
&IGURE 0ILOT WIRE CURRENTS ON THREETERMINAL LINES