GE D60 Instruction Manual page 349

8 THEORY OF OPERATION 8.5 SINGLE-POLE TRIPPING
Depending on response times, the actual trip is initiated either by the Z1 or by the POTT. At the moment TRIP 1-POLE
operand is asserted, the Phase Selector resets and no other trip action could take place. After the trip command is issued
all the picked up elements are forced to reset by the Open Pole Detector.
The TRIP 1-POLE operand initiates automatically a single-pole autoreclose. The AR is started and asserts its AR RIP oper-
and. This operand keeps blocking the Phase Selector so that it does not respond to any subsequent events. At the same
time the operand removes zero-sequence directional supervision from ground distance zones 2 and 3 so that they could
respond to a single-line-to-ground fault during open pole conditions.
1.25 cycles after the AR is initiated, the AR FORCE 3-P TRIP operand is asserted. This operand acts as an enabler for any
existing trip request. In this case none of the protection elements is picked up at this time, therefore no more trips are initi-
ated.
When the Recloser dead time interval is complete it signals the Breaker Control element to close the breaker. The Breaker
Control element operates output relays to close the breaker.
When pole A of the breaker closes this new status is reported to the Breaker Control element, which transfers this data to
the Breaker Failure, Recloser, Open Pole Detector and Trip Output elements. The response at Breaker Failure is depen-
dent on the programming of that element. The response at Recloser is not relevant to this discussion. At the Open Pole
Detector, the blocking signals to protection elements are de-asserted.
If the fault was transient the reset time would expire at the Recloser and the AR FORCE 3-P TRIP and RIP outputs would
be de-asserted, returning all features to the state described at the beginning of this description.
If the fault was permanent appropriate protection elements would detect it and place a trip request for the Trip Output ele-
ment. As the AR FORCE 3-P TRIP is still asserted, the request is executed as a three-pole trip.
The response of the system from this point is as described above for the second trip, except the Recloser will go to lockout
upon the next initiation (depending on the number of shots programmed).
c) SLG FAULT EVOLVING INTO LLG
When an AG fault occurs the events unfold initially as in the previous example. If the fault evolves quickly, the Phase Selec-
tor will change its initial assessment from AG to ABG fault and when the trip request is placed either by the Z1 or the POTT,
a trip-pole trip will be initiated. If this is the case, all three TRIP PHASE A, B and C operands will be asserted. The com-
mand is passed to the Breaker Control element and results in a three-pole trip. At the same time the Recloser is initiated as
per settings of the Trip Output. As the TRIP 3-POLE operand is asserted (not the TRIP 1-POLE operand) the Open Pole is
not activated. Because the AR RIP in progress is asserted, the Phase Selector is blocked as well.
If the fault evolves slowly, the sequence is different: The relay trips phase A as in the previous example. The Phase Selec-
tor Resets, the Open Pole Detector is activated and forces Z1 and Z2 AG, AB, CA and negative-sequence overcurrent ele-
ments to reset. If the Z1 BG element picks up, or Z2 BG element picks up resulting in operation of the POTT scheme, no
trip command will be issued until the AR FORCE 3-P TRIP is asserted. This happens 1.25 cycles after the first trip. If at this
time or any time later a request for trip is placed (due to an evolving fault), a three-pole trip is initiated. The TRIP 1-POLE
operand is de-asserted by the TRIP 3-POLE operand, resetting the OPEN POLE detector. Shortly all three-poles are
opened.
When the dead time expires, the Recloser signals the Breaker Control to close the breaker. At this time all the protection
elements are operational, as the Open Pole Detector is not blocking any elements. If the line-side VTs are used, the Line
8
Pickup element is armed as well. If there is a fault on the line, these elements will pickup the fault and issue next request for
trip. This request results in three-pole trip as the AR FORCE 3-P TRIP is still asserted.
The response of the system from this point is as described above for the second trip, except the Recloser will go to lockout
upon the next initiation (depending on the number of shots programmed).
GE Multilin D60 Line Distance Relay 8-21