Phase Selection - GE L60 Instructions Manual

CHAPTER 9: THEORY OF OPERATION SINGLE-POLE TRIPPING
The operand is asserted 1.25 cycles following autoreclose initiation. This operand acts as an enabler for
AR FORCE 3-P TRIP
any existing trip request. In this case, none of the protection elements is picked up at this time, therefore no more trips are
initiated.
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, autorecloser, open pole detector and trip output elements. The response at breaker failure depends on
the programming of that element. The response at the autorecloser 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, then the reset time expires at the autorecloser and the and outputs are de-
AR FORCE 3-P TRIP RIP
asserted, returning all features to the state described at the beginning of this description.
If the fault was permanent, appropriate protection elements detect this and place a trip request for the trip output
element. As the is still asserted, the request is executed as a three-pole trip.
AR FORCE 3-P TRIP
The response of the system from this point is as described earlier for the second trip, except that the autorecloser locks out
upon the next initiation (depending on the number of shots programmed).
9.2.1.3 SLG fault evolving into LLG
When an AG fault occurs, the events unfold initially as in the previous example. If the fault evolves quickly, then the phase
selector changes its initial assessment from AG to ABG fault and when the trip request is placed either by zone 1 or the line
phase comparison element (ANSI 87PC), a three-pole trip is initiated. If this is the case, all three
TRIP PHASE A, TRIP PHASE B
and operands are asserted. The command is passed to the breaker control element and results in a three-pole
TRIP PHASE C
trip. At the same time the recloser is initiated as per settings of the trip output. As the operand is asserted (not
TRIP 3-POLE
the operand) the open pole is not activated. Because the AR RIP in progress is asserted, the phase selector is
TRIP 1-POLE
blocked as well.
If the fault evolves slowly, then the sequence is different: The relay trips phase A as in the previous example. The phase
selector resets, the open pole detector is activated and forces the zone 1 and zone 2 AG, AB, CA, and negative-sequence
overcurrent elements to reset. If the zone 1 BG or line phase comparison element (ANSI 87PC) picks up, no trip command is
issued until the is asserted. This happens 1.25 cycles after the first trip. If at this time or any time later a
AR FORCE 3-P TRIP
request for trip is placed (due to an evolving fault), then a three-pole trip is initiated. The operand is de-asserted
TRIP 1-POLE
by the operand, resetting the open pole detector. Shortly all three-poles are opened.
TRIP 3-POLE
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
pickup element is armed as well. If there is a fault on the line, these elements pick up the fault and issue the next request
for trip. This request results in three-pole trip as the is still asserted.
AR FORCE 3-P TRIP
The response of the system from this point is as described for the second trip, except the recloser goes to lockout upon the
next initiation (depending on the number of shots programmed).

9.2.2 Phase selection

The L60 uses phase relations between current symmetrical components for phase selection. First, the algorithm validates
if there is enough zero-sequence, positive-sequence, and negative-sequence currents for reliable analysis. The
comparison is adaptive; that is, the magnitudes of the three symmetrical components used mutually as restraints confirm
if a given component is large enough to be used for phase selection. Once the current magnitudes are validated, the
algorithm analyzes phase relations between the negative-sequence and positive-sequence currents and negative-
sequence and zero-sequence currents (when applicable), as shown in the figure.
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L60 LINE PHASE COMPARISON SYSTEM – INSTRUCTION MANUAL 9-39