GE L90 Instruction Manual page 495

9 THEORY OF OPERATION
• Notify the phase selector when a trip operation is imminent.
When notified that a single pole operation has been initiated open pole detector will:
• Initiate blocking of protection elements that could potentially maloperate when a breaker pole is open.
• Instruct the phase selector to de-assert all outputs, as an open pole invalidates calculations.
It is assumed for this discussion that the relay features that are shown on Single pole operation diagram above have all
been programmed for the application and are in service. The description begins with line breakers open at both the local
and remote ends, and the operation of the scheme is described in chronological order.
Because the line is de-energized the line pickup element is armed. The recloser is presently enabled. An operator requests
that breaker control close the breaker, and it operates output relays to close breaker poles A, B and C. This operator man-
ual close request is also forwarded from breaker control to recloser, which becomes disabled, de-asserting its "Enabled"
output. This output is transferred to trip output, where it converts any input request for a single pole operation into a three-
pole operation. At the recloser, the
The breaker closes and status monitoring contacts on the breaker poles change state; the new breaker pole states are
reported to breaker control, which in turn transfers these states to the recloser, trip output, breaker failure and open pole
detector. Because a fault is not detected the
asserts the "Enabled" output, informing the trip output element that single pole trip operations are now permitted. When nor-
mal voltage appears on the line the line pickup element is disarmed. As the local line breaker has not tripped the operator
closes the breaker at the remote end of the line, placing the line in service.
Several scenarios are considered below.
b) SLG FAULT
At this moment the request to trip is placed for the trip output. As the fault is recognized as an AG fault, the TRIP PHASE A
operand is asserted by the trip output. This signal is passed to the breaker control scheme and results in tripping pole A of
the breaker.
Simultaneously with the
TRIP PHASE A
detector. The latter detector responds to the
ΦA
(even before it is actually opened). The
by its auxiliary contact. At this moment the open pole detector responds to the breaker position and continues to indicate
phase A opened. This indication results in establishing blocking signals for distance elements (
operands are asserted). If neutral and negative-sequence overcurrent elements are mapped into the trip out-
POLE BLK CA
put to trigger single-pole tripping, they must be blocked with the
purpose. The
OPEN POLE BLK N
latter operands block phase distance AB and CA elements, respectively (all zones); the
ground distance AG elements (all zones). As a result, the Z1 OP and Z2 PKP operands that were picked-up reset immedi-
ately. The following distance elements remain operational guarding the line against evolving faults: BG, CG and BC.
The operand initiates automatically a single-pole autoreclose. The autoreclose is started and asserts the
TRIP 1-POLE
operand. This operand keeps blocking the phase selector so that it does not respond to any subsequent events. At the
RIP
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.
The operand is asserted 1.25 cycles following autoreclose initiation. This operand acts as an enabler
AR FORCE 3-P TRIP
for 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 is dependent
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 the reset time would expire at the autorecloser and the
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
GE Multilin
AR1 BLK TIME @ MAN CLOSE
AR1 BLK TIME @ MAN CLOSE
operand, the
TRIP 1-POLE
signal by declaring phase A open by asserting
TRIP PHASE A
signal resets only after the breaker actually operates as indicated
TRIP PHASE A
operand must be assigned through the block setting of the overcurrent element. The two
is still asserted, the request is executed as a three-pole trip.
L90 Line Current Differential System
9.3 SINGLE-POLE TRIPPING
timer is started.
times out and the recloser is enabled, which
operand is asserted. This operand activates the open pole
operand, specifically provided for this
OPEN POLE BLK N
OPEN POLE ΦA OP
AR FORCE 3-P TRIP
OPEN POLE OP
,
OPEN POLE BLK AB OPEN
blocks the
AR
and outputs would
RIP
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