9-38
L60 LINE PHASE COMPARISON SYSTEM – INSTRUCTION MANUAL
SINGLE-POLE TRIPPING
CHAPTER 9: THEORY OF OPERATION
9
The operation of the scheme in a single breaker arrangement is described as follows. The line is protected by a L60 using
the 87PC, line pickup, and zone 1 phase and ground distance elements. 87PC and/or zone 1 is configured to issue a single-
pole trip when appropriate (
TRIP 1-POLE INPUT-1
: “
GND DIST Z1 OP
,”
TRIP 1-POLE INPUT-2
: “
PHS DIST Z1 OP
”). It is assumed that
when tripping three poles both Zone 1 and 87PC initiate three-pole reclosing. This is achieved by setting
TRIP RECLOSE
INPUT-1
: “
87PC OP
,”
TRIP RECLOSE INPUT-2
: “
GND DIST Z1 OP
,” and
TRIP RECLOSE INPUT-3
: “
PHS DIST Z1 OP
.”
It is assumed for this discussion that the relay features that are shown in the Single-Pole Operation figure have 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
manual-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
AR1 BLK TIME @ MAN CLOSE
timer is started.
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
AR1 BLK TIME @ MAN CLOSE
times out and the recloser is enabled, which
asserts the “Enabled” output, informing the trip output element that single-pole trip operations are now permitted. When
normal 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 as follows.
9.2.1.2 SLG fault
An AG fault occurs close to the considered relay. Immediately after the fault, the disturbance detector (50DD) picks-up and
activates the phase selector. The phase selector recognizes an AG fault by asserting its
PHASE SELECT AG
operand. The line
phase comparison element (ANSI 87PC) and/or ground distance zone 1 (AG element) responds to the 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
operand, the
TRIP 1-POLE
operand is asserted to activate the open pole detector. This
detector responds to the
TRIP PHASE A
signal by declaring phase A open by asserting
OPEN POLE OP FA
(even before it is
actually opened). The
TRIP PHASE A
signal resets only after the breaker actually operates as indicated 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 (
OPEN POLE BLK AB
,
OPEN POLE BLK CA
operands are asserted). If neutral and negative-sequence overcurrent elements are mapped into the trip output to trigger
single-pole tripping, they must be blocked with the
OPEN POLE BLK N
operand, specifically provided for this purpose. The
OPEN POLE BLK N
operand must be assigned through the block setting of the overcurrent element. The two latter operands
block phase distance AB and CA elements, respectively (all zones); the
OPEN POLE FA OP
blocks the ground distance AG
elements (all zones). As a result, the
Z1 OP
and
Z2 PKP
operands that were picked-up reset immediately. The following
distance elements remain operational guarding the line against evolving faults: BG, CG, and BC.
Depending on response times, the actual trip is initiated either by zone 1 or by the line phase comparison element (87PC).
At the moment that the
TRIP 1-POLE
operand is asserted, the phase selector resets and no other trip action can 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 autoreclose is started and asserts the
AR RIP
operand. 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
can respond to a single-line-to-ground fault during open pole conditions.
The 87PC element must be applied according to the Single-pole Tripping Applications section in the Application of
Settings chapter.
