654 D90
PLUS
LINE DISTANCE PROTECTION SYSTEM – INSTRUCTION MANUAL
SINGLE-POLE TRIPPING CHAPTER 15: THEORY OF OPERATION
Trip 1-Pole Input 1
: “GND DIST Z1 OP”
Trip 1-Pole Input 2: “PHS DIST Z1 OP”
By default the POTT scheme issues a single-pole trip. It is assumed that when tripping three
poles both the zone 1 and the POTT initiate three-pole reclosing. This is achieved by making
the following settings:
Trip Reclose Input 1: “POTT TRIP 3P”
Trip Reclose Input 2: “GND DIST Z1 OP”
Trip Reclose Input 3: “PHS DIST Z1 OP”
It is assumed for this discussion that the relay features that are shown on single-pole
operation diagram 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.
Since the line is de-energized, the line pickup element is armed. The recloser presently is
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
Block
Time Upon Manual 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
Block Time Upon Manual Close timer times out and the recloser is
enabled. This asserts the “Enabled” output, informing the trip output element that single-
pole trip operations are 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 in the following sections.
SLG fault scenario for single-pole tripping
An AG fault occurs close to the considered relay. Immediately after the fault, the
disturbance detector (ANSI 50DD) picks-up and activates the phase selector. The phase
selector recognizes an AG fault by asserting its PHASE SELECT AG operand. Ground distance
zone 1 (AG element) responds to the fault. As the fault is close to the relay, phase distance
zone 1 (AB, CA elements) can respond to this fault as well. In any case, a single-pole
operation is requested by zone 1 via the GND DIST Z1 OP or PHS DIST Z1 OP operands.
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. This
operand activates the open pole detector. The latter detector responds to the TRIP PHASE A
signal by declaring phase A open by asserting the OPEN POLE OP ?A operand (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 (the OPEN POLE BLK AB and 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 ?A OP operand blocks the ground distance AG elements (all zones). As a result, the
To Next Page
Loading...
