Loss Of Potential Supervision (Lop) - ABB REL300 Instruction Manual

function uses the torque control approach, as indicated in Figure 3-9 (page 3-33). The GB func-
tion can be disabled by setting the GBCV to the OUT position.
The directional unit is determined by the setting of "DIRU" which can be set to zero sequence
voltage (ZSEQ), dual (DUAL, zero sequence voltage and/or zero sequence current) or negative
sequence (NSEQ, negative sequence voltage and negative sequence current) for polarization
(see 3.4.11, Selectable Ground Directional Unit, ZSEQ / NSEQ / DUAL).
3.4.3

Loss of Potential Supervision (LOP)

The ac voltage monitoring circuit is called loss-of-potential circuit. In order to prevent undesir-
able tripping due to the distance unit(s) pickup on loss-of-potential, the following logic is used:
• (V
AN
This means that the LOPB will be set if any one of the voltages is below 7Vac (without ∆I), or
if the system detects 3Vo without 3Io (or 3I
(loss-of-potential condition satisfies AND-1; output signal of AND-1 starts the 8/0 and 0/500 ms
timers. The timer output will satisfy AND-1C if there is no output from AND-1B. Output signal
of AND-1C will block all the distance unit (Z) tripping paths via AND-2, AND-3, AND-4, AND-5,
AND-6, AND-172 (also blocks AND-191 and AND-187 for Pilot Systems), if LOPB is set at
YES. Although all distance units are blocked for tripping, the ground backup (GB) and high-set
overcurrent units (ITP and ITG) are operative and converted to non-directional automatically.
The LOPB blocking function can be disabled by setting the LOPB functional display at NO po-
sition. The output of the LOP timer will de-energize the alarm 1 (AL1) relay and cause the failure
alarm. If the LOPB is set at "ALL" and LOP condition exists, the relay will block all types of trip
and turns off the "IN SERVICE" LED.
When applying the LOPB to DIST, it is the intent to block all distance units from tripping, should
LOP condition exist. However, under a special system condition (refer to Figure 3-11, Page 3-
35), both circuits are energized without load current; with no source at terminal B, fault at F
where F is near terminal A, Zone 2 relay at terminal B will be blocked by LOP, and may fail to
trip. This is because the relay at B sees no current, and a low voltage condition exists before
circuit breaker A opens. Another special system condition involves two parallel lines with two
symmetrical sources at both ends. For an evolving flashover fault, at a point equidistant from
both terminals, the conventional LOPB logic will block trip, because the first external fault gen-
erates "3V0 and not 3I
ms timers circuit (in Figure 3-10) are for solving these problems. This logic unblocks the LOPB
circuit and provides a 3500 ms trip window for the distance units to trip if the fault current is
detected within 150 ms after LOP has been set up. This logic has no effect on the conditions:
• if ∆I signal occurs ahead of LOP, or
• if LOP and ∆I signals occur simultaneously
NOTE: The LOPB setting detects a blown fuse condition.
The LOPB has three setting values as follows:
<7Vac) or (3Vo>7Vac) and not ∆I or not (3I
or V or V
BN CN
"on the protected line. Logic AND-1A, 1B, -1C, and -1E 150/0, 3500/200
0
O
> IOS) as shown in Figure 3-10 (page 3-34). The
O
I.L. 40-385.7
>IOS)
3-7