ABB REL-300, Instruction Leaflet

Page: 59 / 135

I.L. 40-385.1B
3-14 (5/92)
pole-A, pole B and C close at a later time (refer to
Figure 3-28). If, due to breaker contact asymmetry,
the first breaker contact to close is the one of the
faulted-phase, the zero-sequence (or negative se-
quence) polarizing voltage will initially have a polari-
ty opposite to its fault-derived polarity, the reverse-
looking ground unit could pick-up for a short period,
issue a blocking order, and maintain it for 50 ms con-
sequently, the correct tripping will be delayed. The
Block-the-Block logic would prevent this delaying.
The Reverse-Block logic also includes the reverse
looking Z3P/Z3G units as shown in Figure 3-32.
3.7 3-ZONE DISTANCE PHASE AND GROUND
WITH INDEPENDENT PILOT PHASE AND
GROUND
There are four impedance units per zone: one
phase-to-phase unit and three phase-to-ground
units (see also Section 3.3). The following table
shows the role of each distance unit per pilot zone
scheme.
Distance Units
Scheme Z1P/Z1G Z3P/Z3G PLTP/PLTG
(Reverse)
POTT/
UNBLOCK ---- Key/Trip
PUTT Start Key ---- Trip
BLOCK ---- Start Key Trip and Stop Key
NOTE: Beyond pilot logic functions, Z1P/Z1G
and Z3P/Z3G perform basic Zone 1 and
Zone 3 functions.
3.8 INVERSE TIME DIRECTIONAL OR NON-DI-
RECTIONAL (SELECTABLE)
OVERCURRENT GROUND BACKUP.
(See Section 3.4.2)
3.9 INSTANTANEOUS FORWARD DIRECTION-
AL OVERCURRENT FUNCTION FOR HIGH
RESISTANCE GROUND FAULT SUPPLE-
MENT TO OVERREACH PILOT.
Supplemental protection is provided on overreach-
ing pilot systems to detect high resistance ground
faults. The instantaneous forward directional over-
current ground function (FDOG) works in conjunc-
tion with the pilot ground distance unit. The FDOG
directional unit is determined by the setting of DIRU
(ZSEQ/NSEQ/DUAL). Refer to Section 3.4.11 for
the setting of DIRU. FDOG is supervised by the Iom
setting. A coordination timer FDGT (T/0) is provided
to allow preference for pilot ground distance (mho)
unit operation. The delay time (T) can be set from 0
to 15 cycles in 1 cycle steps. It is recommended to
set the FDGT timer to 3 cycles or longer for security
reasons.
3.10 INSTANTANEOUS REVERSE DIRECTION-
AL OVERCURRENT GROUND FUNCTION.
Similar to FDOG, the instantaneous reverse direc-
tional overcurrent ground function (RDOG) supple-
ments the pilot zone logic.
3.10.1 Supplement to Reverse Z3G Trip.
In the blocking system, RDOG, supervised by IOS,
provides additional ground fault detection (high re-
sistance) beyond what is available by Z3G (reverse
looking) for carrier start.
3.10.2 Carrier Ground Start on Blocking Scheme
In the POTT/UNBLOCK systems, RDOG supervises
PLTG and prevents keying or tripping on reverse
faults.
3.10.3 Weakfeed System Application
For weakfeed applications, an inherent part of the
logic requires reverse fault detection; Z3P/Z3G and
RDOG supply this requirement.
3.11 LOSS-OF-POTENTIAL SUPERVISION
(LOP, See Section 3.4.3)
3.12 LOSS-OF-CURRENT MONITORING (LOI,
See Section 3.4.4)
3.13 OVERCURRENT SUPERVISION (See Sec-
tion 3.4.5)
3.14 INSTANTANEOUS OVERCURRENT TRIP
(See Section 3.4.6)
3.15 HIGH-SET INSTANTANEOUS DIRECT
TRIP, INCLUDING THREE-PHASE AND
ONE GROUND OVERCURRENT UNITS
FOR SPT/3PT APPLICATION (See Section
3.4.6)
3.16 CLOSE-INTO-FAULT TRIP AND STUB BUS
PROTECTION (See Section 3.4.7)