I.L. 40-386.3
2-8 (10/94)
AND-23; the output signal of AND-23 starts the 500/500 ms timer. The timer output
turns “ON” the non-memory LOI indicator, which is shown in the Metering mode, and
drops out the AL1 relay (Failure Alarm). If the LOI condition exists and LOI Blk (LOIB)
is set at YES, the trip will be blocked after the 500 ms timer times out.
2.4.5 Fault Detector Overcurrent Supervision
For REL 301/302, as shown in Figure 2-13, the distance units do not require overcur-
rent supervision; because the relay normally operates in a background mode, they will
not start the Zone1 and pilot impedance computation until a phase current or a phase
voltage disturbance is detected. This approach can minimize the load problem when
setting the phase overcurrent units. However in order to meet the traditional practice,
a medium set phase overcurrent unit I
M
(any phase I
AM
, I
BM
, I
CM
) has been added (Ver-
sion 1.1) to supervise Zone1Ø, Zone2Ø, Zone3Ø and Pilot Øtrip functions, as shown
in Figure 2-13. This option should not be set to limit Zone3 reach, and traditionally
should be set above the load current.
For coordination purposes the ground trip units Zone1G (Z1G), Zone2G (Z2G), Zone3G
(Z3G), Pilot G (PLTG), and FDOG are supervised by the medium set ground overcurrent
unit (IoM). The Ios setting and RDOG are used for carrier send in a Pilot Blocking sys-
tem.
2.4.6 Highset Overcurrent Trip
The instantaneous overcurrent units (IAH, IBH, ICH and IOH) are forward directional
and set high to detect those faults which occur in the Zone1, therefore, their tripping
will occur via OR-2 for HST, as shown in Figure 2-14. These high set trip functions can
be disabled by setting the Inst Ø (ITP) phase and/or Inst G (ITG) ground to the OUT po-
sition. The directional unit (Inst Ø and Inst G) will be automatically converted to non-
directional protection if the LOP condition occurs and the setting of LOP Blk = YES and
will be blocked if LOP Blk = ALL.
2.4.7 Close-Into-Fault Trip (CIFT)
There are three low voltage units (LVA, LVB and LVC) in REL 301/302. Each unit sens-
es the phase voltage condition in the background mode. The unit can be set from 40
to 60 volts, in 1.0 volt steps. For any phase voltage below its preset value, the LV logic
will produce a logic “1” output signal. The low voltage units are used in CIFT and weak-
feed logic in REL 301/302.
In order to supplement distance unit operation, when the circuit breaker is closed into
a fault and line side potential is used, the Close-Into-Fault Trip (CIFT) circuit operates
as shown in Figure 2-15. It includes logic AND-22 and 100/180 ms and 16/0 ms tim-
ers. If any overcurrent unit (IAL, IBL, ICL or IOM) operates OR-11, at the same time
as one of the phase voltages (VA, VB,VC) is below the preset level of the LV units, then
logic AND-22 is satisfied and produces a trip signal (for 180 ms) after circuit breaker
closes (52b contact opens). Tripping will be via OR-3, (Figures 2-5, 2-6 and 2-7) with
RB and CIF Trip (CIF) targets.
The application of “Close-into-fault” is selected by setting the value field of CIF Trip to
YES or NO.
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