I.L. 40-386.4
2-8
2.4.4
Loss of Current Supervision (Figure 2-12)
The ac current monitoring circuit uses IOM and NOT Vo as criterion, as shown. Under ct short
circuit or open circuit condition, IOM and NOT Vo satisfies AND 23; the output signal of AND 23
starts the 10/0.5 second timer. The timer output turns “ON” the non-memory LOI indicator, which
can be displayed in the Metering mode, and operates the Alarm 1 relay (Failure Alarm). If the
LOI condition exists and “LOI Blk” (LOIB) is set to YES, all trip output will be blocked after the
10 second timer times out.
2.4.5
Fault Detector Overcurrent Supervision (Figure 2-13)
For REL301/302, the distance units do not require overcurrent supervision since the relay nor-
mally operates in a background mode, zone-1 and pilot impedance computation will not start
until a phase current or a phase voltage disturbance is detected. This approach minimizes the
load current 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
) supervises
Zone-1ø, Zone-2ø, Zone-3ø and Pilot ø trip functions. This option should not be set to limit
Zone-3 reach, and traditionally should be set above the load current.
For coordination purposes the ground trip units Z1G, Z2G, Z3G, PLTG, and FDOG are super-
vised by the medium set ground overcurrent unit (IOM). The IOS logic and RDOG are used for
carrier send in a Pilot Blocking system (REL302).
2.4.6
Highset Overcurrent Trip (Figure 2-14)
The instantaneous overcurrent units (IAH, IBH, ICH and IOH) are forward directional and set
high to detect those faults which occur in the Zone-1, therefore, their tripping will occur via OR
2 since these trips are classified as high speed trips. These high set trip functions can be dis-
abled by setting the “Inst Ø” (ITP) phase and/or “Inst G” (ITG) ground to “Disabled”. The di-
rectional characteristic of Inst Ø and Inst G will be automatically converted to non-directional
protection if the LOP condition occurs and the setting of “LOP Blk” is “YES” or will be blocked
if “LOP Blk” is “ALL”.
2.4.7
Close-Into-Fault Trip (CIFT Figure 2-15a)
There are three low voltage units (LVA, LVB and LVC) in REL301/302. Each unit senses the
phase voltage condition in the background mode. The units can be set (“Low V”) from 40 to 60
volts, in 1.0 volt steps. For any phase voltage below the set value, the LV logic will produce a
logic “1” output signal. The low voltage units are used in CIFT and the pilot weakfeed logic in
REL302.
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 logic operates as shown in Figure 2-15a. It
includes logic AND 22, 100/180 millisecond and 16/0 millisecond timers. 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, (for 180 ms) after circuit breaker closing (52b
contact opens), then logic AND 22 is satisfied and produces a trip signal. Tripping is classified
as Time Delay Trip, via OR 3, (Figure 2-6, 2-7) which will produce a Reclose Block signal and
a “CIF Trip target”. “CIF Trip” has three setting possibilities: “CIF Trip”, “No CIF Trip” (dis-
able), or “CIF Trip w/Delay” (enable with time delay insertion). The application of close into fault
with time delay, is explained in the following paragraphs.
A modified close into fault logic is employed for the special application shown in Figure 2-15b.
Two relays, “looking” in opposite directions, control a single breaker, share a single 52b input
