Ratings; Time Overcurrent Unit - GE IBCG51M*Y1A Series Instruction Manual

Ground directional overcurrent relays
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G[K-49822
15, 16 and 17.
Note that the current values on these curves are given as multiples
of the tap setting.
That is, for a given time-dial setting, the time will be the
same for 80 amperes on the 8 ampere tap as for 50 amperes on the 5 ampere tap, since
in both cases the current is 10 times setting.
If
selective
action
of
two
or
more
relays
is
required,
determine
the
maximum
possible short-circuit current of the line and then choose a time value for each
relay that differs sufficiently to insure the proper sequence in the operation of
the
several
circuit
breakers.
Allowance must be made
for the time involved
in
opening each breaker after the relay contacts close.
The ViA relays contain a Hi-Seismic instantaneous overcurrent unit.
This unit may
be set high to trip directly for faults some distance down the transmission line.
In determining the setting for this unit, it will
be necessary to consider faults
directly behind the relay as well as at the remote terminal, because the unit is
non-directional.
The unit should be set with a suitable amount of margin above the
maximum external fault current.
The effects of transient overreach, as illustrated
in Figure 19, should also be taken into account in determining the setting.
RATINGS
The
IBCG relays described
in this
instruction are available
in
50 and
60
hertz
models.
The TOC
(time overcurrent) units have extended (8-to—i) range similar to
the 800 series IAC relays.
The IOC (instantaneous overcurrent) units, when used
(see Table
I),
have extended
(25—to-i)
range.
Ratings of the operating current
circuits of the TOC, JOC and the directional units are shown individually.
However,
since all operating current circuits are normally connected in series, the operating
coil
ratings of all
units should be considered
in determining the rating of the
entire operating circuit.
TABLE H
ONE SECOND RATING OF TOC UNITS
Relay
Range
One Second
Model
(Amps)
Rating (Amps)
IBCG51M
0.5-4.0
70
IBCG51M(— )V1A
IBCG52M
2.0-16
260
IBCG53M
0.5—4.0
140
IBCG53M(- )Y1A
IBCG54M
1.5-12
260
IBCG77M
0.5-4.0
125
IBCG78M
1.5-12
260
5

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