Ground Directional
Relay Type IBCG
ADJUSTMENTS
TARGET AND SEAL-IN UNIT
When used with trip coils operating on currents
ranging from 0.2 to 2.0 amperes at the minimum
control voltage, the target and seal-in tap screw
should be set the
tap. When the trip
coil current ranges from 2 to 30 amperes at the
minimum control voltage, the tap screw should be
placed in the 2.0 ampere tap.
The seal-in
tap screw is the screw holding
the right-hand stationary contact of the seal-in unit.
To change the tap setting, first remove the connect-
ing plug. Then take a screw from the left-hand sta-
tionary contact and place it in the desired tap. Next,
remove the screw from the other tap and place it
back in the left-hand contact. This procedure is
necessary to prevent the right-hand stationary con-
tact from getting out of adjustment.
CURRENT SETTING
The minimum current at which the time
current unit will close its contacts is determined
by the position of
plug in the tap block. The tap
block
IS
marked amperes, as shown
When the tap setting changed with the relay in
its case, the following procedure must be followed:
(1) remove the connecting plug; this de-energizes
the relay and shorts the current transformer sec-
ondary
(2) remove the tap plug and place
it the tap marked for the desired pickup current.
(3) replace the connecting plug.
The minimum current required to rotate the
disk slowly and to close the contacts
with-
in five per cent of the value marked on the tap plate
for any tap setting and time dial position. this
adjustment has been disturbed, it can be restored by
means of the spring adjusting ring. The ring can be
turned by inserting a screw driver blade in the
notches around the edge. By turning the ring, the
operating current of the unit can be brought into
agreement with the tap setting employed. This ad-
justment also permits any desired setting to be ob-
tained intermediate between the available tap settings.
Test connections for making pickup and time
checks on the time overcurrent unit are shown in
Fig. 13 and Fig. 14. Use a source of 120 volts or
greater with good wave form and constant frequency.
transformers or phantom loads should not
be employed in testing induction relays since their
use may cause a distorted wave form.
SETTING
The operating
of the time overcurrent unit
for any
value of current and tap setting is
determined by the time
setting. This operating
time is inversely proportional to the current magni-
tude as illustrated by the time curves in Figs. 16, 1’7
10
and 18. 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
on the ampere tap as for 50
amperes on the 5 ampere tap, since in both cases,
the current is 10 times tap setting.
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 in-
sure the proper sequence the operation of the
several circuit breakers. Allowance must be made
for the time involved in opening each breaker after
the relay contacts close. For this reason, unless
the circuit time of operation is
there should be a difference of about 0.5 second
(at the maximum current) between relays whose
operation is to be selective.
EXAMPLE OF
The time and current settings of the time
overcurrent unit can be made easily and quickly.
Each time value shown in Figs. 16, 17 and indi-
cates the time required for the contacts to close with
a particular time-dial setting when the current is a
prescribed number of times the current-tap, setting.
In order to obtain any particular time-current set-
ting, insert the removable plug in the proper tap
receptacle and adjust the time dial to the proper
position.
The following example illustrates the
procedure in making a relay setting.
Assume that the breaker is being used a cir-
cuit where the circuit breaker should trip on a sus-
tained current of approximately 450 amperes, and
that the breaker should trip in one second on a short-
circuit current of 3750 amperes. Assume further
that current transformers of
ratio are used.
The current tap setting is found by dividing
minimum primary tripping current by the
transformer ratio.
equals 7.5 amperes.
this case, 450 divided
Since there is no 7.5 ampere
the B-ampere tap is used. To find the proper
time-dial setting to
one second time delay al
3750
divide 3750 the transformer ratio.
This
62.5 amperes
current which
is 7.3 times the &l-ampere setting. By referring to
the time-current curves
16. 17 and 113. it will
be seen that 7.3 times the
operating cur-
rent gives a one second time delay for a No. 3.4
time dial setting on an inverse time relay a No. 5.3
time dial setting on a very inverse time relay and a
No. 10 time dial setting on an extremely inverse
time relay.
The above results should checked by means
of an accurate timing device. Slight readjustment of
the dial can be made until the desired time is
obtained.
Aid in making the proper selection of relay
settings may be obtained on application to the near-
est Sales
of the General Electric Company.
