CURRENT BALANCE RELAYS
TYPES IJC52A AND IJC52B
INTRODUCTION
The types UC52A and UC52B relays are used
to protect the exciting winding of regulating trans
formers.
The type UC52A relays consist of three mech
anically separate b u t electrically interconnected
induction disk units mounted in a three unit, single
end case. Each unit consists of a disk actuated by
two U-magnet assemblies.
The disk drives t h e
moving contact. The disk shaft is restrained by a
spiral spring the purpose of which is to hold the
contacts open when the relay is de-energized.
The type UC52B relay is similar to the type
UC52A relay except that it consists of one unit of
the type UC 52A relay mounted in a one-unit, single
end case.
There is a seal-in element mounted on the front
to the left of the shaft of these relays. This element
has its coil in series and its contacts in parallel
with the main contacts such that when the main con
tacts close the seal-in element picks up and seals
in. When the seal-in element picks up, it raises a
target into view which latches up and remains ex
posed until released by pressing a button beneath
the lower left corner of the cover.
The case is suitable for either surface or semi
flush panel mounting and an assortment of hardware
is provided for either mounting. The cover attaches
to the case and also carries the reset mechanism
when one is required. Each cover screw has pro
vision for a sealing wire.
The case has studs or screw connections at
both ends or at the bottom only for the external
connections. The electrical connections between
the relay units and the case studs are made through
spring backed contact fingers mounted in station
ary molded inner and outer blocks between which
nests a removable connecting plug which completes
the circuits. The outer blocks, attached to the case,
have the studs for the external connections, and the
inner blocks have the terminals for t h e internal
connections.
The
relay mechanism is mounted i n a steel
framework called the cradle and is a complete unit
with all leads being terminated at the inner block.
This cradle is held firmly in the case with a latch
at the top and the bottom and by a guide pin at the
back of the case. The cases and cradles are so
constructed that the relay cannot be inserted in the
case upside down. The connecting plug, besides
making the electrical connections between the re
spective blocks of the cradle and case, also locks
the latch in place. The cover, which is fastened to
the case by thumbscrews, holds the connecting plug
in place.
To draw out the relay unit the cover is first
removed, and the plug drawn out. Shorting bars are
provided in the case to short the current transform
er circuits. The latches are then released, and the
relay unit can be easily drawn out. To replace the
relay unit, the reverse order is followed.
A separate testing plug can be inserted in place
of the connecting plug to test the relay in place on
the panel either from its own source of current and
voltage, or from other sources. Or, the relay unit
can be drawn out and replaced by another which has
been tested in the laboratory.
APPLICATION
Regulating transformers, like all power trans
formers, should be provided with differential re
lays to protect against faults within the transform
er. In addition to the differential relays, regulating
transformers require UC current-balance relays
t o protect against faults that might occur in the
exciting winding. Regulating-transformer windings
are usually
10
to
1a
per-cent of the kva capacity of
the main circuit, and therefore their reactance is
such that a fault might occur in the exciting winding
.which would be several times its full-load current,
but not in excess of the normal load current of the
main circuit. Under such conditions the differential
relays will not provide sensitive protection to the
exciting windings. The IJC52A or the UC52B re
lays should be used to protect these windings.
Fig. 5 illustrates the application of one UC 52 A
relay to this type of protection. Similar connections
can be used when three of the UC52B relays are
used except that the relay stud numbers will be dif
ferent.
OPERATING CHARACTERISTICS
The UC 52B relay and each of the three units of
the UC52A relay has two U-magnets. The left-hand
U-magnet coil
(
front view
)
is called the operating
coil as current in it produces torque tending to close
the contacts. The right-hand U-magnet coil is call
ed the restraint coil as current through it produces
torque tending to hold the contacts open.
The percentage ratio of the current in the oper
ating circuit to that in the restraint circuit for pick
up is referred to as percentage slope. The percent
age slope is
1
2
0
%
.
The pick-up characteristics of t h e relay is
shown in Fig. 2. The relay has a minimum pick-up
setting of
3
amperes which is the operating current
required to close the relay contacts when no re
straint current flows.
Thue
•nstrvcliOIII do not purport to cover oil detoils or vorioti0111
in
equipment nor to provide for
rlfi'Y
pouible
contingency to
be
met in connection with insto/lotion, operation or maintenance. Should further information be desired
or
should porticulor problems arise
wllich
ore not covered sufficiently for the purcho-'s purposes, the moffer should
be
referred
to the Genenll flectric c-.
3
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