GEH-1768
UNDERVOLTAGE RELAYS
TYPE IAV
INTRODUCTION
Thes e induction-dis k relays are actuated by a potential operating coil on a
laminated U-magnet.
The dis k s haft carries the moving contact that completes the
contact or contacts .
The disk s haft is res trained by a s piral s pring to give the
proper contact-closing voltage, and its motion 1.s retarded by permanent magnets
acting on the disk to give the correct time delay.
The s eal-in unit is mounted to the left of the s haft as s hown in Figure
1.
This unit has its coil in s eries and its contacts in parallel with the main contacts
s o that when the main contacts close, the s eal-in unit picks up and s eals in.
When
the s eal-in unit picks up, it raises a target into view that latches up and remains
exposed until released by press ing a button beneath the lower-left corner of the
cover.
The relays are all mounted in s ingle-unit double-end cases .
The cas e has s tuds
for external connections at both ends .
The electrical connections between the relay
and the cas e are made through s tationary molded inner and outer blocks between which
res t a pair of removable connecting plugs that complete the circuit.
The molded
outer blocks carry the s tuds for the external connections , while the inner blocks
carry the terminals for the internal connections .
The operating coil is connected
in parallel with both the upper and the lower inner molded blocks, and the trip
circuit is connected in s eries with thes e blocks .
In this way, ins ertion of either
the upper or lower connecting plug will energize the operating coil, but the trip
circuit will not be completed until the s econd connecting plug is ins erted.
For
relays that have contacts clos ed when the relay is de-energized but open under
normal operating conditions , the double-connecting-plug feature allows the relay
contacts
to open before the trip circuit is
completed,
thus
mJ.nl.ml.ZJ.ng the
pos s ibility of incorrect tripping when returning the relay to s ervice after tests
and ins pection.
APPLICATION
Thes e relays are protective devices des igned to clos e trip or alarm circuits
whenever the voltage applied to their operating coils des cends to s ome pre
determined value.
The functions are des cribed in greater detail in the following
paragraphs.
OPERATING CHARACTERISTICS
The Type IAV54E relay has a s ingle circuit-clos ing contact that closes when the
voltage is reduced to s ome predetermined value; thus , the contacts are clos ed at
zero
volts .
This
relay
is
a
time undervoltage
relay
with
invers e
time
characteris tics , s hown in Figure 2.
3
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