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deviations lowers this time band while cor
rection for lesser voltage deviations raises
the time band.
In some cases where cycling loads or
other load conditions produce large voltage
changes of short duration it may be desirable
to increase the damping to obtain longer
time delay and avoid unnecessary tap
changer operation. The time delay may be
increased by decreasing the gap between the
permanent magnet and its keeper. Relays
are shipped set for a damping factor of 1.0.
The magnet keeper is set with its top even
with the 1.0 graduation on the keeper time
multiplier. The magnet engagement setting
is at the 2 .4 graduation on the magnet time
multiplier. This gives a damping factor of
5.3.
Variations in damping factor between 1.0
and 2.4 are obtained by changing the gap
distance between the magnet keeper and the
damping magnet, with the latter set at 2.4.
To increase the damping factor from 1.0 to
2.4, the gap must be decreased. To change
this setting the keeper locking screw must
first be loosened. If, after loosening this
screw, the keeper does not turn easily, re
move the keeper locking screw completely
and check the copper thread protector under
the locking screw to see that it is free.
After making certain that the keeper locking
screw turns easily, a damping factor of 1.0
to 2.4 can be secured by lining up the top of
the magnet keeper with the desired gradu
ation on the keeper time multiplier scale.
Variations in damping factor between
2.4 and 5.3 are obtained by varying the
amount of engagement of the. damping magnet
and disc, with the magnet keeper set at 2.4.
To reduce the damping factor from 5.3 down
to 2.4 this engagement must be decreased to
the position shown in Figure 7. This is done
by loosening the four magnet assembly
mounting screws (See Figure 7) and sliding
the magnet assembly to its new position. A
magnet time multiplier scale is attached to
the permanent magnet to facilitate setting
the magnet engagement. This scale is ref
erenced to the edge of the disc directly above
it. To raise the damping factor after it has
once been lowered, use a reversal of the
above procedure.
CAUTION: The keeper magnet should never be
turned down below the
2.4
graduation. When the
keeper magnet is at or near the
2.4
setting, care
should be exercised to see that mechanical bind
ing does not take place between magnet and disc.
Too close proximity of keeper magnet and disc
could result in overdamping and possible stop
ping of disc moveme nt entirely.
The maximum keeper setting is shown in
Figure 7. After this adjustment has been
completed the locking screw should again
be tightened; but before tightening, be sure
that the piece of copper is still in the hole
so that the keeper adjusting threads will not
be damaged by the keeper locking screw.
The damping factor of any relay as set
may be determined easily by the following
procedure.
1. De-energize the relay.
2. Set 90R scale handle at 105 volts.
3. Set 90L scale handle at 135 volts.
4.
Manually rotate the disk to close
90L contacts.
5. Release the disk and measure the
time to close the 90R contact.
6. Divide the number of seconds meas
ured in step 5 by 5.4. The quotient
is the damping factor for the relay
as adjusted.
7. Move the 90R and 90L scale handles
to the desired limits for voltage band.
Having determined the relay damping
factor, a new curve for relay performance
may be plotted by multiplying the time values
read from the curves in Figure 10 by the
damping factor.
Example:
Assume 10.8 seconds measured in step 5
above. 10.8+ 5.4
=
2, the relay damping
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