GEK-86105
TABLE V
RATINGS OF HIGH DROPOUT INSTANTANEOUS UNIT
PICKUP RANGE
CONTINUOUS
ONE SECOND
RATING (AMPS)
RATING
1
- 4
1.5
35
2
- 8
2.5
75
4
- 16
6
150
7
- 28
10.5
288
10
- 40
15
288
20
- 8 0
25
288
CHARACTERISTICS AND BURDENS
INDUCTION UNIT
The induction unit consists of a conducting disk that passes through the poles of a
permanent magnet and an electromagnet. The disk is free to rotate with a vertically
suspended shaft, but is restrained in one direction by a spring.
When energized
with an alternating current of proper magnitude (set by the tap position), the
electromagnet produces out-of-phase fluxes at its pole faces. These fluxes interact
with induced currents in the disk to produce a torque on the disk.
When this torque
exceeds the restraining force of the spring, the disk begins to rotate at a speed
determined by the magnetic dragging action of the permanent magnet.
A
post attached
to the rotating shaft travels a specific distance (set by the time dial), and makes
electrical contact with a fixed member.
Figure
6
gives the time for the induction unit to close its contacts for various
multiples of pickup current and time dial settings. The time required for this unit
to reset from contact closure to the Number
10
time dial position is approximately
60
seconds.
Burden data for induction unit coils is listed in Table VIa.
The impedance values
are for the minimum tap.
The impedance for other taps at pickup current (tap
rating) varies (approximately) inversely to the square of the current rating.
The
following equation illustrates this:
Impedance of
Any Tap at
:::;
Tap Amps
TARGET/SEAL-IN UNIT
x (Impedance at)
Tap Amps
Minimum Tap
The Target Seal-in units are dual rated according to the values on the tap plate on
the right hand side of the unit.
If the tap selected must be changed, first remove
the connecting plug, then use one screw from the left plate to select the correct
tap. Move the screw from the unwanted tap to the left plate. This will ensure that
the mechanical adjustments will not be disturbed.
Tap screws should never be left
in
both taps at the same time.
6
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