Westinghouse DK-15, Manual

Page: 23 / 96

•
Type
DK-15
and
DK-25 Air Circuit
Breaker
Undervoltage Tripping Attachment
The undervoltage attachment i.s normally mounted on the main panel
to the left of the breaker. It operates to trip the breaker through the
trip bar if the control voltage drops to a value of
35%
to
60%
of rated
voltage. To check the adjustment of this attachment, remove the voltage
from the holding coils, hold the armature against the magnet by hand, and
close the breaker. Now allow the armature to move slowly away from the
magnet under action of the spring in the flexible link. The breaker should
trip by this dead push. Adjustment to provide this operation is made by
shortening or lengthening the flexible link detail.
When the undervoltage attachment is furnished with a time delay
tripping feature, the oil dash pot should be removed by unscrewing the pot
when the above adjustment is checked. Always connect the undervoltage coils
to the line side of the breaker.
Reverse Current Attachment
The reverse current attachment
(
Fig.
12-13)
is used to trip the
breaker when the direction of current flow in that pole is reversed. The
attachment consists of a magnet energized by a voltage coil and an armature
energized by a current coil in series with one pole of the breaker. When
the series coil current is flowing in the proper direction the armature
tends to rotate but is restrained by a stop. When the series current is re­
versed the armature is rotated in the opposite direction against a spring
to trip the breaker.
This adjustment is calibrated and marked on the scale
plate at
10%, 15%, 20%
and
25%
reverse current, based on normal current
rating.
The reverse current armature is reset after a tripping operation
by opening the voltage coil circuit. This can be accomplished by wiring
the voltage coil through an auxiliary switch on the breaker.
Field Discharge Switch
The field discharge contact
(
Fig.
13-14)
is normally mounted on a
two pole breaker in the space left vacant above the breaker toggle linkage.
Correct adjustment in one direction is evidenced by opening of the switch
contact just prior to the arc tips touching during the breaker closing
motion. Similarly, the switch must make contact before the breaker contacts
part
more
than
178"
during
the opening
motion of the breaker.
Auxiliary Switch
The
DK
auxiliary switch shown in Fig.
9
is a compact molded
assembly supplied in either
4
to 8 pole2 and is rigidly mounted on the side
of the main breaker frame. Each pole consists of two silve r posts in the
sections which carry the terminal screws on the reverse side. The moving
contact is a silver bridging member, spring mounted on the sliding bar, and
with an eccentric rolling motion such that adequate wipi ng action takes
place when the sw itch contact is made
•
The terminal screws are readily accessible on the completely as­
sembled breaker and adequate wiring space is provided from the switch
assembly through wiring holes to the rear of the main panel.
Each four point switch is normally assembled with two 11make11 anP.
two "break" contacts, but any pole may be reversed by removing the sliding
bar and inverting the bridging member, thus making possible any desired ar­
rangement.
5
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