Westinghouse DK-15, Руководство пользователя

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Type DK- 1 5 and DK-25 Air Circuit Breaker
Characteristics of Thermal-Magnetic Dual Overload
The general arrangement of this attachment is shown in Fig. 3
with inverse time delay characteristics in Fig. 7. The
100%
calibration
setting of the pointer on the scale plate is the normal rating of the trip
unit and that value of current will just trip the breaker in approximately
30 minutes or longer in a normal ambient temperature. Adjustment of the
thumb screw toward the
150%
calibration setting raises the minimum tripping
current in minute steps as desired.
Ambient correction is explained in Fig.
3
as
1%
increase in cali­
bration for each 2°C. rise in temperature. The attachment is calibrated
for 24oc. ambient, but if it is desired to meet the calibration character­
istics of Fig.
5
at 4ooc., for instance, the calibration adjustment should
be set at approximately
108%
for minimum tripping at normal current rating.
The calibration adjustment can therefore be set as close to the
normal running current of the motor as is desired, depending on ambient
temperature, frequency of starting, etc. Complete protection is thus af­
forded under all conditions of operation.
Full details for adjustment and maintenance of the thermal-mag­
netic trip attachment are explained in Fig.
3.
Replacement of Overload Attachments
Both types of overload trip units may be easily removed. From the
rear, take out two screws that fasten the magnet assembly to the main panel
and disconnect the trip unit upper terminal where it is bolted to the main
pole unit shunt section. In the case of drawout studs the finger cluster
and large nut must also be removed. The trip unit may now be removed. Re­
placement is simply the reverse of this procedure.
After the unit is securely mounted to the panel, only one adjust­
ment is necessary for correct operation with the b�eaker. This adjustment
consists of setting the screw in the outer end of the trip armature lever
to properly trip the breaker with a thin spacer between the armature and
magnet, as explained in Figs. 2 and
3.
Electric Closing Mechanism
Electrically operated DK circuit breakers are equipped with an
entirely self-contained motor mechanism (fig. 11) mounted on the right
side of the breaker frame. Two of the toggle linkage pins serve as dowels
to accurately locate the mechanism insulating base. By removing three bolts
this complete assembly can be taken off the breaker without disengaging any
parts except the wiring.
The closing motor is a single phase commutator type, vertical
shaft motor with ball bearings sealed with lubricant that will normally
last the life of the apparatus.
A single reduction of speed between the
motor shaft and the mechanism crank is accomplished with a worm mounted on
the upper end of the motor shaft engaging a worm gear on the crank shaft.
This gear assembly is lubricated on assembly sufficient for several years
of normal service. An oil seal on the motor shaft prevents any oil or
grease from running down into the motor windings.
The motor is designed to develop an exceptionally high torque for
its size, and is therefore rated for intermittent service. If th.e breaker
is closed more frequently than once every 3 minutes for long periods, the
motor may overheat. A centrifugal speed limiting device is built into the
lower end-bell of the motor to prevent excessive speed at normal and over­
voltage, and to prevent coasting of the mechanism after the limit switch
has cut off the motor current.
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