Westinghouse DK-15, Manual

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Type DK- 1 5 and DK-2 5 Air Circuit Breaker
The moving arc tip can be removed by taking out the wire clip and
nut on the threaded rod , removing two s mall screws that hold the secondary
shunt to the main contact, and removing the arc tip pin. The s tationary
arc tip may be removed by tald..ng out four flat head screws. The new items
may be replaced in the reverse order. Take care to make p1•oper adjustment
as shown in Figs.
2
and 3, and set all poles of the breaker at one time and
then securely lock each adjusting nut with a wire clip .
The moving main contact mat be removed by taking out the bolts at
the upper end of the trip unit, removing two bolts from the rear that hold
this lower section to the panel, and taking out the pin in the contact arm .
The contact and shunt can now be removed intact and replaced in the reverse
order . The stationary main contact can be removed by taking out two bolts
from the rear of the panel on the fiat stu� or removing the finger cluster,
large contact nut, and one bolt from the rear of the panel on the drawout
type. Replacement is made with a complete new upper s tud.
Adjustment of Toqgle Linkage
The toggle linkage in the
DK
circuit breaker is a serie s of links
so arranged that the c losed breaker load is transmitted through succe s s ive
toggles with a reduction at each step , to the fina.l tripping toggle where a
very low , but c on s i stent , load is maintained with one s imple adjustme nt.
This adjusting screw will be found in the front of the main frame behind the
face plate , as shown in Fig s .
2
a.nd
3 .
This adjustment is set s lightly over
toggle to produce a. light tripping load . The factory adjustment should not
vary in service , but can easily be checked or readjusted by reference to the
sketche s . For this operation, use a small spring bala.nce applied to the left
pole trip finger on the trip bar at a point in line with the plunger. This
2 pound tripping load mus t be maintained to insure proper tripping of the
breaker b y the overload trip units and other calibrated attachments .
Dual Overload Tripping Attachments
The
DK
c ircuit breake r i s s upplied with e ither of two distinct
types of adjustable inverse time de lay trip units : -
( 1 )
oil sucker-magnetic
dual overload , and
( 2 )
thermal-magnetic dual overload . Both type s are suit ­
able for either a-c . or d-e . service .
The oil sucker type of time de lay is
des igned for all standard application where overcurre nt tripping is de sired
with time delay that can be adjus ted to a minimum , approaching zero time if
required . The thermal type of time delay, on the other hand, is for applica­
tions which require unusually long tripping time at relatively large over­
loads , as soeiated with motor starting conditions and protections .
In
both
casea any current in excess of ten times normal rating produce s instantaneous
tripping.
Characteristics of
Oil
Sucker-Magnetic Dual Overload
Fig.
2
shows the arrangement of adjustments on this tripping
attachment, and Fig.
6
repre sents the characteris tic inverse time delay.
The
100%
calibration setting is the normal rating of the trip unit, and
that value of current will just trip t� e breaker with no oil in the pot .
Adjustment of the thumb screw toward the
2 00%
calibration setting raises
the minimum tripping current in minute steps as de sired. Rotation of the
molded pot, properly filled with oil as explained on the drawing , varie s
the time delay between 0 and 100% . Thus, any de sired combination of min­
imum tripping current and time delay can be selected as de sired .
2
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