Westinghouse DK-15, Manual

Page: 74 / 96

Type
DK- 1 5 and DK-25 Air Circuit Breaker
The moving arc tip can b e r emoved by taking out the wire clip and
nut on the threaded rod , removing two small s crews that hold the s e condary
shun t to the main contac t , and r emoving the ar c tip pin . The s tationary
arc tip may be removed by taking out four flat head s crews .
The new i t ems
may be repla ced in the rever s e order . Take car e t o mak e proper adjus tmen t
as shown in Figs . 2 and 3 , and set all poles of the breaker a t one time and
then s e curely l ock each adjusting nut with a wire clip .
The moving main c onta ct may b e removed by taking out the bolts a t
the upper end o f the trip uni t , r emoving two bolt s from the r ear that hold
this lower s ection to the panel, and taking out the pin in the conta ct arm .
The con tact and shunt can now b e r emoved inta ct and r eplaced in the rever s e
order . The s tationary main c onta c t can b e removed by taking out two bolts
fr om the rear of the panel on the flat s tu� or removing the finger clus ter ,
large conta c t nut , and one bol t from the rear of the panel on the drawout
typ e . R eplacement i s made with a c omplete new upper s tu d .
Adjustment of Toggle Linkage
The t oggle linkage in the DK c i rcui t ·breaker is a. s erie s of links
s o arranged that the c l o s ed brea.ker l oad is tra.nsmi tted through suc c e s s ive
t oggles with a reduc t i on at ea.ch s tep , to the final tripp ing toggle where a
very low, but c on s i s t ent , l oad i s ma.inta ined wi th one s imple ad justment .
This ad jus t ing screw will be found in the front of the main fra.me behind the
fac e plate, a s shown in Fig s .
2
a.nd
3 .
Thi s a.d justment is set s light ly over
t oggle to produce a. light tripping load . The fac tory ad jus tment should not
vary in s ervice , but can ea s i ly be checked or read justed by referenc e to the
sketches . For this operation , use a small spring bala.nc e applied to the left
pole tr ip finger on the trip bar at a point in line with the plung e r . This
2 pound tripp ing load mus t be ma.intained to insur e proper tripping of the
breaker by the over load trip units and other ca librated a. t tachment s .
Dual Overload Tripping Attachments
The DK c irc uit bre ake r i s supp l i ed wi th e ither of two dis t inc t
types of ad justab le inver se t ime delay tr ip uni t s : - { 1 ) o i l sucker -magnet ic
dual over load , and { 2 ) thermal-magnet ic dual over load . Both typ e s are sui t ­
able
for either
a-c .
or d -e . serv ic e .
The
oil
sucker type of time delay is
designed
for all standard application where overcurrent tripping is d e s ired
w ith time delay tha t can be ad jus ted to a minimum, approaching zero t ime if
required . The thermal type of time delay, on the other hand , i s for applic a ­
t i ons whi ch r equire unu sually l ong tripping t ime a t relat ively large ove r ­
load s , as soc iated with mo tor s tart ing c ond i t i ons and protec tions .
In
both
cases any current in excess of ten times normal rating pr oduc es ins tantaneous
tripping.
Characteristics of Oil Sucker-Magnetic Dual Overload
Fig .
2
shows the arrangement of adjus tments on thi s tripping
attachment , and Fig . 6 repre s ents the character i s t i c inver s e time delay .
The
100%
cal ibration s e tting is the normal rating of the trip unit , and
that value of current will jus t trip th� breaker with no oil in the pot .
Adjustment of the thumb s cr ew toward the
200%
calibration s e tting rai s e s
the minimum tripping current i n minute s teps a s desir e d . R otation o f the
mold�d pot, properly filled wi th oil as explained on the drawing , varies
the time delay b e tween
0
and
100% .
Thus , any desired combination of min­
imum tripping current and time delay can be s elected as de sired .
2
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