Westinghouse DBN-1016 Technical Manual page 23

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CHAPTER l-GENERAl INFORMATION
310
311
312
313
314
315
316
Overcurrent Trip Unit
Yoke Mounting Bolt
Stationary Yoke
329
Scaleplate
'j
~<
330
Upper Annature
*348
*349
350
351
352
353
354
355
356
Spring (Disc)
Spring (Trip)
Crank
Stem Assembly
Lower A"mature
Upper Mounting Bolt
Stationary Yoke .
Spring, Limit
*331 Spring (Instantaneous)
332 Pointer (Instantaneous)
333
Clip
Trip Crank
Link
Lever 334 Screw (Instantaneous)
335
Lever Lower Mounting Bolt
Roller *317
318
*319
320
321
Pin
336 Stationary Yoke
337
Line
Lotch
Spring (L.D. Pickup)
Poinler (L.D. Pickup)
Screw (L.D. Pickup)
Spring (L.D. Dial)
Diol (L.D.)
338 Center Armature
*357
358
359
360
*361
Spring, Latch
Crank
*322
323
324
325
326
327
328
*339 Spring (S.D. Pickup)
340
Pointer (S.D. Pickup)
341
Clip
Lever
Piston
342
Screw (S.D. Pickup)
Spring Piston
Cylinder Valve (L.D. Time)
Screw
*343 Spring (S.D. Volve)
344
Valve (S.D.)
362
363
*364
Pin
345
Bracket
Clip
Diaphragm (Part of
313)
Moulded Cose
346
Screw (S.D. Time)
347
Disc (Reset)
Spring, Follow
*Repair Parts
FIGURE
1-2-10-0vercurrent Trip Device
1-2-1-11 Series Overcurrent Trip
Uni'-
(See Figures 1-2·9 and 1·2.10)
Series overcurrent trip unit provides for
selective protection under three distinct con-
ditions of overcurrent: First, low overcurrents
will trip breaker after LONG DELAY; Second,
moderate overcurrents will trip breaker after a
SHORT DELAY; and third, high overcurrents
will trip breaker INSTANTLY.
Two calibrated long delay pickup settings
are marked on scateplate (329) in amperes (at
approximately 150 and 200% of coil rating). The
long delay time is factory set per Figure 1-2-9.
By turning dial (323) the long delay time can
be approximately halved Or doubled; but is
locked to prevent excessive adjustment. The
short delay piCkup, short delay time, and in-
stantaneous pickup are all fa c tor y set and
sealed. The pickup currents and time delay
are marked on scaleplate.
Figure 1-2-9 shows a typical "Time-Cur-
rent-Curve". The upper line of a given band
shows the MAXIMUM TIME for breaker to
clear the circuit for any given overcurrent.
The lower line shows the MINIMUM time an
overcurrent can exist before returning to nor-
mal without tripping breaker.
The overcurrent trip device is mounted by
bolts (311), (315) and (354) to the pole units.
The stationary yokes (312), (316) and (336) and
the moving armatures (314), (330) and (338)
form a laminated iron loop around the breaker
moving contact arm. Current flow in contact
arm creates a magnetic force between stationary
yokes and the moving armatures in the direc-
tion to pivot armatures clockwise about pin
(318).
When armature (314) rotates, spring (317)
transmits force via lever (353) to stem as-
sembly (313). As stem assembly (313) moves,
projection (A) on link (352) rotates crank (350)
clockwise. Crank (350) via spring (349) and
rivet pin will rotate trip crank (351) to actuate
breaker trip bar. Spring (349) limits force ap·
plied to breaker trip system.
The long delay pickup is adjusted by turn-
ing screw (321) which moves pointer (320) and
lower end of springs (319). Spring (319) holds
down armature (314) unless overcurrent exceeds
calibrated pickup. The rate at which the stem
will rise depends on the vacuum drag on the
diaphragm (327). The diaphragm is part of stem
assembly (313). Valve (324) controls the amount
of
air which can flow into the vacuum chamber.
Turning dial (323) clockwise closes the tapered
long delay orifice. Spring (322) and clip (326)
prevent accidental change in adjustment and
screw (325) prevents excessive intentional ad-
justment.
The instantaneous pickup is factory set by
turning screw (334) which moves pointer (332)
and lower end of spring (331). Spring (331)
will hold down armature (330) until magnetic
attraction of yoke (316) lifts armature. When
1·17