Instantaneous Element Only - Westinghouse DE-ION DB-75 Instructions Manual

MAINTENANCE
On larger overload currents, the action is
essentially the same as above except that the
moving armature (B) will close completely as
soon as the overload is applied.
armature closes, it compresses spring (C)
which applies a force to diaphragm (D). After
a time delay determined by valve (F), the dia­
phragm movement permits the spring to rotate
(J)
the trip crank f ar enough to trip the
breaker by moving the trip lever (K) .
L arge fault currents cause the instantane­
ous armature (M) to close immediately.
armature lifts the trip crank
delaying action and trips the breaker.
S elective Overcurrent Tripping Device
(Refer to Figure 9A)
For small and intermediate overloads, the
operation of this device is the same as for
the standard overcurrent tripping device.
However, the selective o vercurrent tripping
device operates differently when large fault
currents occur.
When the fault current is large enough to
close the short delay armature (M), the link­
age attached to the armature opens valve (P)
which permits air to enter the diaphragm cham­
ber at a much faster rate than through the
long delay valve (F). Tripping is then accom­
plished by the same means as though a small
overload had occurred.
armature (B) has closed, pulling on the com­
pression spring (C) which is restrained by
diaphragm (D) until sufficient air has entered
valve (P) to permit the spring assembly (C)
(J)
to lift crank and trip the breaker by ro­
tating the trip finger (K) .
A discriminator arm is used on the selective
overcurrent trip units to make the unit behave
as an instantaneous type trip unit while the
breaker is being closed and for a short inter­
val of time after closing.
b � having a discriminator latch connection
between the short delay armature bracket and
the trip crank. When this latch is engaged,
the short delay armature will lift the trip
crank directly if the current is greater than
20
the short delay pick-up setting.
rent does not rise above this value, then the
breaker remains closed and the discriminator
When the arm disengages the discriminator latch so that
the trip unit will then revert to its normal
f unction as one having long and short time
d elay characteristics.
Instantaneous Overcurrent Tripping Device
(Single Element)
This manner to trip the breaker at any time when
(J)
the current rises above the calibrated setting.
without any
T he main armature (B), of Figure 7A, is modi­
fied so that it lifts the trip crank-
trjps the breaker directly.
similar to the instantaneous trip of the stand­
ard overcurrent tripping device.
That is; the main
This is achieved
This device operates in an instantaneous
FIG. lOA - SCHEM ATIC DIAGRAM OF
OVER CURRENT TRIPPING DEV ICE WITH

INSTANTANEOUS ELEMENT ONLY

If the cur­
(J)
and
The operation is
I.B. 35-240-1