Time Current Characteristics; Maintenance - Westinghouse DE-ION DB-75 Instructions Manual

FIG.
C HARACTERISTICS OF OVERCUR RENT
TRIPPING DEVICE WITH INSTANTANEOUS
Time-Curr ent Charact eristics
STANDARD OVERCURRENT TRIPPING DEVICE
(Refer to Fig. 7B)
The long delay pick-up adjustment c an
change the position of the upper part of the
curve through the r ange indicated by the
number
by changing the tension on the spring which
controls the force the long delay armature
must oyercome in order to close.
The long delay time adjustment can be used
to shift the knee of the curve over the range
indicated by the Number (4).
is changed by turning the knob,
the bottom of the molded calibration box,
which opens or closed the valve to control
the amount of air entering the d i aphragm
chamber.
LB. 35-240-1
ADJUSTMENT
CURRENT MAGNITUDE
108-
TYPICAL TIME-CURRENT
ELEMENT ONLY
(1).
This adjustment is accomplished
This adjustment
TYPE DB-75 DE-ION AIR CIRCUIT BREAKER
PICK-UP The instantaneous pick-up adjustment can
shift the vertical part of the curve to the
l eft or right as indicated by number (2).
This is achieved by changing the spring force
applied to the smaller instantaneous armature.
The flat portion of the curve at the bottom
represents the minimum time for the breaker
to clear when fault currents exceed ten times
the trip unit rating.
S ELECTIVE OVERCURRENT TRIPPING DEVICE
(Refer to Figure 9B)
The time-current characteristic of this
trip unit is the same as the standard device
except that the position of the flat portion
of the curve can be shifted as indicated by
the number (3).
b y changing the setting of the short delay
time on the calibration box.
controls the maximum opening of the short de­
lay valve and thereby controls the tripping
time when currents are high enough to operate
the short delay armature.
Calibration
Overcurrent tripping devices of this gen­
eral type must be calibrated by using a defi­
nite procedure and technique, as well as spe­
cialized equipment.
have access to such equipment, it is highly
recommended that trip units be returned to
the factory if it appears that they need to
be calibrated.

Maintenance

In ordinary use, this trip unit needs very
little maintenance.
dust should be blown off occasionally.
oil or lubricant should be applied to any of
located at
the pins or links.
unit for cleaning purposes. In the event that
major repair work is needed, it is advisable
to return the unit to the factory.
This adjustment can be made
The adjustment
Because few customers
Any accu mulation of
Do not disassemble the
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