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edge and a pinion attached to the scale pointer.
This serves to expand the scales and permit in-
creased accuracy of setting.
Stationary break contacts can be provided
when required. These are similar to the make con-
tacts and are mounted on a second rotatable plate
in front of the plate which supports the make con-
tacts. This plate is held in position by spring
pressure, but can be moved to any desired position
with reference to the make contacts. A scale on the
supporting plate for the make contacts is used in
locating the break contacts at a definite position.
Rotation of the make contacts by means of the
scale pointer does not change the spacing between
the make and the break contacts.
INSTANTANEOUS UNIT
This is a small solenoid type unit. A cylindrical
plunger moves up and down on a vertical guide
rod in the center of the solenoid coil. This guide
rod is fastened to the stationary core which in turn
screws into the element frame. A silver disc is
fastened to the moving plunger thru a helical
spring. When the coil is energized, the plunger
moves upward carrying the silver disc which
bridges three conical shaped stationary contacts.
After the contacts close the plunger moves slightly
farther before seating against the stationary core.
This assures positive contact pressure.
A Micarta disc on a threaded bushing is
assembled on the lower portion of the guide rod
and is locked in place by a nut. Its position deter-
mines the de-energized position of the plunger and
therefore the pickup current of the element, as in-
dicated by the graduated scale beside the disc.
OPERATION INDICATOR
The operation indicator is a small solenoid coil
connected in the trip circuit. When the coil is
energized, a spring-restrained armature releases
the white target which falls by gravity to indicate
the completion of the trip circuit. The indicator is
reset from outside the case by a push rod in the
cover or cover stud.
CONTACTOR SWITCH
The dc contactor switch in the relay is a small
solenoid type switch. A cylindrical plunger with a
Courtesy of NationalSwitchgear.com
silver disc mounted on its lower end moves in the
core of the solenoid. As the plunger travels up-
ward, the disc bridges three stationary contacts.
The coil is in series with the main contacts of the
relay and with the trip coil of the breaker. When
the relay contacts close, the coil becomes energized
and closes the switch contacts. This shunts the
main relay contacts, thereby relieving them of the
duty of carrying tripping current. These contacts
remain closed until the trip circuit is opened by the
auxiliary switch on the breaker.
CHARACTERISTICS
The type BL-1 relay is designed for use in
applications where the current transformer ratio is
such that with 100 percent of full load on the
protected machine the relay will receive a current
within the limits of 2.5 to 5.0 amperes. For full
load currents within the range, the relay can be set
to operate in accordance with the characteristic
curves shown in Figs. 5 and 6. Note that there are
three initial current conditions shown in each
figure: O%, 70%, and 100% of pointer setting. The
curves are based upon having the initial current
maintained long enough for the moving contact to
stop moving. Then the current is increased to some
percent of pointer setting to obtain the operating
time.
Since an overload might occur at or shortly
after the time a motor is started, or after a motor
has reached a constant temperature rise while
carrying less than full load, Figs. 5 and 6 show how
the operating time will be affected for a zero initial
load and for a 70 percent initial load. As would be
expected, the operating time is somewhat longer
for these conditions, but the protected motor could
carry the overload longer before reaching a
dangerous temperature.
It will be observed that the curves for the 2.5
and the 3.5 ampere settings diverge somewhat as
the overload increases. The amount of divergence
will not seriously affect any application of the
relay. For full load current settings greater than
2.5 amperes but less than 3.5 amperes, the
operating time at any of the higher values of
overload can readily be obtained by interpolation.
I.L. 41-553.1G
5
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