IB 6.2.7.7-3I
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on a used breaker with an interrupter nearing
replacement. As the breaker sees service, and
the contacts start to erode, this value will increase.
The following procedure describes how to
determine the Contact Gap
.
The necessary tools
are: an ink pad and a thin flat straight edge with
approximate dimensions should in Figure A9 in
the Appendix. Proceed with the circuit breaker
withdrawn from the compartment.
WARNING
If the circuit breaker has been energized, or it is
unsure if the circuit breaker has ever been
energized, the mid-band ring (on vacuum
interrupters so equipped) must first be discharged
before any work is performed on or near the
interrupters. A grounding stick must be used to
discharge the ring by fastening the ground cable of
the stick to known ground, and touching the
grounding tip of the stick to each mid-band ring.
Contact Gap Check (
See Figure A9).
1. Open the breaker and discharge the
closing springs.
2. The Racking Mechanism must be in either
the DISCONNECT, TEST or CONNECT
position.
3. Apply ink from the Ink Pad to the end of
the Straight Edge.
4. Slide the Straight Edge along the bottom
of the Molded Chair Assembly until the
Straight Edge contacts the Pushrod. This
will be the first of two markings needed.
See Figure A9.
5. Close the breaker and repeat Steps 3 and
4.
6. The Gap is the distance measured
between the two lines. The acceptable
limits are listed in Table A3, located in the
Appendix.
Contact Sequencing (Synchronization)
Before checking contact sequence, verify that the
Contact Wipe and Gap for each pole is correct.
Refer to the subsections "Contact Wipe" and
"Contact Gap". It is not expected that the contact
sequence should exceed the 4 millisecond limit,
therefore, before attempting to readjust, verify that
the test equipment and procedure are correct.
Also consider, especially when testing with
electronic equipment, that multiple 2 millisecond
vacuum interrupter contact bounces are
permissible during normal closing, and these
bounces can influence the contact time
measurements. If there are any questions,
consult the factory.
If it is determined that the contact sequence is not
within 4 milliseconds, adjustment is required.
Usually, readjustment of one pole should be
sufficient so that all three poles touch within 4
milliseconds. The gap of the pole to be changed
should be decreased if the contacts of that pole
are touching after the other two poles, or
increased if the contacts are touching before the
other two poles. The gap is decreased by turning
the Pushrod
clockwise, and increased by turning
the Pushrod counterclockwise, as viewed from the
top of the breaker.
WARNING
Keep hands clear of all moving parts. Serious
injuries can result if a person comes in contact with
breaker parts when the breaker is being opened or
closed, or closing springs are being charged or
discharged. Use extension tools for manipulating
breaker parts.
Before the Pushrod can be turned, the breaker
must be in the Open position, Closing Springs
discharged and the Pushrod Pin removed. See
Figure A9 in the Appendix. With the breaker
Open, the vacuum in the interrupter maintains a
constant upward force of approximately 25 pounds
on the moving contact and Pushrod. Therefore,
before removing pin, the contact must be held
down in the open position by temporary spacers.
After removing the Retaining Ring and Pushrod
Pin, rotate Pushrod as required.
One quarter (1/4) turn of the Pushrod will change
the gap by approximately 0.019" (0.5mm). After
rotating the pushrod, carefully reposition it
vertically to align the holes and the stud. Replace
the pin and retainer and remove the temporary
spacer. During the readjustment procedure, note
that the Contact Wipe and Contact Gap
dimensions must be maintained. The Contact
