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6.3 VACUUM INTERRUPTER INTEGRITY TEST
Vacuum interrupters used in Type VR-Series circuit breakers are
highly reliable interrupting elements. Satisfactory performance of
these devices is dependent upon the integrity of the vacuum in
the interrupter and the internal dielectric strength. Both of these
parameters can be readily checked by a one minute AC high
potential test. (See Table 6.1 for appropriate test voltage.) During this
test, the following warnings must be observed:
WARNING
APPLYING ABNORMALLY HIGH VOLTAGE ACROSS A PAIR OF CONTACTS
IN VACUUM MAY PRODUCE X-RADIATION. THE RADIATION MAY
INCREASE WITH THE INCREASE IN VOLTAGE AND/OR DECREASE IN
CONTACT SPACING. X-RADIATION PRODUCED DURING THIS TEST
WITH RECOMMENDED VOLTAGE AND NORMAL CONTACT SPACING
IS EXTREMELY LOW AND WELL BELOW MAXIMUM PERMITTED BY
STANDARDS. HOWEVER, AS A PRECAUTIONARY MEASURE AGAINST
POSSIBILITY OF APPLICATION OF HIGHER THAN RECOMMENDED VOLTAGE
AND/OR BELOW NORMAL CONTACT SPACING, IT IS RECOMMENDED THAT
ALL OPERATING PERSONNEL STAND AT LEAST ONE METER AWAY IN
FRONT OF THE CIRCUIT BREAKER.
WARNING
DC HI-POTENTIAL TESTS ARE NOT RECOMMENDED BY EATON. DO NOT
APPLY DC AT ANY LEVEL TO VR-SERIES POWER CIRCUIT BREAKERS
With the circuit breaker open and securely sitting on the floor,
connect all top/front primary studs (bars) together and the high
potential machine lead. Connect all bottom/rear studs together and
the high potential return lead. Do not ground them to the circuit
breaker frame. Start the machine at zero potential, increase to
appropriate test voltage and maintain for one minute.
Successful withstand indicates that all interrupters have satisfactory
vacuum level. If there is a breakdown, the defective interrupter or
interrupters should be identified by an individual test and replaced
before placing the circuit breaker in service.
After the high potential is removed, discharge any electrical charge
that may be retained, particularly from the center shield of vacuum
interrupters. To avoid any ambiguity in the AC high potential test due
to leakage or displacement (capacitive) current, the test unit should
have sufficient volt-ampere capacity. It is recommended that the
equipment be capable of delivering 25 milliamperes for one minute.
The current delivery capability of 25 mA AC applies when all three
VI's are tested in parallel. If individual VI's are tested, current
capability may be one third of this value.
Circuit Breaker Rated
Maximum Voltage
Up to and including 15.0 kV
Vacuum Interrupter Integrity Test Voltage
AC 60Hz
27 kV
50DH-VR-50AXU / 50XU / 75U / 75ARU - 600 / 1200A
6.4 CONTACT EROSION
Since the contacts are contained inside the interrupter, they remain
clean and require no maintenance. However, during high current
interruptions there may be a minimal amount of erosion from the
contact surfaces. To determine contact erosion, close the circuit
breaker and observe the vacuum interrupter moving stem from
the rear of the circuit breaker. If the mark on each stem is visible,
erosion has not reached maximum value thus indicating satisfactory
contact surface of the interrupter. If the mark is not visible, the
vacuum interrupter assembly must be replaced (Figure 6.1).
WARNING
FAILURE TO REPLACE A VACUUM INTERRUPTER ASSEMBLY WHEN
CONTACT EROSION MARK IS NOT VISIBLE OR WIPE IS UNSATISFACTORY,
WILL CAUSE THE CIRCUIT BREAKER TO FAIL TO INTERRUPT AND THEREBY
CAUSE PROPERTY DAMAGE OR PERSONNEL INJURY.
6.5 CONTACT WIPE
To check contact wipe, close the circuit breaker and observe the
drive insulators from the rear of the circuit breaker (Figure 6.2) Since
the indicator to be observed is in the lower rear portion of each pole
unit assembly, a flashlight should be used. Refer to Figures 6.3 and
6.4 for graphical representations of satisfactory and unsatisfactory
contact wipe conditions. If the identified wipe indicator is observed
to be below the top surface of the drive insulator as shown in Figure
6.3, the contact wipe is satisfactory. If the wipe indicator is observed
to be flush with or protruding out past the top surface of the drive
insulator as shown in Figure 6.4, the contact wipe is unsatisfactory.
The pole unit assembly must be replaced when an unsatisfactory
wipe condition is observed.
Figure 6.1. Contact Erosion Mark Visible on Stem
Instruction Book
IB182012EN March 2017 www.eaton.com
Replacement Circuit Breaker
29
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