51
Instruction Booklet
IB131006EN
Effective March 2019
Instructions for installation,
operation, and maintenance of type
VCP-W vacuum circuit breakers
EATON
www.eaton.com
6.4 Vacuum interrupter integrity test
Vacuum interrupters used in Type VCP-W vacuum circuit breaker
elements 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. Refer to Table 24
for the appropriate test voltage.
During this test, the following warning must be observed.
m
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 13 FEET (4 METERS) AWAY
IN FRONT OF THE BREAKER ELEMENT.
With the breaker element open, connect all top primary studs (bars)
together and to the high potential machine lead. Connect all bottom
studs together and ground them along with the breaker frame. Start
the machine at zero potential, increase to appropriate test voltage
and maintain for one minute.
A successful withstand indicates that all interrupters have a satisfac-
tory vacuum level. If there is a break-down, the defective interrupter
or interrupters should be identified by an individual test and replaced
before placing the breaker in service.
m
WARNING
AFTER THE HIGH POTENTIAL IS REMOVED, AN ELECTRICAL CHARGE
MAY BE RETAINED BY THE VACUUM INTERRUPTERS. FAILURE TO
DISCHARGE THIS RESIDUAL ELECTROSTATIC CHARGE COULD RESULT IN
AN ELECTRICAL SHOCK. ALL SIX PRIMARY TERMINALS AND THE CENTER
RING OF EACH VACUUM INTERRUPTER OF THE CIRCUIT BREAKER SHOULD
BE GROUNDED TO REDUCE THIS ELECTRICAL CHARGE BEFORE COMING IN
CONTACT WITH THE PRIMARY CIRCUIT.
To avoid any ambiguity in the AChigh 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.
ONLY AC HIGH POTENTIAL TESTS ARE RECOMMENDED.
EATON DOES NOT RECOMMEND DC POWER FREQUENCY
WITHSTAND VOLTAGE TEST.
Table 24. Test voltage (insulation and vacuum integrity).
Breaker rated
maximum voltage
Vacuum interrupter integrity test voltage
AC 60 Hz
Up to and including 5 kV
15 kV
7.5 kV - 17.5 kV
27 kV
24 kV and 27 kV
45 kV
The current delivery capability of 25 mA AC and 5 mA DC apply
when all three vacuum interrupters are tested in parallel. If indi-
vidual vacuum interrupters are tested, current capability may be one
third of these values.
m
CAUTION
SOME DC HIGH POTENTIAL UNITS, OPERATING AS UNFILTERED HALF-
WAVE RECTIFIERS, ARE NOT SUITABLE FOR USE TO TEST VACUUM
INTERRUPTERS BECAUSE THE PEAK VOLTAGE APPEARING ACROSS THE
INTERRUPTERS CAN BE SUBSTANTIALLY GREATER THAN THE VALUE READ
ON THE METER.
6.5 Contact erosion and wipe
Since the contacts are contained inside the interrupter, they remain
clean and require no maintenance. However, during high current
interruptions there may be a minimum amount of erosion from the
contact surfaces. Maximum permitted erosion is about 1/8 in.
(3.18 mm). To determine contact erosion, close the breaker and
observe the vacuum interrupter moving stem from the rear of the
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 pole unit assembly must be
replaced (Figures 27 and 28).
The adequacy of contact wipe can be determined by observing the
vacuum interrupter side of the operating rod assembly on a closed
circuit breaker. Figure 29 shows the procedure for determining the
contact wipe. If the wipe is not adequate, the vacuum interrupter
assembly (pole unit) must be replaced. A field adjustment is not
possible. Refer to paragraph 7.3.2 for a replacement procedure.
m
WARNING
FAILURE TO REPLACE A POLE UNIT ASSEMBLY, WHEN CONTACT EROSION
MARK IS NOT VISIBLE OR WIPE IS UNSATISFACTORY, WILL CAUSE THE
BREAKER TO FAIL TO INTERRUPT AND THEREBY CAUSE PROPERTY
DAMAGE OR PERSONAL INJURY.
