24
Instruction Book
IB182023EN March 2016 www.eaton.com
AMH-4.76-VR
Replacement Circuit Breaker
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 warning 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 BREAKER.
With the 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 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 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.
Although an AC high potential test is recommended, a DC test
may be performed if only a DC test unit is available, but is not
recommended.
In this case the equipment must be capable of delivering 5
milliamperes for one minute to avoid ambiguity due to field emission
or leakage currents and the test voltage shall be as shown in Table
6.1.
The current delivery capability of 25 mA AC and 5 mA DC apply
when all three VI’s are tested in parallel. If individual VI’s are tested,
current capability may be one third of these values.
WARNING
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.
6.4 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 minimal amount of erosion from the
contact surfaces. 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 vacuum interrupter
assembly must be replaced (Figure 6.1 and 6.2).
The adequacy of contact wipe can be determined by simply
observing the vacuum interrupter side of the operating rod assembly
on a closed breaker. Figures 6.3 and 6.4 show the procedure for
determining the contact wipe. It maybe necessary to use a small
mirror and flashlight to clearly see the “T” shape indicator. If the
wipe is not adequate, the vacuum interrupter assembly (Pole Unit)
must be replaced. Field adjustment is not possible.
WARNING
FAILURE TO REPLACE A VACUUM INTERRUPTER 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 PERSONNEL INJURY.
Vacuum Interrupter Integrity Test Voltage
Breaker Rated Maximum Voltage
AC 60Hz
DC
Up to and including 15.0 kV
27 kV
40 kV
Figurt 6.1. Vacuum Inttrrupttr Showing Contact Erosion
Indicator With Brtaktr Optn
(Shown htrt for clarity purposts only)
Figurt 6.2. Vacuum Inttrrupttr Showing Contact Erosion
Indicator With Brtaktr Clostd
(Indicators art chtcktd only whtn brtaktr is clostd.)
