I.B. 3A74792H08
Page 37
Effective
09/2014
6-4 VACUUM INTERRUPTER INTEGRITY TEST
Vacuum interrupters used in Type VCP-W and VCP-WR
38kV Vacuum 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. Refer to Table
6.2
for the
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 DE-
CREASE 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 FOUR METERS AWAY IN FRONT OF THE
CIRCUIT BREAKER.
With the circuit breaker open and sitting solidly on the
floor or secured in a fixed position, 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 circuit 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 satisfactory 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
circuit breaker in service.
After the high potential is removed, discharge any
electrical charge that may be retained. 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.
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
6.2.
The current delivery capability of 25 ma ac and 5 ma dc
apply when all three VIs are tested in parallel. If
individual VIs are tested, current capability may be one
third of these values.
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
In order to determine if the contacts have eroded to the
extent that the interrupter must be replaced, close the
circuit breaker and observe the erosion mark on each
operating rod from the rear of the circuit breaker. If the
mark on the interrupter stem is measured to be more
than 12 inches from the base of the interrupter, the
interrupter is satisfactory. If the mark is 12 inches or less,
the interrupter assembly must be replaced (Figures
6-2
and
6-3
).
6-6 CONTACT WIPE
The adequacy of contact wipe can be determined by a
simple measurement of each loading spring indicator
with the circuit breaker closed. Refer to Figures
6-4
and
6-5
and measure the indicator distance shown for each
interrupter. If the measurement taken is in the range of
0.91 to 1.22 inches, the contact wipe is adequate for all
circuit breakers except the following:
380VCP-W32,
2500A
380VCP-W40, 1 200A
380VCP-W40,
2000A
380VCP-W40,
2500A
For these breakers, the contact wipe is adequate if the
measurement taken is in the range of 0.79 to 1.06 inches.
Table 6.2 T est Volt age
Circuit Breaker Rated
Maximum Voltage
Vacuum Interrupter Integrity Test
Voltage
Ac 60 Hz
dc
38 KV rms
60 KV rms
85 KV
Summary of Contents for 380 VCP-W 21
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Page 22: ...Page 16 I B 3A74792H08 Effective 09 2014 Figure 3 7 Typical VCP W 38kV Escutcheon ...
Page 23: ...I B 3A74792H08 Page 17 Effective 09 2014 Figure 3 8 Typical VCP W 38kV Escutcheon ...
Page 33: ...I B 3A74792H08 Page 27 Effective 09 2014 compartment Figure 5 5 Charging Schematic ...
Page 38: ...Page 32 I B 3A74792H08 Effective 09 2014 Figure 5 10 Undervoltage Trip Device Configuration ...
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