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25
IB-65020A
Installation
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
disconnecting devices of the circuit breaker
and the metallic mid-band ring, if present,
should be grounded and remain grounded for
at least one minute to reduce this electrical
charge before coming into contact with the
primary circuit.
CAUTION
CAUTION
!
CAUTION
CAUTION
!
Remove all grounding conductors applied
for this test before placing the circuit breaker
back into service.
The tests described in this section are the
only tests required to ascertain insulation
integrity. Because of the design of the
PowlVac® insulation system, no valid data
can be obtained utilizing other types of
high voltage insulation tests.
2) Vacuum Integrity
CAUTION
CAUTION
!
Applying abnormally high voltages across a
pair of contacts in the vacuum, may produce
x-radiation. The radiation may increase with
increased voltage and/or decreased contact
spacing.
The x-radiation, produced during this test with
the voltage specified in Table A and normal
contact spacing, is extremely low and well
below the maximum permitted by standards.
Do NOT apply voltage that is higher than the
recommended value. Do NOT use contact
separation that is less than the normal open
position separation of the circuit breaker
contacts.
Powell recommends AC testing for reliable
verification of vacuum integrity. All
PowlVac CDR 27kV and 38kV circuit
breakers shall be tested with a minimum of
40kVAC applied directly across fully open
contacts for 10 seconds. No dielectric
breakdown during the test period
constitutes a successful test.
Note:
The AC
test does not replace the AC
high potential testing (Hipot) used to
determine “High voltage insulation
integrity.” For more details, see
Ch 4 Installation,
d. p
lAcInG
the
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IrcuIt
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nto
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ervIce
,
1) High
Voltage Insulation Integrity.
Powell offers a compact and lightweight
PowlVac Vacuum Integrity Tester
designed specifically for PowlVac circuit
breakers. If this device is used, refer to
the instruction bulletin provided with the
vacuum integrity tester.