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Installation
PowlVac 38™ ARM 3000A Series 4
Vacuum Circuit Breaker
01.4IB.65131
Powell recognizes the widespread use
of DC hipot equipment in the field and
the desire to use this equipment to verify
vacuum integrity. However, the capacitive
component of the vacuum interrupter
during DC testing may yield false negative
test results, which are often misinterpreted
as vacuum interrupter failure. When DC
testing is performed, a test set providing
a full wave rectified 60kVDC hipot voltage
can be applied for 5 seconds as a
“go-no go” test.
Recording the leakage readings is not
necessary, as a dielectric breakdown will
trip all portable DC hipot test sets. If a
DC test breakdown occurs, the test must
be repeated after reversing the DC high
voltage test supply connection across the
vacuum interrupter. A vacuum interrupter
should be questioned only if it has failed
both tests.
When testing with DC, use a DC high potential
test (hipot) set with full wave rectification.
Many DC high potential test sets use
half-wave rectification. Do not use these
half-wave rectifiers. The capacitance of the
vacuum interrupter in combination with
the leakage currents in the rectifiers and
its DC voltage measuring equipment may
result in applying peak voltages as much as
three times the measured voltage. These
abnormally high voltages may give a false
indication of a defective vacuum interrupter
and may produce abnormal x-radiation.
!
CAUTION
If DC high potential testing (hipot) for vacuum
integrity is required, the DC high potential test
machine must not produce instantaneous peak
voltages exceeding 60kV.
!
CAUTION
No attempt should be made to try to
compare the condition of one vacuum
interrupter with another, nor to correlate
the condition of any vacuum interrupter
with low values of DC leakage current.
There is no significant correlation.
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 in
to contact with the primary circuit.
!
WARNING
