13
PowlVac
®
Electrically-Operated Ground and Test Device
IB-65060
The tests described in this section are the only tests
required to determine the insulation integrity. Be-
cause of the design of the PowlVac
®
insulation
system, no valid data can be obtained using other
types of high-voltage insulation tests.
2) Vacuum Integrity
Powell recommends AC testing and reliable verifica-
tion of vacuum integrity. PowlVac
®
38kV ground and
test devices shall be tested with a minimum of
60kVAC applied across fully open contacts for 10
seconds. No dielectric breakdown during the test
period constitutes a successful test.
NOTE: This test does not replace the AC high
potential testing (HIPOT) used to determine “High
Voltage Insulation Integrity.”
Powell offers a compact and lightweight PowlVac
®
Vacuum Integrity Tester designed specifically for
PowlVac
®
circuit breakers. If the test device is used,
refer to the instruction bulletin provided with the
vacuum integrity tester.
Powell recognizes the widespread use of DC hipot
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.
It is not necessary to record the leakage readings
because 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. Only when the vacuum interrupter has
failed both tests should the operation condition be
questioned.
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 to DC leakage current. There is no
significant correlation.
5.
If the ground and test device is stored for any
length of time, it should be inspected periodically
for rust and to ensure it is in good mechanical
condition. Should the ground and test device be
stored under adverse conditions, it should be
cleaned and dried before performing the commis-
sioning tests and before placing the ground and
test device into an energized circuit breaker
compartment.
D. PREPARING THE ELECTRICAL GROUND AND
TEST DEVICE FOR USE
Before shipment from the factory, all functions of the
ground and test device are thoroughly checked.
Powell Electrical Manufacturing Company recom-
mends that prior to each use, the ground and test
device should be thoroughly checked and the follow-
ing tests be performed in the sequence listed below:
1.
High Voltage Insulation Integrity
2.
Vacuum Integrity
3.
Control Voltage Insulation Integrity
4.
Electrical Operation Check
1) High Voltage Insulation Integrity
The primary circuit insulation on the ground and test
device may be checked phase-to-phase and phase-
to-ground using a 2500V insulation resistance tester.
Since definite limits cannot be given for satisfactory
insulation values when testing with an insulation
resistance tester, a record should be kept of the
insulation resistance tester readings, as well as the
temperature and humidity readings. The records
should be used to detect any weakening of the
insulation system from one check period to the next.
To check insulation integrity, the AC high potential
test described below is strongly recommended.
The ground and test device insulation should be
tested with the ground and test device vacuum
interrupter contacts in the closed position. Test each
pole of the ground and test device separately, with
the other 2 poles and the frame grounded. Perform
the field dielectric test described in ANSI Standard
C37.20.2, at the voltage level appropriate for the
equipment. This test should check all primary phase-
to-ground and phase-to-phase insulation.
