GE Industrial Solutions PowerVac with ML-18 or ML-18H Mechanism - Manual (Page 15)

15
individually check each interrupter by connecting the hi-pot
machine “Hot” lead to the primary bus bar and the ground lead
to the load side bus bar. If the machine has a center point
ground, the connections can be made either way. Apply 36 kV
(rms) 60 Hz at 500 vps and hold for 10 seconds. If no
breakdown occurs, the interrupter is in acceptable condition.
After the high potential voltage is removed, discharge any
electrical charge that may be present through the internal
ground of the test machine or by a grounded cable to one of
the phase bus bars.
If a failure of a vacuum bottle should incur during the integrity
test, the test procedure should be reviewed and the pole
piece cleaned. GE failure rate for vacuum bottles is 0.0007 per
field unit.
Note the voltage level at failure on the first test, and retest
the phase pole piece. If the pole piece passes test, the
vacuum bottle is acceptable - STOP
STOP STOP STOP. If the test fails again but
at a higher voltage level than was observed in the first test,
clean the pole piece and retest. If a failure of the integrity test
occurs a third time, consider the vacuum bottle to have lost
vacuum and replace the complete pole piece as described
under Repair of Interrupter Assembly.
CAUTION: MANY DC HIGH POTENTIAL MACHINES ARE
HALFWAVE RECTIFIERS. THIS TYPE OF HIPOT TESTER
MUST NOT
NOT NOT NOT BE USED TO TEST VACUUM INTERRUPTERS.
THE CAPACITANCE OF THE POWERVAC BOTTLES IS VERY
LOW AND THE LEAKAGE IN THE RECTIFIER AND ITS DC
VOLTAGE MEASURING EQUIPMENT IS SUCH THAT THE
PULSE FROM THE HALFWAVE RECTIFIER MAY BE IN THE
NEIGHBORHOOD OF 120 kV WHEN THE METER IS
ACTUALLY READING 40 kV. IN THIS CASE, SOME PER-
FECTLY GOOD BOTTLES CAN SHOW A RELATIVELY HIGH
LEAKAGE CURRENT SINCE IT IS THE PEAK VOLTAGE OF 120
kV THAT IS PRODUCING ERRONEOUS BOTTLE LEAKAGE
CURRENT. IN ADDITION, ABNORMAL X-RADIATION WILL
BE PRODUCED.
Although a AC hi-potential test is recommended for checking
the vacuum integrity, a DC hi-potential test can also be
conducted on the vacuum interrupter. If a DC Hi-potential test
set is to be used, test voltage should not exceed 50kV DC,
and should be applied for 10 seconds. Interrupters must be
cleaned as previously discussed. If failure occurs, reverse the
polarity and retest. If the interrupter passes the second test,
STOP. The interrupter is acceptable. If the interrupter fails the
second test, we recommend a final test with an AC Hi pot
before replacement.
No attempt should be made to try to compare the condition
of one vacuum interrupter with another nor to correlate the
condition of any interrupter to low values of dc leakage
current. There is no significant correlation. After the high
potential voltage is removed, discharge any electrical charge
that may be retained.
An acceptable AC high potential machine is available from: GE
Company, Burlington, Iowa, Catalog Number 282A2610P001.
Acceptable AC high potential machines are:
Hipotronics Model 7BT 60A
Hipotronics Model 60HVT
James G. Biddle Catalog 222060
Phoenix Model 660-10P
Acceptable DC high potential machines are:
Hipotronics Model 860PL
Hipotronics Model 880PL
GE/Programma VIDAR
9.5—Insulation Tests
The primary circuit insulation on the breaker may be checked
phase to phase and phase to ground using a 2500 Volt or
other suitable megohmeter.
Since definite limits cannot be given for satisfactory insulation
values, a record should be kept of the megohmeter readings
as well as temperature and humidity readings. This record
should be used to detect any weakening of the insulation
from one check period to the next. Generally, readings should
equal or exceed 10,000 megohms.
To measure the breaker secondary circuit insulation
resistance, disconnect the motor leads and thread a wire
connecting together all secondary disconnect pins except
#24, the ground pin. The measurement is made by
connecting a 500 Volt megohmeter from the wire to ground.