29
2. After the high-potential voltage is removed,
discharge any electrical charge that may be
retained.
CAUTION:
MANY DC HIGH-POTENTIAL MA-
CHINES ARE HALFWAVE RECTIFIERS. THIS TYPE
OF HI-POT TESTER MUST 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 RECTI-
FIER MAY BE IN THE NEIGHBORHOOD OF 120
KV WHEN THE METER IS ACTUALLY READING
40 KV. IN THIS CASE, SOME PERFECTLY GOOD
BOTTLES CAN SHOW A RELATIVELY HIGH LEAK-
AGE CURRENT SINCE IT IS THE PEAK VOLTAGE
OF 120 KV THAT IS PRODUCING ERRONEOUS
BOTTLE LEAKAGE CURRENT. IN ADDITION, AB-
NORMAL X-RADIATION WILL BE PRODUCED.
The following is a list of acceptable hi-potential
machines.
AC machines: Hipotronics
Model 7BT 60A
Hipotronics
Model 60HVT
Biddle
Cat. 222060
Phoenix
Model 7BT 60A
DC machines: Hipotronics
Model 860PL
Hipotronics
Model 880PL
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.
CAUTION:
DISCONNECT THE SURGE SUPPRES-
SORS BEFORE HI-POTTING THE CIRCUIT
BREAKER.
Since definite limits cannot be given for satis-
factory insulation values, a record should be
kept of the megohmeter readings as well as tem-
perature 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 insu-
lation resistance, with a megohmeter discon-
nect the motor leads and thread a wire connect-
ing together all secondary coupler pins. The
measurement is made by connecting a 500 Volt
megohmeter from the wire to ground.
PowerVac
®
5kV Vertical Lift
Chapter 9. Electrical Checks
This test of the vacuum interrupter will deter-
mine its internal dielectric condition and vacuum
integrity.
CAUTION:
DISCONNECT THE SURGE SUPPRES-
SORS BEFORE HI-POTTING THE CIRCUIT
BREAKER AND VACUUM INTERRUPTERS.
The vacuum integrity test is performed using
an AC hi-potential tester. A vacuum integrity
test of the interrupter is required to insure that
no loss of vacuum has occurred.
With the breaker open, individually check each
interrupter by connecting the hi-pot machine
“Hot” lead to the primary bushing and the
ground lead to the load side bushing. If the
machine has a center point ground, the con-
nections can be made either way.
For the Vacuum Integrity Test, Apply 27 kV (rms)
60 Hz at 500 vps and hold for 10 seconds. If no
breakdown occurs, the interrupter is in accept-
able condition. After the hi-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 bushings.
If a failure of a vacuum bottle should occur dur-
ing 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.
1. Note the voltage level at failure on the first
test, and retest the phase pole piece. If the
pole piece passes re-test, the vacuum bottle
is acceptable. STOP.
2. If the test fails again, but at a higher-voltage
level than was observed in the first test,
clean the pole piece and retest.
3. 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 Inter-
rupter Assembly, Chapter 12.
Although a AC high-potential test is recom-
mended for checking the vacuum integrity, a DC
high potential test can also be conducted on
the vacuum interrupters at 40 kV and held for 10
seconds with the restrictions noted as follows.
1. No attempt should be made to compare the
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.
