Insulation resistance test
Purpose
The purpose of this procedure is to describe the proper
connections and procedure when performing an insulation
power factor test on a voltage regulator.
Required Equipment
●
●
120 V variable power supply
●
●
Cable lead jumper rated for nominal current
●
●
Insulation power factor test equipment
Procedure
WARNING
Hazardous Voltage . This procedure must only be
performed on a regulator that has been removed from
service . Failure to comply can cause serious injury or
death .
1. Remove the unit from service as described in
2. Conduct this test with the regulator located in the
maintenance shop or other suitable location.
otee:
N
The regulator tank must be isolated from ground
potential.
CAUTION
Equipment Damage . When connecting external power to
the voltage regulator control, make sure the polarity of
the power source is correct . Reverse polarity will result
in control damage .
CAUTION
Equipment Damage . Only an AC power supply is to be
used to energize the control externally . Do not use a
DC-to-AC voltage inverter . Failure to comply can cause
excessive harmonics to be generated and result in
damage to the front panel .
3. Place the regulator in the 16 Lower position. Power
the control using an external power source to enable
tap-changer operation. See Service Information
MN225003EN,
CL-7 Voltage Regulator Control
Installation, Operation, and Maintenance Instructions
,
for detailed information on powering the control
externally.
4. Place a jumper, rated for nominal current, tying all the
bushings together.
5. Close
C
knife switch on the back panel.
6. Using the variac on the tester, bring the voltage up to
the desired test level. Refer to the instructions provided
with the test equipment for guidelines on voltage test
levels.
7. Read the test value in mega-ohms; then compare the
reading with the baseline reading:
●
●
If the new reading is
lower than the baseline
reading
, further testing and evaluation of the
insulation is recommended.
otee:
N
This test is very sensitive to contamination on
the regulator bushings.
●
●
If the new reading is the
same as or higher than
the baseline reading
, no further testing is indicated.
Freeing a stalled tap-changer
Purpose
The purpose of this procedure is to free a tap-changer that
has experienced a mechanical jam that prevents operation.
Required Equipment
●
●
Voltmeter
●
●
Terminal-board tool
●
●
Screwdriver (screw-type terminal boards only)
Procedure
1. Confirm that a stall has occurred. If the tap-changer is
stalled between tap positions with the holding switch
closed, a voltmeter placed between terminals
R1
and
G
or
L1
and
G
on the back panel will read approximately
120 Vac. The terminal measuring 120 Vac will be the
direction the tap-changer was moving when stalling
occurred. There will likely be a floating capacitive
voltage in the other direction greater than 120 Vac.
After determining the stall direction, the steps of this
procedure can be used to reverse the direction of the
tap-changer to free the mechanism.
2. Place the
CONTROL FUNCTION
switch in
OFF
position.
3. Place the
POWER
switch in
OFF
position.
4. Close the
C
switch on the back panel of the control.
5. Open the
V1
disconnect switch on the back panel of
the control, removing power from the control.
CAUTION
Hazardous Voltage . The lead terminal “HS” could have
120 V present when disconnected from the terminal
board . Do not touch the lead terminal or allow the
terminal to make contact with any surface . Failure to
comply can cause personal injury or blow a fuse .
6. Disconnect the orange wiring harness lead from the
HS
terminal on the terminal board located on the
back panel; this removes power from the tap-changer
holding switch.
7. Close the
V1
disconnect switch.
8. Place the
POWER
switch on
INTERNAL
.
34
VR-32 and EVER-Tap™ Voltage Regulator
InstallatIon, operatIon, and MaIntenance InstructIons
MN225008EN June 2020
