Howard HI-102 Overhead Transformer - Manual (Page 11)

Document 2.4.95, Revision 0
May, 2013
11
Fluid-Filled Overhead Distribution Transformers
Pre-Energization Inspection and Tests
After the transformer has been installed, but be-
fore it is energized, the following tests and checks
should be performed at a minimum to ensure that
the transformer is ready to be energized. The trans-
former should not be energized without successfully
completing these tests and checks.
▲
! DANGER
FAILURE TO FOLLOW THE INSTRUCTIONS
BELOW WILL RESULT IN DEATH OR SERIOUS
PERSONAL INJURY, AND COULD ALSO RESULT
IN DAMAGE TO THE EQUIPMENT .
Be aware of dangerous voltages and avoid
personal contact with live terminals.
▲
! WARNING
FAILURE TO FOLLOW THE INSTRUCTIONS
BELOW COULD RESULT IN DEATH OR SERIOUS
PERSONAL INJURY, AND COULD ALSO RESULT
IN DAMAGE TO THE EQUIPMENT.
• Only qualified personnel with appropriate
equipment should measure transformer
voltages.
• Wear personal protective equipment (PPE)
to prevent injury from potential arc-flash or
contact with dangerous voltages.
• Make sure the transformer is securely and
effectively grounded at all times.
• Current transformer (CT) leads, if present,
must be connected to a metering load or
shorted together and grounded to prevent
dangerous voltages at the CT terminals.
• After successful completion of the
recommended tests and checks, energize the
transformer from a remote location.
1. Ratio Test—Using a transformer turns ratio tester
(TTR), perform a ratio test to verify the primary-
to-secondary winding ratio. The measured
value should be within 0.5% of the voltage ratio
indicated on the transformer nameplate. If the
transformer is provided with high-voltage taps
(or low-voltage taps on step-up/step-down trans-
formers having low-voltage ratings above 600
Volts), measure the ratio at each tap position to
ensure that each of the ratios is correct.
When internal low-voltage windings have been
reconfigured by the user as described above in
“Reconfiguring the Low-Voltage Internal Con-
nections”, the ratio test will confirm that the
transformer has the correct output voltage and
polarity. Follow the instructions and safety pre-
cautions provided by the TTR equipment manu-
facturer. For additional information about ratio
testing, refer to IEEE Standard C57.12.90.
2. Insulation Resistance Test—Perform a 1,000-
Volt insulation test (Megger test) to measure the
resistance of the insulation between windings
and from each winding to ground. Follow the
instructions and safety precautions provided
by the test equipment manufacturer. Prior to
the test, bushings must be thoroughly cleaned
with denatured alcohol to remove any moisture
or contaminants that could influence the test
results. Measured resistance should be at least
1.0 GΩ.
3. Multiple-Voltage Switch Setting—On transform-
ers provided with a multiple-voltage switch,
check the switch setting to make sure it is set
to the correct position and that the locking
screw, if provided, is engaged. When specified,
the multiple-voltage switch may be mounted
internally and accessibly only after removing the
transformer cover or, if provided, the handhole
cover. Before removing the cover or handhole
cover, refer to “Opening the Transformer Tank”
for instructions.
4. Tap Switch Setting—On transformers provided
with taps, check the tap switch setting to ensure
it is set to the proper position for the required
voltage, and that the locking screw, if provided,
is engaged. When specified, the tap switch may
be mounted internally and accessible only after
removing the transformer cover or, if provided,
the handhole cover. For transformers provided
with both taps and multiple-voltage windings,
make sure the tap switch is in the position
indicated on the nameplate when the multiple-
SECTION 4: INSPECTION AND TESTING