Howard HI-110 Network Transformer - Manual (Page 11)

Document 2.4.128, Revision 2
August, 2012
11
Network Transformer Instruction Manual
BEFORE AND AFTER INITIAL ERGIZATION
Pre-Energization Inspection and Tests
After the transformer has been installed, but before
it is energized, the following tests and checks should
be performed at a minimum to ensure that the
transformer is ready to be energized. Do not energize
the transformer without performing these tests and
checks.
1. Continuity and Winding Resistance Test
Perform a continuity test to confirm
continuity of all windings. Perform a winding
resistance test and compare the measured
values with factory test data. An increase of
more than 10% may indicate a loose internal
connection.
2. Ratio Test
Using a transformer turns ratio (TTR) tester,
perform a ratio test to verify the proper
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, measure the ratio
at each tap position to verify that each of
the ratios is correct. Follow the instructions
and safety precautions provided by the TTR
equipment manufacturer. For additional
information about ratio testing, refer to IEEE
Standard C57.12.90.
3. 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. Insulation resistance should
measure at least 1.0 GΩ.
An insulation resistance test must not
be performed on a wye-wye connected
transformer with an Ho-Xo bushing without
first disconnecting the internal connection
between the primary and secondary neutrals.
This connection can be found on a terminal
FAILURE TO FOLLOW THE INSTRUCTIONS
BELOW COULD RESULT IN DEATH OR SERIOUS
PERSONAL INJURY AND MAY ALSO RESULT IN
DAMAGE TO THE EQUIPMENT.
• Do not energize the transformer using single-
phase switches or fuses. Use only gang-
operated three-phase switches to energize a
three-phase transformer
• Do not energize the transformer if the
primary switch handle is in the “GROUND”
position
• Do not operate the transformer with any of
the primary phases open.
• Only qualified personnel with appropriate
equipment should measure transformer
voltages.
• Wear personal protective equipment to
prevent injury from potential arc-flash or
contact with dangerous voltages.
• Make sure the transformer is properly
grounded at all times.
• Insulated dead-end caps or plugs must be
installed on all unused dead-front high-
voltage bushings. Dust caps must not be
used in place of insulated dead-end caps or
plugs.
• CT leads, if supplied, must be connected
to a metering load or shorted together and
grounded to prevent dangerous voltages at
the CT terminals.
• Do not operate the tap switch while the
transformer is energized from either the
primary or secondary side.
WARNING
SECTION 4: INSPECTION AND TESTING
DANGER
FAILURE TO FOLLOW THE INSTRUCTIONS BELOW
WILL RESULT IN DEATH OR SERIOUS PERSONAL
INJURY AND MAY ALSO RESULT IN DAMAGE TO
THE EQUIPMENT.
Be aware of dangerous voltages and avoid
personal contact with live terminals