HIGH-POTENTIAL, DC PROOF TESTS
62. General.
- High-potential, dc proof tests
are ordinarily limited to 1- minute duration un-
less otherwise specified. It is a pass or fail
type of test and no particular significance is
placed upon current values. The principal
advantage over the more common ac proof
test is the smaller, simpler test apparatus.
less otherwise specified. It is a pass or fail
type of test and no particular significance is
placed upon current values. The principal
advantage over the more common ac proof
test is the smaller, simpler test apparatus.
63. Voltages for High-Potential DC
Tests on Machines.
Tests on Machines.
- High-potential, dc
proof tests for generators, if used in the field,
should be performed in accordance with
Standard Techniques for High-Voltage
Testing, IEEE Standard No. 4, 1978, or its
latest revision. The test voltage values
should be approximately 1.7 times the ac,
rms, voltage values given in table F. ANSI
C50.10 (1977) provides that for ac
should be performed in accordance with
Standard Techniques for High-Voltage
Testing, IEEE Standard No. 4, 1978, or its
latest revision. The test voltage values
should be approximately 1.7 times the ac,
rms, voltage values given in table F. ANSI
C50.10 (1977) provides that for ac
machinery windings rated 6,000 volts and
above, and when agreed upon by the man-
ufacturer and the user, the test voltage may
be a direct voltage of 1.7 times the ac, rms,
test voltage. IEEE No. 95 (1977)
recommends that a ratio of 1.7 be used for
maintenance overvoltage tests.
above, and when agreed upon by the man-
ufacturer and the user, the test voltage may
be a direct voltage of 1.7 times the ac, rms,
test voltage. IEEE No. 95 (1977)
recommends that a ratio of 1.7 be used for
maintenance overvoltage tests.
64. Cables.
- High-potential, dc proof tests
are preferred by manufacturers for tests of
cables. Duration of the test is less critical
than with ac proof tests. For certain tests, a
duration of 5 to 15 minutes is recognized by
the IPCEA (Insulated Power Cable Engineers
Association). For maintenance tests of
cables, it will ordinarily be advantageous to
use the test technique described in
cables. Duration of the test is less critical
than with ac proof tests. For certain tests, a
duration of 5 to 15 minutes is recognized by
the IPCEA (Insulated Power Cable Engineers
Association). For maintenance tests of
cables, it will ordinarily be advantageous to
use the test technique described in
TURN-TO-TURN TESTING
65. General.
- A turn-to-turn fault in a
rotating machine generally results in localized
overheating due to the very high current
developed within the shorted turn. Eventually
the ground insulation is destroyed by the
melting of the copper and a phase-to-phase
or phase-to-ground fault occurs. Testing for
turn-to-turn faults is generally not performed
as a routine maintenance test but is used:
overheating due to the very high current
developed within the shorted turn. Eventually
the ground insulation is destroyed by the
melting of the copper and a phase-to-phase
or phase-to-ground fault occurs. Testing for
turn-to-turn faults is generally not performed
as a routine maintenance test but is used:
a. To establish the quality of the windings
in new machines for warranty purposes;
and
in new machines for warranty purposes;
and
b. To establish the quality of an old
winding for reliability purposes.
winding for reliability purposes.
For more information on turn-to-turn fault
testing, refer to IEEE Standard No. 522,
1977, "IEEE Guide for Testing Turn-to-turn
Insulation on Form-wound Stator Coils for
Alternating-current Rotating Electric
Machines-For Trial Use."
testing, refer to IEEE Standard No. 522,
1977, "IEEE Guide for Testing Turn-to-turn
Insulation on Form-wound Stator Coils for
Alternating-current Rotating Electric
Machines-For Trial Use."
21 (FIST 3-1 12/91)