MIL-STD-705C
METHOD 302.1b
HIGH POTENTIAL TEST
OBSERVE SAFETY REGULATIONS. The voltages used in this method are
CAUTION:
dangerous to human life. Contact with the leads or the windings under test may
cause severe, and possibly fatal, shock. Arrange the high voltage leads so that
they are not in a position to be accidentally touched. Keep clear of all
energized parts. Always reduce the test voltage to zero and ground the winding
under test before making any mechanical or electrical adjustments on the
equipment. When grounding windings which have been tested, always connect the
connection wire to ground first, and then to the winding. Never perform this test
without at least one other person assisting. The generator frame shall be
securely grounded to the building ground or earth ground.
302.1.1 General. The generator insulation materials must be capable of
withstanding, without damage, voltages higher than rated for definite periods of
time to preclude damage during transient loading and short circuit conditions.
This test should be performed after the equipment is completely assembled so that
damage to the insulation which might have occurred during manufacture and assembly
will be detected.
302.1.2 Apparatus. A variable alternating current, high voltage, current-
limited power source shall be required.
302.1.3 Procedure.
302.1.3.1 Preparation for test.
a.
Adequately ground the high potential apparatus to a solid electrical
ground in accordance with instructions accompanying the apparatus. Also,
connect the main frame of the generator set and all windings of the
generator, not under test, to the same ground.
Unless rectifiers and semiconductors are specifically designed to
b.
withstand the specified test voltage they should be removed or
disconnected from the circuit along with any radio suppression capacitors
prior to conducting the tests.
Raise, or remove, brushes from commutator and slip rings, if applicable.
c.
Isolate the generator power output windings, the generator field windings,
d.
and the exciter armature and field windings if a part of the set. This is
accomplished by disconnecting the various windings from the associated
control circuits or other connections. Static excitation systems feeding
the field excitation from the ac generator shall be tested with all
rectifiers and capacitors disconnectd, unless such rectifiers and
capacitors are designed to withstand the specified test voltage.
Connect the high voltage lead from the test apparatus to the winding or
e.
circuit under test. All other windings and circuits must be securely
connected to ground.
Method 302.1b
1
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