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Section 1
An Introduction to Impulse Testing with the MegaPulse series tester
The impulse test is designed to simulate impulse surges which occur in everyday life due to nearby lightning
strikes, switching transients, and other high-frequency faults on the power distribution network. Impulse
testing is the fundamental method for empirical verification of the adequacy of insulation. Other methods of
ensuring adequate insulation (AC or DC Dielectric Withstand testing, measurement of over-surface creepage,
through-air clearance, or distance-through-insulation) are all extrapolated from the results of impulse testing.
The impulse test is performed to ensure that the insulation in question will be able to function properly when
subjected to similar impulse surges in the field.
Safety Precautions
The impulse withstand test can generate voltages in excess of 800V peak at potentially lethal current levels.
Currents of as little as 5 mA at 120 volts can cause death; the MegaPulse can deliver currents of more than
100 Amps peak for a very short time duration. The potential for serious injury or death exists and personnel
should be aware when they conduct this test.
Test Personnel
Personnel require special training to conduct the impulse test. They should understand electrical
fundamentals clearly and be aware that high voltage is adept and creative at completing a path to ground.
Instructions should include a warning against any metal jewelry. Operators should not allow others in the
testing area, especially when tests are being conducted. Organization is to be stressed. The operator should
keep the area free of unused leads and equipment.
Testing Area
The area used for conducting the impulse test should be as remote as possible from normal production line
activities. Only personnel conducting the test should be allowed in the area, and it should be taped or roped
off to preclude casual entry by other employees. In addition, the area should be marked "WARNING - HIGH
VOLTAGE TESTING" or the equivalent to warn others of the nature of the testing taking place.
The bench being used should be non-conductive, and any exposed metal parts should be tied together and
grounded. If a conductive surface must be used, it should be grounded. Because of sparking during an impulse
test failure, it is not safe to conduct impulse testing in combustible atmospheres.
It is imperative that a good ground be provided to the MegaPulse tester. Before connecting the equipment,
ensure that the building wiring provides a low-resistance ground. If the MegaPulse tester is used on a high-
resistance grounding circuit, dangerous high voltages may be present to the operator. In addition, the power
to the Testing Area should be provided with an easily reached shutoff switch which can be actuated by
personnel outside the Area if needed.
CAUTION:
Plug on power cord is disconnect device. The power to the Testing Area should be provided
with an
easily reached shutoff switch
which can be actuated by personnel outside the area if needed.
