6
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 16 KV 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 3500 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 actually 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.
