Shocking electronics

Standards define test impulses, mostly

By Jeff Lind, Compliance West

Electronic products must pass some level of immunity test when subjected to conducted or radiated energy. Some of those tests include subjecting the equipment under test to electrical impulses – short duration single events using defined voltage and current waveforms. Engineers also use impulse tests to verify electrical spacings on PCBs (printed circuit boards) and to periodically check motor-insulation.

Current waveform

Several international standards define impulse waveforms, but only at certain points, in how a voltage or current will rise and fall. The waveform shape, peak voltage, impedance, and application of the pulse vary and depend also on the characteristic of the test object. The test pulse you use depends on the standard you apply because standards define impulses differently.

Waveform Definition

The IEC has at least two International Standards that define impulse tests and their waveforms. Use IEC 60060-1High-voltage test techniques - Part 1: General definitions and test requirements,when testing insulation systems and use IEC 61000-4-5Electromagnetic compatibility (EMC) - Part 4-5: Testing and measurement techniques - Surge immunity test, for switching and lightning-transient tests. Many standards that define testing of specific products reference one or other of these two standards.

In some end-use standards, both the insulation system of the DUT (device under test) and the ability of the device to withstand lightning and switching transients are important. The requirements of IEC 60060-1 and IEC 61000-4-5 are different, so the authors of the end-use standard must decide which standard to reference. A relevant example is IEC 61730-2, the Standard for PV (photovoltaic) panels, which references IEC 60060-1 as its impulse standard definition, which is applicable to insulation systems. In the PV standard, the authors note that the test is, "To verify the capability of the solid insulation of the module to withstand over-voltages of atmospheric origin. It also covers over-voltages due to switching of low-voltage equipment". While this scope would be closer to that of IEC 61000-4-5, the authors elected to conduct the test under the requirements of an insulation impulse test, which they deemed a better definition of their test program.
Jeffrey D. Lind has over 33 years of electrical engineering experience. He launched his career working at UL (Underwriters Laboratories) and then for AtariTM and Sega GremlinTM. In 1997, Lind started Compliance West. He received his Bachelors of Science in electronic engineering from Cal Poly San Luis Obispo.

The full article appeared in Test & Measurement World

Waveform_02 Current waveform
lightning107 Testing insulators using high-voltage current at the NEETRAC facility south of Atlanta (Photo: Gary Meek)
lightning Natural static discharge