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Impact of standards on test impulses

Posted: 11 May 2012 ?? ?Print Version ?Bookmark and Share

Keywords:International Electrotechnical Commission? IEC 60060-1? Coupling-Decoupling Network?

Electronic devices should pass some level of immunity tests 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 and to periodically check motor-insulation.

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 varies among standards. The test pulse you use depends on the standard you apply because standards define impulses differently.

Waveform definition
The International Electrotechnical Commission (IEC) has at least two standards that define impulse tests and their waveforms. Use IEC 60060-1, "High Voltage Test Techniques" when testing insulation systems and use IEC 61000-4-5, "Testing and Measurement Techniques〞Surge Immunity Test," for switching and lightning-transient tests. Many standards that define testing of specific products reference either of these two standards because these two standards.

In some end-use Standards, both the insulation system of the device under test (DUT) 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 photovoltaic (PV) 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 overvoltages of atmospheric origin. It also covers overvoltages 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.

IEC 60060-1
IEC 60060-1, the insulation system definition standard, defines a waveform by a rise time, peak value, decay time, and tolerances. These parameters are all that is needed to completely define a voltage or current waveform. Since these insulation tests are conducted on open circuits, this is all that is needed, and IEC 60060-1 notes that the specified waveshape should be delivered to the DUT. Footnotes to Paragrpah 19.2 give guidance should the DUT be capacitive or reactive and allow some deviation in waveform shape and peak voltage in that case. Because the waveform will check an insulation system, no significant capacitance or reactance is anticipated, so no the standards gives no impedance specification. Thus, no current requirement exists in the case of a voltage tester. This may seem to be a problem if the DUT is capacitive, but in our experience raising power offers little improvement in the resulting waveform.

The end-use standard defines peak voltage. Furthermore, these tests are always conducted on equipment that's not connected to mains power or otherwise energized.

IEC 61000-4-5
IEC 61000-4-5, the definition standard for lightning and switching transient testing, defines a waveform by a rise time, peak value, decay time, impedance, and tolerances. Because the tests can be conducted in many configurations, the waveform is judged into an open circuit (voltage waveforms) and/or short circuit (current waveforms). IEC 61000-4-5 specifies only a 2 次, 1.2x50/8x20 combination generator, but by Appendix 2, guidance regarding the tester's impedance is given depending on the location of the test application:

???2 次, mains testing
???12 次, mains to ground testing
???42 次, secondary to ground testing

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