Electrical fast transient tests: applications and limitations

Recent proposals advocate fast-transient tests demonstrating external overvoltage interference immunity. The test waveforms represent electrostatic discharge effects of reignitions occurring during switching sequences. The rationale for requiring the tests is based on the assumption that interfering transients generated by power circuit switching will couple into adjacent power or signal lines, and will then propagate toward susceptible equipment. The authors describe specific measurements conducted for two typical low-voltage power line configurations, namely, a three-conductor line in a steel conduit and a three-conductor cable with a nonmetallic jacket. An attenuation model is proposed that provides a tool for understanding the significance of the line parameters and extends the usefulness of results to general cases. The two line configurations and their models yield similar results for measurements and for computations