Injected waveforms and their effect on protection element response

The paper is a continuation in a series that identifies more of the developing issues in relay testing - what was once well understood in a protection element's response is today a challenge in testing modern protection systems. Modern algorithms and the complexity of the combined protection element(s) scheme logic creates variable and sometimes unacceptable testing results when compared to manufacturer specifications or other performance criteria. Legacy testing methods and techniques will never yield correct results. The paper compares various types of test waveforms based on test methods used over the past 30 years. Why they are used, when they are effective and for what types of protective elements they are intended. It also compares various protective element responses to the various waveforms of the test methods discussed. This includes overcurrent, directional overcurrent, over/under voltage, frequency elements, distance elements, and differential elements comparing electromechanical, static, and digital relay designs. The paper summarizes these comparisons and explains why great care must be used when choosing a test injection method.