A major concern in trying to detect this condition with a digital
relay is that with frequency and voltage waveshapes not sinusoidal
and at normal system frequency, overvoltage and frequency
measurements will be effected to where the digital relay may not
operate. The measurement of peak overvoltage rather than RMS
provides the best solution to detection of this type of event. IEEE
1547 does not mention the possibility of ferroresonance―another
shortcoming of the standard. An example of a ferroresonance
voltage waveform is shown in Fig. 6 and was taken from field tests
conducted in New York State in the 1980’s.