Performance of an over/under voltage relay at non-sinusoidal conditions

The effects of non-sinusoidal voltages on the performance of an over/under voltage relay were experimentally studied. The frequency and amplitude of individual harmonics were adjusted with a programmable power source and the operating times of the relay are examined. The relation between the harmonic voltages and relay behavior is determined. The measurements show that the relay may operate slower or faster than expected when distorted voltages have third harmonic component.