A new technique to improve AC coil contactor switching in presence of voltage sags

Total complaints related to voltage sags are about 80 % of all the complaints due to power quality transients. AC Contactors are designed to disconnect the load or circuit they control when the main power supply is intentionally interrupted. The sensitivity of AC coil contactors to the applied voltage is thus a potentially weak link in industrial processes. This paper shows the test results obtained from extensive laboratory testing carried out on AC coil contactors to voltage sags with variation in value of point on wave angle of voltage sags. The testing was carried out considering various sag magnitudes, durations and point on wave initiation angles of supply voltage waveform. Voltage tolerance curves for AC contactor have been plotted which gives an idea about equipment malfunction for different sag events. This kind of typical equipment sensitivity data might be useful for the future sag assessment methods. Line to line transformer is also suggested for improving AC coil contactor behavior during voltage sags