Effect of point on wave angle on sensitivity of AC coil contactor and SMPS to voltage sags

Total complaints related to voltage sags are about 80% of all the complaints due to power quality transients. 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. Another device recognized as sensitive to voltage sags is switch-mode power supply (SMPS) which provides low voltage dc power to almost every type of computer, control and instrumentation equipment. Line voltage sags shut down and/or damage SMPS with consequent shut down of the equipment connected to it. This paper shows the test results obtained from extensive laboratory testing carried out on ac coil contactors and SMPS of a PC system 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 both the equipment have been plotted which gives idea about equipment malfunction for different sag events This kind of typical equipment sensitivity data might be useful for the future sag assessment methods. A ride through solution is also suggested for improving ac coil contactor behavior during voltage sags.