Point-on-wave voltage sag impact on AC contactor sensitivity: a comparative study

Voltage sag is primarily defined by its root-mean-square (rms) magnitude and duration, but the Point-on-Wave (PoW) at which it occurs also plays a crucial role. The sensitivity of AC contactors to voltage sags can significantly impact industrial operations, particularly in petrochemical plants where trip events lead to substantial financial losses. A collaborative study between a major petrochemical company and TNB Energy Services (TNBES) explored the effects of PoW voltage sags on operational AC contactors. Following findings presented at CIRED 2019, further tests were conducted in 2018 and 2021, focusing on different firing angles from 0° to 90° in 15° increments. The results revealed that AC contactors from the older substation exhibited greater variations in immunity levels, suggesting that prolonged operation and aging components contribute to increased sensitivity to voltage sags. Comparing sample results from 2018 and 2021, this study further highlights that PoW variations evolve over time, influencing long-term equipment reliability. Findings reinforce the importance of PoW considerations in voltage sag immunity assessments, particularly for aging industrial equipment.