Influence of air conditioning to voltage sags

Air conditionings, as common household appliances, are widely used in homes. However, in 2023, they caused a significant incident in a southern Chinese city, triggering widespread overcurrent and zero-sequence protection activations in low-voltage residential distribution transformers, resulting in a loss of approximately 10% of the total load. To explore the response characteristics of air conditionings to voltage sags, this paper investigates their physical and electrical models and simulates their behaviour under voltage sag conditions. Relevant experiments were conducted to verify that air conditionings exhibit varying tolerance levels under different operating conditions, with higher sensitivity to voltage sags at high fan speeds. The peak restart current is approximately 3.9 times the normal operating current, potentially causing current overload in the grid after a voltage sag. By estimating the capacity of residential transformer substations, it was found that the restart current of air conditionings could exceed the transformers’ maximum capacity, triggering protection mechanisms and affecting grid stability. This paper highlights the potential threat of voltage sags to residential electrical safety and provides a reference for improving it.