Effect of time delay of high-speed autoreclosing on variable frequency drives and other loads

Autoreclosings are an important function in feeder protection designed to automatically clear intermittent faults on overhead lines. However, the short interruptions associated with them also impair power quality and may cause malfunction of electrical apparatus and inconvenience to customers. Traditionally, the time delay for high-speed autoreclosing has been set as short as possible, in the range of 0.3...0.5 s, limited mainly by the time required for the deionization of the air on the fault arc path. For many modern loads, such a short delay causes malfunction and even complete halt of the device or system, requiring user intervention before operation may be continued. In this study, laboratory and field measurements were conducted to VFDs, electronically controlled ventilation unit with cooling and domestic refrigerator and freezer units to find an optimal delay for high-speed autoreclosing. The results clearly indicate, that currently used 0.3...0.5 s delay is too short and the optimal time delay would be in the range of 2...5 s.