Method for line-ground fault detection in variable frequency drives

An Industrial-Power-Converter-System (IPCS) is a system made up of several power converters, such as Adjustable Speed Drives (ASDs), filters, and reactive power-compensation components. An IPCS requires the ability to accurately detect and isolate electric faults to avoid further compromising the integrity of the system. A rather common type of electric fault is the line-to-ground fault. It can occur either from a phase line to ground or from a winding to ground. Due to the complexity and asymmetry of IPCSs, reliably detecting cable line-to-ground faults is a formidable task. In this paper, challenges and solutions to such challenges are discussed. In [1], advantages of using current signature over voltage signature are discussed. In this paper, a reliable line-to-ground fault detection method based on identifying current signature uniquely linked to the occurrence of the fault is presented. The selected signature greatly reduces nuisance tripping. Furthermore, a simple but powerful method to set a threshold for the selected signature is introduced.