Phaselet-Based Arc Flash Relay Against Low Voltage Side Arcing Current Faults in MV-LV Power Transformers

Arcing current faults (ACFs) are undesired transient events that can occur in different power system equipment, including medium voltage-to-low voltage (MV-LV) power transformers. The main challenge in detecting, identifying, and responding to low-voltage (LV) side ACFs (in a MV-LV power transformer), is due to low magnitudes of MV side currents triggered by a LV side ACF. As a result, MV side protective devices fail to detect and respond to LV side ACFs. In many cases, the reduced ability to detect and respond to LV side ACFs prolongs the duration of LV side ACFs, and leads to a significant increase in the incident energy (may exceed acceptable limits). In this article, an analysis of MV side currents is developed to extract signature information to ensure accurate and fast detection and identification of LV side ACFs. The proposed signature of a LV side ACF is the high frequency components (with non-stationary phases) extracted from MV side currents. Desired frequency components can be extracted using a multi-channel filter bank that is composed of digital high pass filters with linear phase responses. Such digital filters are designed using phaselet functions to ensure a simplified implementation of the desired filter bank. The accuracy and response speed of the proposed approach are utilized for designing a new arc flash relay (AFR) for MV-LV power transformers. The phaselet-based AFR is implemented and tested for a 35 kVA transformer during several transient events including LV side ACFs. Performance results reveal accurate and reliable detection, identification, and response to LV side ACFs with negligible sensitivity to loading level and/or ACF type (series or parallel).