Digital Protection Against Arcing Current Faults on the Secondary Side of a Three Phase Power Transformer

This paper discusses challenges in detecting, identifying, and responding to low voltage (<1000V) arcing current faults (ACFs), which can occur on the secondary side of 3$\phi$ medium voltage-to-low voltage power transformers. Secondary side ACFs trigger currents with magnitudes lower than those triggered by conventional faults, thus reducing the ability of medium voltage (MV) side protective devices to detect and respond to such faults. In many cases, the reduced ability to detect and respond to LV side ACFs prolongs the duration of these ACFs, and leads to a significant increase in the incident energy (may exceed acceptable limits). This paper presents an analysis of MV side currents to extract signature information to detect and identify LV side ACFs. The desired LV side ACF signature is extracted as high frequency components that have non-stationary phases. Such frequency components can be extracted using a multi-channel filter bank composed of digital high pass finite impulse response filters, which have linear phase responses. The non-stationary phase approach is tested 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).