D-Q-Axis Reference Frame

This paper presents the application of the multi-frame digital interconnection protection for co-generation systems. The multi-frame digital interconnection protection is constructed from two frequency frames, one frame to detect islanding events and the other frame to detect faults on either side of the point-of-common-coupling (PCC). Islanding events are detected based on the wavelet packet transform high frequency sub-band, which is extracted from the d-q-axis components of the instantaneous 3φ apparent powers determined at PCC. The detection of faults, on either side of PCC, is achieved by extracting the magnitudes and phases of the high frequency contents present in PCC currents. The high frequency contents present in PCC currents are extracted by a phaselet filter bank that is composed of 6 digital high pass filters. The multi-frame digital interconnection protection is experimentally tested on a 3.6 kVA co-generation system for islanding events, different faults on both sides of PCC, and non-transient conditions. Test results demonstrate the ability of the proposed interconnection protection to initiate accurate, fast, and reliable responses to various types of transient disturbances.