This paper presents the application of the multiframe digital interconnection protection for cogeneration systems. The multiframe digital interconnection protection is constructed from two frequency main frames; one frame to detect islanding events and the other frame to detect faults on either side of the pointof- common-coupling (PCC). Islanding events are detected based on the wavelet packet transform high-frequency subband, which is extracted from the d-q-axis components of the instantaneous 3f 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 six digital high-pass filters, which are designed to implement six phaselet subframes. The multiframe digital interconnection protection is experimentally tested on a 3.6 kVA cogeneration system for islanding events, different faults on both sides of PCC, and nontransient conditions. Test results demonstrate the ability of the proposed interconnection protection to initiate accurate, fast, and reliable responses to various types of transient disturbances.