A new digital relay for loss of grid to protect embedded generation

The authors describe a new digital protection algorithm for detecting loss of grid for a small or medium sized embedded generator operating in parallel with a utility supply which has been shown to operate correctly for loss of grid conditions, during independent operation, and after an out-of-sychronism reclosure with the utility. It also remains stable during severe load fluctuations while operating in parallel with the utility. The algorithm has been formulated to be suitable for an integrated digital protection for an embedded generator. The test platform used to demonstrate practical algorithm operation was similar to that used by commercially available protection relays. Laboratory tests have supported results from computer simulation. These tests also demonstrated the successful operation of the algorithm in the presence of high levels of current and voltage waveform distortion and harmonic interference