A pilot protection scheme for active distribution networks based on waveform similarity of positive-sequence current fault components

When a fault occurs in distribution networks (DNs) incorporating distributed generation (DG), the fault characteristics markedly differ from those of conventional DNs. As the penetration rate of DG gradually increases, the reliability and sensitivity of traditional three-zone current protection cannot be ensured. In response to the declining performance of traditional protection schemes in active distribution networks (ADNs), a novel pilot protection scheme for ADNs is proposed, based on the waveform similarity of positive-sequence current fault components (PSCFCs). Initially, the amplitude and phase characteristics of PSCFCs at both ends of faulty and non-faulty zones are analyzed when a Motor Type Distributed Generator (MTDG) or an Inverter-Interfaced Distributed Generator (IIDG) is connected to the DN. It is concluded that the phase difference between PSCFCs at both ends of a faulty zone is relatively small, while that of a non-faulty zone approaches 180 degrees, serving as the foundation for constructing the protection action criterion. Subsequently, Kendall's correlation coefficient (KCC) algorithm is employed to assess the waveform similarity of PSCFCs at both ends of each zone. If the KCC is greater than zero, it indicates a high similarity in the PSCFC waveforms at both ends of the zone; conversely, a negative KCC suggests low similarity. To address the issue of reduced waveform similarity at both ends of the faulty zone due to increased transition resistance, an auxiliary criterion is established using the amplitude ratio of PSCFCs at both ends of each zone. When the amplitude ratio exceeds a predetermined threshold, the original KCC is improved using the sgn function and multiplied by an amplification factor to enhance the discrimination in improved KCC values between faulty and non-faulty zones. Utilizing the improved KCC for fault location, if the value exceeds zero, the zone is judged to be faulty; otherwise, it is deemed non-faulty. Finally, simulations validate that the proposed protection scheme is robust against various factors such as fault location, fault type, transition resistance, and white noise, demonstrating high protection reliability.