Study on digital comprehensive protection system based on double CPU for underground high-voltage distribution networks

With the application of arc extinction coil compensation technology for underground HV distribution networks, the selectivity of leakage protection in current comprehensive protection system is affected heavily. On the basis of analyzing the failure law of leakage, the principle of leakage is proposed, which initiate in the zero sequence voltage and act for protection in accordance with the phase of fifth harmonic. At the same time the insulation monitoring, short-circuit, overload protection principles are expounded. In order to satisfy real-time and reliability requirements for the relay protection in HV distribution networks, there are onerous tasks for data acquisition, calculation, display, control, communication and so on. Therefore double CPU comprehensive protection system is designed, which combines DSP with microcontroller. Hardware structure & software block diagrams are introduced as well. Finally, the measuring results are given in this paper. Those results show that the protective system is good practice in stability and reliability.