Research On The Earth Potential Interference Of The Substation And Protection Measurements

These years, accidents of secondary cable overburning, secondary equipment misoperation due to inhomogeneous partial potential of earthing network happen frequenly. The essential reason is insulation level and anti-interference ability of secondary system is weak, which is prone to cause accidents in case of improper protection measurement. The earth potential interference due to lightning current and short circuit has already been a major problem that troubles safety and stable operation of secondary equipment in substation, thus it is necessary to research on earth potential interference in substation, propose effective protection measurement.In order to demonstrate damage by earth potential interference to substation secondary system, this paper analyze path, coupling mode of earth potential interference due to lightning current and short circuit. Field test is done on several substation in Changsha and Xinyang, focus on earthing mode of primary and secondary system and adopted protection measurements. Combined with field test data on equipment touch voltage, potential distribution of network and guide circuit of 220kV Shagang substaion in Xinyang, analyze the major problem on anti-interference is voltage sharing of network is imperfect, earthing mode of shielded cable and secondary system is improper, protection for power supply is not enough.Focus on weakness of anti-interference measurement, this paper analyze on methods that could reduce interference. distribution of earth potential due to lightning current and short circuit, together with influence on secondary cable by network current. Proof the validity of theory calculation by lab experiment, search for best measurement that could reduce the influence on secondary voltage due to network current with ATP simulation. Discuss difference earthing modes of shielded cable and secondary system, together with the effects on anti-interference. Besides, experiment is done to argue that the shielded cable should be earthing on control equipment, secondary equipment should adopt equipotential bonding. In view of anti-interference in power supply in secondary system, low-pass filter with piezotransistor is proposed to eliminate interference.It is a comprehensive protection for earth potential in substation, normally, protection methods should be settled from these aspects: voltage sharing, earthing and shielding, so as to improve the anti-interference ability of substation, ensure the safety and stable operation of secondary equipment.