Research On Single-phase High Resistance Grounding Protection Method For Low-resistance Grounding Distribution Network

Grounding fault protection is the basic supporting technology to ensure the distribution network equipment and personal safety,which has an important impact on the quality of power supply.With the wide use of the neutral point through the low-resistance grounding method in China’s medium voltage distribution network,the safety problem caused by the large grounding fault current of the low-resistance grounding distribution network(LRGDN)can not be ignored,and good grounding fault protection performance is particularly important..Single-phase grounding fault is the main fault type of LRGDN,and grounding fault protection includes zero-sequence power direction protection and zero-sequence current protection,and is mainly based on zero-sequence current protection.The zero-sequence current protection setting needs to avoid the feeder capacitance current reliably.With the increase of the cable usage of the distribution network,the increase of the feeder capacitance current raises the protection value,and the ability of reflecting the transition resistance is reduced.At present,the research has mainly identified the single-phase high resistance grounding fault by introducing the zero-sequence voltage to construct the protection feature quantity.The complexity of the protection feature increases the difficulty of practical application.The ability to reflect high resistance grounding fault is limited since the influence of the distribution network on the asymmetry of the parameters is not considered.The problem that the single-phase high resistance grounding fault is difficult to be removed effectively is still very prominent.Therefore,this paper analyzes the single-phase grounding fault characteristics of the LRGDN and proposes two single-phase high resistance protection methods.The main contents are as follows:(1)Aiming at the fact that the single-phase high resistance grounding fault characteristics are not obvious and susceptible to the capacitance parameter,a single-phase high resistance grounding protection method based on the zero-sequence power variation is proposed.This method takes into account the influence of the asymmetry of the capacitance parameter and involves voltage parameters,and detects the fault by reflecting the active power of the single-phase grounding transition resistance by the zero-sequence power variation,and has good selectivity.The method has good selectivity,and is less affected by line capacitance current and parameter asymmetry.The ability to identify transition resistance is 7 to 10 times higher than that of zero-sequence current protection.(2)For the zero-sequence current protection,the lack of mutual comparison of the zero-sequence currents of the feeders results in a problem that the setting value is high and the reaction transition resistance is weak.A single-phase high resistance grounding protection method based on zero-sequence current comparison is proposed.This method identifies the single-phase high resistance grounding fault by constructing the ratio of the feeder zero-sequence current to the neutral point branch current.The method does not involve voltage parameters plus its setting calulation is simple,and reflects the same transition resistance capability as the zero-sequence power direction protection.