基于热稳定原理的中性点小电阻接地系统间歇接地故障保护

受环境因素及电弧自身燃、熄弧特性影响,间歇接地故障燃弧持续时间常小于保护动作时限,传统接地故障保护难以有效动作.分析小电阻接地系统接地故障特征,并比较出线与中性点零序电流关系,基于接地电阻器在故障期间发热、故障消失后散热的热稳定原理,提出一种中性点小电阻接地系统间歇接地故障保护方法.该方法利用零序电流构造故障期间的发热特征能量,利用热量差构造故障消失后的散热特征能量,发热特征能量越限后保护动作.经仿真与现场录波数据验证可知,该方法不易受故障间隔时间与过渡电阻影响,可作为现有中性点小电阻接地系统的出线后备保护,提高系统运行可靠性.

Intermittent Grounding Fault Protection Based on Principle of Thermal Stability for Low Resistance Neutral Grounded System

Affected by environmental factors and characteristics of arc ignition and extinction, arc duration of intermittent grounding faults is generally shorter than the protection operate time. Therefore, it is difficult for traditional protection to operate effectively. In this paper, characteristics of grounding faults in low resistance neutral grounded systems are analyzed. Then relationships between zero-sequence current of the feeder lines and the neutral point are compared. Based on the thermal stability principle that grounding resistors generate heat during faults and dissipate heat after faults, a protection method is proposed for intermittent grounding faults in low resistance neutral grounded systems. In this method, the characteristic energy of thermal accumulation during the faults is constructed using zero sequence current, and the characteristic energy of thermal dissipation after the faults is constructed using the difference of heat. The protection operates when characteristic energy of thermal accumulation exceeds the operation setting value. It is verified by simulation and field record data that this method is not likely affected by fault interval time and transition resistance, which can be used as backup protection for feeder lines in low resistance neutral grounded systems to improve system operation reliability.