The Development Of Dynamic Intelligent Neutral Grounding Device In Distribution Networks

Reliability and security of distribution network is closely related to the neutral grounding mode.At present,There are two main neutral grounding mode in China’s distribution network: Petersen coil grounding mode and low resistance grounding.When distribution network which neutral point is arc suppression coil grounding occurs single-phase transient ground fault,fault currents can be compensated by Petersen coil,so that the fault residual current is less than the limit value of self-extinction,which makes the insulation of fault point recovery and improves the reliability of distribution network.But when distribution network occurs single-phase permanent ground fault,such as insulated wire paragraphs,etc.,Petersen coil does not make the insulation of fault point recovery so that it has a security problem,but also line selection is difficult because of the small fault residual current.Low resistance grounding can accurately and rapidly select and remove the fault line coordinating with zero-sequence protection,but it will blindly remove fault line no matter single-phase ground fault is permanent or transient,which reduces the reliability of distribution network,and also increases the abrasion of distribution switching device,so that its life drops.Therefore,in order to solve the problems of neutral grounding mode,we have developed a dynamic intelligent distribution network neutral grounding device.Firstly,paper analyzes several major neutral grounding mode of distribution network and separately discusses the advantages and disadvantages.Against the problems of grounding mode,paper proposes that the neutral grounding mode of distribution network should be dynamically changed basing on the nature of the single-phase ground fault.Secondly,basing on this method dynamic intelligent neutral grounding device in distribution network is developed,then the structure of this device is designed and main function and operating principle of this device are explained.At the last,the primary structure,secondary structure and software of device are designed,in which the secondary structure focuses on the control system design,and software design introduces a general flow chart,then the important software modules are explained in detail,which include data acquisition module,Petersen coil control module,troubleshooting module.The prototype of dynamic intelligent neutral grounding devices have been developed complete.prototype was accessed to the real value simulation of 10 k V distribution network we built in our laboratory for capacitive current measuring experiments,automatic tracking and measuring experiment,single-phase ground fault transient experiments and single-phase permanent ground fault experiments.Experimental results show that the device can run stably and reliably,accurately measure capacitive current of distribution network,reasonably handle single-phase transient ground fault and single-phase permanent ground fault in distribution network,has all the basic functions of the design requirements.Dynamic intelligent neutral grounding device combines the advantages of arc suppression coil grounding and low resistance grounding,at the same time it overcomes the disadvantages of both,effectively improving the reliability and security of distribution network.