Research And Design Of A New Monitoring Device For DC Insulation

The DC system is mainly composed of battery,charging device,DC feeder panel,DC power distribution cabinet,monitoring device,dbranch feeder and so on,which forms a huge and complex DC power supply network.It provides stable working power for the relay-protection and automation device,circuit breaker operation and accident lighting in the substation,which plays an important role in the safe and reliable operation of the power system.Due to many devices in the substation,complicated feeders and bad operating environment,DC insulation faults such as DC grounding,AC entering DC system,abnormal voltage of battery set will often occur.If it is not found and handled in time,it will lead to serious consequences and bring serious threat to the operation safety of power system.It is particularly important to deploy a fully functional insulation monitoring device for DC system.In view of the fact that the function of DC insulation monitoring device widely used in China is not perfect and the sensitivity of fault detection is not high enough to meet the requirements of substation,this paper proposes a new design scheme of DC insulation detection device which can detect and record DC system faults quickly and accurately.And it can be installed without power outages.Firstly,this paper introduces the basic configuration and equivalent circuit model of DC system.Combining with the parameters of ground resistance and distributed capacitance,the paper analyzes the causes of incorrect operation of relay protection caused by insulation faults such as DC grounding,loop network and AC entering DC system.Secondly,the paper expatiates the design scheme of the new insulation monitoring device from the aspects of device structure,software flow,fault detection principle and hardware design.The device is designed for a discrete structure with convenient installation and flexible expansion.It adopts the combination of balanced bridge and switching bridge and the host computer design of FFT algorithm to deal with voltage sampling signal,which has extremely high fault detection sensitivity.In addition,through the research of small current signal detection technology,the open current transformer with high precision and low zero drift is developed,which is convenient to transform the operation substation.The sensitivity,accuracy and stable operation ability of the new insulation monitoring device are tested,through that the installation,debugging and operation analysis of the new insulation monitoring device in a 220kV substation and a 110kV substation.It is proved that the technical indexes of this device reach the design target,improve the insulation monitoring function of dc system,and lay a solid foundation for the safe and stable operation of power grid.