Research Of Distributed Insulation Monitoring Device Based On Unbalanced Bridge And Differential Current Detecting Method

The DC system is the operating power in power plants and substations whichinclude signal circuit,protection device, the control loop, automatic devices andautomated systems. The reliability of DC system have a direct impact on thesecurity of power system operation. When one point grounds in DC system, itgenerally will not immediately produce the serious result. However, if there isanother point grounding, may cause the misuse of the signal device, the relaycircuit, and even cause the short circuit of the DC power operation, lead to seriouspower system accident. Therefore, insulation monitoring device is necessary in DCpower system. The insulation monitoring device will set a warning singal whenthere is one point grouding, so as to prevent the power system failure caused by anaccident due to insulation failure.In this paper, several traditional insulation detecting method was compared, anda detailed analysis of their advantages and disadvantages was given. On this basis,the method used by the device was proposed--that is combining the unbalancedbridge with differential current method.The highlights of the paper are the formulasto detect the grounding resistance to positive bus and negtive bus and algorithm ofthe grounding resistance of each branch under different circumstances; the designprinciple of the entire device system, and introducing insulation monitoring devicesfrom two aspects of the hardware and software.Distributed DC system insulation monitoring device includes the test unit, themonitoring unit, the LCD module and the keyboard unit. This article focuses on themicro-controller, the voltage acquisition circuit and the switch control circuit, theamplifier circuit, LCD circuits and so on.The design contains flowchart, softwaredesign and analysis of the experimental results.