Damped AC Voltages Partial Discharge Detection System For 35kV Power Cables

The traditional methods to detect cross linked polyethylene(XLPE)include direct current withstand voltage method(DC),very low frequency voltage method(VLF)and power frequency withstand voltage method(AC).But the first two-methods have disadvantages of high test voltage,long test time,and insufficient equivalence with power frequency.AC method can simulate the operation of cable,but it needs a large capacity power supply and the overall volume is big,which is not convenient for on-site test.Damped AC voltages partial discharge detection system(DAC)is a new on-site test to diagnose off-line power cables.Currently,the domestic DAC is mainly used for lOkV cable,and the DAC for 35kV and above cable depended on import.So the paper has developed a DAC for 35kV power cable.The DAC includes solid switch,inductor,controllable high voltage DC source,data acquisition&control system and power cables.The difficulty is how to develop a solid-state switch with synchronous trigger,balanced voltage in series and no partial discharge(PD),it is also essential to design other key parts with small volume and good performance,etc.Firstly,the paper developed a solid-state switch for 35kV DAC using insulated gate bipolar transistors(IGBT)in series.A trigger circuit based on electromagnetic trigger was designed.In order to solve the unbalanced voltage distribution of multistage IGBTs in series,the RCD snubber circuit was designed.Capacitance discharge was used to maintain solid switch conduction,which avoided the electromagnetic interference.Besides,we designed the structure and insulation of high voltage side to ensure the stability and to reduce the volume.The experimental results show that the presented solid-state switch with good synchronization,partial discharge inception voltage higher than 62.5kV and conduction time less than 420ns,meets the practical demand and can be effectively applied in cable damped AC voltages test system.Secondly,the paper designed the other key parts including inductor,data acquisition&control system,the shielding box and component box.The designed system integrated the relevant parts and achieved the voltage isolation,and has a advantage of clear modules,easy assembly and small size,which is easy to transport.Finally,the paper set up a test platform of damped AC voltages detection system in the laboratory,then developed a test software based on LabVIEW and formed a complete detection system.The experimental results verify the effectiveness of system to produce damped AC voltages and detect partial discharge.