Research On Insulation On-line Monitoring And Fault Line Discrimination Of Ship Distribution System

The ship's power supply system generally adopts a neutral point ungrounded operation mode.When the first single-phase ground fault occurs,the system can maintain normal power supply within a short time.If not resolved in time,it is likely that a phase-to-phase short circuit would occur and damage the ship power supply system.Therefore,on-line insulation monitoring is critical to the continuity and reliability of ship power supply.This paper introduced the research status of on-line insulation monitoring and fault line detection over the world,and analyzed the advantages and disadvantages of the existing insulation on-line monitoring methods.According to the actual working characteristics of the ship's power grid,this paper selected the low-frequency ac injection method to extract the injected signal,calculate the insulation resistance and distributed capacitance,and evaluate the insulation state of the system.For the need of the application,the hardware development and software design of insulation on-line monitoring system were carried out.The simulation software was used to analyze the performance of the low frequency ac injection method.In the insulation on-line monitoring system,low frequency ac injection source,signal acquisition circuit,signal conditioning circuit,A/D conversion circuit,main control unit circuit were designed.Considering that there is a lot of noise interference on the ship's site,a digital filter was added to denoise during the system software design.When measuring insulation parameters,a FIR filter suitable for the system was designed to effectively filter out noise and improve the accuracy and precision of insulation parameter measurement.For fault branch search,an improved wavelet threshold denoising algorithm was proposed to denoise the collected leakage current signal to quickly find the fault branch.Based on MCGS configuration software,the human-machine interface was developed,which makes the monitoring results more intuitive display and more convenient to monitor the insulation state of the system.Through the design of the hardware and software of the insulation monitoring system,a device suitable for the insulation monitoring of ship's power grid was developed.The preliminary test was carried out in the laboratory to verify the practicability of the device.