Research On The On-line Insulation Monitoring System For The Coal High-voltage Cable

Compared with other types of cables,the XLPE cable have a better electrical and thermal performance. More importantly, XLPE cables will not cause fire and explosion,but other cables filled with oil may cause. These excellent features are very appropriate for mine power network, which has special environmental conditions on the underground. Therefore, XLPE cables have been widely used in coal mine power supply system. However, reasons such as rarely be maintained, not be replaced timely and the moisture environment in the mine may lead to the decreasing insulation state of XLPE cables. This decreasing insulation will finally bring about some failures in XPLE cables. It also makes an adverse affect on the safety of mine.In order to solve the problem, this paper uses the partial discharge detection method to monitor the insulation state of the mine cables on-line and give an early warning.This method will reduce the possibility of cable failures. Research of this article includes the following four parts:Firstly, comprehensive analysis and consideration into the environment application of mine high-voltage cables have be taken, so that chose a suitable underground cable online insulation monitoring method. Partial discharge signals are collect from the cable,and then send them to the IPC through the photoelectric conversion. The IPC uses the wavelet threshold de-noising method to processing them and extracts their eigenvalues.Different early warning information and advices are given at the distinct levels of the issue by the look-up table, so as to achieve the purpose of real-time monitoring and early warning of cable’s insulation state.Secondly, in order to ensure the monitoring system is able to extract the partial discharge signal from the XLPE cable, its propagation characteristic in the cable is analyzed in theory. And the simulation result proved the attenuation and reflection characteristics of the partial discharge signal. Some research on predicting the insulation drop point is also done based on the reflected characteristics of the signal. This provides a theoretical foundation in the manufacture of the monitoring system.Thirdly, for the partial discharge signal of the cable is weak and may easily be disturbed by the electromagnetic noise in the mine, a kind of threshold de-noisingmethod based on wavelet analysis has been put forward. The simulation results show that this method used to process the partial discharge signal mixed with noise could achieve a good result. Then, in order to ensure the effectiveness in the practical application, so this method was also used to process the on-site PD signal. The result confirmed the feasibility of this method.Lastly, through the design of hardware and software, the on-line insulation monitoring system device for XLPE cable used in coal mine has been produced successfully. In the laboratory, a preliminary experiment was conducted to prove the device usability, and finally the on-site test in the coal field also reached the expected requirements.