煤矿电网普遍采用的是中性点不接地工作方式，对电网的绝缘状态进行在线监测，有利于及时发现故障隐患，快速准确地判断故障线路，对提高电网的运行安全和供电可靠性具有重大意义。 本文针对煤矿电网的运行特点，提出了基于附加低频电源的电缆绝缘参数监测方法，即向电网叠加低频信号，通过测量低频电压、低频电流，实现电缆对地绝缘电阻和对地电容的测量。理论分析表明，该方法不仅能检测电缆绝缘参数，而且还可实现绝缘支路故障定位。 采用MATLAB/SIMULINK仿真技术，对分析结果和测量绝缘参数的方法进行了仿真。仿真实验表明，建模及理论分析结果正确；附加低频电源测量绝缘参数的方法可准确的测量对地绝缘电阻和对地电容，测量精度高；不仅能实现分支电缆出线对地绝缘参数的在线监测，还可实现井下电网的选择性漏电保护；导线分布电容大小对测量精度有影响；信号频率的选择直接影响到测量精度。 最后采用附加低频电源法设计以C8051F020单片机为控制核心的检测单元，包括设计系统硬件和软件。给出各个模块的硬件电路和该电路的原理分析，并给出系统软件流程图；设计并实现了低频信号源。 理论分析和仿真实验表明，该测量方法具有测量准确、通用性广的特点，具有良好的工程应用前景。

A method of non-grounded neutral point is widely used in the power system of mine.We can quickly find out the faulty line via the online insulation monitoring system, and it’s important to improve the security of performance and reliability of power system’ s supply. By analyzing the behavior of mine’s power system, a new method based on additional low frequency signal is presented. A low frequency signal is injected into low voltage underground power system. By measuring low-frequency voltage and low-frequency current, insulation parameters can be calculated. And theoretical analysis shows that, this method can not only measure cable’s insulation parameters, but also carry out faulty location of the insulation branch. By MATLAB/SIMULINK simulation technology, analysis result and the method of measuring insulation parameters are simulated. Simulation experiment shows that, modeling and theoretical analysis results are correct, the method of additional low frequency power measuring insulation parameters can exactly measure insulation resistance and capacitance to ground, the measuring accuracy is good, it can carry out not only on-line monitoring ,but also selective leakage protection of underground electric network, the value of distributed capacitor has effect on measuring precision, the selection of signal frequency has direct effect on measuring precision. In the end, the detection unit with C8051F020 as its core and adopting measuring method basing on additional low frequency signal, including hardware and software designs. Each model’s hardware circuit and principle analysis of these circuit is given, and system software flow sheet is also given. Low frequency signal source is designed and realized. Theoretical analysis and simulation results show that the method is accurate, and it can apply to many areas. It has good prospects for engineering applications.