For problem of difficult line selection caused by small current of fault line with uncertain direction when single-phase grounding fault happens in resonant grounding system, the paper theoretically analyzed change law of zero-sequence voltage and zero-sequence current at the time of single-phase grounding fault. It built simulation model of small current grounding system in Matlab and did simulation analysis of isolated neutral system and resonant grounding systems under conditions of full compensation, over compensation and under compensation separately. The simulation analysis result was the same as the theoretical one. Finally it got conclusions, namely when single-phase grounding fault happens, isolated neutral system can use line selection methods based on steady state component of amplitude and direction while resonant grounding system cannot, and the both systems can use the same line selection method based on transient state component.

For the deficiency of single line selection principle, the paper proposed integrative line selection strategy, namely zero sequence admittance method, zero sequence susceptance increment method and zero sequence conductance method based on steady-state fault component, mutual integral of transient current based on transient-state fault componet. A line selection device for small current single-phase grounding fault was developed based on the above method. The line selection device can select different line selection algorithm according to different neutral grounding through keyboard, and realize integrative line selection based on steady-state and transient grounding fault. The experiment result showed that the line selection device is effective for high impedance grounding fault and arcing grounding fault.

The reason that existing mine HV explosion-proof switches fail to operate or operate incorrectly which are influenced by stray interference signal is analyzed in this paper.Then improved Fourier algorithm which can realize filtering decaying DC component is derived.It puts forward time-sharing amplitude AC cable monitor wire protection principle with the terminal connected to a resistor based on this algorithm.It's proved by theoretical analysis,experiment and operation that this method is preferable to filter DC and decaying DC signal and stray current of frequency division,power frequency and high-frequency,especially can absolutely filter interference signal of the same frequency with additional AC.This method supplies new thoughts to improve the precision of monitor wire protection.

由于煤矿高压电网中性点接地方式的改变,造成井下高压防爆开关的漏电保护在应用中存在不少误动和拒动现象,详细分析了漏电故障时各开关所测零序分量的特征和造成原有漏电保护不准确的原因。提出了根据中性点接地方式的不同采用分类漏电保护的新方法,该方法构成的高压综合保护装置通过实验和运行表明,提高了漏电保护动作的准确性。

Based on the analysis of leakage characteristic of different neutral grounding modes in mine low-voltage electric network,advantages and disadvantages of different grounding modes are compared in detail from the aspects such as contact current of person and leakage protection,and the conclusion that neutral grounding by high resistance or reactance series high resistance is much more preferable to mine low-voltage electric network is derived.In allusion to characteristic of neutral grounding mode above,the application of zero-sequence conductance in mine low-voltage electric network selective leakage protection is discussed,and the superiority such as the accuracy in leakage protection action and setting easily is analyzed.The stability of operating value and quick-activity in the leakage protection of addition DC power are improved by communication lockout and comparative method.The efficiency of the above method is proved by experiment.

Using wavelet analysis to realize single-phase grounding protection is easy to produce misjudgement and missed sanction and the method using magnitude and direction of transient component to realize single-phase protection needs calculate frequency and phase of transient component accurately.To solve above problems,the paper proposed a single-phase grounding protection method that needs not zero-sequence voltage transient component and needs not calculate frequency and phase of transient component combing with lots of experiment data of simulated arcing fault of 6 kV power networks and analyzed implementation principle of the method in details.The experiment result showed that the method has simple calculation,no filtering and higher accuracy.

The paper introduced a design scheme of intelligent protection device of magnetic starter based on W79E834,expounded design of hardware and software,implementation of protection function of the device.The device has protection functions such as short circuit,over-current,phase failure,earth leakage lockout and energy metering.The device has run in some coal mine and its result of field running showed that the device solves many problems existing in the simulation protection devices of coal mine,such as low precision,easy to fail and no energy metering,and so on,which realizes intellectualization and digitization of small flame-proof switch.

Based on the four output-leg topology of a three-phase to two-phase ac-ac matrix converter,two line voltage synthesis strategy was developed.The output voltages were synthesized from the instantaneous values of input voltage and the base voltage is defined as the input phase value that had the highest absolute value.According to the output voltage value,one terminal of output circuit is connected to the base phase and the three switches connected to another terminal are controlled by PWM to gain the desired sinusoidal output voltage and input current.The biggest voltage transfer ratio can reach to 1.5 when the input power factor is 1.Numerical simulation and experiment based on the dSPACE system were carried out and the results show the correctness and effectiveness of the proposed control algorithm.

This paper conducts a thorough research to the problem of short circuit override trip and inaccurate leakage protection action mainly existing in HV flameproof switchgear comprehensive protection.A method of using communication atresia of microcomputer protection to solve the problem of short circuit override trip is put forward.Moreover,it puts forward classification leakage protection principle respectively using mobility method,conductivity method and admittance increment method to realize leakage protection,according to the differences of neutral grounding mode and arc suppression coil control mode in coal mine power network.Proved by experiments and practical application for more than one year,this comprehensive protection of HV flameproof switchgear designed by above-mentioned principle which has the characteristic of preventing short circuit override trip,accurate leakage protection action and strong adaptability etc,basically solves many problems in existing protection and has high value of promotion.