Many industrial power systems have been operatedwith floating neutral or high resistance grounding. Withtraditional fault detection methods, based on zero sequencecurrent, it is difficult to satisfy the requirement of distributionautomation (DA). In order to improve this, some noveltechniques for ground fault feeder detection are presented in thispaper, and they are implemented by using the informationobtained from the feeder terminal unit (FTU). The faulty feederis identified with fuzzy analysis. These protection schemes havebeen verified by EMTP simulation. A prototype has beendeveloped and tested in a dynamic power system. Results showthat these proposed protection schemes have high sensitivity androbustness to detect all kinds of ground faults.

As a result of deregulation, distributed generation(DG) systems with distributed generators installed in the middleor low voltage networks become popular in distribution systems.Traditional protections developed in radial systems are difficult incoordination and in protecting against high impedance fault(HIF), sometimes it may cause nuisance tripping in the DGsystems. A decentralized multi-agent based protection withcapability of HIF detection, fault location and load shedding forthe DG systems is proposed in the paper. Digital relay is designedas a relay agent which is capable of searching for informationfrom other relay agents, interacting with other relay agents andperforming tasks of protection with autonomy and cooperating.The agent based protection scheme is also presented. EMTPsimulation results show that the proposed agent based protectionscheme can remove the influence of load switching operations,protect against HIF, electric shock. The prototype of relay agentis developed, the research is now in progress on testing theprototype in dynamic power system.

Many High impedance ground faults (HIGF) that happen in low voltage (LV) system often cause customer supply lost, fire and human safety hazard. Traditional ground fault protection is provided by Residual Current Circuit Breaker 0RCCB). The RCCB often causes nuisance tripping and is difficult to detect HIGF. Wavelet analysis based HIGF protection is developed in the paper. Wavelet transform is applied to filter out some frequency bands of harmonics from residual current and line current. The root mean square (RMS) value of harmonics are calculated using their wavelet coefficients directly. HIGF is identified from disturbance by the RMS difference between the residual current and the line current. The digital protection scheme is designed. EMTP simulation results show that the new protection is able to detect HIGF and prevent electric shock with high sensitivity and robustness.

介绍了传统的消弧线圈自动调整方法。提出采用注入变频信号，寻找系统谐振频率，测量补偿度、电容电流，进行消弧线圈自动跟踪调谐的新方法。测量时无需调整消弧线圈挡位。能适用于老式消弧线圈补偿度的测量。在一个配电网中只需安装一台自动调整消弧线圈，就能实现整个配电网的自动调谐，无需通信配合。该技术已在现场运行多年，效果良好。

Power quality is influenced by neutral grounding methods in distribution systems. Optimization for neutral grounding methods is discussed in the paper. Petersen-coil in parallel with high resistance earthed technique has a better performance in safety and power quality than other neutral point grounding techniques. To improve power quality, a novel method for measurement of zero sequence impedance in distribution systems is presented, Petersen-coil inductance is adjusted to compensate the total capacitance, and the resistor which is in parallel with the Petersen-coil is adjusted to control the over-voltage; some other novel techniques for grounding fault feeder protection based on testing the fault resistance or the energy dissipated in the fault point are also presented. The method of Petersen-coil tuning has been developed. Experimental results show that the optimization for neutral grounding methods and the protections proposed can improve the power quality by reducing the over-voltage, the residual current and the grounding fault duration