注入信号法发电机定子接地保护受定子绕组对地电容的影响，灵敏度较低，难以满足大型机组高灵敏度继电保护的要求。而采用外加小电抗器、选择合适的注入信号频率，以补偿定子绕组对地容抗、测量故障接地电阻或测量信号电压、信号电流相位差进行接地保护则可改善大型机组定子接地保护的灵敏度。计算、分析与仿真表明：该方法具有较高的灵敏度。

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

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 mining power systems utilize ineffectivelygrounded sources to restrict the residual current of single-phaseearth fault in order to reduce outage and shock hazard. Inpractice, with the system expansion, topology changing, andinsulation aging, the potential residual current and zero-sequencevoltage for earth fault vary dynamically and some arcing earthfaults can easily cause over-voltage and induce multiple faults. Inorder to improve the system safety, on-site condition monitoring,safety evaluation, and preventive maintenance for earth fault areproposed in this paper. Some techniques for online parametersmeasurement based on resonance-measurement principle arepresented. Power system operation states are classified intonormal secure state, alert state, incipient fault state, and faultstate. Some security enhancement methods (preventive action andremedial action) for each state are implemented. The prototypefor safety evaluation has been developed and installed in industrypower systems for several years.

传统的基于故障稳态量的常规故障定位及基于故障暂态行波的行波定位都存在一定的局限。文中对常规定位模型进行改进，既简化了计算，又提高了精度；同时对行波定位进行改进，采用专用行波传感器，提高GPS同步时钟精度与采样频率，并利用小波变换进行行波波头检测，从而提高了定位精度。把常规定位和行波定位有机结合，研制了输电线路故障综合定位系统。动模实验、高压冲击试验和RTDS 试验都表明该综合定位系统具有很强的鲁棒性和很高的定位精度。