Electrical equipment of the floating nuclear power plant operates in a long-term vibration environment. Ground faults occur frequently and are often accompanied by arc, a reliable arc suppression algorithm for the generator stator winding is necessary. In this paper, an active arc suppression method is proposed by connecting a controllable voltage source to the generator neutral point. Through regulating the neutral point voltage to be equal in amplitude and opposite in phase to the fault potential, the fault point voltage can be clamped to a low level to achieve arc suppression. Since the generator's phase potential contains certain harmonic components, the controllable voltage source includes fundamental and third-order harmonic components. To accurately calculate the output voltage, online calculation methods for the fault location, fault potential and grounding capacitance are proposed. The accuracy of the fault location method is verified by simulation and dynamic test. And simulation results based on PSCAD/EMTDC software show that the proposed method can achieve effective arc suppression at different ground fault conditions.

Three-phase AC excitation is adopted in the variable speed pumped storage generator-motors, which is different from the DC excitation in traditional synchronous generators. The special rotor winding structure makes the existing rotor ground fault protection methods no longer applicable. Therefore, a rotor ground fault protection method for variable speed pumped storage generator-motor is proposed in this paper. Considering that there is no precondition for additional installation of the injection device at the rotor winding neutral point, the rotor ground fault protection scheme is proposed by connecting the injection device through current limiting resistors outside the rotor winding terminals. The key parameters of injection source, band-pass filter, and current limiting resistance are analyzed and calculated. Then, the online calculation methods of grounding resistance and grounding current are proposed based on the injection equivalent circuit. On this basis, the composite protection criterion considering grounding resistance and grounding current is constructed, and the protection outlet mode is clarified. Simulation and experiments verify the effectiveness of the proposed method.

The stator ground fault location of large generators can guide rapid maintenance. In this paper, a location criterion without fault transition resistance is constructed by using the fundamental potential and the third harmonic potential of the faulty winding simultaneously. The above potentials of the faulty winding are corresponding to the fault position. To precisely locate the grounding fault, it is necessary to clarify the analytical relationship between the faulty winding potential and the fault position. However, the existing methods often take the coil potential as the unit to analyze the winding potential, which has theoretical errors for the generators with short-pitch winding. Aiming at this problem, a more precise analysis method for winding potential is established by taking the slot conductor potential as the unit. To solve the location criterion, the optimization model for each slot conductor of the faulty phase is constructed. The slot conductor with the smallest optimal objective function value is judged as the faulty slot conductor, and the corresponding decision variable is judged as the fault position. Simulation and experiments verify the effectiveness of the proposed method, which can still meet the needs of engineering applications under multiple adverse conditions.

The traditional fault location methods are not effective for the multisource active distribution network and are difficult to meet both requirements of timeliness and fault tolerance simultaneously. In this paper, a fault location method for active distribution networks which combines both improved matrix algorithm and optimization algorithm is proposed. The improved matrix algorithm is constructed to determine the fault section hypothesis by using the causal relationship between the alarm information and the fault section. Subsequently, network splitting is used for causal verification to check whether the alarm information is distorted. If the alarm information is normal, the fault sections can be quickly located by the above matrix algorithm. If the alarm information is distorted, the optimization model is constructed by using the fault section hypothesis selected by the matrix algorithm. The discrete particle swarm optimization (DPSO) algorithm is used to solve this optimization model, which can accurately locate the real fault sections. Hence, the advantages of both matrix algorithm and optimization algorithm are complementary. Simulation results show that the proposed method has the advantages of both high timeliness and fault tolerance in a complex active distribution network.

The arc suppression device based on ground fault transfer (GFT) has been preliminarily applied in the medium voltage distribution network (MVDN). An accurate travelling wave (TW) fault location method is proposed to extend the use of the ground fault transfer device. D-PMU is used as a travelling wave detection tool to record the transient voltage travelling waves of fault grounding and bus active grounding during arc suppression. Then, the faulty section is identified through the time difference of travelling wave arrival at the upstream and downstream measurement points. On this basis, the fault location equations of the arrival time and distance of the upstream travelling wave are established, and an accurate fault location method based on the arrival time difference of the travelling wave is proposed. The simulation model is established by PSCAD/EMTDC, and the results show that the method has high location accuracy, and the absolute error is less than 30 m. It is not affected by the TW velocity, the fault conditions, or the distributed power sources.

The rotor winding of variable speed pumped storage generator-motor (VSPSGM) is a special three-phase winding structure, which not only makes the traditional rotor ground fault location method no longer applicable, but also increases the faulty phase selection problem. Therefore, the faulty phase selection and location method of rotor ground fault for VSPSGM is proposed in this article. Firstly, the relationship between the phase characteristics of the rotor winding potential and the working conditions is summarized according to the generation mechanism of the induced potential. The piecewise function is used to accurately analyze the amplitude and phase variation of the winding potential. On this basis, a reliable faulty phase selection method for rotor ground fault is proposed based on phasor trajectory analysis. Furthermore, the optimization model of ground fault location is constructed according to the geometric relationship of neutral point to ground voltage phasor, fault point to ground voltage phasor, and fault winding potential phasor. The accurate position of the ground fault can be obtained by solving the optimization model. This technique has been validated through simulations and experimental tests.