Two-phase Short Circuit Fault Research Articles

An Optimized Active Power Backflow Suppression Strategy for Cascaded H-Bridge PV Grid-Connected Inverter During Inter-Phase Short-Circuit Fault

Active power backflow is a unique problem of three-phase isolated cascaded H-bridge (CHB) PV inverter during asymmetric grid voltage fault, resulting in the continuous rise of H-bridge dc-bus voltages and that the inverter will be eventually shut down and off-grid due to voltage out of control. The existing methods are able to completely suppress the active power backflow during single-phase short-circuit fault and two-phase short-circuit fault, but fails in a large operating zone when inter-phase short-circuit fault occurs. For this issue, this paper proposes a novel multiple specific harmonic voltages injection method based on the existing fundamental-frequency zero-sequence voltage compensation strategy, which calculates and injects the optimal third, fifth, seventh and ninth harmonic voltage according to the fault type, drop depth and the normalized power, for minimizing the amplitude of three-phase modulation voltages and then significantly shrinking active power backflow zone of three-phase isolated CHB PV inverter. Then, the area of the active power backflow zones for different control methods is quantitatively calculated and compared by adopting the polynomial fitting to show the advantages of the proposed method. Finally, experimental results are achieved by a low voltage and low power experimental prototype to verify its effectiveness and feasibility.

A Short-Circuit Protection System Considering the Negative Sequence of Fault Current Available to Long Distribution Lines

A fault current measured at a distribution substation is small in case of a two-phase short-circuit fault near the end of a long distribution line. This characteristic makes it difficult to settle the overcurrent relay installed at the root of line because the load current could hardly be distinguished from the fault current. On the other hand, a negative-sequence current relay likely isolates such a two-phase short-circuit fault, but it may not operate properly due to effects of load on the distribution line. This study sets a proposal of short-circuit protection system considering the negative sequence of fault current that can be applied to long distribution lines. It also demonstrates how useful the proposed system is for isolating such a two-phase short-circuit fault on a long distribution line.

An Optimized LVRT Control Strategy of Cascaded Modular Medium-Voltage Inverter for Large-Scale PV Power Plant

Active power backflow is an inherent problem of three-phase cascaded H-bridge (CHB) photovoltaic (PV) grid-tied inverters during low-voltage ride through (LVRT), probably resulting in no balanced operating point of the system, and the inverter will be shut down and off-grid due to overvoltage fault. Aiming at this issue, this article first reviews the existing control methods and analyzes their limitations in application, that is, they cannot effectively suppress active power backflow under the scenario of deeper voltage drop and lower output power. On this basis, an optimized LVRT control strategy for cascaded modular medium-voltage PV power generation system is proposed, which adopts different control methods to suppress active power backflow under three types of asymmetric grid drop conditions: single-phase short-circuit fault with ground, two-phase short-circuit fault with ground, and two-phase short-circuit fault without ground, enhancing the adaptability of CHB PV grid-connected inverters to different output powers and different drop depths during grid voltage failure and then improving LVRT capability of the system. Finally, the effectiveness and feasibility of the proposed control strategy are verified by experimental results.

Optimal tuning of PI controllers using adaptive particle swarm optimization for doubly-fed induction generator connected to the grid during a voltage dip

This paper proposes the adaptive particle swarm optimization (APSO) technique to control the active and reactive power produced by a variable wind energy conversion system and the exchanged power between the electric grid and the system during a voltage dip (VD). Besides, to get the variable speed wind energy maximum power, a maximum power point (MPP) methodology is utilized. The system under study is a 5 MW wind turbine connected via a gearbox to a doubly-fed induction generator (DFIG). The DFIG stator is branched directly to the electrical network, while the Back-to-Back converters couple the rotor to the grid. The decoupled vector control of the rotor side converter and the grid side converter is established primarily by a conventional proportional-integral (PI) and a second level by an intelligent PI whose gains are tuned using the proposed control. The performances and results obtained by APSO tuned PI controllers are analyzed and compared with those attained by classical PI controllers through the MATLAB/Simulink. The superiority of the advised technique is examined during a two-phase short-circuit fault condition and confirmed by the reduced oscillations.

Fault identification based on BP neural network and wavelet packet in power systems

This paper proposes a fault identification method based on BP neural network and wavelet packet, which extracts the fault transient eigenvalues of the three-phase current and zero-sequence current from measurement data under the fault conditions. Firstly, the eigenvalues of three-phasors are sampled under the typical faults, such as single-phase ground fault, two-phase short-circuit fault, two-phase ground short-circuits fault, and three-phase short-circuit fault. Secondly, the three-phase current and the zero-sequence current are subjected to wavelet packet transform to extract the eigenvalues, which are viewed as the input of the neural network to determine the fault type. Finally, simulation results show that the proposed method can give reliable identification results under different fault conditions.

针对两相短路故障的时间窗自动提取算法设计

本文针对输电线路两相短路故障，提出了一种基于工频分量单端故障测距原理的时间窗提取算法。此算法利用故障电流的差值对时间窗进行定位。首先利用PSCAD/EMTDC仿真软件搭建输电线路分布参数模型，对输电线路发生两相短路故障进行仿真建模，然后将仿真结果导入MATLAB，最后利用所提时间窗自动提取算法对故障点进行定位。经过对测距结果的分析，本文所提时间窗自动提取算法在输电线路发生两相短路故障后能有效对时间窗进行提取，可以为微机保护装置时间窗的快速准确选取提供参考。 This paper proposes a new time window automatic extraction algorithm of two phase short circuit fault based on power frequency component of the single-ended ranging principle. The time window automatic extraction algorithm is based on the differences of the phase current of fault phase to locate the time window. First, the transmission line distributed parameter model is built by using PSCAD/EMTDC simulation software to simulate two-phase short circuit fault. Then, the results of the two-phase short circuit fault simulation are used to the input of MATLAB. Finally, the algorithm proposed in this paper is used to locate the fault point. The result of the fault location verifies that the algorithm is feasible. The algorithm proposed in this paper can effectively extract the time window of two phase short circuit fault which can provide reference to the microcomputer protection device.

Analysis on Torsional Stresses in Turbo-Generator Shafts due to Two-Phase Short-Circuit Fault

Taking a 660MW turbine generator shaft system as a target system, the torsional stresses responses are calculated under two-phase short-circuit fault by the finite element (FE) method which can obtain torsional stresses in local areas accurately. The results show that torsional stresses threaten the safety of shafts appear at the first several cycles of the vibration. And the amplitude of stress in weak cross sections located between the low pressure cylinder and the generator is much greater. In addition, the proportion of torsional stresses frequency components in different sections is distinct. The results are helpful to improve the safety management level of the unit.

Single-line-to-ground fault test of a 3-phase superconducting fault current limiting reactor

The current limiting behavior of a 3-phase superconducting fault current limiting reactor (SCFCLR) in a model power system at a single-line-to-ground (SLTG) fault is experimentally confirmed. A small arc gap is attached on one phase of the model transmission line. A single-line-to-ground fault is activated. The behavior of the grounding current and the arc is observed. It is shown that: (1) the fault current is limited to a very small value by the large zero-phase-sequence reactance of the SCFCLR, and the self-extinction of the fault arc is observed; (2) the power flow is not disturbed by a SLTG fault at all, and no power system disturbances are observed; and (3) the windings do not quench for a SLTG fault. A supplementary experiment for a two-phase short circuit fault was also carried out. >