Single-phase Fault Research Articles

Single phase fault diagnosis and location in active distribution network using synchronized voltage measurement

To ensure the safe operation of the active distribution network (ADN), accurate fault diagnosis and location are crucial to improve the reliability indices and reduce the outage time. This paper proposes a characteristic model-based method for the single phase to earth fault in the ADN system. Firstly, the characteristic model of the fault factor extracts the phasor distribution characteristics of the voltage and current along the distribution feeder line and estimates the current contribution of DG units to the fault point. Based on the minimum entropy theory, the solution of nonlinear characteristic model is transformed to a single-objective optimization of the characteristic entropy and the diagnosis criteria is formulated. Then, the two-stage fault location scheme for single phase fault is proposed. The fault diagnosis stage estimates the suspicious fault section to reduce the search area and the fault location stage locates the exact fault distance. The Fibonacci search algorithm is utilized for fault location to the optimize iterative and minimize the respond time. The proposed scheme is general for all DG types and overcomes the requirement of its individual model parameters. The proposed method is validated in the IEEE 34-bus distribution test system using the phasor measurement unit (PMU). Test results of the model-based diagnosis and location method can reveal accurate fault location and rapid response at different fault impedance and small time delay comparing with the radial basis function neural network (RBF), and wavelet neural network (WNN) method.

Extension of Space-Vector-Signal-Injection-Based MTPA Control Into SVPWM Fault-Tolerant Operation for Five-Phase IPMSM

This article presents a new fault-tolerant drive for a five-phase interior permanent magnet synchronous machine (IPMSM) to achieve the maximum torque per ampere (MTPA) operation under open-circuit faults. In the postfault space vector pulsewidth modulation strategy, the voltage vectors are reconstructed by the reduced-order transformation matrix, which is derived from the optimal reference fault-tolerant currents under single-phase and double-phase fault. The z subspace is particularly controlled to reduce the total harmonic distortions of current under single-phase fault, and the distributions of space voltage vectors are established to realize the fault-tolerant operation under double-phase fault. Meanwhile, the high-frequency signal is injected into the space vector under fault condition inherently to detect the MTPA points. Therefore, this method is parameter independent in the tracking of the MTPA point under postfault operation. Besides, the proposed method can effectively reduce the amplitudes of the fault-tolerant currents and improve the torque and efficiency performances compared with $i_{d}= 0$ fault-tolerant control. Finally, on an IPMSM prototype drive system, the effectiveness of the proposed method is verified by the experiment.

Impact of wind power grid connection and interline short circuit faults on power grid

With the gradual increase of electricity demand in China, wind power and other power generation has developed rapidly, which makes the structure of power grid more complex. The complex structure increases the risk of short-circuit fault of power grid. The rapid development of wind power intensifies the randomness of power grid operation. This paper uses MATLAB/Simulink to model power system, construct simulation, and analyse the influence of grid-connected wind power and short-circuit faults on grid stability. The results show that the fluctuation and impact of the active power on the user side are significantly weakened compared with those of the single wind power grid when the high-power stable power supply is connected to the wind power grid. The single-phase short-circuit fault has no disturbance to the user of the grid, and the two-phase short-circuit and three-phase short-circuit have greater impact on the voltage, current and speed of the user end.

Fault detection and classification in wind turbine by using artificial neural network

Wind turbine is one of the present renewable energy sources that has become the most popular. The operational and maintenance cost is continuously increasing, especially for wind generator. Early fault detection is very important to optimise the operational and maintenance cost. The goal of this project is to study fault detection and classification for a wind turbine (WT) by using artificial neural network (ANN). In this project, a single phase fault was placed at 9 MW doubly-fed induction generator (DFIG) WT in MATLAB Simulink. The WT was tested under different conditions, i.e., normal condition, fault at Phase A, Phase B and Phase C. The simulation results were used as inputs in the ANN model for training. Then, a new set of data was taken under different conditions as inputs for ANN fault classifier. The target outputs of ANN fault classifier were set as ‘0’ or ‘1’, based on the fault condition. Results obtained showed that the ANN fault classifier outputs had followed the target outputs. In conclusion, the WT fault detection and classification method by using ANN were successfully developed.

Operating Region and Boundary Control of Modular Multilevel Converter Station Under Unbalanced Grid Conditions

To determine the operating region of modular multilevel converter (MMC) station under unbalance grid conditions, this paper proposes the analytical and point-scanning methods. First, the imbalance of PCC voltages is expressed in terms of two proposed indexes for single phase fault (SPF), which can be directly calculated from the grid parameter and grounding impedance. Next, the algebraic equation to solve the PCC voltage for the given PCC power is presented. The existence of PCC voltage is considered as one constraint. Moreover, the other constraints for transformer rating, converter rating, ac current and output voltage are also analyzed to adapt the unbalance conditions. Based on the proposed method, the effect of the grid imbalance on the operating region of MMC is analyzed and then the common constraints to confine the operating region are determined. Following that, the boundary control is proposed to limit the operation of MMC on the boundary of the operating region under unbalanced conditions. The open and modular control structure allows more constraints to be considered for the boundary control. The simulation results validate the correctness of the proposed methods to define the operating region and the effectiveness of the boundary control.

FCS-MPC-Based Fault-Tolerant Control of Five-Phase IPMSM for MTPA Operation

This article proposes a new fault-tolerant control strategy based on finite-control-set model predictive control (FCS-MPC) for interior permanent-magnet synchronous motor (IPMSM) drives under open-circuit faults, including single-phase and double-phase faults. In particular, the double-phase fault will cause a big disturbance to the performance of the motor, but there is no research focused on it with FCS-MPC. The key of this method is that a z subspace orthogonal to the fundamental space is proposed to reduce the total current harmonic distortions under the single-phase fault. And the distributions of space voltage vectors under a double-phase fault are established to realize the fault-tolerant operation. On the other hand, most of the research is focused on the fault-tolerant control of $\text{i}_{d}= 0$ , which is not suitable for the IPMSM, due to the ignorance of the reluctance torque. Hence, the proposed strategy is extended into the maximum torque per ampere operation by virtual signal injection, then the amplitudes of phase currents can be reduced and the efficiency of the system can be improved under fault conditions. Compared with the existing fault-tolerant control schemes, the proposed strategy can realize the fault-tolerant operation under open-circuit faults with faster control response and higher operation efficiency, which has been validated by experimental results.

Fault Tripping Criteria in Stability Control Device Adapting to Half-Wavelength AC Transmission Line

Because of the long distance and huge distributed capacity of half-wavelength AC transmission lines (HWACT), the fault characteristics of HWACT lines differ a lot from those of conventional lines. In this paper, the unique fault characteristics at the measuring points are simulated and the adaptation of conventional fault tripping criteria in HWACT lines is analyzed. It is pointed out that the stability control devices may operate incorrectly when the fault occurs far from the measuring point of the HWACT line. The fault location is determined by the starting time difference of the devices at both sides of the line. With the fault location and distributed element model of HWACT line, the voltage and current of the fault point are calculated and the new fault tripping criteria based on the electrical quantities of both the fault point and the measuring points are proposed. The simulation results show that the new criteria can distinguish the single-phase fault from phase-to-phase fault correctly and reliably.

Control of Smart Transformer Under Single-Phase to Ground Fault Condition

In low voltage (LV) electric distribution grid, the continuity of power supply service is degraded by various grid faults. Even under single phase to ground faults, the continuous operation capability of healthy phases is also limited. The smart transformer (ST) can establish each phase voltage independently and thus can switch the operation mode from three-phase to two-phase operation during single phase faults, ensuring continuous power supply in two healthy phases and minimizing outage area. However, different from the three-phase operation mode, both high 2nd-order oscillation in dc-link and high current in neutral conductor challenge system performances and reliability under the two-phase operation. Thus, an improved two-phase voltage control strategy is needed either to limit the neutral current amplitude avoiding over ampacity (reducing the power losses and suppressing neutral potential variations), or to suppress dc power oscillation (preventing the lifetime reduction of dc-link capacitors). This paper focuses on the control system design of ST voltage control for the two-phase operation to improve the grid voltage quality. The simulation and experimental results clearly verify the effectiveness and correctness of the proposed strategy.

Performance improvement in long overhead lines associated to single-phase faults due to atmospheric discharges

In this research, a new analysis is proposed to detect the correct extinction of secondary arc in the re-closure protection, for long overhead lines in 220 kV. A new methodology for increasing the success rate of single-phase reclosing is proposed, with transient analysis (EMPT-ATP) have been done for over voltage detection in long overhead transmission lines, re-closure effect and probability, maneuver of line reactors, transient recovery voltages (TRV) caused by secondary arc phenomenon, unbalanced transmission lines and resonance. Finally, a case study is implemented with real fault conditions. Later, in the discussion section, the relation to the strength of the grounding system is analyzed and over voltage effects in the power system with the verification of the secondary arc extinction and the correct procedure of analysis.

Sensorless field oriented control for five-phase induction motors with third harmonic injection and fault insensitive feature

The paper presents a solution for sensorless field oriented control (FOC) system for five-phase induction motors with improved rotor flux pattern. In order to obtain the advantages of a third harmonic injection with a quasi-trapezoidal flux shape, two vector models, α1–β1 and α3–β3, were transformed into d1– q1, d3– q3 rotating frames, which correlate to the 1st and 3rd harmonic plane respectively. A linearization approach of the dual machine model in d – q coordinate frames is proposed by introducing a new additional variable “x” which is proportional to the electromagnetic torque. By applying the static feedback control law, a dual mathematical model of the five-phase induction motor was linearized to synthesize a control system in which the electromagnetic torque and the rotor flux can be independently controlled. The results shows the air gap flux shape in steady as well transient states under various load conditions. Moreover, the implemented control structure acquires fault tolerant properties and leads to possible emergency running with limited operation capabilities. The fault-tolerant capability of the analyzed machine was guaranteed by a special implemented control system with a dedicated speed observer, which is insensitive to open-phase fault situation. The experimental tests have been performed with single and double-open stator phase fault. A torque measurement was implemented to present the mechanical characteristics under healthy and faulty conditions of the drive system.

Series Capacitor Compensated AC Filterless Flexible LCC HVDC With Enhanced Power Transfer Under Unbalanced Faults

This paper introduces significant performance enhancements to the ac filterless LCC HVDC by including fixed series capacitors at the primary side of a converter transformer. In terms of technical performance, 1) the amount of active power that can be transmitted is increased by more than 60% compared with ac filterless LCC HVDC, especially under severe unbalanced fault such as single-phase fault (most common fault in power systems); 2) the required voltage level of the controllable capacitor for Commutation Failure (CF) elimination is reduced by more than 70%, which leads to considerable reductions of the associated costs and losses. In terms of economic performance, due to the reduction of the required voltage from controllable capacitors (hence, the number of power electronic devices), the cost of the proposed converter station is lower than that of the ac filterless LCC HVDC. Theoretical analysis is presented to illustrate the performance enhancements and select the size of the series capacitor. Simulation results for various kinds of faults and cost analysis are presented to validate the technical and economic performances of the proposed method. Comparisons are made with ac filterless LCC HVDC. Finally, various practical issues and possible solutions are discussed.

A New Method For Fault Section Location Based on Zero-Mode Of Fault Current Phase

When there is a single-phase fault appearing in an indirect grounding electric power system, in order to quickly locate the ground fault section. So here, a new method is proposed which is based on the oringinal localization algorithm. The method of phase section positioning is based on the zero mode of current’s phase, when the fault is in this section, there is an opposition before and after the detection point. The simulation model was built by MATLAB, and the simulation conclusion are same as the theoretical proof.

Influence of transition resistance and fault moment on DC system commutation process caused by two‐phase fault of AC system

Commutation failure caused by the fault of AC system at inverter side seriously affects the safety and stability of high-voltage direct current (HVDC) system. Although two-phase fault is a typical asymmetrical fault, the studies on commutation failure caused by two-phase fault are few compared with the studies on commutation failure caused by three-phase fault or single-phase fault. In this study, the features of two-phase fault occurring on commutation bus is analysed theoretically. The analysis shows that the transition resistance will affect the amplitude and phase of the commutation voltage at Y-Y and Y-D1 transformer valve sides. Furthermore, the change regularity of the commutation voltage along with the change of transition resistance is given. Taking interphase short circuit as an example, the influence of different fault moments on commutation process is studied. For the first commutation process before the fault, the possible cases of commutation failure are given for fault moments in one cycle. For the first commutation process after the fault, a calculation method of critical voltage drop is given. Simulation results verify the correctness of the analysis.

A Novel 10kv Switchgear Bus Arc Protection Based on the Principle of Voltage Lockout

10kV switchgear bus arc protection based on current lockout criterion has the disadvantage of insufficient sensitivity when single-phase fault occurred. This paper proposes a new type of 10kV switchgear arc protection on the basis of voltage lockout. The electrical characteristics of 10kV ungrounded systems of various short-circuit fault are analyzed by simulation calculation. Analysis results show that the new 10kV switchgear voltage lockout arc protection has a higher sensitivity than arc protection based on the current lockout.

Seamless Control of Grid-Connected Inverter during Single Phase Disconnection after Single Phase Fault in a Weak Grid

With the increasing penetration of renewable energy in power systems, the requirement of fault ride through (FRT) capability becomes imperative for the stability of the grid. However, the topology and operation of the power system during the fault and fault clearance, especially during single phase disconnection, is seldom taken into account in most existing control schemes for grid-connected inverters. In this paper, a novel seamless positive-sequence current control method based on phase voltage with equal 120 degree dephasing and zero-sequence voltage decomposition is proposed. It realizes a smooth and rapid transition between normal operation, single phase fault, single phase disconnection without mode change, and injects no negative-sequence current to the grid during single phase disconnection which may last long and cause dangerous overheating of the rotor of conventional generators in a power system. The results obtained from the simulation and experiment demonstrate the effectiveness of the proposed method.

A Novel Fault Location Method for a Cross-Bonded HV Cable System Based on Sheath Current Monitoring.

In order to improve the practice in the operation and maintenance of high voltage (HV) cables, this paper proposes a fault location method based on the monitoring of cable sheath currents for use in cross-bonded HV cable systems. This method first analyzes the power–frequency component of the sheath current, which can be acquired at cable terminals and cable link boxes, using a Fast Fourier Transform (FFT). The cable segment where a fault occurs can be localized by the phase difference between the sheath currents at the two ends of the cable segment, because current would flow in the opposite direction towards the two ends of the cable segment with fault. Conversely, in other healthy cable segments of the same circuit, sheath currents would flow in the same direction. The exact fault position can then be located via electromagnetic time reversal (EMTR) analysis of the fault transients of the sheath current. The sheath currents have been simulated and analyzed by assuming a single-phase short-circuit fault to occur in every cable segment of a selected cross-bonded high voltage cable circuit. The sheath current monitoring system has been implemented in a 110 kV cable circuit in China. Results indicate that the proposed method is feasible and effective in location of HV cable short circuit faults.

Simulation Analysis of Overvoltage of Single Phase Grounding Fault in Paralleled 12-Pulse Rectifier System

In order to solve the problem of overvoltage of single phase grounding fault of paralleled 12-pulse rectifier system, firstly the common mode wave problem of monopole in DC side at fault is analyzed. Secondly, the transient overvoltage of the system at the AC side single phase fault is analyzed by simplifying the charging and discharging circuit of capacitances on DC side. Finally, the theory of frequency extinguishing arc is used to simulate the intermittent arc grounding overvoltage. It is proved that the capacitance on DC side also affects the AC overvoltage in the system that provides a basis for the better suppression of overvoltage in the project. The correctness of the conclusion is verified by PSCAD/EMTDC simulation software in the analysis process.

Analysis and mitigation of low-frequency resonance in a long-distance UHVDC ±1100 kV system

Low-frequency resonance may seriously threaten the stable operation of a long-distance ultra-high-voltage-direct-current (UHVDC) system. In this paper, the impedance model of long-distance UHVDC systems was analyzed for various disturbances. For different disturbances, the positions of voltage sources in the simulated DC loop are different. Taking the first ±1100-kV DC power transmission project with a length of 2688km as an example, the frequency characteristics of the DC-loop impedance were studied using the PSCAD/EMTDC simulation platform. The effects of various operating modes and the firing angle of the converters on impedance–frequency characteristics of the DC loop were discussed. The effect of the length of DC transmission lines on the DC-loop resonant frequency was studied. The distance is the most important factor determining the system low-frequency resonance. Faults in an AC grid, such as phase-to-phase short-circuit and single-phase faults, are shown to produce 50-Hz positive sequence harmonics on the AC side and 100-Hz disturbances in the DC loop. Two methods of mitigating low-frequency resonance were proposed and the effects simulated. Installation of the blocking filter in the neutral bus of the converter station can reduce the amplitude of the resonance overvoltage.

Commutation Failure Elimination of LCC HVDC Systems Using Thyristor-Based Controllable Capacitors

The adverse impacts of commutation failure (CF) of a line-commutated converter (LCC)-based high-voltage direct current (HVdc) system on the connected ac system are becoming more serious for high-power ratings, for example, the development of ultra-HVdc systems. Aiming to solve the problem of CF particularly for higher power/current LCC HVdc systems, this paper proposes a new method, which utilizes a thyristor-based controllable capacitor (TBCC), to eliminate CFs. The topology of the proposed TBCC LCC HVdc and its operating principles are presented. Then, mathematical analysis is carried out for the selection of component parameters. To validate the performance of the proposed method, modified LCC-HVdc and capacitor-commutated converter (CCC)-based HVdc systems based on the modified CIGRE HVdc system are modeled in a real-time digital simulator. Simulation studies for zero impedance single-phase and three-phase faults are carried out, and comparisons are made with both LCC-HVdc and CCC-HVdc systems. Furthermore, voltage and current stress of the TBCC are investigated and power-loss calculations are presented. The results show that the proposed method is able to achieve CF elimination under the most serious faults while the increase of power losses due to the TBCC is small.

Nature of fault determination on transmission lines for single phase autoreclosing applications

Maintaining system stability and power supply need to have an efficient detection and fast elimination of faults on transmission lines by the protection system. To clear transient single-phase faults on high voltage (HV) and extra high voltage (EHV) transmission lines, involving electrical arcs, single phase auto-reclosure (SPAR) has been pointed out as the most recommended device. However, SPARs cannot distinguish between transient and permanent faults. In the presented study, a new algorithm has been proposed to tackle this issue, identifying transient and permanent faults, for the purpose of single-pole auto-reclosing applications. In this method, the arc-voltage amplitude has been calculated using voltage harmonics at the fault location. Provided that this amplitude is large enough, the transient fault state will be immediately declared, enabling the AR; otherwise, the scheme deduces that a permanent fault has occurred and AR will be blocked. To evaluate the accuracy of the proposed scheme, rigorous simulations have been performed considering a wide array of different conditions including fault location, fault resistance and arc-voltage gradient, where, in all cases, the highest reliability has been achieved.