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Single phase line‐broken (SPLB) fault is one kind of high impedance fault (HIF). When a SPLB fault occurs, there are four scenarios: SPLB fault with neither side conductors grounded (SPLB‐NSCG), with source side conductor grounded only (SPLB‐SSCG), with load side conductor grounded only (SPLB‐LSCG), with both side conductors grounded (SPLB‐BSCG). Traditional HIF detection methods using current or voltage characteristics have low sensitivity to SPLB fault. In this paper, voltage characteristics are analysed firstly in the cases of the first three scenarios of SPLB fault, respectively. Theoretical analysis finds that the voltage at both the sides of the disconnection point is significantly different. A high sensitive SPLB fault detection method based on differential voltage is proposed for radial distribution network with different data synchronization ability. Finally, SPLB fault location methods based on centralized intelligent mode feeder automation (FA) and intelligent distributed mode FA are proposed. Simulations based on PSCAD verify that the proposed SPLB fault detection method is feasible, highly sensitive and immune to the neutral grounded mode, fault scenarios and fault resistance. [ABSTRACT FROM AUTHOR]

Accurate fault location plays an important role in the fault clearance of the transmission line. However, because of the influence caused by fault resistance and the remote end system, there are four unknowns in the two equations built by the fault phase. Thus, the equations cannot be solved. In this paper, a single-terminal fault location method for transmission lines integrated by the inverter-type source is proposed. For a single-phase to ground fault or phase-to-phase fault, due to the specific control strategy, the equivalent positive and negative-sequence impedances of the converter are unequal in most cases. However, the positive and negative-sequence impedances of other elements are approximately equal, and the boundary condition at the fault branch is definite. Combining the boundary condition and the sequence impedance difference, two uncorrelated equations can be built. Substituting them to the equations built by the fault phase, the fault location can be calculated accurately. And the influence caused by fault resistance and the remote end system is eliminated. The simulation results show that the proposed method can achieve fault location accurately. Moreover, it has higher reliability and is independent of control strategy, fault distance and fault resistance. [ABSTRACT FROM AUTHOR]

Existing nonunit protection schemes inevitably require setting, which is a serious problem in practical engineering. Faults occurred at different fault zones will result in different equivalent models, therefore, the fault zone can be determined by recognizing which equivalent model the fault fits well with. In this article, this “model recognition” idea is introduced in fault identification and a “setting-less” protection method is proposed. First, the Peterson equivalent circuits when faults occur at backward external zone, internal zone, and forward external zone are presented, respectively. Accordingly, the corresponding three fault voltage expressions are derived, which are defined as three fault modes. Then, the three fault modes are used to approximate the measured fault voltage using Levenberg-Marquardt optimal approximation method. The fault mode that best fits the measured fault voltage is recognized as the final determined fault mode, which is used for fault identification without setting threshold value. Numerous test studies carried out in Power Systems Computer Aided Design/Electromagnetic Transients including DC (PSCAD/EMTDC) and real-time digital simulator have demonstrated that the proposed method can be utilized for different multiterminal dc systems and is effective under different fault locations, different fault types, and high fault impedances. The proposed method does not require high sampling frequency and has good robustness against measuring noise. [ABSTRACT FROM AUTHOR]

The multi-terminal hybrid LCC/MMC HVDC has been applied to overcome the simultaneous commutation failure problem caused by the multi-infeed LCC-HVDCs in the East China. The high-speed and selectivity line protection method is required for the multi-terminal hybrid HVDC system. In this paper, the reflection and refraction of the fault traveling waves at different kinds of line terminals are characterized by transfer functions. Then the fault voltage as well as its first peak time at different line terminals when different internal and external faults occur are derived respectively. The conclusion proves that the first peak time of line-mode fault component voltage (FPTV) for internal faults is smaller than that for external faults, which is independent of fault impedance and fault type as well. Therefore, a FPTV-based non-unit ultra-high-speed dc line protection method is proposed. The algorithm is implemented in the developed protection prototype and validated in the Kun-Liu-Long three-terminal hybrid HVDC RTDS test system. The test results show that the proposed method can fast and correctly identify line faults in the multi-terminal hybrid HVDC system, even with 500 Ω fault impedance. Comparing with the traveling wave protection method of ABB, the proposed method improves the sensitivity when high-impedance faults occur. [ABSTRACT FROM AUTHOR]

To identify the fault area more accurately and improve the reliability and sensitivity of the traditional protection principle on DC lines, an active injection for single-ended protection in the DC grid is proposed. Considering the influence of fault impedance, the effect of frequency-dependent parameters, numerical differential error, and the strength of DC boundary, high controllability of hybrid modular multilevel converter is utilized to inject sinusoidal signals with different frequencies into the line at DC terminal of each converter. Then the single-ended fault identification equation is constructed to preliminarily identify the fault area. According to the amplitude difference of the injection signals in different fault areas, the fault areas of the DC grid can be further distinguished. Simulation results verify the effectiveness of the proposed protection principle, improved reliability and sensitivity of protection, and full length protection of line without DC boundary. [ABSTRACT FROM AUTHOR]

Hybrid AC/DC transmission grids require high-speed operation and high reliability for relay protection. Traditional derivative-based traveling wave protection methods have exposed the problems of low sensitivity and low reliability. In this paper, the fault traveling wave is analyzed considering the attenuation, distortion, and boundary effect of the DC transmission line as well as three converter types. The expressions of the fault initial traveling wave are derived and the conclusions show that 1) the expressions of the fault initial traveling wave at the end of the transmission line have the formation of a(1 − exp(−bt)); 2) the index of the exponential function in the fault initial traveling wave expression is related to the fault location, and is not affected by the fault impedance and line attenuation. Then a Levenberg–Marquart fitting method is proposed to fit the measured zero-mode fault current initial traveling wave and extract the index coefficients. Finally, a novel traveling wave protection method for DC transmission lines is proposed using the obtained index coefficients. The simulation results show that 1) the proposed protection method can complete fault identification within 1 ms, even with high fault impedance; 2) the proposed protection method has high robustness to the influence of the noise. [ABSTRACT FROM AUTHOR]

The fast and selective protection using fast dc circuit breaker to break the fault current and isolate faulty lines satisfies the requirement of fault clearance in HVDC grids. However, traditional derivative-based traveling wave protection suffers from low-sensitivity problem when high-impedance faults occur. Based on the analysis of the fault initial traveling wave, it is concluded that the distortion degree of the fault initial traveling wave is related to the location of the fault, and the amplitude of the fault initial traveling wave is related to the fault impedance. Then a Levenberg–Marquart (LM) optimal approximation method is proposed to extract the fault distance information from zero-sequence fault current initial traveling wave. The optimal approximation parameters respectively reflecting the fault distance and fault impedance can be obtained. A non-unit traveling wave protection scheme is proposed based on the parameters. A ±400 kV modular multilevel converter (MMC) HVDC grid test system is built in PSCAD/EMTDC to verify the proposed method. The simulation results show that the parameters can directly correspond to the fault distance and fault impedance, and the proposed method can fast and reliably identify dc line faults. Finally, the sensitivity of the proposed method is studied by comparing with three different methods. [ABSTRACT FROM AUTHOR]

The result of single-ended traveling wave fault location method based on wavelet transform will be affected by false wavelet transform modulus maxima (WTMM) points. In this paper, fault distance/impedance information contained in the wave front of the traveling wave is analyzed first. Then, the fitting method based on generalized logistic function is proposed to extract the fault information. Based on the fitting results, a predictor–corrector fault location method is proposed, which includes the following content. First, the fitting coefficients of the zero-mode fault current wave front are used to estimate fault distance and fault impedance interval. Second, the arrival time of the line-mode fault current reflected wave can be calibrated and the distance calculation formula can be selected according to the fault distance estimation interval. Last, the fault distance will be corrected to be within the fault distance estimation interval, if the first reflected wave is undetected. A model of ±400 kV DC transmission project is built in PSCAD/EMTDC. The simulation results show that the fitting coefficients can directly correspond to fault distance/impedance. The proposed method can effectively eliminate the influence of the false WTMM points, and give the accurate fault location results as well as fault impedance interval. [ABSTRACT FROM AUTHOR]

Highlights • Feature extract method : Used CEEMDAN algorithm to extract the CFC of transient zero mode current. • Detection criterion : Constructed the starting criterion and discrimination criterion respectively, and realized the HIF accurate detection. • Solved the HIF detection difficulty in DC distribution network, and the needed data window of the criteria is only 2 ms, and criteria is accurate, the calculation speed is faster. Abstract Aiming at DC distribution network, we proposed a novel high impedance fault detection method in the paper, it main procedures are as follows: Firstly, used the algorithm of complete ensemble empirical mode decomposition with adaptive noise (CEEMDAN) to extract the first intrinsic mode function (IMF) of the characteristic mode. Secondly, calculated the singular point of mutation and the cumulative slope by the acquisition of the first order difference operation, and then, achieved to distinguish the fault state and the normal state by the comparison between the slope and the starting threshold. Thirdly, identified the first IMF with Prony algorithm to obtain the parameters of characteristic frequency components (CFC) and direct current components (DC), and calculated the energy ratio between them, and then, distinguished small impedance fault (SIF), medium impedance fault (MIF), high impedance fault (HIF) and load switching (LS) by different values of energy ratio. A large number of experiments show that the proposed method is accurate and effective. Compared with other methods, this method shows its merits in feature extraction accuracy, detection accuracy and calculation speed. [ABSTRACT FROM AUTHOR]

• A single-terminal fault location method for inverter-interfaced system that is less influenced by fault resistance and system parameters. • Compared to traditional single-terminal fault location method, the proposed method does not require the assumption about the phase-angle of sequence impedance. • Both symmetrical and asymmetries faults can be solved by the method. • A single-terminal fault location method that needs a small amount of calculation. Single-terminal fault location methods are easily affected by fault resistance and system parameters, and they always utilize iterative algorithm to solve fault distance. To improve their performance, an improved single-terminal fault location method for inverter system based on active control is proposed in this article, which can be used for symmetrical and asymmetrical faults. First, the problem that influences the performance of fault location method is analyzed. And to solve it, a control strategy that can create two fault statuses during fault stage is proposed. Then, using the electrical quantities under the different fault stages, two irrelevant equation groups can be established, and fault distance can be solved by single-terminal data. The PSCAD/EMTDC results demonstrate that the method can achieve fault location accurately, which just requires a small amount of calculation. And it is less affected by fault resistance and system parameters. [ABSTRACT FROM AUTHOR]

• The scheme is proposed for a DC power system with fault ride-through capability. • The effects of distribution parameters and fault impedance are taken into account. • The proposed scheme has the capability of fault property discrimination and fault location. • The proposed scheme is less affected by the DC boundary, sampling rate, and noise. • The proposed scheme is a control and protection integration method for permanent fault discrimination. A fault property discrimination scheme for hybrid multi-terminal power systems is proposed to avoid blind reclosing under permanent fault and improve power supply reliability. The proposed scheme uses the amplitude distribution characteristics of the injection step voltage signal under temporary faults and permanent faults. The relationship between the measurement value and the calculation value of the injection signal is investigated for the distributed parameter models. A method for identifying single-end fault property based on measurement and calculation values is proposed. When a permanent fault is detected, the fault distance is determined by locating the voltage distribution calculation point along the line that equates to the measurement value at the remote end. The fault property discrimination scheme for adaptive reclosing is composed of fault detection and location methods. As demonstrated by simulation analysis under various fault scenarios, the proposed scheme is less affected by fault distance, fault resistance, sampling rate, and noise. [ABSTRACT FROM AUTHOR]

Highlights: [•] Terminal currents of DC cable have same changing direction for internal faults. [•] Terminal currents of DC cable have opposite changing direction for external faults. [•] Pilot protection is proposed by using two terminal currents in low sampling rate. [•] Frequency-dependent cable model is adopted to verify the validity of pilot. [•] The new pilot can identify faults reliably and rapidly in different conditions. [ABSTRACT FROM AUTHOR]

Based on the ratio of the sum of the fault component voltage phasors across the two terminals in the transmission line to the sum of the current phasors through the same line, which is defined as fault component integrated impedance in this paper, a new transmission-line pilot protection principle is proposed. When an external fault occurs, the amplitude of the fault component integrated impedance that reflects the capacitance impedance of the line becomes large; When an internal fault occurs, the amplitude of the fault component integrated impedance which reflects the impedance of the system source and the line, becomes relatively small. Therefore, the fault in the line can be detected according to this characteristic. The criterion is not affected by the current through the capacitance and is not affected by the fault resistance. It can be applied to the line with or without shunt reactor. Also, it can be easily set. Both the simulation results with Electromagnetic Transients Program and dynamic model data verify the validity of the proposed principle. [ABSTRACT FROM AUTHOR]

• Based on a control and protection coordination. • Taking into account the fault current limiting stage for the protection principle. • The amplitude distribution of injection signal is used to distinguish permanent fault. • Considering the fault impedance and distributed parameter model. • Less affected by the sampling rate and noise. To further improve the capability of fault identification for protection and adaptive reclosing, a fault identification scheme based on a control and protection coordination strategy for a hybrid multi-terminal HVDC system is proposed. The protection principle for fault isolation is constructed based on the difference of the polarity characteristic of fault current between the fault line and non-fault line in the uncontrolled fault stage and fault current limiting stage. In the adaptive reclosing stage, an active fault identification scheme based on the amplitude distribution law of the injection signal along the line is proposed. Intensive simulation studies prove the fault identification scheme can identify the fault area in various fault scenarios and identify permanent faults to carry out adaptive reclosing. [ABSTRACT FROM AUTHOR]

Due to the special fault features of the inverter-interfaced system, traditional phase selectors exist adaptability problems. In this paper, a novel voltage phase selector based on a two-stage control strategy is proposed, which is not influenced by the special features of the converter. First, the fault features of the converter during fault ride through (FRT) operation are analyzed. Second, using the high controlled-ability of the converter, the control strategy is divided into two stages by adding disturbances to the power references of the control system at the second control stage. On this basis, a novel superimposed sequence network is defined as the subtraction of the compound sequence networks under the first and the second control stage. Then, the phase-angle differences of sequence voltages in the novel superimposed sequence network are analyzed, which are not influenced by the fault features of the converter and can be used to establish phase selection criteria. The simulation results show that the proposed phase selection scheme is immune to the fault features of the converter system, fault resistance, fault location and the operation modes of the remote end system. [ABSTRACT FROM AUTHOR]

• The proposed scheme is based on single terminal and independent of the DC boundary. • The proposed scheme used signal injection strategy needed for fault identification and improve reliability. • The proposed scheme is for the multi-terminal DC grid. • The proposed scheme is for fault isolation and system recovery stage. Effective fault identification scheme plays an important role in the fault isolation stage and system recovery stage of multi-terminal DC grid. Therefore, an active detection based single-end DC fault identification scheme is proposed to improve the reliability and sensitivity of fault identification. The control strategy is suggested of the generation of sinusoidal signals at different frequencies by the hybrid modular multilevel converters. Based on the blocking effect of the fault branch on the injection signal, by introducing the improved correlation discrimination algorithm, a single-end fault identification scheme is proposed by using the amplitude difference between the measured and calculated values of injection signals. The proposed scheme can be used for fault isolation and adaptive system recovery. Intensive simulation studies prove the improved sensitivity, and reliability of the proposed scheme for the full length of transmission line without relying on DC boundary. Moreover, the scheme can identify the permanent fault during the system recovery stage. [ABSTRACT FROM AUTHOR]

• A fault location method is based on the single-frequency injection signal. • Parameter identification method is utilized to realize fault location. • Fault impedance and distributed parameters of lines are considered. • Fequency parameters of line and numerical differential error are considered. • Less affected by sampling rate and does not need additional devices. The traditional fault location methods on DC lines are facing many challenges such as low reliability and unsatisfied location accuracy. To ensure a more reliable fault recovery of DC line, a single-ended fault location method based on active detection is proposed for hybrid modular multilevel converter based high voltage DC transmission systems. The high controllability of hybrid MMC is utilized to activate the control strategy of injecting a sinusoidal signal. Furthermore, based on parameter identification and compensation methods for the distributed parameter model, the fault location equation with fault impedance parameters is formulated. Finally, the fault location can be identified under different fault scenarios. Simulation results verify the effectiveness and accuracy of the proposed active detection method. The proposed method can pinpoint the fault location with a lower sampling rate, its accuracy is not influenced by increasing of the line length and variation of the fault impedance. [ABSTRACT FROM AUTHOR]

Abstract: This paper proposes a kind of new Individual Phase Impedance (IPI) and a novel pilot protection scheme for transmission line based on the IPI. The IPI is calculated by the ratio of the voltage difference of fault-superimposed component to the current difference of fault-superimposed component at both terminals of the protected line. The IPI has accurate mathematical expressions and reasonable physical definitions for various line models. The calculated result of IPI can be used to distinguish the internal faults from the external faults. When the IPI is identical to the value of line positive-sequence impedance, the external fault is detected; otherwise, the internal fault is detected if it differs from that value. The feature of the pilot protection scheme is that the inter-phase coupling relation and the distributed capacitance based on the three-phase line model are directly considered and included in the IPI expression. The novel pilot protection can be used for long distance HV transmission lines with some preeminent performances which are deficiency in the conventional directional comparison pilot protection and current differential protection. The test results obtained by EMTP simulation and from a laboratory model of a simplified real power system have demonstrated that the pilot protection is of high reliability and good adaptability. [Copyright &y& Elsevier]

• The research model is a hybrid three-terminal HVDC system model. • Wavelet threshold denoising and improved LMD algorithm are combined to calibrate the wave head. • A fault location method for hybrid three-terminal HVDC transmission line immune to wave velocity. To reduce the impact of traveling wave velocity, wave head recognition, and LMD (Local Mean Decomposition) end effect and mode mixing on location accuracy, this paper presents a fault location method based on improved LMD for hybrid three-terminal HVDC transmission lines, which is not affected by wave velocity. Firstly, the improved LMD is used to get the time when the fault traveling wave first arrives at the four measuring terminals. Then the fault branch is identified according to the ratio of the time of the fault traveling wave arriving at the measuring terminal. Finally, the equation is listed according to the principle of traveling wave location and the measurement equation which is not affected by the wave velocity is deduced. A hybrid three-terminal HVDC transmission system model is built by PSCAD to simulate various faults and output fault data under various fault conditions. MATLAB is used to process the fault data and verify the location algorithm. The simulation results show that the location method proposed in this paper is not affected by fault distances, fault types, infeed levels and transition resistances. In addition, it has higher accuracy than LMD based on CSI (Cubic Spline Interpolation) algorithm, wavelet packet location algorithm and double-ended location method of using wave velocity calculation. [ABSTRACT FROM AUTHOR]