Transmission Line Pilot Protection Research Articles

Novel pilot protection for transmission lines with large-scale wind farms based on trajectory distance characteristics

In terms of integrating large-scale wind farms into power systems, the fault characteristics of power systems have undergone fundamental changes, potentially leading to the rejection and misoperation of traditional protections. To address these issues, a time-domain pilot protection based on trajectory distance characteristics is proposed. A novel trajectory distance calculation method is introduced to improve the one-way distance (OWD) algorithm, which is used as a metric to quantify the distance between current trajectories to identify internal and external faults. To overcome the adverse impact of nonideal conditions, a metric, namely the ratio of nonsimultaneous points is proposed. Faults are identified using two metrics. Validation results from PSCAD/EMTDC and hardware-in-the-loop platform demonstrate that the proposed protection can operate within 15 ms in most cases and has excellent robustness against diverse nonideal conditions, including tolerating noise with 10 dB signal-to-noise ratio. Moreover, it considerably outperforms traditional and new differential protection methods.

Pilot protection based on the quasi-directional element of LCL-tuned half-wavelength transmission line

To create HWTL characteristics, the electrical distance of AC transmission lines is compensated to half the power frequency wavelength by utilizing tuned circuits. The LCL-tuned circuit exhibits low-pass filtering characteristics, blocking the transmission of high-frequency signals. Measurement devices were installed on both sides of the tuned circuit to assess its filtering characteristics. Based on these characteristics and by employing wavelet transformation to extract the high-frequency energy of the voltage signal on both sides of the tuned circuit as the directional protection criterion, a quasi-directional element was developed. It was determined that, if the high-frequency wavelet energy ratio exceeds one, the fault occurs in the forward direction of the tuned circuit, and if the ratio is less than one, the fault occurs in the reverse direction. Consequently, a pilot protection algorithm was formulated. The directional protection element was integrated with the tuned circuit differential protection to establish the LCL-tuned half-wavelength transmission line pilot protection scheme. This scheme mitigates the need for extensive data synchronization between both sides, and numerous simulations have demonstrated its effectiveness throughout the entire line length, regardless of transition resistance, fault type, noise and outgoing line.

Biweight Midcorrelation Based Transmission Line Pilot Protection Algorithm

Biweight Midcorrelation Based Transmission Line Pilot Protection Algorithm

Amplitude Based Pilot Protection for Transmission Line

Abstract: Distance protection and differential protection schemes are the two primary types of protection schemes employed in gearbox line protection today. However, industrial practice has shown that commonly used gap prevention techniques are limited in tripping speed and selectivity. The timing of the samples in each of the two relays located at the gearbox line terminals also affects the differential protection mechanism. On the other hand, pilot safety schemes using only the communication link to exchange local decision-making about fault conditions are not affected. These method include protection of Extra High Voltage (EHV) and Ultra High Voltage (UHV) transmission lines. Synchronization of time. The problem of creating a fast and accurate fault detection system for the safety of EHV/UHV transmission lines, which is crucial in present power systems, is the subject of this master's thesis. The protection method described in this thesis is the foundation for the detection and analysis of waves travelling wave along transmission at fault initiation. This method compares the arrival of the first traveling waves at both ends of the protected line with respect to direction. This will establish whether the fault is located in the safe zone or not. Based on high voltage transmission network safety requirements a suitable phase sequence algorithm is developed to control single phase tripping. Finally, through simulations conducted in the MATLAB environment, practical design concerns for incorporating the newly proposed protection algorithm into a numerical relay unit are investigated.

Waveform differential based pilot protection for transmission line connected to renewable energy sources

Affected by the control objectives of the inverter, the short-circuit characteristics of renewable energy sources are quite different from those of traditional synchronous generators. As a result, the performance of traditional protection is degraded, and may lead to mis-operation and rejection, posing hazards for the safety of the power grid. In this research, the fault characteristics of renewable energy sources and traditional synchronous generators are analyzed and compared. Then, according to the difference between the fault transient current waveforms of two power sources, a pilot protection principle based on Canberra distance is proposed. Considering the phase angle error and amplitude error during normal operation, the protection constant is theoretically set to 0.35. Simulations and field experiments show that the protection principle reliably distinguishes the faults inside and outside the zone in different scenarios. The protection is less affected by short-circuit current amplitude and abnormal data, because the numerator of Canberra distance signifies the difference between the transient current waveforms and denominator normalizes the difference. In addition, the Canberra distance is 1 when the output of renewable energy sources is 0, so the proposed protection is also applicable to the scenario where the renewable energy sources output is 0.

Singular Value Decomposition Based Pilot Protection for Transmission Lines With Converters on Both Ends

The modular multilevel converter-based high voltage direct current transmission (MMC-HVDC) technology has become an effective integrating method for large-capacity offshore wind farms. However, if AC side faults occur between the MMC and the wind farm, conventional current differential protection methods based on phasor measurements might not detect the large fault current at the wind farm and the MMC, resulting in poor protection performance. In the worst case, MMC blocking may occur during faults near the MMC station, causing relay refusal. The fault currents provided by both converters are analyzed in detail. Due to the fault-ride-through control objectives, it is proved that the singularity of fault current between wind farms and MMC is different. Therefore, a novel singular value decomposition (SVD) based pilot protection is proposed to solve this problem. A Hankel matrix is established for the short-circuit current at each end of the AC line. The Hankel matrix rapidly detects the singularity of the signal and its derivative, and the SVD method uses a short time window to extract the waveform features. This approach enables the detection of the fault features before MMC blocking in the worst-case fault scenario and prevents the incorrect fault identification caused by the minor amplitude of fault current provided by the converters. A detailed model of an offshore wind farm connected to the MMC-HVDC system is established in the real-time digital simulator (RTDS). A protection device compliant with industry standards is used to implement the SVD-based protection algorithm. Hardware-in-loop dynamic experimental tests are conducted to verify the performance of the proposed protection method. The experimental results demonstrate that the SVD-based protection method has excellent performance during various fault scenarios.

A novel pilot protection scheme for transmission lines based on current distribution histograms and their Bhattacharyya coefficient

The current waveform characteristics at both ends of a transmission line under different disturbances are represented by means of probability distribution histograms. By adopting the Bhattacharyya distance (BD) algorithm to quantify the similarity of current distribution histograms, a novel scheme of pilot protection for transmission lines based on Bhattacharyya coefficient (BC) is put forward. The proposed scheme can correctly identify internal faults, external faults, and faults accompanied with current transformer (CT) saturation of transmission lines. It also shows good performance in the cases of abnormal samples. The validity of the proposed scheme is evaluated by various simulation and dynamic analog experiment tests.

A New Approach to Transmission Line Pilot Protection in the Presence of Inverter-Interfaced Distributed Generators

In recent decades, the penetration of inverter-interfaced distributed generators (IIDGs) in power systems has increased significantly due to the environmental and economic benefits. The increasing participation of IIDGs and the developments of power electronic technologies have raised the possibility of controlling the power injected by IIDGs for regulating the voltage level, especially during short-circuit fault conditions, following the regional grid codes. When a short-circuit fault occurs on the transmission line connected to the IIDGs bus, a dramatic voltage drop occurs. In this situation, the IIDG injects the reactive power fast that disrupts the performance of the distance relay as a result of which the operation of the relay in different operational conditions may either over reach or under reach. In this article, a comprehensive analysis is accomplished regarding the errors imposed on the estimated impedance of the distance relay, due to the voltage control of IIDGs, in single and double-circuit transmission lines. Then, an impedance-based pilot protection method is proposed to enhance the performance of the transmission line protection relays affected by the reactive power injected by the IIDGs.

Spearman Correlation-Based Pilot Protection for Transmission Line Connected to PMSGs and DFIGs

The power output generated by wind farms (WFs) is integrated directly or indirectly into the grid through power electronic devices and the fault current is significantly different from that of conventional synchronous generators) and exhibits a limited amplitude, a controlled phase angle, rich harmonics, and strong nonlinearities. Therefore, the traditional ratio braking type differential protection may have low sensitivity or may even refuse to operate. In order to solve this problem, a pilot protection method based on Spearman's rank correlation coefficient is proposed in this article. When the system operates normally or an external fault occurs, a traversing current flows through the transmission line, so the current waveforms on both sides are the opposite. When an internal fault occurs, there are large differences in transient current waveforms on both sides. Spearman's rank correlation coefficient can be used to measure the degree of correlation between the waveforms on both sides to distinguish between faults inside and outside the zone. Compared with existing protection based on fault characteristics of WFs, the proposed method shows good performance when the power output of WFs is weak and the circuit breaker recloses with permanent failure. Both simulation results and field-testing data validate the proposed method.

Similarity Comparison Based High-Speed Pilot Protection for Transmission Line

To solve the following problem: the action speed of protection based on a phasor is restricted by the length of the filtering algorithm time window and the vulnerability to false data, a new pilot protection principle for transmission lines based on waveform similarity is proposed in this paper. By comparing the discrete point sets of current sampling values, a waveform similarity-based algorithm called the Hausdorff distance distinguishes the difference between both side currents of a protected transmission line, realizing fast identification, and removal of the fault. Based on the characteristics of the algorithm, setting methods and protection criterion are discussed. Finally, an improved Hausdorff distance algorithm is proposed to cope with false data. The effectiveness and advantages of the proposed algorithm are validated with theoretical analysis and extensive simulation test results.

Fault component integrated impedance-based pilot protection scheme for EHV/UHV transmission line with thyristor controlled series capacitor (TCSC) and controllable shunt reactor (CSR)

This paper analyzes the fundamental frequency impedance characteristic of a thyristor controlled series capacitor (TCSC) and presents a novel transmission line pilot protection scheme based on fault component integrated impedance (FCII) calculated for a transmission line with TCSC and controllable shunt reactor (CSR). The FCII is defined as the ratio of the sum of the fault component voltage phasors of a transmission line with TCSC and CSR to the sum of the fault component current phasors where all the phasors are determined at both line’s terminals. It can be used to distinguish internal faults occurring on the line from external ones. If the fault is an external one the FCII reflects the line’s capacitive impedance and has large value. If the fault is an internal one on the line the FCII reflects the impedance of the equivalent system and the line and is relatively small. The new pilot protection scheme can be easily set and has the fault phase selection ability and also it is not affected by the capacitive current and the fault transition resistance. It is not sensitive to compensation level and dynamics of TCSC and CSR. The effectiveness of the new scheme is validated against data obtained in ATP simulations and Northwest China 750 kV Project.

Enhanced transmission line pilot impedance and pilot protection

This study proposes a novel pilot protection for transmission lines by using enhanced transmission line pilot impedance (ETLPI). The ETLPI is defined by the ratio of the voltage difference of fault-superimposed component to the current summation of fault-superimposed component at both terminals of the protected line and used to distinguish the internal faults from the external faults. For the external fault, the amplitude of ETLPI is greater than the positive-sequence impedance of the protected line, whereas it is smaller than the positive-sequence impedance for the internal faults. The pilot protection scheme based on the ETLPI has the feature of avoiding the influence of line distributed capacitance and the saturation of current transformer (CT) as well as the transient response of coupling capacitor voltage transformers (CCVT). Therefore the pilot protection is suitable for different length transmission lines. Both theoretical analysis and test results obtained from EMTP digital simulation and the physical simulation have demonstrated that the pilot protection is of high reliability and good adaptability.

Transmission line pilot protection principle based on integrated impedance

Based on the ratio between the sum of two terminal-voltage phasors of the transmission line and that of two terminal-current phasors of the same line, which is defined as integrated impedance in this study, a novel transmission line pilot protection principle is proposed. When an external fault of the transmission line occurs, the imaginary part of the integrated impedance which reflects the capacitance impedance of the line is negative and with a great modulus. When an internal fault of the transmission line occurs, the imaginary part of the integrated impedance of faulty phase which generally reflects the impedance of the system source and the line is either positive or negative and with a relatively small modulus. According to such a characteristic, the external fault and the internal fault of transmission line can be distinguished. The criterion proposed in this study is not affected by the capacitive current. It can be applied to the line with or without shunt reactor. Moreover, the threshold of the criterion can be easily set. Simulation results of electro-magnetic transient program (EMTP) and dynamic physical test data both verify the high sensitivity and reliability of the proposed principle.

Transmission line pilot protection based on phase segregated model recognition

A new type of transmission line pilot protection based on phase segregated model recognition is presented, since the capacitance model and the inductance model are established, respectively, for the external fault and the internal fault. When the internal fault occurs, the capacitance model error is larger than the inductance model error. When the external fault occurs, the inductance model error is larger than the capacitance model error. By computing the model error, the actual state of transmission lines is obtained. Theoretical analysis and electromagnetic transients program (EMTP) simulation demonstrate that this novel protection principle is unnecessary to compensate the distribution capacitance current and has fast operation speed and good performance on resisting transition resistance and transient components.