Line Pilot Protection Research Articles

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

Protection for AC transmission line between DFIG wind farm and MMC station

The characteristics of power electronic controlled sources are reflected at both ends of the AC line applied to the integration of long-distance wind farms into the MMC-HVDC converter station, and the fault characteristics of the system have undergone fundamental changes. For the doubly-fed wind power AC transmission line with a modular multilevel converter, the short-circuit current characteristics provided by the power supply at both ends of the line lead to the inadaptability of longitudinal differential protection. In view of the significant difference in the complexity of the short-circuit current component provided by the doubly-fed wind power and the converter at both ends of the AC transmission line, a line pilot protection idea based on the complexity of the current component is proposed. The complexity of the current component is characterized by singular entropy theory, and then the singular entropy algorithm and its scheme for pilot protection are constructed. A refined electromagnetic transient model of MMC-HVDC for doubly-fed wind farms is built in PSCAD for simulation verification. The simulation results show that the proposed method can quickly and reliably identify various types of internal and external faults, and solve the problem of incorrect action of traditional protection in this scenario. In addition, the scheme is not affected by fault type, location, or transition resistance.

Line Pilot Protection of Flexible DC Grid Based on Traveling-Wave JS Divergence

The proportion of renewable energy mainly including hydropower, photovoltaic and wind power is growing rapidly. DC transmission technology has become the main tool of new energy transmission. The protection scheme of the voltage source converter-based high voltage DC (VSC-HVDC) power grid is the prerequisite for the DC system. But, problems such as high resistance faults, distributed capacitance, and noise interference reduce the reliability of existing protection schemes. To solve the problem of resistance and noise interference in existing protection schemes, a double-ended protection scheme based on traveling wave JS divergence is proposed. First, the flexible HVDC transmission system is analyzed, according to which the expression of traveling wave power is derived, and its fault characteristics are summarized. Subsequently, a combined algorithm of the JS divergence based on the energy of the S-transform was proposed, and the modified algorithm was used to express the fault characteristics of traveling wave power. Finally, a flexible DC transmission system model is built. The performance of the scheme is verified by setting different interference factors (resistance, noise, distributed capacitance, synchronization error).

An AC line pilot protection scheme for AC/DC hybrid system based on composite mode power difference

This paper proposes a new AC line pilot protection scheme for AC/DC hybrid system on the basis of composite mode power difference, which can avoid the incorrect operation of AC line protection resulting from commutation failure. By analyzing the post-fault conducting states of inverter valves, the expressions of injection current from DC system in different operating states of inverter are derived. And combining the fault network of AC system, the models to calculate the 0/1/2-mode power injected from the backside systems of AC line are built. Then, the 0-mode power and 2-mode power are used to construct the composite mode power difference. Considering that the composite mode power varies with system topology, this paper forms the protection criterion according to the composite mode power difference which is related with the difference between system models of the backside systems in internal and external fault cases. Simulations based on RT-LAB platform confirm that, the presented method can correctly distinguish between different types of internal and external faults, and it is highly immune to the fault resistance and commutation failure.

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.

A new principle of UHVDC line pilot protection based on trigger angle control characteristics

Abstract A new principle of UHVDC Line pilot protection based on internal parameters of the trigger angle of converter is proposed, in order to improve the ability of the protection to withstand transition resistance. Through the analysis of UHVDC control system, it is found that, due to the regulation of control system, in terms of trigger delay angle of rectifier side and trigger leading angle of inverter side, the change tendency in internal fault and external fault is different. Thus, the protection criterion is constructed. Compared with the traditional protection principle using voltage and current to establish protection criteria, this principle uses internal parameters as protection quantity. The simulation based on PSCAD/EMTDC verifies the effectiveness of the protection principle.

Phase-Space-Based Pilot Main Protection for a Transmission Line Immune to Timing Attack and Controllable Shunt Reactors

Pilot current differential protection for transmission lines is an important part of ensuring the safety of the power grid. The loss of data synchronization due to cyberattacks and the uncertain compensation degree of controllable shunt reactors will evidently deteriorate the performance of pilot current differential protection and may lead to the maloperation of the protection if no effective countermeasure is implemented. To address the above-mentioned problems, a novel line pilot protection criterion based on the recognition of the phase space trajectory is proposed. First, the basic principle of phase space and its parameter selection scheme are analyzed. Then, the fault component instantaneous power difference (FCIPD) is selected as the time series for phase space reconstruction, and the distribution characteristics of the phase space trajectory of the FCIPD under different conditions are analyzed. Subsequently, a novel pilot main protection criterion for a transmission line is proposed. PSCAD/EMTDC-based simulation results verify that the proposed criterion is immune to timing attack and controllable shunt reactors and has the advantages of free setting, high speed, and high-fault-resistance tolerance capability.

A fast protection scheme for VSC based multi-terminal DC grid

This paper proposes a novel protection scheme for voltage source converter based multi-terminal direct current (VSC-MTDC) grid, in which DC line pilot protection applies polarity comparison of initial current travelling wave and DC busbar protection is based on sampled value current differential theory. This DC line protection utilizes modulus maximum of wavelet transform to get the polarity of initial current travelling wave on two ends of DC lines to distinguish internal faults from external faults. Current differential protection based on sampling values is adopted as DC busbar protection, which has the characteristics of fast operation speed and less computation compared to conventional current differential protection. A two-level voltage source converter (VSC) based four-terminal DC grid is built on the PSCAD platform and each VSC is equipped with resistive superconducting fault current limiters (R-SFCLs) to limit the short circuit current. Thus, DC circuit breakers can be used to break the DC fault current. The simulation results verify the validity and feasibility of the proposed VSC-MTDC grid protection scheme.

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.

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.