Pilot Protection Research Articles

Time-Domain Fault Detection and Location Scheme for Flexible DC Distribution Networks

Accurately detecting and locating the fault point of the DC line is significant for eliminating the fault and restoring the power supply of the flexible DC distribution network as soon as possible. Firstly, a direction pilot protection scheme for a complex DC distribution network is proposed based on the integral of the current superposition to identify the fault direction. Then, an online time-domain fault location method based on the least square (LS) method to solve the overdetermined equations is proposed by analyzing the fault loop circuit after the DC line fault. The proposed location scheme utilizes fault data at both ends of the line to eliminate the theoretical impact of fault resistance, and the calculation of the current difference method is discussed to reduce the location error of whether the fault current-limiting reactor (CLR) exists. Finally, various simulations by PSCAD/EMTDC V4.5 demonstrate that the proposed scheme has high protection reliability and location results after different fault positions and resistances. The proposed scheme has low requirements for the sampling rate, fault data length, and implementation costs, which can meet practical application requirements.

Pilot protection based on mode distance for transmission line connected to renewable energy station

Abstract Affected by the inverter control strategy, fault characteristics of the wind turbine are essentially different from the traditional synchronous power supply, leading to a decrease in sensitivity and even rejection of traditional differential protection. In view of the above problems, this paper studies the fault current waveform distinction between the wind turbine and the synchronous power supply, and uses the mode distance to measure the current waveform difference. The simulation experimental system is built and the results show that the mode distance can reliably identify the faults in and out of the area in various fault scenarios, effectively working out the kinks of the degradation of the differential protection.

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 similarity of the traveling waves between the quadratic fitting curve and the calculated curve for the All-DC wind power transmission system

The All-DC wind power generation system can effectively solve the harmonic resonance problem caused by large-scale wind power AC collection and transmission, gradually becoming a hot topic in future research. However, there are few studies on the relay protection of the All-DC wind power transmission systems. In the All-DC wind power systems, there are differences in topology, control strategies, fault characteristics, boundary characteristics, etc. At the same time, existing pilot protection has problems such as strict information synchronization requirements and selection of setting values through simulation. Therefore, the proposed pilot protection based on the similarity of the traveling wave between the quadratic fitting curve and the calculated curve for the All-DC wind power system transmission lines. Firstly, the difference of the 1-mode initial current waveform characteristics is analyzed in the time domain at both ends. Then, the least squares method is introduced to fit the differential curves of the current forward and backward traveling waves at two terminals. The differential characteristics of the differences between the fitted curve, the calculated curve, and the measured curve under the influence of internal and external errors are analyzed. Finally, the calculated value of traveling wave current during external metallicity fault is used as the standard. By comparing the fitting curve of current traveling waves and the difference in the calculation curve to distinguish internal faults from external faults. The simulation results show that the proposed protection principle can fault resistance of 2200 Ω and noise interference of 20 dB. In addition, the proposed method does not require strict data synchronization, higher sampling frequency, and setting value through simulation.

Enhanced pilot protection scheme for half-wavelength transmission line based on the conservation of traveling wave energy

The half-wavelength transmission system is a viable technology for long-distance and large-capacity power transmission. It can safely and efficiently transmit a large amount of clean energy to remote load centers. However, the traditional traveling wave protection methods have reliability and speed limitations for HWTL lines. To overcome these limitations, this paper proposes a novel and robust pilot protection scheme based on the conservation of traveling wave energy at the protection installation. The proposed scheme uses the constant equation relationship between fault-traveling waves, reflected waves and refracted waves at the measurement end to significantly improve the reliability and effectiveness of the protection mechanism. The blocking protection operation logic constructed by the inequality directional element is used to improve the rapidity of the pilot protection scheme. The theoretical analysis and real-time digital simulator (RTDS) digital-analog hybrid test demonstrate that the action equation of the proposed protection scheme is explicit to the operating value. The novel scheme exhibits enhanced resilience against high transition resistance and the impact of impulse corona while ensuring both reliability and rapidity.© 2017 Elsevier Inc. All rights reserved.

A Pilot Protection of Negative Sequence and Additional Network Considering Photovoltaic Integration

Background: Introducing pilot protection in active distribution networks containing PV can improve the reliability and selectivity of protection. However, the basic communication facilities of the existing distribution network make it difficult to meet the requirements of data synchronization, and the PV T-connection to the network leads to sudden changes in the impedance angle. Methods: Therefore, pilot protection of a negative sequence and additional network considering PV is proposed. The scheme is based on the feature that the PV model only outputs positive sequence components after a fault. For asymmetrical faults, the negative sequence impedance detected at both ends of the protection is utilized to construct a comparative negative sequence impedance protection criterion. For symmetrical faults, the voltage characteristics of the faulty additional network are utilized to construct a protection criterion. Results: Finally, an actual distribution network model with PV is constructed in PSCAD to verify the effectiveness and reliability of the protection method. Conclusion: The protection method is selective and reliable and is not affected by high penetration rate and PV fault characteristics.

A Novel Pilot Protection Scheme Based on Differential Voltage for Hybrid LCC/MMC HVDC Transmission Lines

A Novel Pilot Protection Scheme Based on Differential Voltage for Hybrid LCC/MMC HVDC Transmission Lines

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.

A pilot protection method for the transmission line of wind farm-flexible DC system based on high-frequency inductance difference coefficients

Conventional protection schemes for wind farm-flexible flexible direct current (DC) system transmission lines are susceptible to malfunctions in external fault scenarios and exhibit limited immunity to fault resistance in internal fault scenarios. In the pursuit of enhancing pilot protection performance, a novel protection method based on high-frequency inductance difference coefficients is proposed. Firstly, the fault transient characteristics of both the wind farm and the flexible DC converter are analyzed, deriving their respective transient models. Subsequently, a high-frequency fault component network comprising inductive impedances is constructed. Then, a protection criterion based on high-frequency inductance difference coefficients is formulated. Finally, the proposed method is subjected to simulation tests on the RT-LAB platform. The results validate its capability to accurately identify the locations of internal and external faults, demonstrating robust immunity to fault resistance. Because it operates independently of synchronous information interaction, it functions rapidly.

A pilot protection based on low frequency component model for HVDC transmission lines

AbstractReliable and fast identification of high‐voltage direct current (HVDC) transmission line faults is important to the safety of power system. In traditional DC transmission line protection, differential protection is invulnerable to high fault resistance, but it needs long time delay for the influence of distributed capacitance current. In order to solve this problem, a novel pilot protection is proposed. The characteristics of the voltage and current processed by low‐pass filter under different fault conditions are analysed, and based on it the protection criteria is proposed. When external fault occurs, it reflects the line capacitance where the first forward fault traveling wave passes, which is increasing until equal to the whole line capacitance, then remains constant. However, when internal fault occurs, its value is negative in the initial stage, and after that its value is very different from the whole line capacitance. The analysis proves that this pilot protection method has fast operation speed, and can be applied for a relatively long period of time. What is more, the applicable time of superposition principle is considered in the analysis, which is not considered in many literatures. An UHVDC system is modelled for simulation in PSCAD/EMTDC, and the correctness and effectiveness of the proposed scheme is verified.

A pilot protection scheme based on high‐frequency transient current waveform similarity for AC lines connected to HVDC inverter station

AbstractAffected by inverter station commutation failure and fast control, line fault characteristics are obviously different from traditional AC transmission line fault characteristics. The existing protection methods for AC line connected to line commutated converter based high voltage DC (LCC‐HVDC) inverter station (ACLs) have the problems of complex setting, weak anti‐noise and high demand for data synchronization. This paper proposes a pilot protection scheme based on high‐frequency transient current waveform similarity. Firstly, with analyzing the fault traveling wave propagation process, the obvious differences are found in the transient current waveforms at both ends of the line when internal and external faults occur. Then the similarity of transient current waveforms is measured with the improved longest common similar subsequence (LCSS) method. And the weak high‐frequency current is extracted with the improved synchronous squeezed S‐transform (SST) method. Finally, a large number of power systems computer aided design (PSCAD) simulation results show that the proposed protection method does not require strict data synchronization, has strong anti‐noise performance, and is tolerant to the influence of abnormal point fluctuations.

Multi-terminal negative sequence directional pilot protection method for distributed photovoltaic and energy storage distribution network

After high proportion of distributed photovoltaic and energy storage is connected to the distribution network by distributed multi-point T-connection, the traditional two-terminal directional pilot protection criterion will be affected by the output characteristics of distributed generation (DG) fault current, which leads to the wrong judgment of the fault direction. In response to the asymmetric fault of typical high proportion of DG T-connected to rural distribution network under the background that DG generally adopts negative sequence current suppression strategy, the paper studies the characteristics of negative sequence power direction when the measuring points of the main line and branch lines of DG distribution network in forward fault or backward fault under the negative sequence current suppression strategy, and puts forward a multi-terminal directional pilot protection method of distribution network with high proportion of DG based on negative sequence power direction, which solves the problem that the traditional two-terminal directional pilot protection in DG distribution network is not applicable. Finally, the correctness of the protection criterion is verified in Pscad/Emtdc.© 2017 Elsevier Inc. All rights reserved.

A Backup Protection Based on Compensated Voltage for Transmission Lines Connected to Wind Power Plants

Due to the influence of complex control, the short circuit current provided by wind power generation units will exhibit new characteristics, such as limited amplitude and controlled phase, affecting the performance of traditional protections. This paper analyzes the work principle and defects of one kind of multiphase compensated distance protection. Drawing on the idea of fault identification by multiphase compensated distance protection, novel pilot protection using the compensated voltage on both sides is proposed. The proposed method has a strong anti-fault resistance ability. The test results indicate that the proposed method can distinguish the internal faults and external faults reliably, unaffected by the new characteristics of short circuit current.

Transient pilot protection based on directional traveling wave principle for wind power transmission line

The short-circuit current from the new energy power generator presents special characteristics such as frequency shift, restricted amplitude, unequal positive and negative sequence impedance, high percentage of harmonic content, etc., resulting in the risk of misoperation or rejection of conventional protection. By analyzing the propagation characteristics of traveling wave in the transmission line after the fault, this paper reveals difference between traveling wave waveforms at both ends of the line under internal fault and external fault. The similarity between forward traveling wave and reverse traveling wave at both ends of line is higher when an external fault occurs, while the similarity between the forward traveling wave and reverse traveling wave is lower after internal fault. According to this difference, a pilot protection algorithm based on discrete Frechet distance is proposed, which can calculate similarity coefficient of forward traveling wave and reverse traveling wave at both ends of line to construct protection criteria, and then identify internal and external fault. Through the analysis of PSCAD/EMTDC and experiment platform of hardware-in-the-loop test verify that the proposed protection algorithm can accurately and reliably distinguish internal and external fault.

Pilot protection based on novel comprehensive impedance of positive sequence fault component for distribution network

The integration of distributed power sources into the distribution network has changed the topology of traditional distribution networks, resulting in changes in fault characteristics, and brought severe challenges to conventional current protection of distribution network. This article proposes a protection method based on the comprehensive impedance of a new positive sequence fault component. Analyze the fault characteristics of positive sequence fault voltage and current during faults inside and outside the line area connected to different types of distributed power sources. The positive sequence fault components of voltage and current at both ends of the section are used to calculate the estimated line impedances. A novel comprehensive impedance is obtained by their subtraction. The ratio of comprehensive impedance to line impedance is constructed. The protection criterion for short circuit fault is given. The simulation experiments illustrate the effectiveness of proposed protection algorithm, not affected by the fault types, locations, permeabilities of distributed generations, has strong ability to withstand transition resistance.

Innovative probabilistic approach to reduce zone-2 time delay setting of distance relays

The time delay of distance relay zone-2 has considerable impacts on the protection system performance. Traditional deterministic techniques for adjustment of this parameter only consider the worst cases, even with a low probability of occurrence. This leads to the increment of the fault clearing time for most of the high-probability scenarios and endangers the system's stability. To diminish this issue and achieve a suitable tradeoff between protection system selectivity and operation time, a novel probabilistic framework is proposed in this paper for proper adjustment of zone-2 time delay. This framework includes two major parts; the fault and protection system are appropriately modeled in the first part, and then in the second part, the Monte Carlo method is employed as the computational engine for analyzing the system attributes under different conditions considering local and pilot protection schemes. Finally, two indices are proposed for the quantitative assessment of operation speed and selectivity of the protection system. The simulation studies fairly reveal that the operation speed of zone-2 is significantly improved using the proposed settings. In addition, the obtained results indicate that the proposed probabilistic approach not only improves the dependability, but also does not endanger the security of the protection system.

Biweight Midcorrelation Based Transmission Line Pilot Protection Algorithm

Biweight Midcorrelation Based Transmission Line Pilot Protection Algorithm

Setting-Less Pilot Protection for MTDC Systems with Weak or No Line Boundary Based on Model Differences Between Forward and Backward Faults

Setting-Less Pilot Protection for MTDC Systems with Weak or No Line Boundary Based on Model Differences Between Forward and Backward Faults

Energy-based Directional Pilot Protection for Distribution Networks with IBDGs Considering Unmeasured Load Switching

Energy-based Directional Pilot Protection for Distribution Networks with IBDGs Considering Unmeasured Load Switching

Energy-Function Based Pilot Protection Scheme for Hybrid UHVDC Transmission Applying Improved Hausdorff Distance

Energy-Function Based Pilot Protection Scheme for Hybrid UHVDC Transmission Applying Improved Hausdorff Distance