Proposed Protection Algorithm Research Articles

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.

Enhanced Non-Communication-Based Protection Coordination and Advanced Verification Method Using Fault Impedance in Networked Distribution Systems

In recent years, the networked distribution system (NDS), which is normally connected to the distribution line (DL), was actively studied as the topology of the future distribution system for reasons such as improving supply reliability, improving line utilization, and increasing the capacity of distribution generators (DGs). However, the NDS creates new issues in terms of protection coordination because of its bidirectional power flow and fault current flow. The issues associated with conventional protection schemes in the NDS include malfunction of protective devices due to bi-directional fault currents and failure of protection coordination due to communication failures between protective devices. When applying a conventional protection method in the NDS, the protection schemes become complicated, and there is a risk of protection coordination failure due to communication failure between protective devices. To solve this problem, this paper proposes an effective and innovative non-communication-based protection algorithm for protection coordination in the NDS. The proposed protection algorithm utilizes fault impedance characteristics, which allow not only determination of whether a fault occurred, but also the ability to identify the exact fault point. Therefore, the proposed method is expected to be sustainably utilized and contribute to developing protection schemes and devices in various system topologies and scenarios in the future. Additionally, this paper addresses the overall concept of hardware-in-the-loop simulation (HILS) and directly verifies the proposed protection algorithm using HILS. Therefore, this study establishes a sustainable foundation for future research on protection coordination using HILS.

Two-terminal traveling-wave-based non-homogeneous transmission-line protection

This paper presents a two-terminal traveling-wave-based protection algorithm applied to non-homogeneous transmission lines comprising any number of sections with different topologies and considering the effect of the sampling rate. Existing two-terminal traveling wave protection functions cannot protect the line under close-in faults and present limitations in non-homogeneous transmission lines. However, the effects of the sampling rate, considered in the proposed method, result in well-defined protection and unprotected zones, essential for protection security and coordination to deal with the issue of close-in faults in non-homogeneous transmission lines. Furthermore, the algorithm can accurately detect the faulted section, allowing its use in advanced protection functions such as adaptive automatic auto-reclosing and high-speed protection schemes. A protection device was modeled considering a sampling frequency equal to 1 MHz, including functions to detect traveling waves via wavelet transform, and the proposed protection algorithm to discriminate line internal from external faults, and to select the faulted section. The algorithm was evaluated using a large number of ATP fault simulations. The results show that the algorithm is robust and reliable for protection devices installed in non-homogeneous lines.

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.

Current trajectory image-based protection algorithm for transmission lines connected to MMC-HVDC stations using CA-CNN

In the presence of an MMC-HVDC system, current differential protection (CDP) has the risk of failure in operation under an internal fault. In addition, CDP may also incur security issues in the presence of current transformer (CT) saturation and outliers. In this paper, a current trajectory image-based protection algorithm is proposed for AC lines connected to MMC-HVDC stations using a convolution neural network improved by a channel attention mechanism (CA-CNN). Taking the dual differential currents as two-dimensional coordinates of the moving point, the moving-point trajectories formed by differential currents have significant differences under internal and external faults. Therefore, internal faults can be identified using image recognition based on CA-CNN. This is improved by a channel attention mechanism, data augmentation, and adaptive learning rate. In comparison with other machine learning algorithms, the feature extraction ability and accuracy of CA-CNN are greatly improved. Various fault conditions like different network structures, operation modes, fault resistances, outliers, and current transformer saturation, are fully considered to verify the superiority of the proposed protection algorithm. The results confirm that the proposed current trajectory image-based protection algorithm has strong learning and generalizability, and can identify internal faults reliably.

Pilot Protection Based on Zero-Sequence Current Resistance-Capacitance Component for Large-Scale Inverter-Interfaced Power Stations

At present, zero-sequence current protection is generally used as the main protection for single-phase ground faults in resistance-grounded inverter power stations. However, limited by the principle, it is difficult for current protection to take into account selectivity and rapid action when the neutral point resistance is large, so there is protection mismatch with the inverter-type power supply for low voltage ride through leads to the risk of large-scale disconnection of non-fault lines. Aiming at the above problems, firstly, a fault analysis model of the inverter power station considering the capacitance to ground is established to study the distribution characteristics of resistive and capacitive zero-sequence currents in the collection system, when single-phase ground short circuit occurs on different types of lines. Then, based on the characteristic difference between the resistance and capacitance components of the zero-sequence current flowing through the two ends of the tie line in case of internal and external faults, a zero-sequence pilot protection algorithm is formed. Compared with the traditional zero-sequence current differential protection, the proposed protection algorithm only transmits logic information without synchronous sampling, and has significant economy. Finally, the feasibility and effectiveness of the proposed protection algorithm are verified by an engineering simulation example.

Residual-based Short-Circuit fault detection and isolation in LVDC microgrid

Designing protection for a DC microgrid is challenging due to its DC nature and heavily capacitor-dominated DC bus that induces high amplitude current spike during short-circuit faults. Moreover, for small-scale applications such as residential DC microgrids, low line-resistance cables increase the fault detection time constraint. Thus, this paper proposes a fast short-circuit fault detection and isolation method based on current residual computation for a standalone residential DC microgrid. The proposed method continuously compares the computed residual from sensed branch currents to their respective defined thresholds. These thresholds are predetermined by analyzing the microgrid operation in healthy mode, considering both steady-state and transient operations. The protection device isolating the faulty branch is then activated once the corresponding residual exceeds its threshold. The protection scheme is validated through a processor-in-the-Loop simulation approach, during which the power stage of the system remains simulated on the host computer using PSIM software, while its control algorithm is executed from a Texas Instrument TMS320F28335 hardware target. The proposed protection algorithm is able to discriminate transient perturbations due to load connection from short-circuit faults. Furthermore, the algorithm implementation is not limited by the size of the DC microgrid nor by the type of the connected loads.

An anti-islanding protection based on RoCoF compliant with ENTSO-E and IEC 62116

In case of unintentional islanding, distributed generation units must be able to detect it and disconnect from the grid in less than 2 seconds. In this work, a Rate of Change of Frequency (RoCoF) method has been developed for islanding detection. Since these algorithms are conditioned by the requirements of grid codes, ENTSO-E network code and IEC 62116 have been taken into account. The RoCoF anti-islanding algorithm has been developed in MATLAB-Simulink and implemented through rapid prototyping techniques in an FPGA ALTERA Cyclone V. To check the proposed protection algorithm, simulation tests have been carried out. Finally, the RoCoF anti-islanding protection has been validated using FPGA in the loop and experimentally in a real 20- kW inverter.

A new differential protection algorithm for transmission lines connected to large-scale wind farms

The fluctuated output power of the large-scale wind farms (WF) and their fault transient characteristics have an adverse effect on the current differential protection systems of the transmission lines. With increased transmission line length and in the case of weak output power from the WF, the differential current between both line ends increases in normal conditions since the capacitive current is comparable to the load current. This paper proposes a new differential protection algorithm for transmission lines connected to large-scale wind farms. The proposed current differential protection algorithm is developed based on the signs of the phase current samples at both line ends, instead of utilizing directly the current magnitudes. The similarity between the signs of the phase current samples at both line ends is evaluated utilizing the signed correlation criterion, and the fault detection index is calculated to discriminate the internal faults from other events. In addition, a new online technique is introduced to adjust the protection settings considering the different output power levels of the WF. The conducted PSCAD/EMTDC simulation studies confirm the acceptable performance of the proposed protection algorithm for numerous normal and fault scenarios, including different fault resistances and inception angles as well as all fault types. The effect of line length, type of wind turbine generator, and different values of WF output power are also considered.

Current trajectory coefficient based time domain line protection for battery storage energy stations

On account of distinctive fault signatures, the extensive integration of large-scale battery energy storage stations (BESSs) results in severe performance degradation of relaying protection. Firstly, the performance problems of classic current differential protection and recently proposed cosine similarity coefficient-based pilot protection are illustrated. Subsequently, the trajectories of two current pairs in two-dimensional space, i.e., fault path current and current on BESS-side, fault path current and current on grid-side, are described and relationship of these three currents is analyzed. On this basis, this paper presents current trajectory coefficient-based time domain protection algorithm for transmission lines connecting BESSs. It describes the basic principle of protection algorithm and designs the operating and restraining regions of two current trajectories. The authors widely assessed the performance of proposed protection algorithm under internal fault by varying fault location, type, resistance and operating state of BESS. Furthermore, the security of proposed protection algorithm was also tested under various nonideal conditions, including severe current transformer (CT) saturation, CT measurement error and outliers. The results indicate that proposed protection algorithm offers gratifying performance in operating speed, dependability, security and selectivity, and outperforms current differential protection and recently proposed pilot protection.

Performance Improvement of Transformer Differential Protection During Cross-Country Fault Using Hyperbolic S-Transform

A cross-country fault is a fault occurring at two different locations of the same circuit, simultaneously or with a short time delay and possibly involving different phases, which is a challenge for the protection system. On the other hand, one of the main problems in transformers’ differential protection is the distinction between inrush current and other faults, such as cross-country faults, internal faults, and saturation of current transformers (CTs) during external faults. In this article, for the first time, external electrical faults and internal mechanical faults, such as radial deformation (RD) and axial displacement (AD) of winding, were considered as cross-country faults in a real winding. The transformers’ winding is modeled based on the detailed model, and the parameters were practically validated in the laboratory. Differential currents are sampled during different disturbances simulations by EMTP software, and feature extraction is performed using hyperbolic S-transform (HST) in MATLAB environment. As a final point, cross-country faults were distinguished from other faults and events by calculating various S-transform indices, including mean square sum absolute deviation (MSSAD), correlation coefficient (CC), and minimum–maximum (MM). The obtained results confirmed that the proposed protection algorithm is very efficient in detecting and distinguishing cross-country faults, even in the presence of noise.

Integrated busbar protection scheme utilizing a numerical technique based on coherence method

A Busbar (BB) is one of the most important elements of a power system, which links a variety of elements such as generators, power transformers, transmission lines and loads. The BB fault current magnitude is very large, which has to be immediately cleared in order to minimize the failure in the power system, and to avoid the CT saturation effects. This paper presents a novel BB protection scheme based on closed-tripping characteristics of coherence coefficients computed for BB current signals. Three-phase current signals of each circuit connected to the protected busbar are measured for calculating nine cross-coherence coefficients. These coefficients are compared with each other and with a pre-determined threshold value to identify the fault location, classification and direction discrimination, as well as to differentiate the internal and external faults with CT saturation extent. The scheme is tested under different types of external and internal faults with variations of faulty phase(s), fault locations, fault resistances, fault inception angles, and power flow angles. ATP platform is used for power system simulation, and MATLAB software is applied to validate the proposed protection algorithm. The simulation results prove that the scheme is fast, where its operating time is within a sub-cycle time range, and it has the ability to discriminate between internal and external faults with/without CT saturation condition. Moreover, the numerical technique is immune to CT saturation effect, and it is simple, effective, secure, reliable, stable and feasible.

Protection of active distribution networks incorporating microgrids with multi-technology distributed energy resources

The protection of active distribution networks incorporating microgrids with high penetration of Distributed Energy Resources (DERs) can be challenging if traditional protective relays are used. This is mainly due to the changes in the power flow, fault current level, difficulty in protection coordination, changes in system topology, and system operating conditions. This paper proposes three new protection algorithms for active distribution networks with large penetration level of inverter-based DERs. These protection algorithms comprise of an adaptive differential protection algorithm, incremental transient energy-based directional protection, and a rate-of-change of current protection. The proposed protection algorithms were tested with a distribution network integrated with wind, solar, diesel generator, and battery storage DERs which are capable of operating in islanded mode forming local microgrids. The distribution system and the proposed protection functions modelled and simulated using the Real-Time Digital Simulator (RTDS®). The results obtained from tests validate the proposed algorithms; and their capability to correctly detect and timely isolate faults without resulting in nuisance tripping of the DERs.

Transmission line protection algorithm based on voltage sequence component under high penetration of inverter-based resources

• Protection challenges under high penetration of inverter-based resources • A novel protection algorithm is proposed which uses voltage sequence components to identify faulty events occurrence in transmission line network. • The proposed protection algorithm reliability has been investigated under different network's impacts. • The proposed protection algorithm sensitivity is tested on a big transmission network under different contingency scenarios. A new protection algorithm based on sequence voltage components is proposed in this paper. The new algorithm helps overcome the sensitivity and maloperation issues of the traditional protection schemes in the transmission line network, especially with a high penetration level of inverter-based resources. In this algorithm, the differential fault sequence components are used to identify faulty events in the transmission network. The fault voltage component across the protected line is compared to a setting value of multiple parameters-based voltage makes the final decision of tripping for internal faults only. The proposed algorithm has been tested on a 400kV, 50 Hz single circuit transmission line network supplied with a mix of 90% wind turbines and 10% synchronous generators. The new algorithm simulation testing showed high accuracy when it comes to rapid trip activation with high discrimination reliability between internal and external events. High impedance with different fault locations has been tested to improve the proposed algorithm reliability. The study also performed on the IEEE 9-bus system to validate the proposed algorithm under various faults when strong and weak infeed performed into a bigger transmission network.

Compensation voltage moduli comparison‐based wide‐area protection algorithm independent of data synchronism and integrity

Secondary direct-current loss within a substation is a severe event. In China, each line protection device is generally powered by one set of secondary direct current (DC) power system within a substation of 110 kV voltage level. In this case, the line protection devices will be immediately taken out of service when the secondary DC is lost, and the lines protected by them will lose their corresponding protections. Once a fault occurs on the line, only the remote back-up protection can be relied on to isolate the fault, which expands the fault influence and increases its clearance time. To handle the above problem, a novel wide-area protection algorithm based on compensation voltage moduli comparison is proposed, which is independent of multi-terminal data synchronism. Then, a comprehensive protection strategy composed of the proposed protection algorithm and the original local distances protection is proposed. The results from a power systems computer aided design/electromagnetic transients including DC (PSCAD/EMTDC)-based simulation verify that the proposed protection algorithm has higher sensitivity. The comprehensive protection strategy could cope with most line faults effectively, even if only partial data are available, the selectivity and speed of which are better than that of distance protections.

A Novel Protection Algorithm for Medium Voltage Collector Feeder In Wind Farm Based On Quadrature Directional Algorithm With Laboratory Investigation

A protection scheme for medium voltage wind farm collector feeder has been presented in this paper. The scheme is based on quadrature directional angle. This scheme is convenient for small WTG with capacity less than 1MVA. It uses the voltage signal at the collector bus and the current signals at each WTG zone to calculate the quadrature directional angle of each zone which connected to protected feeder, any fault occurs at any parallel feeder or at power grid is considered as an external fault. A part of Zafarana wind farm which is connected to 220 kV system of the Egyptian network is simulated by using MATLAB package to verify the proposed protection algorithms. The results covered a wide variety of fault scenarios; these results proved the ability of the proposed algorithm to differentiate between in-zone and out-of-zone faults. To verify the effectiveness of the proposed scheme it is tested in the laboratory by using induction machine, synchronous generator and DC Motor to simulate the power system, the current and voltage transformer are used to transfer the current and voltage signals respectively of the power system to the data acquisition system connected to pc by sampling frequency of 10 kHz. Lab- View package is used as software. The experimental results indicate that they are compatible with the simulated results and the proposed technique is stable, reliable, and fast during the discrimination between internal and external faults.

A Novel Structural Similarity Based Pilot Protection for Renewable Power Transmission Line

The wide application of power electronic component in power system with renewable energy sources has changed the fault characteristics of conventional power system, resulting in the performance degradation of conventional protection, and even the risk of maloperation and rejection. This brings challenges to the security and stability of the power grid. Therefore, in order to solve these problems, a novel principle of pilot protection based on structural similarity and square error method is proposed. The structural similarity criterion makes use of the difference of fault characteristics between renewable sources and synchronous generators to identify internal faults, while the square error auxiliary criterion is used to solve abnormal calculation of the existing similarity based protection. The detailed model of grid-connected renewable energy power plant is built in Real Time Digital Simulator (RTDS) and the proposed protection algorithm is solidified in the industrial protection device. The effectiveness of the proposed principle is verified by hardware-in-loop dynamic simulation experiments. Compared with conventional differential protection, the proposed protection shows excellent performance in speed and reliability during various faults. In addition, a field short-circuit test is carried out in a real wind farm to verify the effectiveness of the proposed protection scheme. It is proved that this proposed method has the prospect for industrial application.

New Algorithm for Protection of Double Circuit Transmission Lines Using Modal Currents

This paper presents a new protection algorithm for double circuit transmission lines using the sum of ratios of modal currents. Relay-operating characteristics is proposed using the complex ratio of modal currents. The proposed algorithm estimates modal domain line parameters and identifies the faulty phases for single pole-tripping applications even during inter-circuit faults. The scheme is sensitive to high resistance internal faults and also detects internal faults with outfeed. The proposed scheme is immune to mutual coupling and is found robust to uncertainties in parameter estimation due to measurement inaccuracies. The scheme is tested for its effectiveness to deal with current transformer saturation and synchronisation error. The scheme protects series compensated double circuit transmission lines even in the presence of current inversion. Exhaustive case studies in electromagnetic transient program (EMTP)/alternate transient program are performed on 400 kV, 300 km, double circuit transmission lines and the proposed protection algorithm is implemented in MATLAB. The results confirm the superiority of the proposed scheme.

Online Detection of Power Swing Using Approximate Stability Boundaries

This paper presents a power swing detection algorithm in multi-machine power systems, which uses wide-area synchrophasor measurements and is based on Zubov's stability boundaries. Zubov's boundary method, an approximation of the famous Lyapunov function, is very common for numerical analyses of power system stability. This work extends the concept of Zubov's approximation boundaries to online protection applications. First, the proposed protection algorithm constructs a series of Zubov's stability boundaries on power angle-frequency (δ-ω) plane for generators based on real-time measurements from phasor measurement units/merging units. Then, it tracks the trajectory of each generator in the δ-ω plane after the disturbance to differentiate out-of-step (OOS) conditions from stable swings. The proposed approach is suitable for online applications, which is a significant improvement over the existing methods for swing detection since it does not require offline studies and network reduction. Effectiveness of the proposed method is shown using a single-machine infinite bus and New-England 10-machine 39-bus systems. The proposed method is also implemented in a hardware-in-the-loop setup with a customized IEC 61850-based OOS relay, and performance is compared with a commercially available relay.