Differential Protection Of Transmission Lines Research Articles

A New Approach to Current Transformer Saturation Compensation for Transmission Line Differential Protection

A non-linear autoregressive network with external inputs (NARX) model to reconstruct the current transformer (CT) secondary waveform distortion in the presence of protected transmission lines is presented. The qualitative analysis carried out on the autonomous model reveals the accurate performance of the current differential relay, because of the ability of the NARX to make accurate predictions and signal reconstruction even when faced with noisy or incomplete datasets. The suggested method uses samples of the line-protected remote current signal to produce a desired waveform. The unsaturated section is artificially expanded because it can estimate up to one sample after saturation with a respectable level of accuracy. The proposed method is evaluated by MATLAB and PSCAD software. The effectiveness of the suggested method for different fault types under varied situations has been proved. The simulation outcome confirms the method’s high accuracy concerning the unusual system conditions in the presence of CT saturation.

Time-Domain Differential Protection of Transmission Lines Based on Bayesian Inference

This paper presents a time-domain differential protection method based on the Bayes’ Theorem and on the current samples to determine the fault occurrence probability as a function of time. It also describes the theory involved in developing the proposed protection method when considering the differential protection of transmission lines. The authors performed fault simulations using an existing electrical system modeled in EMTP varying the fault type, phases involved, fault resistance, inception angle, and fault location, and carried out a sensitivity analysis regarding high impedance faults, current transformer saturation, noisy data, misalignments between terminal samples and power swings. The authors also tested the proposed method against actual fault events from four existing transmission lines of the Brazilian interconnected power system. All results indicate that the proposed solution is fast, accurate, secure, and dependable.

Ultra-High-Speed Transmission Line Differential Protection using an Error Index of Bergeron Equation

The Ultra-high-speed and simplicity of protection schemes have been a subject of study in recent years. Therefore this document develop a differential protection method in transmission lines using voltage and current traveling waves signals, where the transmission lines are modeled through distributed parameters and expressed by telegraph's equations which is solved using Bergeron's equations, these equations depend on instantaneous signals and historical components. Using an error index that compares the voltage and current signals from the line ends, the fault is detected. Furthermore, signals with synchronized measurements with the same time stamp are considered. This method uses simple criteria and fast operation time, because it uses algebraic operations and a time window between 1 and 2 ms. A power system is modeled on ATPDraw and many faults cases are simulated; several conditions such as inception angle from voltage signal, fault resistance, fault distance and internal/external faults are considered. In the case of three-phase systems, the use of Clarke's modal decomposition is proposed. Good results in the operation are obtained and comparing with traditional algorithms this method presents low operating times.

Mathematical and experimental evaluation of an incremental differential protection function embedded in a real transmission line relay

This paper evaluates, mathematically and experimentally, a transmission line differential protection function based on incremental currents, which are not influenced by pre-fault conditions, such as charging and loading levels. In the mathematical analysis, the trajectories for each phase, for all types of faults, are demonstrated by analytic deduction of incremental current ratios. For the experimental assessment, the Alternative Transients Program (ATP) was employed to submit a 500 kV 200 km long transmission line into a wide variety of faults. In addition, a 500 kV transmission line of the Brazilian interconnected system was also modeled via ATP, so that different faults scenarios could be applied to it. Also, for this last set of cases, the algorithm was embedded into a real commercially available relay to assess its performance. In order to carry out a broad evaluation of the incremental algorithm performance, sensitivity analyses were made. The results reveal that the incremental function operates for a bigger variety of faults including ones that the conventional function does not operate.

Zero-sequence longitudinal differential protection of transmission lines

This paper explains a new, earth fault-sensitive algorithm for the longitudinal differential protection of transmission lines. The sensitivity of longitudinal differential protection in radial networks was examined. In particular, problems which can influence the protection’s speed and reliability were considered, such as great line length and the presence of resistance at fault position. In addition, the algorithm was tested for isolated and low-impedance earthed networks. The paper’s thesis is that rather than the stabilization current, the direction of the zero-sequence currents brought to the relay should be used. The zero-sequence currents’ direction is identified without using any voltage inputs. The suggested algorithm was compared to algorithms used by renowned relay manufacturers. Various types of external and internal faults were simulated. The results prove that the described algorithm is prompt and highly reliable under all the aforementioned conditions which can cause unwanted irregularities in the operation of the longitudinal differential protection.

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 New Principle of Traveling Wave Differential Protection for HVDC Transmission Lines

This paper proposes a new principle of traveling wave differential protection of HVDC transmission line. By analyzing the relationship between the forward traveling wave current and the backward traveling wave current on the line, the differential criterion is proposed by using the measured value and calculated value of the same side current. This criterion eliminates the unbalanced current caused by the attenuation of the current amplitude in the long transmission line in theoretically, so the unbalanced current is small and the sensitivity is higher than conventional differential protection. The results from theoretical analysis and simulation show the proposed traveling wave differential protection can correctly distinguish whether the fault is internal or external and is suitable for the backup protection of HVDC transmission line.

Sequence‐component‐based current differential protection for transmission lines connected with IIGs

Current differential protection is normally designed as the primary protection for the high-voltage transmission lines. However, for the transmission line that is connected with the large-scale inverter-interfaced generators (IIGs), the performance of the conventional current differential protection is significantly affected by the difference between the sequence components of the fault currents on both sides of this line. This may result in the mal-operation of protection relays. This study proposes a sequence-component-based current differential protection from a suitable fault model of IIGs under positive-sequence control strategy. A differential coefficient is introduced to overcome the low sensitivity and poor reliability of the conventional differential protection. The proposed scheme discriminates the internal faults accurately from the external faults and the normal operating conditions. Additionally, the robustness analysis shows that this scheme is immune to different fault resistances, fault locations, and system parameters. Simulation results in power systems computer-aided design/electro-magnetic transient design and control validate the effectiveness of the proposed sequence-component-based protection scheme.

An algorithm for longitudinal differential protection of transmission lines

This paper describes a new algorithm for longitudinal differential protection of transmission lines. Classic stabilization is an unreliable method for avoiding unnecessary relay tripping in case of current transformer saturation during faults outside the protected zone. There are various methods for detecting current transformer saturation. The paper’s thesis is that rather than the stabilization current, the direction of the currents introduced into the relay should be monitored. The proposed algorithm has been compared to the algorithms used by renowned relay producers. Different types of faults have been simulated, both within and outside of the protected zone, and the paper demonstrates how the relay trips when the algorithm in question is used. The results have proven that current transformer saturation does not affect protection operation, and that a prompt relay response is obtained for faults occurring within the protected zone.

Time frequency response-based current differential protection of wide area compensated power system networks

This paper presents a time-frequency response approach suitable for current differential protection of transmission lines in an interconnected power system network. The current differential protection scheme efficiently discriminates between the internal and external faults in the protected zone of a transmission network and exhibits stability and robustness. For detecting the occurrence of a fault on the transmission line a cumulative sum average (CUSUM) technique is used and the fault classification and location are determined using the spectral energy of the average and differential currents based on a recent matrix version of the fast discrete S-transform (FST). This new formulation uses intelligent frequency scaling, bandpass filtering, and suitable interpolation techniques to reduce the computational overhead of the algorithm by almost 30 times in comparison to the earlier conventional S-transform. Further, the new protection scheme will be a viable and competing one with the advent synchrophasors technology and wide area high speed communication and GPS systems. Also, its viability is tested for the wide area network with a STATCOM placed at the middle of one of the transmission lines injecting reactive currents which requires the detection of the occurrence of the fault before or after the compensating device.

Time frequency response-based current differential protection of wide area compensated power system networks

This paper presents a time-frequency response approach suitable for current differential protection of transmission lines in an interconnected power system network. The current differential protection scheme efficiently discriminates between the internal and external faults in the protected zone of a transmission network and exhibits stability and robustness. For detecting the occurrence of a fault on the transmission line a cumulative sum average (CUSUM) technique is used and the fault classification and location are determined using the spectral energy of the average and differential currents based on a recent matrix version of the fast discrete S-transform (FST). This new formulation uses intelligent frequency scaling, bandpass filtering, and suitable interpolation techniques to reduce the computational overhead of the algorithm by almost 30 times in comparison to the earlier conventional S-transform. Further, the new protection scheme will be a viable and competing one with the advent synchrophasors technology and wide area high speed communication and GPS systems. Also, its viability is tested for the wide area network with a STATCOM placed at the middle of one of the transmission lines injecting reactive currents which requires the detection of the occurrence of the fault before or after the compensating device.

Transmission lines differential protection based on an alternative incremental complex power alpha plane

This study proposes a new concept of transmission line differential protection based on an alternative alpha plane of incremental complex power, where the restraint characteristic is simply defined as its left-half-plane, so that no settings are required to define it. As the incremental complex power is evaluated per phase, the proposed algorithm is inherently phase segregated, not requiring additional faulted phase selection logics. A simple harmonic restraint strategy along with an external fault detection logic provides security for external faults with current transformer saturation. Aiming to evaluate the performance of the proposed algorithm, a wide variety of fault scenarios are simulated for a 500 kV transmission line 200 km long using the Alternative Transients Program. The obtained results reveal the proposed algorithm provides a fast and reliable line protection, being robust against variations in fault parameters, sources strength and loading conditions, as well as power swing situations and line energisation manoeuvres. Accordingly, one can suppose the proposed algorithm might be successfully used in numerical transmission line relaying.

Communication Channel Reconstruction for Transmission Line Differential Protection: System Arrangement and Routing Protocol

Natural disasters may be of significant impact on overhead transmission lines and cause communication outage related to pilot protection. This paper aims at reconstructing communication channels and maintaining functions of pilot-wire differential protections after the main channel fails. With the development of smart grids as well as new communication technologies, wireless sensor networks (WSNs) have been potential means for realizing reconstructed communication channels (RCCs) without further installation. For a reliable design, system arrangement and the communication structure were presented. Theoretical planning of sensor nodes was formulated, which enjoys advantages such as high reliability, cost optimization, and capacity of satisfying the connectivity of the communication network. To meet the need of time delay, a novel routing protocol for WSNs was proposed with three stages including route establishment, route discovery and route maintenance, which ensured the directional propagation of data packets. Practical experiments and simulation results indicate that the proposed RCC scheme can satisfy time delay of protection relaying in emergency communication channel, as well as guarantee the connectivity of networks when some WSN nodes are damaged.

Adaptive CWT‐based transmission line differential protection scheme considering cross‐country faults and CT saturation

In this study a new adaptive continuous wavelet transform (CWT)-based current differential protection scheme is proposed to cope with problems of conventional current differential protection in transmission lines. Current transformer (CT) saturation is a major problem for protection engineers in current differential protection systems. The mentioned problem is highlighted when an external fault occurs and causes mal-operation of differential protection. In this study, three phase currents at both ends of transmission line have been sampled and used as input signals to the proposed method using appropriate communication link. In addition, CWT with the aid of Mexican hat as a mother wavelet has been employed to extract high-frequency information of signals and detect fault occurrence and CT saturation in each phase. As a result, the proposed technique is able to prevent unwanted trip due to CT saturation during external faults. Nevertheless, simulation results confirm sensitivity and security of the proposed protection technique in facing with second internal fault of cross-country faults after a short delay.

Simulation of longitudinal differential protection of transmission lines with additional stabilization and APU system

This paper explains the algorithm for the longitudinal differential protection of transmission lines with automatic reclosing. Classic stabilization is not sufficient for avoiding of unnecessary operations caused by saturation of current transformer. This problem can occur during the fault plased outside of the protected zone of the transmission line. It is shown how unnecessary operation can occur during the outside fault whithout using of additional stabilization. The different types of faults were simulated and comparison of relay operations with and without additional stabilization is presented. The simulations were performed on the three-phase model of the transmission line formed by using of MATLAB/Simulink program.

A new time-frequency approach for hybrid differential and impedance protection of transmission lines

A new current differential protection of transmission lines is presented in this paper using an S–transform variant having very fast computational speed suitable for real–time applications. The conventional S–transform used earlier for transmission line protection has large computational overhead and thus is not suitable for generating decisions regarding the occurrence of a fault and its type on a transmission line. The new S–transform variant is based on different types of frequency scaling, band pass filtering, and interpolation techniques to achieve a significant reduction of computation time in comparison to the original S–transform. For wide area protection as in the case of smart grid the current differential protection is realised by extracting the relevant features from the current signals at both the sending end and receiving end terminals from the new S–transform generated contours. This paper focuses on the fault detection, classification, and location aspects using a new S–transform variant applied to synchronised measurement of the differential and average energy of current signals. Digital simulation results using EMTP for a long distance transmission line show the computational speed and efficiency of this new algorithm.

Current Differential Protection of Transmission Line Using the Moving Window Averaging Technique

We propose a new approach to current differential protection of transmission lines. In this approach, we transform the instantaneous line current(s) by using a moving window averaging technique. If the time span of moving window is equal to one-cycle time, then the steady-state value of the transformed current is zero for a periodic signal which is composed of fundamental and harmonic frequencies. Signal distortions (e.g., a fault) cause the transformed currents to deviate from the nominal zero value. This permits the development of a sensitive, secure, fast, and yet simple current differential protection scheme. The scheme can be applied in toto to series-compensated transmission lines. Results on a four-machine ten-bus system and comparative evaluation with state-of-the-art methods brings out promise of the proposed method.

Laboratory Investigation of Using Wi-Fi Protocol for Transmission Line Differential Protection

Pilot wire differential protection is one of the most common methods for protecting short transmission lines. The conventional protection scheme has drawbacks, such as malfunction due to line disconnection and limited line length. A laboratory investigation of transmission line protection using Wireless Fidelity (Wi-Fi) communication protocol for data sharing between the relays located at the two ends of the transmission line is presented in this paper. The protection algorithm is based on current signals measured at both ends of the transmission line. The data is exchanged through the wireless communication network. The relay decision is based on data sharing obtained through wireless communication network. The suggested technique satisfies high degree of reliability and stability.

GPS synchronized digital current differential protection for transmission lines

Abstract This paper describes a newly developed digital current differential protection for transmission lines. The proposed protection is different from existing ones in two aspects: one is using GPS time information to implement synchronized sampling at all terminals of the protected line. Another is the application of new differential algorithm based on fault component instantaneous value. To evaluate the performance of the protection, both the EMTP simulation study on the new algorithm and the dynamic simulation test on the prototype of the protection are conducted. The test results have proved the correctness of the new algorithm and the feasibility of the protection scheme. This paper starts with brief introduction to overall scheme of the protection, then focuses on describing the principles of GPS based synchronized sampling and new differential algorithm. The simulation results are also presented.

A new microcomputer-based approach for pilot differential protection of transmission lines

This paper presents a theoretical and experimental study of a new technique for pilot differential protection of transmission lines. The difference currents obtained from post- and pre-fault line currents, adjusted by calculated charging currents, are used to minimize the desensitizing effect of load and line charging currents. The experimental results are from a laboratory 16-bit microcomputer-based relay that was developed to test some of the features of this new approach. Off-line test results for various types of faults on a lumped parameter long transmission line model and real-time test results for a short transmission line model are presented.