Distance Protection Of Transmission Lines Research Articles

Error analysis and improved method of time-domain distance protection for wind power transmission lines

Time-domain distance protection has a good transient performance and operation speed when applied to wind power transmission lines. In this paper, the error analysis and improved method of phase-to-phase time-domain distance protection are investigated. Firstly, based on the time-domain mathematical model, the location error caused by fault resistance is analyzed, and then the algorithmic convergence and accuracy of conventional phase-to-phase distance relay are evaluated. To solve the computational non-convergence problem, an improved phase-to-phase distance relay is proposed, in which the instantaneous negative-sequence current is used to improve the location accuracy, especially during the fault transient stage of wind farms. In order to avoid the protection overreach problem, the threshold selection method is designed based on the maximum allowable error of the calculated distance. According to the proposed method, the corresponding protection device is developed. And the hardware-in-the-loop (HIL) test system is built based on the real-time digital simulation (RTDS) platform. Extensive experimental tests are carried out, to verify the feasibility and superiority of the proposed time-domain distance protection.

Modified distance protection of transmission lines originating from DFIG-based WPPs by considering the impact of fault-induced rotor frequency and LVRT requirements

This paper focuses on the protection of transmission lines connected to doubly-fed induction generator (DFIG)-based wind power plants (WPPs). DFIG-based wind turbines (WTs), which are connected to the AC grid via reduced-size converters, impose additional challenges on the reliable operation of distance relays due to their distinctive fault current characteristics, converter protective actions, and voltage or reactive control strategy of the converter. In this paper, a modified distance protection scheme is proposed which is able to reliably estimate the fault distance under the aforementioned challenges. The proposed scheme consists of two main components: phasor correction and fault resistance elimination. The phasor correction component eliminates the impedance error due to the fault-induced rotor frequency component of the DFIG short-circuit current. The fault resistance elimination component eliminates the impedance error due to the fault resistance during non-solid faults, which cannot be eliminated by conventional methods as a result of the variable nature of the equivalent impedance of the DFIG-based WTs during faults. Various simulation results are exhibited to validate the effectiveness of the proposed scheme in detecting and identifying all different types of faults on transmission lines emanating from DFIG-based WPPs.

An Algorithm to Mitigate the Infeed Effect on Overreaching Distance Zones Settings

This paper revisits the analysis of the well-known infeed effect on transmission lines distance protection. A new adaptive algorithm to overcome this drawback is proposed, which requires solely impedance data and the operational status of power apparatus to perform overreaching distance zones settings. A comparison of the proposed strategy and the traditional one is performed. The obtained results demonstrate that the proposed settings ensure the correct operation of overreaching zones. Thereby, the backup coverage is improved significantly, besides avoiding distance zones overlapping between adjacent lines. It reveals the proposed strategy usefulness and value from the practical point of view, since it can be implemented with technology readily available on the market.

Transmission Line Distance Protection Algorithm Based on Bayesian Inference

This paper presents a distance protection method based on estimating the resistances and inductances seen by the relay using a least-squares (LS) approach combined with the application of Bayesian inference (BI) to determine fault probabilities in the protected zone over time. The use of BI in the presented algorithm increases the security and reliability of the LS-based line protection approach, which, although fast, may yield impedance estimates with numerical inaccuracies and therefore configures a solution capable of detecting faults internal to the protected zone rapidly and dependably. The authors tested the proposed algorithm using data sets obtained from transmission line fault simulations performed in Alternative Transients Program (ATP), which considered noisy measurements, current transformer (CT) saturation, capacitive-coupling voltage transformer (CCVT) transients, switching onto fault, close-in faults, frequency variations, uncertainties in the line’s parameters, and power swings. Furthermore, the authors tested the presented method against measurements recorded by field protection equipment during seventy-nine actual fault events on four existing 500 [kV] lines. The results indicate that the proposed algorithm is a fast, secure, and reliable distance protection solution and that using BI to the LS-based distance protection approach increases security while maintaining fast fault detection.

Distance Protection of Transmission Lines in Presence of Inverter-Based Resources: A New Earth Fault Detection Scheme During Asymmetrical Power Swings

Although it is commonly assumed that power swing is symmetrical and will have identical effects on all three-phase voltages and currents, there is another type of power swing, which is asymmetrical and mainly occurs during single-pole tripping (SPT), the impact of which on power systems integrated with the inverter-based resources (IBRs) has not been investigated so far. Since the likelihood of the occurrence of asymmetrical power swing is increasing in today's heavily loaded transmission lines, this article investigates the impact of IBR integration on the performance of distance protection during single-pole tripping. Furthermore, a new scheme is proposed to detect earth faults that occur during asymmetrical power swings to enhance the performance of power swing blocking functions. To do so, the superimposed component of the zero-sequence current during SPT is extracted. Then, the moving average window is used to calculate the average of both zero-sequence current and its superimposed component. Furthermore, to enhance the security of the proposed scheme, a new technique based on the phase angle shift between the three-phase currents is devised to detect the asymmetrical power swing conditions. This article shows that as the penetration level of IBRs increases, the standard reclosing dead-time needs to be revisited otherwise it can create an unstable power swing condition, even during SPT. Moreover, this article shows that the proposed earth fault detection scheme can efficiently detect all single-line-to-ground faults occurring during SPT.

Line Voltage Based Distance Relay Using a Multistage Convolutional Neural Network Classifier

This paper presents a novel proposed method for the fault diagnosis in distance protection of transmission line, by which the real time voltage signal is the only required relay input. Unlike conventional protection schemes, the current signal is excepted without influencing the basic functions of the relay as a protecting and a monitoring device to detect and locate the fault. The new method is based on a pre-trained Convolutional Neural Network (CNN) with a combination of the higher order spectral estimations, which performs a deep learning classification with a very high accuracy. This research has succeeded in proposing an efficient 2D CNN model that takes the Short-Time Fourier Transform (STFT) of the signal for high accuracy fault detecting, locating, and classifying. The performance of the proposed models is tested using a new large dataset prepared using Simulink/ Matlab. The results show a high numerical performance evaluation that validates the consistency of the proposed methods.

Time-domain distance protection of transmission lines based on the conic section general equation

This paper presents the development, implementation, and testing of a time-domain distance protection algorithm based on the behavior of voltage and current signals over time and on the conic section general equation that describes this behavior. The authors used six existing electrical systems modeled in ATP/EMTP to perform fault simulations varying the fault type, phases involved, fault resistance, inception angle, and fault location. Besides, the authors carried out a sensitivity analysis regarding the sampling frequency influence, noisy data, dynamic behavior of capacitor voltage transformers, power swings, and close-in faults. Finally, the authors tested the proposed method against an actual fault event on a 500 kV Brazilian transmission line. The results presented in this paper indicate that the proposed solution is robust, fast, accurate, secure, and dependable.

A novel instantaneous value based incremental quantities distance protection for AC transmission lines

Conventional distance protection elements are predominantly based on voltage and current phasors. As a result, those elements require the half-cycle/full-cycle time window to estimate the accurate voltage and current phasors. Using information in the transients of voltages and currents is a possible way to improve the distance protection operation speed. To break free of phasor limitations, this paper presents a novel incremental quantities distance protection algorithm based on instantaneous values of voltage and current. Firstly, the instantaneous voltage distribution along the AC transmission line is analysed. Then, the principle of the incremental quantities distance protection is presented. The influence of fault angle on the presented algorithm is also analysed and a solution is proposed to deal with the relative small fault angle conditions. Finally, an extensive simulation results based on PSCAD/EMTDC simulation verify the performance of the presented incremental quantities distance protection.

Adaptive Mho Distance Protection for Interconnected Transmission Lines Compensated with Thyristor Controlled Series Capacitor

This paper proposes an adaptive dynamic Mho distance relay based on a phase comparator scheme for protecting interconnected transmission networks compensated with a Thyristor Controlled Series Capacitor (TCSC). The proposed relay uses an impedance index factor to initiate the fault detection subroutine. The RMS of the positive sequence current of the faulted loop and the TCSC terminal current are compared for TCSC zone identification. A phase comparator for ground and phase distance elements is proposed, relying on the positive sequence voltage as a polarized memory quantity, while the operating and polarizing quantities are developed using estimated TCSC impedance to mitigate its negative impact. The proposed scheme is easy in implementation and independent on synchronized data transfer, as minimum communication requirements are needed. To evaluate the performance of the proposed scheme, extensive simulation studies were carried out on an IEEE9 bus system compensated with TCSC for different firing angles covering four modes of TCSC operations, different fault types, and fault locations. In addition, an IEEE-39 bus network, as a large interconnected system, is tested for validation purposes. The achieved results designate the precision of the proposed scheme. Moreover, the results indicate its effectiveness for fault resistance tolerance, close-in three phase faults, and stable power swing phenomenon compared with conventional relays.

A new approach to eliminate impacts of high-resistance faults by compensation of traditional distance relays’ input signals

Ground impedance measuring elements of digital distance relays, responsible for line to ground faults, are highly prone to underreach in case of high-resistance faults. To tackle this problem for the distance protection of parallel transmission lines, this paper presents an effective approach by compensating the input signals to the existent traditional distance relays. For this objective, the fault distance is estimated innovatively within a short duration by analyzing the line sequence networks in time domain. The fault distance is employed to generate the signals compensating the under-operation distance relays’ instantaneous input signals measured by instrument transformers, in a way as to eliminate the high fault resistance-caused underreach. The proposed approach would not threaten the relay security in normal operating conditions, irrelevant-circuit and external faults. Further, it would not interfere with the relay phase elements. Performance of the proposed approach is examined through comprehensive simulation studies conducted in PSCAD/ EMTDC for a variety of influencing situations and the results would reveal that the proposed approach is able to fully prevent underreach incidents arising from high-resistance faults, without having a significant impact on the relay response time.

An Accelerated Distance Protection of Transmission Lines Emanating From MMC-HVdc Stations

Compared with synchronous generators, modular multilevel converter-based high voltage direct current (MMC-HVdc) stations have unique fault behaviors, potentially impeding the correct operations of distance relays of lines connecting MMC-HVdc stations. To minimize the adverse effect caused by the fault resistance and MMC-HVdc stations, a new zone 1 protection criterion based on projected reference impedance is presented. According to the polarity of direction factor and the amplitude comparison of projected reference and measured impedances, the internal and external faults can be accurately distinguished. To shorten the response time of distance relays for the faults occurring in transmission lines emanating from MMC-HVdc stations, especially for the faults in the protection deadzone of zone 1, an accelerated distance protection based on the new zone 1 protection criterion is presented, ensuring that distance relays at two ends can clear the internal faults at high speed. Furthermore, the proposed protection scheme remains unaffected by fault resistance and operates well under different fault locations. The performance of the proposed scheme is assessed by more than 2100 digital simulations.

Accelerated distance protection for transmission lines based on accurate fault location

The accelerated operation of distance relay is an important issue to improve the power system stability. The zone-1 of distance relay usually covers about 80% of the transmission line length with an instantaneous operation, while during resistive faults the coverage of zone-1 may be reduced considerably. Therefore, the conventional distance relay cannot cover the whole line length with fast fault clearance. To address the above problem, a non-pilot protection scheme based on the accurate fault location estimation is proposed. When a fault occurs at the end section of the line, after the fast remote circuit breaker (RCB) operation, the accurate amount of fault current can be obtained. Using this current, the accurate fault location is calculated, and as a result, the accelerated trip can be issued to the local circuit breaker (CB) for the faults occurring at all the total line length including the end section faults. The obtained fault location formula is independent of the fault resistance and remote source impedances and can be applied to both single- and three-pole CB operation modes. The proposed high-speed protection scheme is evaluated in the WSCC 9-bus system. Numerous PSCAD simulation studies verify the effectiveness and applicability of the proposed scheme.

Transmission Line Distance Protection Under Current Transformer Saturation

Conventional transmission line distance protection approaches are subject to malfunction under reverse fault-induced current transformer (CT) saturation for the typically employed breaker-and-a-half configuration. This paper addresses this issue by proposing a new distance protection approach that combines the blocking and unblocking criteria of distance protection based on the values of incomplete differential current, operation voltage, and current harmonic content. The proposed approach is verified by theoretical analysis, dynamic simulation testing, and field operation to ensure that the obtained distance protection is reliable and refrains from operating unnecessarily under reverse fault-induced CT saturation in the breaker-and-a-half configuration. Meanwhile, the proposed approach is demonstrated can operate reliably when forward faults occur or various reverse faults are converted to forward faults.

A Novel Two-step Distance Protection for Flexible HVDC Transmission Lines

DC line fault is one of the key problems that must be solved in a flexible HVDC system. During quite a long time between the existing main protection and backup protection of the HVDC line, there is no line protection method to detect the fault, which may lead the protection at the AC side to act before the backup protection of the DC line. To solve the problem, a novel two-step distance protection for flexible HVDC lines is proposed in this manuscript. Firstly, based on the uniform distributed parameter model, the equivalent lumped parameter model of the HVDC transmission line at low frequency is analyzed. Secondly, according to the time domain differential equation and the least squares algorithm, novel distance protection based on the iterative calculation of fault distance is proposed, which can eliminate the influence of distributed capacitive current and improve the precision of calculation. To improve the rapidity and reliability of the distance protection, low pass filters with two different cut-off frequencies are used to process the electrical quantities. Finally, simulation results show that the proposed distance protection can respond to metallic poleto-ground faults and pole-to-pole faults rapidly and reliably.

Analysis of the FACTS devices impact on the transmission line protection operation

The effect of the static synchronous compensator (STATCOM) on distance protection of a high-voltage transmission line is studied in this article. To carry out the research stated in the topic of the paper, an experimental scheme was developed, equipment was selected, the operation settings of the 3 stages of distance protection were calculated and quad characteristics were built on their basis. All listed above, as well as further experiments, were carried out by the real time digital simulator. The STATCOM model was integrated in the scheme and set next. A series of experiments was carried out: two-phase and three-phase short circuits in various nodes of the scheme with and without the compensator and in various connection nodes. After all the experiments were carried out, appropriate conclusions were made about the impact of FACTS devices on the operation of distance protection. Possible ways to solve detected problems were also proposed.

Enhancing Distance Protection of Long Transmission Lines Compensated With TCSC and Connected With Wind Power

Thyristor controlled series compensation (TCSC) is widely used in long transmission lines to mainly improve power transfer capability. However, TCSC produces complicated impedance that negatively affects distance protection operation. The wind energy generation system produces additional complexity to the distance protection performance due to the variation of wind speed and fault current level. This paper proposes an integrated scheme to change adaptively the settings of the Mho distance protection by shifting the relay characteristics considering the bad impacts of TCSC, wind power and fault resistance. The proposed scheme achieves its main stages starting from fault detection, until relay tripping decision procedure including online estimation for preliminary fault location, impedance of TCSC and fault resistance using limited communication requirements. By extensive MATLAB simulations, the performance of the proposed scheme is examined compared with the conventional Mho relays under different fault locations, fault inception angle, fault resistance, different wind power penetration, different wind speeds and different TCSC firing angles. The achieved results ensured that the proposed scheme improves significantly Mho distance relay operation and avoids under-reaching and over-reaching problems irrespective of the large shunt capacitance along the transmission line, and also without identifying the parameters of TCSC such as the capacitance, the inductance or the firing angle.

Traveling Wave-Based Transmission Line Earth Fault Distance Protection

This paper proposes a one-terminal traveling wave (TW)-based transmission line earth fault distance protection function. It only needs the detection of the first incident modal earth fault-induced TWs, so that, the challenging detection of wavefronts reflected from the fault point is not required. Both the sampling frequency effect and inaccuracies on the wave propagation velocity are considered in order to define the distance protection zone. Simulated fault records were played back in an actual relay, allowing the comparison between a commercially existing time-domain distance protection element and the proposed one. The proposed function is more accurate and significantly reduces transmission line distance protection tripping times without dependability losses.

A novel algorithm for improving the differential protection of power transmission system

Current differential protection is simple in principle and is immune to power swings, load encroachment and mutual coupling problems. It provides simultaneous tripping at both ends of the transmission line and multi phase auto reclosing can be easily enabled because of its accuracy in determining the faulted phase and its communication channels. Conventional differential protection has certain issues to be dealt with before using it as a best alternative to distance protection for power transmission lines. Many researchers strive to improve the sensitivity of the current differential protection. Sensitivity and safety are opposing elements and increased sensitivity may sacrifice safety. In this paper, a new differential protection algorithm is proposed using the polarity of the terminal current DC transients. Different cases are studied in order to illustrate the applicability of the proposed differential approach. The proposed algorithm is able to detect high resistance faults and is not affected by line charging current, CT saturation. It improves the sensitivity without compromising the safety of the system. Simulations are carried out on 10 Bus system using PSCAD® software and obtained results are used for illustrating the efficiency of the proposed differential protection.

Adaptive Distance Protection for Transmission Lines Incorporating SSSC With Energy Storage Device

A Static Synchronous Series Compensator incorporating energy storage device (SSSC-ES) at the DC bus enables the exchange of true power with the system in addition to line reactance compensation. This facilitates improved control of real and reactive power in a transmission system. However, the four-quadrant operation of SSSC presents additional problems for the accurate operation of conventional transmission line protection. In this paper, an in-depth analysis of the effect of emulated reactance and resistance by SSSC-ES installed at the center of a hybrid series compensated line on the performance of distance relay is carried out. An investigation is performed with all possible operating modes and control strategies of SSSC-ES, and the possibility of mal-operation of distance protection are explored. A novel adaptive setting based on constant reactance and constant resistance emulation control strategy of SSSC is proposed for quadrilateral distance relay to prevent the mal-operation. MATLAB / SIMULINK is used for the simulation study.

ANN Distance Protection for Transmission Lines

ANN Distance Protection for Transmission Lines