Distance Relay Operation Research Articles

Performance Evaluation of Distance Relay Operation in Distribution Systems with Integrated Distributed Energy Resources

This article presents the evaluation of the performance of the distance relay (ANSI function 21) when integrating Distributed Energy Resources (DERs) in a Local Distribution System (LDS). The aim is to understand the impacts of and the necessary modifications required in the operation of distance relays, considering different levels of DER aggregation, and identifying any threshold levels before issues arise. To achieve this, first, a comprehensive review was carried out to analyze the impacts generated in the protection systems. Second, by using the DigSilent Power Factory software, the implementation of the distance relay using a IEEE 13 Node Test Feeder was validated. The aggregation of the three fundamental types of DG, synchronous machines, solar panels, and wind turbines, was evaluated. The threshold at which distributed generation power injection begins to compromise distance protection performance was identified. This study compares the outcomes of using mho and quadrilateral protection schemes.

Signal Envelope-Based Adaptive Power Swing Blocking

This research paper proposes detection of faults during power swings by using a peak envelope-based method to prevent incorrect distance relay operation. Distance relays should not operate during power swings except to remove a correctly detected fault event. In this study, distinction between faults and power swings is achieved by correctly observing fault occurrence based on dynamic thresholds generated by peak envelopes. The method utilizes a DC offset current in determining the fault inception and fifth harmonic voltage to assess the fault clearance. If the current surpasses the calculated threshold due to fault existence, the relay is allowed to operate. Re-blocking the relay after fault clearance is achieved in the case of a higher value of the voltage than the threshold value. Current and voltage data obtained from two different test systems simulated in PSCAD for various scenarios have been used in the proposed algorithm developed in MATLAB. In order to show the effectiveness of the proposed method, the results on the second test system have also been compared to the results of selected methods in the literature. It has been perceived that the developed method has a high accuracy and provides an appropriate time range for relay and breaker operation.

A Novel Methodology for Fault Sensing in Presence of Power Swing for Transmission Line with Thyristor Controlled Series Compensator

Digital distance relaying is implemented in extra high voltage (EHV) transmission network for speedy and reliable fault detection. But it should not activate in case of slow transients known as power swings. However, for occurrence of any type of fault during power swing, the relay should sense the faulty condition and send trip command to concerned circuit breaker. The detection of fault in a transmission line network with TCSC during the power swing condition has become further complex due to transients generated by series capacitor and the metal–oxide varistor (MOV) protecting it. This paper firstly presents effect of TCSC on distance relay operation for varied TCSC degree of compensation and firing angle values. Further, a discrete wavelet transform-based fast acting fault and swing classification algorithm is proposed which can sense all types of faults during slow as well as fast power swing in first decomposition level and within 0.001 sec. The proposed utilizes optimized threshold values both for swing and fault sensing by using Honey Bee Optimization Algorithm (HBOA). The proposed novel algorithm is coded in MATLAB software and the test system comprising of 400kV, 50Hz parallel transmission line network along with TCSC is built using MATLAB Simulink environment with sim power systems toolbox. It is tested for high/low resistance faults, symmetrical/asymmetrical faults and close-in/far end faults by changing TCSC compensation level and firing angle value. The simulation results prove the accuracy of proposed methodology for swing and fault classification.

Fault Coordination Control for Converter-Interfaced Sources Compatible With Distance Protection During Asymmetrical Faults

In this article, distinctive fault characteristics of converter-interfaced renewable energy sources (CIRESs) will result in the misoperation of traditional distance relays. To handle this issue, a new fault coordination control method is proposed to ensure the correct operation of distance relays. Combined with sequence boundary conditions, the relationship between the apparent reactance and the CIRES positive-sequence current angle is revealed. Based on this, a reasonable current angle is generated by adjusting current references of the controller to make the apparent reactance equal to the actual line replica reactance, so distance relays can detect the fault distance correctly. The proposed control method shows good performance for high resistance faults and operation in weak grids. Meanwhile, the proposed method is economical because it does not require revising the controller structure, and only local measured data are used. Furthermore, fault ride through requirements such as current limitation and reactive current injection are still being realized. Simulation analysis is performed in PSCAD and real-time digital simulator to validate the recommended scheme.

Data window selection for removal of decaying DC component in current phasor estimation for distance protection

In distance protection, the fault current signal is usually distorted by the decaying direct current (DC) and harmonics preventing accurate and fast estimation of the fault current phasor. This paper presents a method based on the carefully selected data windows and least square (LSQ) method to improve the performance of the current phasor estimation. The method comprises a short and variable data window for fast operation of distance relay for close faults and a fixed data window for the accurate operation of the relay for faults close to the boundary of Zone 1. The short and variable data window can achieve high speed in the phasor estimation in a quarter of cycle, whereas the second algorithm uses a fixed data window with an excellent frequency response to increase the accuracy of the phasor estimation. The proposed method is first tested using mathematical formulation under different conditions such as different characteristics of the DC component, noise, harmonics and frequency deviation. Then the method is tested by more realistic samples taken from a simulated transmission system under different fault conditions for flexibility, speed and accuracy. All the test results validate the aforementioned features of the proposed algorithms.

Online vulnerability assessment of Zone-3 distance relays against static load Encroachment: A novel approach based on fault chain theory

One of the main factors in triggering cascading outages is the undesired operation of zone-3 vulnerable distance relays under static load encroachment. In this paper, to avoid the contribution of vulnerable relays in cascading outages, a novel online vulnerability assessment method based on fault chain theory is proposed to identify the critical relays. The main idea is to use the fault chain theory to model the process of valid successive line outages that occur step by step and lead to load encroachment into zone-3 distance relay. A novel normalized prediction index based on relay margin change, margin sensitivity variation, load encroachment factor and overload tolerance of the line is proposed to predict the next possible outage. The distance relays involved in most fault chains are identified as vulnerable relays requiring to be controlled. A suitable index is presented to detect the critical relays. In this regard, an optimal control strategy is also proposed to restore the acceptable operating margins of the identified vulnerable zone-3 distance relays in the system’s emergency condition. The validity of the proposed approach is evaluated on New England 39 bus system to confirm the effectiveness and benefits of the proposed method. The obtained results are exciting.

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.

Analysis of the Impact of a Modular SSSC on the Operation of Transmission Line Protection Relays using a Hardware-In-the-Loop Configuration

This paper evaluates the impact of a modular Static Synchronous Series Compensator (m-SSSC) on the operation of communication-assisted line distance and differential protection relays. The m-SSSC system incorporates an over-current protection feature to trigger the bypass mode of operation during grid faults. A case study is analyzed for a 220 kV transmission line and an m-SSSC with a reactive power rating of 80 MVAr per phase using a Hardware-In-the-Loop configuration. The obtained results show the impact of the m-SSSC system on the distance protection operation during some cases of high resistive faults. The differential protection operation was not affected by the mSSSC.

Secured Zone 3 Operation Against Fault Induced Delayed Voltage Recovery Event

Prolonged voltage level reduction caused by the fault induced delayed voltage recovery (FIDVR) event may lead to a decrease in distance relays security. Therefore, some distance relays are prone to mal-operation under severely prolonged depressed-voltage conditions, and their security should be considered in the FIDVR event studies. The present paper investigates the possible operation of distance relay during the FIDVR event and proposes an auxiliary protection algorithm to effectively prevent its mal-operation during short-term dynamic voltage transient. The proposed algorithm estimates the critical time and voltage level at which the impedance trajectory arrives in Zone 3 of the critical relays using the rate of change of the impedance trajectory, relay margin index, and time-variant NERC/WECC severity indices. Then, the critical voltage is compared with the expected voltage level at the estimated critical time calculated by piecewise cubic spline interpolation (PCSI) method and three consecutive voltage phasors to decide about the block of relays which entering the impedance trajectory to their Zone 3 is probable during the FIDVR event. The efficacy of the proposed method is demonstrated by simulating some short-term voltage transient scenarios on the IEEE 39-bus test system.

Supervising Vulnerable Third Zone Distance Relay to Enhance Wide-Area Back-Up Protection Systems

Under dynamic stressed situations, distance relays are quite prone to zone-3 mal-trippings which are recognized as one of the primary causes for cascaded tripping in power systems and recent power black-outs. Our proposed algorithm enhances the zone-3 back-up protection logic by ensuring secure distance relay operation during such stressed scenarios. A parameter namely relay vulnerability index (RVI) is estimated using phasor information to rank the vulnerable relays in real time based upon the intensity of stressed conditions. Once the set of highly vulnerable relays (HVR) are recognized, an intelligent relaying logic using wide area information monitors these HVR relays. Thus, the proposed scheme effectively supervises the traditional zone-3 relay to identify fault under stressed situations. Performance analysis on IEEE 39 bus New England power system network has demonstrated high accuracy for various stressed and faulted conditions where conventional zone-3 relays mal-operate. Efficacy of the suggested scheme is validated by implementing it on RTDS platform as a part of Controller Hardware-in-Loop testing. Our proposed algorithm efficiently enhances the back-up protection operation of transmission network and significantly improves the security of distance relays without affecting the dependability.

A Time-Frequency based backup protection scheme for enhancing grid security against power system blackout

For the stable operation of the smart grid, the development of a faster, reliable, and secure protective relay algorithm is essential. From the past blackout reports, it is revealed that during different system critical operating conditions distance relay meets dependability and selectivity challenges and operates unnecessarily. To restrict the operation of distance relay only to fault conditions, an intrinsic time-scale decomposition (ITD) based backup protection scheme is proposed. The ITD method decomposes current signals into baseline and residual components. A reliable index is defined as the energy of a significant baseline component that has the highest kurtosis value. The energy-based index effectively accomplishes symmetrical fault-system stress events discrimination task. For technical evaluation of the method, different power system models such as the IEEE-39 bus test system and the Indian Eastern Region Grid (IERG) were considered and simulated using EMTDC/PSCAD software. The response of the method is compared with other existing techniques. The method uses an adaptive threshold selection approach to detect a fault condition and thus the response is independent of system configuration and structure. With this advantage, unintentional tripping of the power system during different critical operating conditions can be avoided.

A new relaying scheme for protection of transmission lines connected to DFIG‐based wind farms

This paper presents a new protection scheme with low communication capacity requirement for protecting lines connected to a doubly-fed induction generator (DFIG)-based wind farm (WF). The proposed relaying scheme addresses the line protection challenges which stem from the non-synchronous frequency component of the current fed from a DFIG-based WF during a short-circuit fault. The fault current frequency of a DFIG-based WF deviates from the synchronous frequency during a fault, which affects the operation of distance relays. In such a scenario, the distance relay located at the WF terminal may lose its coordination with downstream relays, resulting in unnecessary tripping. The proposed scheme relies on the impedance trajectory captured by the local relay, local fault current characteristics, and the frequency tracking of the fault current measured at the distance relays located at the two ends of the transmission line connected to a DFIG-based WF. The reliable performance of the proposed scheme is verified on a 4-bus test system under balanced and unbalanced faults during super- and sub-synchronous operating modes of the DFIG as well as its robustness against power system disturbances.

Protection collaborative fault control for power electronic-based power plants during unbalanced grid faults

The controlled fault characteristics of power electronic-based power plant during unbalanced grid faults can heavily affect the proper operation of distance relay. In order to solve this issue, a fault control scheme is developed for the power electronic-based power plant, which is compliant with grid protection during unbalanced grid faults. Firstly, we analyze the essential problem of the distance relay on the transmission line connecting the power electronic-based power plant. Subsequently, we build the equivalent fault models of power electronic-based power plant in the sequence systems based on the reactive power supporting requirements defined in the modern fault-ride-through rules and the protection demands. From the analytic equation of apparent impedance in different fault loops, a novel protection collaborative fault control scheme to determine the proper current command angle of the power electronic-based power plant during unbalanced grid faults is deduced. Simulation results prove that the proposed fault control of power electronic-based power plant can improve the accuracy of reactance measurements in distance relay, which in turn reduces the malfunction risk of the relay.

S-Transform based fault detection algorithm for enhancing distance protection performance

This paper presents a new fault detection algorithm based on the Fast Discrete Stockwell Transform. The algorithm can improve the functionality of existing distance protection and resolve shortcomings identified during the fault detection process in case of fault occurrence in systems with a high penetration of power electronics-based generators. Reported results of the operation of commercial distance relays of four different vendors show that all relays experience difficulties during ungrounded faults. An RTDS testbed is developed for extensive hardware in the loop testing, comprising electromagnetic transient models of Type-3 and Type-4 wind generators. The proposed algorithm successfully overcomes the identified problems for cases where commercial relays maloperate. The threshold parameters for the fault detection are set by using the energy content attributed to the Fast Discrete Stockwell Transform time–frequency domain signal. Other distance protection modules such as the determination of directionality, phase selection and the computation of the impedance, which are necessary for the protection selectivity, are developed based on currently available solutions applied in commercial relays. The new algorithm has been extensively tested using RTDS for various fault conditions and the obtained results are reported in the paper.

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.

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.

Adaptive fast protection technique for uncompensated/compensated double‐circuit transmission lines connected to large‐scale wind farms

The penetration of large-scale offshore wind farms in power grids has a negative effect on the operation of the conventional distance relays. In this study, a new protection technique is presented for uncompensated/compensated double-circuit transmission lines utilising one-end current measurements. The proposed protection technique does not require any information regarding the transmission line parameters, wind farms, or the compensation devices. In addition, the errors in phasor estimation due to the generated sub-harmonics and inter-harmonics by the wind generators are avoided as the current samples are directly used. Comprehensive studies are implemented on PSCAD/EMTDC software considering numerous cases of external and internal faults. In addition, the double-circuit transmission line is modelled using the frequency-dependent phase model and the mutual-coupling between both circuits are considered. The recorded results confirm the high efficacy of the proposed protection technique with respect to fault type, fault location, and fault resistance.

Adaptive Mho Characteristic-Based Distance Protection for Lines Emanating From Photovoltaic Power Plants Under Unbalanced Faults

The exclusive fault characteristics of photovoltaic (PV) power plants and the existence of fault resistance cause a high probability of failure in operation and unwanted operation of distance relay with conventional mho or quadrilateral characteristic. Different from the fixed operation zones of conventional mho and quadrilateral characteristics, the adaptive mho characteristic presented herein can adaptively adjust its operation zone to solve the aforementioned issues. The basic principle of adaptive mho characteristic-based distance protection is described and the uniform expression of adaptive setting impedance is derived. Subsequently, taking the fault characteristics of PV power plant into consideration, the method of solving the phase angle of fault current is presented, which is the key to calculating adaptive setting impedance. The performances of the proposed protection scheme are evaluated by extensive digital simulations. The proposed protection scheme exhibits satisfactory robustness against the fault resistance and excellent adaptability to different grid codes. It can not only discriminate the internal and external faults occurring in the lines emanating from the PV power plant but also correctly identify the fault direction.

An Accurate Non-Pilot Scheme for Accelerated Trip of Distance Relay Zone-2 Faults

The delayed operation of distance relays zone-2 element for the faults at the end of the line is excessive. It reduces the fault clearing speed and therefore, is one of the main factors that can endanger power system stability. This paper proposes an impedance-based scheme for discrimination between the last 20% of the line length faults and the adjacent line faults, which are covered by the relay zone-2. The suggested non-pilot scheme uses a modified fault location formula for the accelerated zone-2 operation of distance relays. The negative- and zero-sequence components of local signals are utilized to calculate the accurate fault location after the remote circuit breaker (CB) operation. The proposed algorithm is independent of fault resistance, power flow direction, pre-fault condition, and it can clearly distinguish internal faults from the adjacent line faults. Simulation results show that the proposed method can identify the remote CB operation and thus can accelerate the tripping of zone-2 within a very short time for different fault locations, fault types, fault resistances, and load angles. Also, accurate fault location has been achieved under all simulation conditions.

A graph theoretic approach to accelerate natural cutset prediction during an out-of-step condition

When an out-of-step (OOS) condition occurs in a power system, it splits into multiple islands. This uncontrolled separation happens due to distance relay operation on the lines where electrical centers appear. Real-time phasors obtained from Phasor Measurement Units (PMUs) can be used to track the evolution of electrical centers and identify the natural boundary of separation (cutset). Interestingly, electrical centers do not appear simultaneously on the cutset lines; instead, they evolve at different rates. Hence, the cutset is identified only when the signature of the last electrical center appears. We aim to accelerate the cutset prediction so that the complete cutset is identified when the first electrical center is predicted. For this, we propose a computationally efficient algorithm based on the application of graph theory and clustering technique. Thus, the proposed scheme addresses the significant delay in cutset prediction and thereby increases the time available for controlled islanding. Test results on standard IEEE systems and the All India test system validate the scheme.