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Locating a fault in double-circuit transmission lines is a challenging task due to the mutual coupling effects between adjacent circuits of the line. Also, performance of impedance-based fault location schemes for double-circuit lines is adversely affected by fault resistance. Accurate fault location in double-circuit lines can be achieved if fault location schemes utilize reliable communication links. However, the communication links are not available or enabled in all transmission lines. To overcome such difficulty in fault location in double-circuit lines, a new fault location scheme is proposed for double-circuit transmission lines by using voltages and currents data extracted from single-end of the line. Only the negative-sequence current and voltage phasors during the fault are processed for calculating the fault location. The proposed fault location formula is derived by applying the Kirchhoff's voltage law around the parallel circuits and shunt capacitances loops. Obtained formula is applicable for all types of unbalanced faults and accordingly classification of fault types and phase selection are not required. The proposed scheme is immune to the fault resistance and insensitive to mutual coupling effects. Evaluation results verify that the accuracy of the proposed algorithm is very high under various fault resistances, fault locations, and fault types. [ABSTRACT FROM AUTHOR]

• Proposal has distance protection scheme for the lines connected to the PV plants. • The proposed scheme is independent of PV plant parameters and fault resistance. • In this method the exact fault location is also calculated. The output power of the inverter-interfaced photovoltaic (PV) plant has the continuous variations due to the properties of PV modules and environmental conditions. These variations fundamentally affect the performance of the conventional distance protection during nonmetallic faults. This paper proposes a positive sequence network-based distance protection scheme for the transmission lines connected to the PV plants. Different from the adaptive mho and quadrilateral characteristics, the proposed scheme is independent of PV plant parameters and fault resistance. In this method, the Thevenin equivalent parameters of the grid seen from the PV plant are calculated. Thevenin equivalent parameters are calculated using prefault current and voltage data at the local terminal, without additional costs related to the requirements of the communication channel. The obtained parameters are used in the fault resistance compensation. Furthermore, by eliminating the fault resistance effect on the relay impedance, the exact fault location is also calculated. Since the fault line impedance formula is derived only from the positive sequence network, the proposed method is applicable to different grid codes. The efficiency of the proposed scheme is evaluated on the Western System Coordinating Council (WSCC) 9-bus and IEEE 30-bus test systems. The obtained simulation results verify the validity of the proposed scheme under various fault and PV plant conditions. [ABSTRACT FROM AUTHOR]

Distance relays are often used in the protection of the transmission lines connected to the wind farms. The distance relay using the transmission line impedance measurement identifies the type and location of the fault. However any other factors that cause the failure of the measured impedance, makes the relay detect the fault in incorrect location or do not detect the fault at all. One of these factors is the fault resistance which directly increases the measured impedance by the relay. One of the methods to eliminate relay under-reach effect is using of the trip boundaries. Trip boundaries are changing with wind variation and following with output power of the wind farms. Therefore, trip boundaries should continuously change proportional by the wind speed. In this paper, a method is provided based on the combination of distance and differential protection. In this method, using active power calculation in both ends of the transmission line, fault resistance is calculated and its effects are directly deducted from the calculated impedance by the relay. Therefore, variable trip boundaries are not needed anymore. Also in this method, unlike the technique that the trip boundaries are used, the exact location of fault and its distance from the relay also is calculated. Detailed model of a doubly-fed induction generator (DFIG) driven by a wind turbine is used in the modelling. Results of studies show that the presented method eliminates properly the mal-operation of relays under all different fault resistance conditions. [ABSTRACT FROM AUTHOR]

Distance relay identifies the type and location of fault by measuring the transmission line impedance. However, any other factors that cause miscalculating the measured impedance make the relay detect the fault in incorrect location or do not detect the fault at all. One of the important factors which directly increases the measured impedance by the relay is fault resistance. Another factor that indirectly changes the impedance of the transmission line is static synchronous compensator (STATCOM). When a fault occurs, measured signals by the relay change due to the variation of current injected by the STATCOM and it makes the calculated impedance to be incorrect. This paper provides a method based on the combination of distance and differential protection. At first, faulty transmission line is detected according to the current data of buses. After that the fault location is calculated using the proposed algorithm on the transmission line. This algorithm is based on active power calculation of the buses. Fault resistance is calculated from the active powers, and its effect will be deducted from calculated impedance by the algorithm. Furthermore, by choosing the appropriate data bus, the effect of STATCOM is eliminated and fault location will be detected. [ABSTRACT FROM AUTHOR]

In this study, the effects of the delta-hexagonal phase shifting transformers (PSTs) on the operation of distance relays and their trip boundaries are investigated under different fault resistances and locations. Existence of fault resistance in phase-to-ground faults creates an unreliable operation of distance relays. Trip boundaries are used to determine the fault resistance effects on the impedance calculated by the relay. Moreover, PSTs are used to control the power flow in transmission lines. Finally, a feasible method for eliminating the PSTs detrimental effects on the operation of the distance relays is presented. This method, which uses the voltage difference between the PST terminals, is getting prevalent in modifying the operation of the distance relays even under the high resistance faults. Phasor measurement units (PMUs) are used to calculate this voltage as PMU signals and a remote signal system is used to transmit them to the system protection centre. All the simulations are conducted with Electro-Magnetic Transient Program. [ABSTRACT FROM AUTHOR]

Distance relays detect transmission line faults and their locations by measuring the voltage and the current signals. Also, phase shifting transformers (PSTs) are used to control the power flow in electrical power systems. PSTs protect transmission lines from thermal overloading, improve the stability of transmission system and control the power flow between different networks. Unfortunately, existence of PST in a transmission line vitiates the operation of protection relays by altering the voltage and current signals. In this paper, the effects of the delta–hexagonal PST on the operation of distance relays are investigated by both analytical and computational methods under different fault types and locations. Results of investigations reveal that the PST causes the distance relays to under-reach. Finally, a feasible method for eliminating the PST detrimental effects on the operation of the distance relays is presented. This method uses the voltage difference between the PST terminals to modify the operation of the distance relays. The phasor measurement units (PMUs) are used to calculate this voltage and remote signal systems are used to transfer it to the system protection center (SPC). All the simulations are conducted with electro-magnetic transient program (EMTPWorks). [ABSTRACT FROM AUTHOR]

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Abstract: In this paper the impact of Static Synchronous Series Compensator (SSSC) on the impedance calculated by distance relay is investigated. Analytical results are presented and verified by detailed simulations. Six different phase to phase and phase to ground measuring units of the distance relay are simulated to resemble the behavior of the relay. It is shown in this paper that zero sequence of the injected voltage by 48 pulse SSSC converter has the most impact on the apparent impedance seen by the phase to ground fault measuring unit and cause under reaching of distance relay. It can be concluded from the results that SSSC located in the middle of the transmission line cause to divide trip characteristics of distance relay into two separate parts. It is also shown that the over-reaching operation of distance relay might happen in some cases in the presence of SSSC. All the detailed simulations are carried out in MATLAB/Simulink environment. [Copyright &y& Elsevier]

Abstract: The impact of Static Var Compensator (SVC) on the apparent impedance seen by the transmission line distance relay is investigated in this paper. Analytical results are presented and verified by detailed simulations. It is shown that the connection type of the windings of the shunt coupling transformer of the SVC has a remarkable effect on the apparent impedance seen by the distance relay. Six different phase to phase and phase to ground measuring units of the distance relay are simulated to resemble the behavior of the relay. The impact of SVC is more pronounced on the apparent impedance seen by the phase to ground fault measuring units than the others as is shown by the results. Simulation results include different power system operating conditions, SVC control system settings and different fault-type scenarios. The impact of SVC on the relay tripping boundaries is also clearly demonstrated. Detailed and sophisticated models are used for simulating distance protective relay in a digital simulation environment. [Copyright &y& Elsevier]

By utilizing multiline voltage-source (VSC)-based flexible ac transmission system (FACTS) controllers, independent controllability over each compensated line of a multiline system can be achieved. While VSC-based multiline FACTS controllers emerged as a new opportunity to control two independent ac systems, the main constraints and limitations that are presented to the conventional transmission-line protection systems need to be investigated. In this paper, the impacts of VSC-based FACTS controllers on distance relays while controlling the power flow of compensated lines are evaluated analytically and by detailed simulations for different fault types and locations. [ABSTRACT FROM PUBLISHER]

• The proposed non-pilot scheme is based on the accurate fault location estimation. • This method can be applied to both single- and three-pole CB operation modes. • The proposed method is independent of the line impedance variations and remote source impedances. In multi-zone distance relays, zone-2 has an intentional time delay which is considered for the coordination among the other distance relays. This delay is unnecessary for faults that occur at the end of the protected line and causes the fault to be cleared after hundreds of milliseconds. On the other hand, high-speed fault clearance is an important issue of ensuring the stability of the power system. To address the above problem, an auxiliary fault location (AFL) element based on the proper Kirchhoff voltage law (KVL) loop in the negative- and zero-sequence circuits are designed for distance relays. The input signals to the AFL are the measured signals by local distance relay. The proposed AFL can reduce the zone-2 intentional time delay from 18-28 cycles to 3 cycles. In addition to this, AFL can improve limitations associated with similar methods such as the dependence of these methods to the fault resistance, remote source impedances, and line parameters variation. The AFL can accurately calculate the fault location, before issuing a trip command. Furthermore, to increase the accuracy, the shunt capacitances of the line are compensated by the algorithm. Numerous PSCAD simulation studies verify the effectiveness and applicability of the proposed scheme. [ABSTRACT FROM AUTHOR]

• The proposed non-pilot scheme is based on the accurate fault location estimation. • This method can be applied to both single- and three-pole CB operation modes. • The proposed method is independent of the fault resistance and remote source impedances. 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. [ABSTRACT FROM AUTHOR]

• A pilot scheme to enhance the fault location for TCSC compensated line is proposed. • In this method only the current data at remote-end should be sent to the local-end. • The proposed algorithm is independent of fault resistance, and TCSC parameters. This paper introduces a communication-aided scheme to enhance the fault detection, and fault location calculation for a thyristor-controlled series capacitor (TCSC) compensated transmission lines. In the proposed method only the current data at the remote-end should be synchronously sent to the local-end. Since the remote-end voltage data do not use in local-end, compared with the conventional pilot impedance-based protection schemes, the proposed method significantly reduces the requirement of data transmission bandwidth. The proposed algorithm is independent of fault resistance, power flow direction, and pre-fault condition. In the proposed method the TCSC parameters are not utilized in the derived fault location formula and as a result, the performance of the proposed method is not impacted due to variations in TCSC parameters. Several major factors are taken to investigate the accuracy of the proposed method, including measurement errors and power swing conditions. The simulation results prove the high accuracy and acceleration of the proposed scheme during all fault cases. [ABSTRACT FROM AUTHOR]

• This method is only based on the current data in relay location. • The proposed method is completely analytical. • A negative-sequence based approach used to fault location estimation. This paper introduces an accurate fault location algorithm for double-circuit transmission lines compensated by Static Var Compensator (SVC). The proposed algorithm is based on the negative-sequence circuit of the transmission system and it depends only on the current data available from one end of the line. Since only magnitudes of current signals are required, there is no need for data synchronization. The proposed technique uses the COMTRADE fault files available from digital distance relays and it can effectively locate the all types of unbalanced faults, regardless the high fault resistance, effect of mutual coupling and SVC current injection information. As one formula can be used for all types of fault, classification of fault types and phase selection are not required. The shunt capacitances of the line are considered by utilizing the distributed parameters model of the transmission lines. The proposed algorithm is rigorously investigated for various fault scenarios in SVC compensated transmission system. The simulation cases in the MATLAB environment verifies that the proposed scheme has excellent performance. Test results are compared with a conventional fault location technique to illustrate the accuracy of the proposed algorithm. [ABSTRACT FROM AUTHOR]

• A non-pilot method based on the KVL loop in the negative-sequence circuit is proposed. • The input signals to the method are the measured voltage and current signals by local distance relay. • The proposed method is independent of fault resistance, power flow direction, and SC parameters. Obtaining the accurate fault location in the series compensated double-circuit transmission lines (SCDCTL) is a challenge due to the presence of series compensator, fault resistance, and mutual the coupling between parallel lines. Although by using the pilot fault location methods, the effect of all the aforementioned factors can be eliminated and the location of the fault can be calculated. However, the number of communication channels available for pilot schemes is limited. In addition, the reliability of the communication links for long transmission lines may be particularly reduced. On the other hand, most of the non-pilot methods need to calculate the series compensator data and the accuracy of the fault location in them depends on the accuracy of the series compensator parameters. To improve the limitation of conventional impedance-based methods, this paper presents a non-pilot accurate fault location element (FLE) for conventional distance relays in SCDCTL. The main concept of the proposed method is considering the proper Kirchhoff voltage law (KVL) loop in the negative-sequence circuit of SCDCTL. Consideration of the shunt capacitances of lines ensures accuracy of the achieved fault location formula. It is shown that the designed FLE can improve limitations associated with similar methods such as the dependence of these methods to the fault resistance, mutual coupling between the parallel lines, and the series compensator (SC) parameters. To investigate the performance of the proposed FLE, several factors are considered in the simulation analysis including different fault resistances, fault locations, and fault types. Besides, the influence of current transformer (CT) saturation, measurement errors, external faults, bypassing of the Metal Oxide Varistor (MOV), and effect of noise on the proposed scheme is studied. Evaluation study using PSCAD verify the effectiveness and applicability of the proposed scheme. [ABSTRACT FROM AUTHOR]

• An accurate bi-level single-end fault location algorithm is proposed. • The iterative nature of the method leads to its independency of fault resistance. • It converges very quickly and in a few iterations. • It can be applied to both transposed and un-transposed transmission lines. • It is robust to measurement noise and uncertainties in lines parameters. To guarantee continuous and reliable operation of power systems working near their stability margins, it is necessary to clear faults quickly. For this purpose, accurate and fast fault location methods are required. Single-ended phasor based methods are a category of fault location strategies which are favourable due to simplicity of their implementation. However, enhancing the accuracy of these methods is a challenging task due to unavailability of data from the remote end of the line. In this paper, a novel fault location method that requires the measured data of one end of the line is proposed. As a result, this method does not need communication links. The proposed method is bi-level and in its first level, fault characteristics such as current, voltage, and impedance of the fault are calculated for a given fault location obtained from Level-2. Then, based on the calculated fault characteristics, fault location is updated in the second level. The presented fault location method considers magnetic coupling between lines and it is also applicable for both transposed and un-transposed lines. Numerous simulation studies verify the accuracy of the proposed method in presence of uncertainties such as noise, fault impedance and error in input line parameters. Furthermore, although the proposed method is based on a bi-level iterative approach, the presented results confirm that it converges quickly in 2 or 3 iterations. [ABSTRACT FROM AUTHOR]