Double-circuit Line Research Articles

Intelligent relaying scheme for series-compensated double circuit lines using phase angle of differential impedance

Abstract The paper presents a comprehensive intelligent relaying scheme using phase angle of differential impedance (PAODI) for series compensated double circuit transmission lines. The differential impedance (DI) is the ratio of differential voltage phasors of any phase across two ends of the transmission line to the differential current phasors of the same phase of the same transmission line. The PAODI of each phase are used as inputs to the data mining model known as decision tree (DT) to generate final relaying decision to identify the faulty phase(s) involved. The proposed scheme is extensively validated for different fault scenarios including inter-circuit and cross-country faults on the series-compensated parallel transmission developed on Real Time Digital Simulator (RTDS) platform. The test results obtained indicate that the proposed PAODI based intelligent relaying scheme is both dependable and secure in protecting series compensated double circuit transmission lines with a response time of less than 1 and 1/2 cycles.

An Integrated Fault Phase Selection Scheme for Double Circuit Lines on the Same Tower

For double circuit lines on the same tower, traditional phase selectors for single lines can not operate correctly in crossing-line faults. To ensure the performance of faults phase selection in the single lines and meanwhile achieve accurate phase selection in crossing-line faults, an integrated fault phase selection scheme based on fault component current is proposed. Firstly, faults are divided into single lines faults, same-name-phase crossing-line faults and non same-name-phase crossing-line faults, then the phase selection is classified. The process with adaptive capacity can automatically select the suitable phase selector not affected by fault types. Simulation results via PSCAD/EMTDC show that the phase selection scheme based on fault component current has good performances for different fault types, fault location and transition resistance.

Application Analysis of Expanded Conductor in 1000kV UHV Double-Circuit Line

This paper discusses the feasibility and effectiveness of the application of expanded conduct in 1000kVultra high voltage AC (UHVAC) transmission line. Through the comparison and analysis between expanded conduct and conventional conduct in transmission capacity, mechanical properties, project investment, annual cost and other aspects, it shows that the initial investment of expanded conduct is 4% lower than that of conventional conduct; and the annual cost of expended conductor is superior to that of conventional conduct when transmission capacity, power price and use hours are low.

One-end impedance based fault location in double-circuit transmission lines with different configurations

• One-end impedance based fault location method for double-circuit transmission lines with eight different configurations. • Developed in phase coordinates and does not require six-order sequence component transformation. • Fault data for verification are obtained using MATLAB – Simulink. • Results shown that the method is accurate and robust. A one-end impedance based fault location method suitable for double-circuit transmission lines with different end configurations is presented in this paper. The effect of mutual coupling of the circuits is taken care of in developing the algorithm. The method is developed in phase coordinates and hence it does not require the complicated six-order sequence component transformation. It is applicable to both symmetrical and unsymmetrical lines. Depending on the terminations at both ends of the line, eight different cases are discussed. The fault data required to evaluate the effectiveness of the method are obtained by simulating faults in different types of double circuit lines using MATLAB/Simulink. The accuracy of the proposed technique is evaluated by comparing the computed fault location with the actual fault location in the simulated models. It is shown that the method is accurate and robust for small errors in estimated equivalent source impedances.

Double Circuit EHV Transmission Lines Fault Location with RBF Based Support Vector Machine and Reconstructed Input Scaled Conjugate Gradient Based Neural Network

AbstractA new algorithm is developed to enhance the solution for the problems associated with double circuit transmission lines for the mutual coupling between the two circuits under fault conditions and which is highly variable in nature. The algorithm depends on the three-line voltages and the six line currents of double circuit lines at one end. It relies on the application of Support Vector Machine (SVM) and frequency characteristics of the measured single end positive sequence voltage and current measurement of transient signals of the system. Fault resistance, mutual coupling between two circuits and initial prefault conditions are considered. The accuracy of this method has been assessed using a fault simulation software program. In the first state, the accuracy of the method was determined on the basis of SVM reconstructed method. In the second state, this method utilizes voltage and current data acquired at one common end of the two lines. This paper proposes a new hybrid approach for fault locat...

Zero sequence behaviour of a double-circuit overhead line

Positive, negative and zero sequence series impedances (in Ω/km units) are the first step for power flow and short circuit analyses and are also necessary for setting the distance relays. The paper is devoted to the computation of zero sequence series impedance (in Ω/km units) (self and mutual) in double-circuit overhead lines (OHLs) with one or more earth wires. A systematic comparison with matrix approaches demonstrates that IEC 60909-2 formula adds the zero sequence self and the zero sequence mutual impedance between the two circuits. This approximation of having a unique value of zero sequence impedance is misleading and gives great errors when phase-to-ground short circuit occurs along a circuit. It is worth noting that the zero sequence mutual impedance between parallel circuits installed on the same tower may be as high as 50% (or more) of the zero sequence self impedance of a circuit alone. Consequently, zero sequence mutual impedance between the two circuits cannot be neglected or mixed. MCA (Multiconductor Cell Analysis) shows that the simplified IEC approach underestimates heavily (more than 18%, depending upon the spacing between the circuits) the phase-to-ground fault current for a fault occurrence along one circuit of the double circuit.

Analysis of Key Factors Affecting Double-Circuit Transmission Lines Parameters and Transposition Schemes

Double-circuit transmission lines parameters symmetry would affect the normal operation of the transmission lines and relay protection actions directly. This paper analyzes the impacts of three different phase sequence arrangements on parameters symmetry of conventional un-transposed double-circuit lines, and requirements can be met by the parameters symmetry for double-circuit transmission lines with different types and different length. Took practical engineering requirements into consideration, a simple and admissible suggestion on phase sequence arrangements and the transposition modes is given. The research results provide useful guidance and reference for future designs of double-circuit lines, especially for the compact one.

Adaptive distance relay algorithm for double circuit line with series compensation

With the onset of fault, nonlinear operation of Metal Oxide Varistor (MOV) in series compensated line introduces error in distance estimation. Distance relay reach accuracy depends on several factors. Mutual coupling effect in double circuit line is highly nonlinear and depends on circuit configuration, fault resistance and remote source infeed. This may lead to inadvertent operation of distance relay for faults outside the operating zone. Variations in system condition, effect of shunt capacitance effect and fault resistance influence distance relay healthy operation. Adaptive setting in digital platform is a greater advantage to estimate the change-in system condition and modify the relay characteristics using the recent information. This paper presents an adaptive algorithm for protection of double circuit series compensated line using local end information. The adaptive algorithm is derived for single-line-to-ground fault condition. A 400kV two source system is considered and simulated using EMTDC/PSCAD.

Circulating Unbalanced Currents of EHV/UHV Untransposed Double-Circuit Lines and Their Influence on Pilot Protection

This paper elaborates on the reasons for current unbalance in extremely high voltage/ultra-high voltage (UHV) double-circuit transmission-line systems based on analyses of a typical tower structure and feasible phase arrangements. In addition to the studies of the system under normal operation condition, the unbalanced currents of the double-circuit line under the condition of external faults are first investigated. The frequency-dependent model of UHV double-circuit lines is built using the ElectroMagnetic Transients Program including DC (EMTDC) software package. Simulation results and real data obtained from the power utility show that the circulating unbalanced currents in both cases of normal operation and external fault conditions cannot be ignored due to their high magnitude. The significant influence of the circulating unbalanced currents on pilot directional protection of double-circuit lines is proven and verified by various simulation tests and real field data. Consequently, an improved scheme is proposed to overcome the influence of circulating unbalanced current and significantly improve the reliability of pilot directional protection.

The Loadability of Overhead Transmission Lines—Part II: Analysis of Double-Circuits and Overall Comparison

This is the second part of an investigation aimed at providing a thorough technical comparison between traditional and alternative overhead power transmission lines based on the loadability characteristics. The previous Part I outlined and applied the fundamentals of the loadability analysis to three comparable single-circuit lines. In Part II, the analysis is broadened to three comparable double-circuit lines: traditional three-phase ac double-circuit lines (assumed as the reference system for the comparison) and bipolar HVDC lines and nonconventional combined ac-dc lines. As in Part I, the loadability analysis takes into account thermal limits, voltage drop, power losses, and - when feasible - steady state and transient stability. Part II also performs an overall comparison among the different systems in single-circuit and double-circuit configuration to draw final conclusions.

Analysis of Induced Voltage on Telecommunication Line in Parallel Distribution System

A current flowing through a distribution conductor produces induced voltage, which is harmful to a telecommunication line. Previous research on induced voltage has been focused on single- circuit lines in the distribution system. However, the double-circuit lines, referred to as parallel distribution lines, are widely used in distribution systems because they have significant economic and environmental advantages over single-circuit lines. Therefore, a study on the induced voltage in double-circuit lines is needed. This paper presents a method of calculating the induced voltage in a parallel distribution system using four-terminal parameters and vector analysis. The calculation method is verified by the Electromagnetic Transient Program (EMTP) simulation.

Improved first zone reach setting of artificial neural network‐based directional relay for protection of double circuit transmission lines

This study proposes an artificial neural network-based protection scheme for double circuit transmission line with improved first zone reach setting up to 99% of line length. The proposed scheme involves three stages. The first stage makes the discrimination among normal condition and faults. The second stage identifies the zone/section of the fault from the relay location. If a forward fault is detected in its first zone then the third stage is activated, which classifies the fault type and identifies the faulty phase. The three-phase currents and voltages measured at only one end of the double circuit line are used to calculate discreet Fourier coefficients. Thus, this technique does not require any communication link. The algorithm is presented in detail and extensively tested using the simulink model of a 400 kV, 300 km distributed parameter line simulated in MATLAB® 2009a in the time domain. The simulation results show that all types of shunt faults (forward as well as reverse), its zone/section and faulty phase can be correctly identified within a half cycle time. This method is adaptive to the variation of fault type, fault inception angle, fault location, fault resistance, single circuit operation and CT saturation. The main advantage of the proposed scheme is that it offers primary protection to total line length using single end data only and back up protection for the adjacent forward and reverse line section also.

New Methodology of Fault Identifier for the Double Circuit Line on the same Tower

High voltage overhead transmission line is an important part of the power system to ensure the safe operation of the entire power system, which is of great significance. Power line fault not only has adverse effects to the social economy, and it may also affect the stability of the power system. Transmission line faults including permanent fault and transient fault are identified quickly and accurately, which has important practical engineering significance. This paper presents a method which can be used to identify the permanent fault and transient fault of double-circuit transmission line on the same tower, fault transient voltages and currents extracted from both ends of transmission lines are as a signal source which is decomposed into a series of harmonics in order to establish a criterion function, and then the transient and permanent fault can be identified based on the changes of criterion function value.

The Loadability of Overhead Transmission Lines—Part I: Analysis of Single Circuits

This paper provides a methodology for a thorough technical comparison between traditional three-phase ac lines, on the one hand, and possible (in some cases unconventional) alternative solutions that include HVDC lines, four-phase ac lines, and combined ac-dc lines, on the other. The comparison is based on the loadability curves, which are calculated here for all of the considered lines taking into account thermal limits, voltage drop, power losses, and-when feasible-steady-state and transient stability. The focus is on four-phase ac and combined ac-dc lines, for which the loadability curves are derived for the first time, whereas the loadability curves of three-phase ac lines-well-known in the literature-are derived and used here just as the natural reference for the comparison. Due to the great deal of theoretical and numerical developments, the study is split in two. Part I analyzes single-circuit lines of comparable loadability at the thermal limit (three phase, four phase, and monopolar HVDC). Part II broadens the analysis to double-circuit lines of comparable loadability at the thermal limit (three-phase, bipolar HVDC, and combined ac-dc) and performs an overall comparison among the different systems in single-circuit and double-circuit configuration.

Fault location for three-terminal transmission lines using fault voltage sequence components

ABSTRACTA new fault location algorithm for three-terminal high or extra-high voltage transmission lines is presented and validated. The algorithm is based on the transmission line model with lumped parameters considering the distributed capacitance of lines. Only the sequence component of fault voltage is used in fault location to avoid the influence of saturated current transformer. In location formulas, positive sequence components are used for symmetric faults and negative sequence components are used for non-symmetric faults. The schemes for the following three different conditions of three-terminal lines are discussed in detail: single-circuit line with T-connection networks, single-circuit line to double-circuit line with T-connection networks, double-circuit line with T-connection networks. A new faulted branch selection method is proposed. The hypothetical fault distance of each branch is calculated and compared to accurately determine which branch is faulty. ATP simulation indicates that the location precision is satisfied no matter the measurements are synchronised or unsynchronised at three terminals. A quantitative comparison with the other known algorithms reveals that the presented new algorithm has higher location accuracy and can judge fault branch more accurately.

Directional Relaying During Single-Pole Tripping Using Phase Change in Negative-Sequence Current

Single-pole tripping (SPT) operation imposes problem to many power network relaying schemes. In this paper, the directional relaying issue for faults during the SPT condition is addressed. Algorithms applying negative-sequence components of fault voltage and current for directional relaying find limitations during SPT as the prefault signals also contain negative-sequence components. This paper proposes a directional relaying algorithm during SPT using phase change in negative-sequence current. The proposed technique is an attractive option since it does not use the fault voltage signal in the decision process. The performance of the proposed technique is evaluated using data simulated with EMTDC/PSCAD for single- and double-circuit lines.

Grounding of an Overhead Line Conductor During Work Within the Vicinity of High Voltage

This paper describes ensuring safe working conditions for workers performing electrical installation work and maintenance on overhead lines within the vicinity of high voltage. Due to harsh operating conditions and the necessity of ensuring uninterrupted electricity supply, it is sometimes necessary to replace a conductor on a double-circuit overhead line with one circuit for normal operations. In such cases, there is a high-risk of conductor swing that may cause contact with the phase conductor of the adjacent energized circuit. The presented special “sliding grounding clamp” has been designed and constructed in order to carry the fault current to ground. It enables a good flow of the current from the drawn conductor and, thus, protects the workers from excessive “step and touch” voltage on the worksite. The sliding grounding clamp has been constructed, and tested in practice. It has also been granted a Slovenian national patent.

Research on a New Fault Phase Selector of Protective Relay for Double Circuit Lines on same Tower

Aiming at the misoperation of the conventional phase selector by phase current-difference during some cross country faults, a fault phase selector is developed. Based on the fault lines of the corresponding fault phase are selected, a novel synthesis fault phase selector using voltages and currents in single circuit at single side is proposed, which is based on comparing the difference of fault voltages to make sure all the fault phase in the lines and judging the phase degree and amplitude condition of the fault currents. Used this scheme and the phase current difference, the fault phase may be picked up correctly in double circuit lines on the same tower, especially in cross country faults.

The Influence on Lightning Invasion Waves from UHV Substation Bus Arresters

Ultra high voltage (UHV) AC transmission is a trend in the modern transmission technology development, the UHV substation is the center in the power system. The lightning invasion waves pose a serious threat to the safety of the substation, therefore it is very important to improve the features of the substation anti-lightning. The arresters of UHV substation bus sides, the role of restraining the lighting invasion waves on main transformer have been researched. Applying ATP-EMTP, a simulation model of the lightning over-voltage invasion substation along the double-circuit self-reliance transmission line was built. Whether and how the number of arresters influences the lightning waves were analyzed comparatively. The maximum amplitude of the lightning current can be reduced when the arresters installed in the bus side, and the protective effect of the transformer can be improved effectively.

Directional relaying for double circuit line with series compensation

In this paper, a directional relaying algorithm for the protection of double circuit line with series capacitor is presented. The method uses four classifiers based on positive and negative sequence components which are combined with a voting technique to derive the direction of fault. The technique is evaluated using data simulated with electromagnetic transients including DC/power system computer added design (EMTDC/PSCAD) for a series compensated double circuit line. Results for voltage inversion, current inversion, high resistance far end fault, single pole tripping and cross country fault are presented. The proposed technique is found to be accurate.