Estimation of Zero-Sequence Impedance Parameters in Double-Circuit Lines Using Disturbance Recorder Data

Transmission of electrical energy is the most important component of an electric power system. Optimization, modernization of the electric power transport system, increasing the capacity, as well as variability of connection arrangements, while maintaining the required level of reliability and safety, is regarded today as an urgent task for the energy industry as a whole. The article is devoted to the problem of determining the efficiency of the circuit design solution for a double-circuit three-phase power transmission line with an additional mode of operation — «with a split back-up phase» and determining its main reliability indicators. A circuit design solution for a double-circuit power transmission line with expansion of operating modes is presented in detail. The functional redundancy of the transmission line in accordance with the circuit design solution is based on switching of a conventional double-circuit power transmission line in the emergency mode to the single-circuit split-phase mode, which is the second working circuit. The ways of increasing the natural power of a double-circuit power transmission line are considered. The results of calculation of the capacity of a line with a split back-up phase and a comparison of the main parameters of overhead transmission lines with an additional mode of operation — with a split back-up phase — and power lines in conventional modes of operation, are presented. The results of calculations of reliability indicators are presented, such as the probable relative number of hours of interruption of power supply and the undersupply of electrical energy. A comparison of options have shown that the probable relative under-supply of the electric power of a double-circuit overhead transmission line with an additional operating mode — with a split back-up phase, is lower by approximately 13% than that of a conventional double-circuit power line, which will positively affect the maneuverability and reliability of the entire system.

Power transmission through ring transmission systems

With the development of the power system, the double-circuit lines on the same pole are more and more widely used in a UHV (EHV) AC transmission system. Because of a coupling of the double-circuit lines, the values of the secondary arc current and recovery voltage on double-circuit lines are higher than that of the single-circuit lines. These will affect the possibility of successful single pole autoreclosing. The methods that reduce the magnitude of secondary arc current and recovery voltage should be used to ensure the successful autoreclosing. In this paper, the formulas of calculating the secondary arc current and the recovery voltage on double-circuit lines on the same pole are presented, and the factors affecting the secondary arc current and the recovery voltage are discussed. Using EMTP, calculated the secondary arc current and the recovery voltage of a double circuit lines on the same pole. The simulation results were in accordance with the theoretical analysis.

Accurate knowledge of transmission line (TL) impedance parameters helps to improve accuracy in relay settings and power flow modeling. To improve TL parameter estimates, various algorithms have been proposed in the past to identify TL parameters based on measurements from Phasor Measurement Units (PMUs). These methods are based on the positive sequence TL models and can generate accurate positive sequence impedance parameters for a fully transposed TL when measurement noise is absent; however, these methods may generate erroneous parameters when the TLs are not fully transposed or when measurement noise is present. PMU field‐measure data are often corrupted with noise and this noise is problematic for all parameter identification algorithms, particularly so when applied to short TLs. This paper analyzes the limitations of the positive sequence TL model when used for parameter estimation of TLs that are untransposed and proposes a novel method using linear estimation theory to identify TL parameters more reliably. This method can be used for the most general case: short/long lines that are fully transposed or untransposed and have balanced/unbalance loads. Besides the positive/negative sequence impedance parameters, the proposed method can also be used to estimate the zero sequence parameters and the mutual impedances between different sequences. This paper also examines the influence of noise in the PMU data on the calculation of TL parameters. Several case studies are conducted based on simulated data from ATP to validate the effectiveness of the new method. Through comparison of the results generated by this novel method and several other methods, the effectiveness of the proposed approach is demonstrated. Copyright © 2010 John Wiley & Sons, Ltd.

This paper deals with problems connected to the distance protection of double-circuit transmission lines. Because of the zero sequence mutual coupling of parallel circuits, the relay "sees" incorrect impedance. In this paper, the authors develop an adaptive model which solves problems of single-line-to-ground faults on a single line. Different operation modes change short circuit currents (I/sub k1/ - phase-to-earth short circuit current and I/sub k3/ - three-phase short circuit current) on both ends. In fact, the parameters of the active network will be changed. The idea was to develop an adaptive model with different independent Kohonen networks. Each network is trained with short-circuit examples according to the switching mode and operation mode. Input parameters are voltage, current, switching mode and operation mode. The developed adaptive model was tested on a double-circuit 400 kV transmission line.

This paper deals with problems connected to distance protection of a double-circuit transmission lines. Because of the zero sequence mutual coupling of parallel circuits, the relay sees incorrect impedance. Behavior of distance relays, which protect multi-circuit lines, is that they underreach when the parallel circuits are in service and that they overreach when the parallel circuits are out of service and earthed at both ends. In this paper an adaptive model was developed which solves problems of single-line-to-ground fault on a single line. From the local measurements and from the transmission line theory error factor can be calculated, which is the ratio of the calculated impedance seen by relay and the desired impedance at a fault distance. The aim of the adaptive model is to improve accuracy of the distance relay (to compensate error factor), according to the local measurements using a self-organizing neural network or the so called Kohonen network.

Fault detection, classification and location from the relay end in a double circuit transmission line are challenging tasks because of mutual coupling between the two circuits. In this paper, combined unsupervised and supervised neural networks-based fault detection, classification and distance location techniques are presented for a double circuit line. This technique does not require communication link to retrieve the remote end data. Zero sequence current compensation for healthy phases can also be avoided. Artificial neural network employs a reduced set of input features, i.e., the fundamental components of three phase voltages and the six phase currents of the two parallel lines at one end of the line only. The simulation results show that single phase-to-ground faults can be correctly classified and located after one cycle from the inception of fault. The complexity of the possible types of faults, fault locations, high path fault resistances, fault inception angles, mutual coupling effects and remote end in-feed do not affect the performance.

A precise analytical method for fault location in double-circuit transmission lines

With the changing technologies in the field of power system relaying, new protection concepts addressing new technologies are coming to the market. Therefore we need to keep track of international experiences and activities taking place in the field of modern protective systems. This paper gives a bibliographical survey, mathematical formulations, and general backgrounds of research and developments in the field of protection of multiterminal lines and double-circuit lines during the past 50 years, based on more than 100 published articles. Different techniques for parallel line protection and various methods for multiterminal lines are studied and an evaluation of them is undertaken with their advantages and disadvantages for identification of optimum technique as applied to specific applications. At the end, the philosophy of a new adaptive digital distance relaying scheme is also conceptualized. The collected literature has been divided into many sections so that new researchers do not face any difficulty in carrying out research in any specific area of the next generation's adaptive distance protection.

Due to the technique and economic considerations, transmission lines in the power grid are usually untransposed, which leads to the result that the line parameter is asymmetric. For double-circuit lines on the same tower, asymmetric line parameters may cause unbalanced currents even under normal operation, which will have a negative impact on the line temperature, line loss and even relay protections. This paper firstly investigates the line parameters and current characteristics of the double-circuit lines on the same tower under normal operating mode. Then, we provide a method to analyze the current characteristics including circulating current and the net through current, and effects of phasing arrangement on each kind of unbalanced components are analyzed. Finally, based on the actual parameter of tower and transmission line in power grid, unbalanced currents of a certain double-circuit line are analyzed with full consideration of different phasing arrangements. With the help of analysis results, some useful conclusions and suggestions to limit the current unbalance are listed in the last part of this paper.

Double circuit lines, operated in parallel, have become popular in the Portuguese transmission network. When a new line is constructed between two substations, the towers are initially built to encompass two circuit lines even if only one bay is constructed at each substation line ends. The two circuits are operated in parallel having the advantage of postpone the cost of constructing new bays in the substations to the time where the power transfer demand requires. The present paper describes the impact of such topology on the selectivity performance of distance protection used on transmission lines. An analytical model is presented to evaluate the impedance seen by the distance protection for several types of faults along the line revealing the underreach effect. A numerical simulation using ATP/EMTP is conducted to validate the analytical model results. At the end, some solutions and recommendations are proposed to mitigate the problems encountered.

A distance Protection/Fault location algorithm for Double-Circuit transmission lines with asymmetrical circuits during Cross-Country faults

Maintaining selectivity among protective devices in interconnected power systems is of crucial importance. Therefore, it is necessary to install distance relays on both ends of the transmission lines to ensure efficient main and backup protection of the system. In this study, the zones and tripping time settings of distance relay for phase and ground protection of interconnected power systems are set and implemented in the professional DIgSILENT PowerFactory software. The interconnected test system IEEE 9-bus test system is used to validate the proposed methodology. The obtained results have approved that the setting and coordination of distance relays ensure adequate system protection against various fault types and locations.

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.

In this paper, the influence of the Static Var Compensators (SVC) on distance relay protection when connected to the sub-transmission network of the Nigerian 132-kV grid system is investigated. This is carried out by monitoring the error margin of the fault locator associated with the distance protective relays when SVC is connected to the transmission line. The location of the SVC is selected such that there is a common primary source of power to the sub-transmission network (Ikorodu-Sagamu 132-kV transmission line) and the SVC, which is a shunt-connected device located on Ikorodu 132-kV bus. The fault is simulated at 33.6 km and 60.4 km respectively from the Ikorodu 132-kV sub-station in Matlab/ Simulink model and the simulation results obtained are used to investigate the influence of SVC on distance protective relay when connected to the 132-kV power transmission line. The results of the line faults are obtained with respect to earth for both zones one (1) and two (2) when SVC is connected and disconnected for all shunt type of faults. Thus, indicating under-reach and over-reach characteristics of the distance relay, when the SVC is connected and disconnected, while the transmission line protection showed no under-reach or over-reach characteristics for line-to-line fault for both zones with the SVC connected or disconnected. The results of this study show that though SVCs improve the quality of power to consumers, there is a tendency for under-reach and over-reach characteristics of the protective relay to be displayed when the relays are disconnected and connected, which introduces error margins to the fault locator in distance protective relays. Therefore, more detailed dynamic simulations are recommended for reducing the error margin.