Protection Of Series Compensated Transmission Lines Research Articles

Complex plane based adaptive method for protection of series compensated transmission line using phasor measurement unit data

Though differential relays are preferred for the protection of series-compensated transmission line (SCTL), they may mal-operate during current inversion, high resistance internal faults and current infeed/outfeed situations. Therefore, a new protection scheme for SCTL using Phasor Measurement Unit data, that adaptively manages the operating region in the current ratio complex plane according to the percentage compensation level, is presented. Boundaries of the operating region are determined adaptively based on the estimated impedance value of the series compensation. Usefulness of the technique is confirmed by generating cases covering wide range of fault parameters, compensation level, and load angle on an existing 400 kV Indian SCTL using PSCAD software as well as through Hardware in Loop simulation employing the Real Time Digital Simulator. Reported outcomes reveal the ability of the suggested algorithm in sensing all types of internal faults. Its performance remains unaffected during current/voltage inversion, operation of MOV and/or airgap during high fault current conditions, current infeed/outfeed situation, and external fault with current transformer saturation condition. Impact of the presence of noise in the acquired signals is also analyzed. The suggested technique is applicable for SCTLs having different voltage levels and power flow conditions. The proposed method has higher responsiveness during high resistance internal faults up to 500 Ω and better steadiness during external faults compared to numerous prevailing methods.

Back-Up Protection Scheme for Series-Compensated Transmission Line Connected to Wind Farm

Series compensation poses serious challenges to the protection schemes of transmission lines (TLs). Moreover, with the penetration of distributed generation (DG), the conventional protection schemes fail to detect the fault and identify the faulty phase as the backfeed currents from the DG units mask the faulty phase. This work presents an algorithm for the protection of series-compensated TLs (SCTL) integrated with wind farms. The algorithm uses the phase difference between the positive sequence currents at the two ends of the TL to discriminate internal and external faults. The faulty phase for internal fault is identified from the difference in complex power at the two ends of the TL. Extensive simulations with several fault and system parameters assess the reliability and applicability of this technique.

Current mapping strategy for improving two-terminal series-compensated line current differential protection

This paper presents a particular case of the generalized alpha plane called current mapping strategy (CMS) formulation applied to differential protection of series-compensated transmission lines. The proposed formulation presents two unique features, control over the internal fault settlement region (FSR) and the use of an operation characteristic (OC). The FSR and the OC are two concentric circles defined on the alpha plane. Additionally, the proposed CMS allows the user to adjust the center and radius of the FSR and OC, according to the desired sensitivity and security of the protection. To validate and test the performance of the improved CMS, numerous computer simulations have been carried out using the Alternative Transients Program (ATP) on a 400 km long series-compensated, 500-kV transmission line. Furthermore, analysis of an extensive database of cases is conducted to highlight the CMS’s sensitivity. The obtained results demonstrate the effectiveness of the settings of the CMS and a smooth trajectory to the FSR. The CMS also proved to be stable and reliable even under severe subsynchronous oscillations and outfeed conditions.

Study and Solution of Current Differential Protection Disability for High Series Compensation Transmission Line

With the increasing day by day integration of large-size generators and tighter among the power systems, in internal fault, the fault current of Series Compensated (SC) lines could also be upturned. Therefore, the differential protection of SC transmission lines may stop working to operate because of less sensitivity. In this research article the causes for the current overturning in SC lines and its effects differential protection. The working characteristics of differential protection are analyzed by focusing on multiple-factors, for example, different series compensation degrees, types of fault, system operation mode, the difference of power angle, points of the fault, and transition resistance. An enhanced standard based on the current amplitudes and phases on both sides of the series compensated lines is proposed. Furthermore, to make stronger the operation characteristics of differential protection, the triple-fold line is chosen to get better sensitivity for internal faults in the article. The results are efficient to improve the protection sensitivity of SC lines during the internal fault. The PSCAD/EMTDC simulation and the power system dynamic physics simulation demonstrate that protection sensitivity is increased in the improved scheme. Keywords : Differential Protection, Series compensation, EHV/ UHV, Current reverse, sensitivity analysis. DOI: 10.7176/CTI/10-06 Publication date: August 31 st 2020

A Novel Backup Distance Protection Scheme for Series-Compensated Transmission Lines

Conventional distance protection applies the positive-sequence impedance to protect a line against short-circuit faults. Series-compensated lines may considerably change the positive-sequence impedance of the fault path and cause the distance relays to maloperate. To overcome this problem, the mutual impedance between phases of a transmission line is used for the design of a new distance protection scheme. The voltages and currents of both ends of the line are applied to compute the mutual impedance between the relay and the fault point. The proposed scheme has a reliable performance in protection against single-phase and double-phase-to-ground faults and, therefore, it can be used as a backup protection. Simulation results approve the efficiency of the proposed method in protection of series-compensated transmission lines.

Optimized echo state networks using a big bang–big crunch algorithm for distance protection of series-compensated transmission lines

Distance protection of transmission lines compensated by Thyristor-Controlled Series Capacitor (TCSC) suffers malfunction due to series variable voltages injected by TCSC. To mitigate the problem, echo state networks (ESNs) are used in this paper through the voltage compensation technique by subtracting estimated TCSC voltages from measured phase voltages where fault loop observed by the relay contains TCSC. The design parameters of ESNs are optimized using a big bang–big crunch (BB–BC) algorithm with an especial random generation scheme in big bang phase. Main features of our study are: (a) only locally measured phase currents at the relaying point is used, assuming firing angles and other variables of TCSC are not accessible there; and (b) high accuracy of estimations is achieved using optimized ESNs for a large number of test cases. The method is tested on a 400km, 500kV line for all fault types using Matlab/Simulink. Tests for 7680 cases with varying fault resistance, fault inception-angle, fault location, load angle and compensation degree show much improved accuracy of estimations by ESN in comparison to time-delay neural network (TDNN), radial basis function neural network (RBFNN), nonlinear autoregressive network with exogenous inputs (NARX) and Elman network particularly at instants immediately after fault incidence. The effectiveness of the ESN-based method is examined using two distance relay algorithms.

High-speed superimposed-based protection of series-compensated transmission lines

This study presents a sub-cycle power frequency-based fault direction discrimination and fault classification algorithm for the series-compensated transmission lines. Also, it provides an accurate estimation for the fault occurrence instant which is helpful in synchronised waveforms-based pilot protective schemes. The proposed algorithm is based on capturing the initial change in the voltage and current waveforms caused by occurrence of a fault. The high-frequency components of the fault signals are first filtered out, and then the signals are sampled at a relatively low sampling rate. Unlike the conventional relative-phase-angle-based directional relays, the proposed algorithm is not affected by the current and voltage inversion phenomena due to the presence of series capacitor in the fault loop. Extensive simulation studies are performed to evaluate the proposed algorithm performance. The obtained results show that the proposed algorithm provides a simple and a very fast and reliable protection technique for power transmission lines. This algorithm also covers non-compensated transmission lines and is able to well discriminate the fault direction even if the post-fault voltage amplitude becomes too small. It is also tested using some real data recorded from a high-voltage transmission system.

Usage of Wavelet Transform in the Protection of Series-Compensated Transmission Lines

This paper presents a new method for the boundary protection of series-compensated transmission lines, as well as fault classification. The boundary protection is based on detecting distinct frequency bands contained in the transient fault current wave. Discrete wavelet transform, using db4 as a mother wavelet, is used to capture two bands of frequencies in the transient current signal. The spectral energies of these two bands are obtained and used to determine if the fault is internal or external to the protected zone. Fault classification is done using the discrete wavelet transform. Using Haar as the mother wavelet, the coefficients of a frequency band in the range of 1 kHz-3 kHz are obtained for the three phase and ground currents. The average value of the coefficients of each current wave is then computed and used to classify the faulted phases. The basic principle of the protection scheme is described and its response to the series-compensated transmission lines is studied for a wide range of compensation levels, fault conditions, fault types, and fault locations. The stability of the algorithm under various load switching cases is also tested. Fault simulations are performed using power system computer-aided design/electromagnetic transient and direct current program and the results are then interfaced to MATLAB, where the algorithm is implemented. It is found that the proposed method gives reliable results in the boundary protection and fault classification of series-compensated lines.