Transmission lines protection techniques based on wavelet transform

Abstract

Development of different modules of a transmission line digital relaying system is outlined in this thesis. Different modules such as fault detection, phasor estimation, phase selection and fault location are designed, implemented and tested. The developed distance-relaying algorithm is suitable for protecting single circuit transmission lines and is employed in conjunction with current differential protection to protect double-circuit transmission lines. A new distance relaying algorithm based on Wavelet Transform (WT) is developed. The measured three current and three voltage signals at the relay location are digitized and decomposed into different frequency bands using WT. A fault can be detected from the highest frequency band of the current signals and the phase(s) on fault can be identified. All voltage and current fundamental frequency phasors can be estimated from the frequency band that contains the fundamental frequency accurately and the impedance to the fault can be calculated. Simulation studies have been performed on a typical power system model usrng PSCAD program. The proposed algorithm is examined under different operating conditions including internal, high resistive and external faults. Further studies have been performed to examine the performance of the algorithm during line charging. The results obtained indicate that the proposed algorithm has the ability to rapidly detect faults and correctly classify all types of internal faults within one cycle of the fundamental frequency. The WT distance-relaying algorithm has been implemented on a Digital Signal Processor (DSP) board. Using a physical model of a transmission line with a microalternator connected at one end and a large system at the other end, extensive experimental studies have been conducted and the performance of the proposed WT distance-relaying algorithm is verified. The developed WT distance-relaying technique is combined with the current differential technique to protect parallel transmission lines. The new algorithm is proposed to overcome the problems that result from the sole use of either of these two techniques. The scheme depends on the three line voltages and the six line currents of the two parallel lines at each end. Fault detection, fault discrimination and calculation of the phasors of the measured signals are done by using WT. By comparing the magnitudes of the estimated current phasors of the corresponding phases on both lines, internal faults on the parallel lines can be identified. Also, by calculating the distance element of the phases on which a disturbance is detected and have a very small current difference magnitude, external faults and same phase faults on both circuits can be identified. Studies show that all types of internal faults at different operating conditions can be correctly identified in less than one cycle of the fundamental frequency. The results presented in this thesis confirm the feasibility of the proposed transmission line WT relaying techniques.