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This paper presents a multifunctional scheme to reinforce the protection of Extra High Voltage (EHV)/Ultra High Voltage (UHV) transmission lines. The proposed scheme employs d–q transformed traveling waves and the time of incidence of first traveling waves at both ends of the line for fault detection and location respectively. Furthermore, the faults are classified using energy values of approximation coefficients and the phasors are estimated from the approximation coefficients. The traveling waves are nothing but detail coefficients. The detail and approximation coefficients are obtained using discrete wavelet transform multi-resolution analysis (DWT-MRA) of the 3-ɸ current signals. The proposed algorithm detects and locates a fault within a quarter cycle. The proposed scheme has been implemented on a two-bus and the WSCC-9 bus systems in EMTDC/PSCAD software to verify the efficacy and reliability. Also, it has been realized on a laboratory model of an EHV transmission line of length 200 km using NI cDAQ-9178 chassis, NI-9227 current sensor card, and LabVIEW software. The simulation and hardware results evince the protection reinforcing property of the proposed multifunctional scheme. [ABSTRACT FROM AUTHOR]

In this paper, a detailed study of the modes of hidden failures (HFs) in protection systems is carried out, and probabilistic modeling methodology is used for analyzing the impact of HFs on the power system cascading events. Further, the probabilistic model of HFs based on impedance and line power flow is hypothesized for qualitative evaluation of HF's impact on power system cascading disruptions. Numerous case studies have been carried out on the IEEE-118 bus system to assess the effect of HFs by fitting the probability model of line outage based on impedance and power flow. This analysis has successfully identified the most sensitive transmission lines in the network which are having the highest tendency to trip in case of protective system HFs. Also, it has been shown that the probability of major blackouts will be reduced to a more significant extent if the self-checking and monitoring features are incorporated into digital relays. The qualitative analysis of protection system HFs could be helpful in planning, service and maintenance scheduling of a power system as well as determining the locations where an investment warrants the protection system reliability. [ABSTRACT FROM AUTHOR]

A digital relay can be conceived as a digital signal processor in which the values of line currents and voltages are continuously monitored and processed. Hence, the heart of the digital relay is the software used for implementing the relaying algorithms in an efficient way. Assessment of software reliability is an area of utmost importance for such software-based systems for safety-critical applications such as digital relaying of power transmission lines. But software testing of safety-critical systems is particularly challenging because of the availability of meager failure data. Therefore, this article presents a methodology for estimating software reliability of digital relaying using statistics of extremes. The unique advantages of using such a methodology are the independence of the evaluation of the test sampling order, the amount of available data, and a priori knowledge about the underlying distribution of any parameter. The case studies demonstrate the efficacy of proposed methodology for evaluating the software reliability for digital relaying of transmission lines. [ABSTRACT FROM AUTHOR]

Digital relay is a special purpose signal processing unit in which the samples of physical parameters such as current, voltage and other quantities are taken. With the proliferation of computer technology in terms of computational ability as well as reliability, computers are being used for such digital signal processing purposes. As far as computer hardware is concerned, it has been growing steadily in terms of power and reliability. Since power plant technology is now globally switching over to such computer-based relaying, software reliability naturally emerges as an area of prime importance. Recently, some computer-based digital relay algorithms have been proposed based on frequency-domain analysis using wavelet-neuro-fuzzy techniques for transmission line faults. A software reliability allocation scheme is devised for the performance evaluation of a multi-functional, multi-user digital relay that does detection, classification and location of transmission line faults. [ABSTRACT FROM AUTHOR]

In the present milieu, changes in regulations and the opening of power markets have manifested in the form of large amount of power transfer across transmission lines with frequent changes in loading conditions based on market price. Since conventional distance relays may consider power swing as a fault, tripping because of such malfunctioning would lead to serious consequences for power system stability. A frequency domain approach for digital relaying of transmission line faults mitigating the adverse effects of power swing on conventional distance relaying is presented. A wavelet-neuro-fuzzy combined approach for fault location is also presented. It is different from conventional algorithms that are based on deterministic computations on a well-defined model for transmission line protection. The wavelet transform captures the dynamic characteristics of fault signals using wavelet multi-resolution analysis (MRA) coefficients. The fuzzy inference system (FIS) and the adaptive-neuro-fuzzy inference system (ANFIS) are both used to extract important features from wavelet MRA coefficients and thereby to reach conclusions regarding fault location. Computer simulations using MATLAB have been conducted for a 300 km, 400 kV line and results indicate that the proposed localisation algorithm is immune to effects of fault inception, angle and distance. The results contained here validate the superiority of the ANFIS approach over the FIS for fault location. [ABSTRACT FROM AUTHOR]