F. B. Costa

Boundary Wavelet Coefficients for Real-Time Detection of Transients Induced by Faults and Power-Quality Disturbances

In the last few years, much research has been focused on wavelet coefficients for high-speed detection of transients induced by faults, high impedance faults (HIFs), and some power-quality (PQ) disturbances. However, the performance of the wavelet coefficient-based analysis in the real-time disturbance detection substantially changes with the choice of the mother wavelet, presents time delay for long mother wavelets, and may fail when the transients are overdamped, which limits the applicability of the conventional wavelet coefficients in actual digital relays. Therefore, in order to overcome all of the aforementioned drawbacks of the wavelet coefficients, this paper proposes a new wavelet decomposition process which provides additional wavelet coefficients with border distortions of a one-cycle sliding window (boundary wavelet coefficients), yielding the real-time detection of the transients scarcely affected by the choice of the mother wavelet, with no time delay for compact and long wavelets, as well as a more reliable disturbance detection than the conventional wavelet coefficients, even in cases of damped transients. In addition, a boundary wavelet coefficient requires equivalent computational burden of a conventional wavelet coefficient. The performance of the proposed boundary wavelet coefficients was assessed through the real-time analysis of records with faults, HIFs, and some PQ disturbances as well as with simulated data from transmission and distribution power systems, taking into account the effects of the fault inception angle, resistance, and distance.

Real-Time Traveling-Wave-Based Fault Location Using Two-Terminal Unsynchronized Data

In this paper, a new two-terminal traveling-wave-based fault-location algorithm is proposed. Its main advantage over similar two-terminal algorithms lies in the fact it does not require the data from both line terminals to be synchronized. In order to do so, the algorithm is applied in real time, and a communication system is used, whose data-transmission latency is taken into account in the proposed formulation. The fault locator routines were implemented using the real-time digital simulator (RTDS), such that a wide variety of fault scenarios in a 230-kV transmission line 200 km long was evaluated in real time, considering communication systems with different latency variability levels. The obtained results indicate the proposed algorithm is able to locate faults using either synchronized or unsynchronized two-terminal data, whereas classical methods work properly for synchronized measurements only.

Real-time classification of transmission line faults based on Maximal Overlap Discrete Wavelet Transform

The analysis of fault-induced transients in three-phase overhead transmission lines can provide extensive information about the fault type, detection, location, direction, and sustained time in satisfactory agreement with real application in protective relays. In this paper, the wavelet coefficient energies of the Maximal Overlap Discrete Wavelet Transform regarding the fault-induced transients were used for real-time fault classification in transmission lines. The performance of the real-time fault classification was evaluated by means of the Real Time Digital Simulator (RTDS) and good results were obtained. The performance of the method was also off-line evaluated with actual oscillographic records of a Brazilian Power System Utility and good results were also obtained.

A wavelet-based algorithm to analyze oscillographic data with single and multiple disturbances

This paper presents a discrete wavelet transform approach to recognize disturbances by the analysis of electromagnetic transients in transmission lines using oscillographic data. It is usual that different types of disturbances simultaneously exist in an oscillographic record supplied by a monitoring device in a transmission line. However, most of the existing methods treat the events as a single type. Thus, the performance of these methods might be limited and impracticable for real applications in power systems. In this framework, the proposed approach overcome this problem by the ability to analyze single and multiple disturbances in actual oscillographic records. Other distinctive feature of the proposed method is that it can recognize faults, some events related to power quality and normal maintenance operation in transmission lines. Sliding data windows of the detail spectral energy with length equivalent to one cycle of the fundamental power frequency are used to achieve wavelet-based information for detection and classification tasks. The performance of the method was evaluated for actual data and excellent results have been obtained.

Real-time detection of voltage sags based on wavelet transform

This paper presents a wavelet-based method for real-time detection of voltage sags in transmission lines. The wavelet coefficient energies of the phase voltages and currents are used for real-time detection of the transients at both beginning and end times of voltage sags. On the other hand, the voltage sags are identified in real-time by means of the approximation coefficient energy analysis. The voltage sag diagnosis method was evaluated by using the Real Time Digital Simulation (RTDS).

Haar Wavelet-Based Method for Fast Fault Classification in Transmission Lines

The application of Haar wavelet transform for fault classification in transmission lines is proposed. The faulted phases identification is carried out by the analysis of the energy of the detail coefficients of the phase currents. In addition, by the analysis of the smooth coefficients of the neutral current, the ground faults can be distinguished from phase to phase ones. The algorithm was evaluated with EMTP-simulated faults. The obtained results reveal that the proposed method can accurately identify transmission line faults from a wide variety of power system operating conditions, within the first half-cycle after the beginning of the fault

Power Transformer Differential Protection Using the Boundary Discrete Wavelet Transform

Currently, the differential function is the most used for the power transformer protection, leading to a reliable discrimination between internal faults and other events. However, the conventional phasor-based differential protection function presents difficulties in the detection of some internal faults and its performance depends on the harmonic restraint and blocking functions in order to avoid relay misoperation during inrush currents. However, internal faults and other disturbances present transient, which can be properly detected by using the wavelet transform. This paper recreates the phase current and the negative-sequence current differential elements by means of the boundary wavelet coefficient energy. The proposed method was evaluated by using representative simulations of internal faults, external faults, and transformer energizations in two different power systems. By using the boundary wavelet coefficient energy instead of phasor estimation, the proposed method was quite fast, accurate, was not affected by inrush currents in transformer energizations and fault clearance, and could be used in a real-time application with low computational burden. In addition, the proposed method presented no failure in fault with overdamped transients, was scarcely affected by the choice of the mother wavelet, presented no time delay associated with the wavelet filtering, and was not affected by typical noise.

Two-Terminal Traveling-Wave-Based Transmission-Line Protection

This paper proposes a two-terminal traveling-wave-based transmission-line protection using only the first wavefront arrival time at each line terminal (polarity and magnitude of transients are not required), leading to a simple, accurate, and fast protection. In real time, the protection system detects internal and external faults and identifies the fault directionality. In addition, the protection zone and the protection operating time are also formulated. The effects of the sampling rate and the traveling-wave propagation velocity estimation are considered, and some paradigms, such as the need of a high-sampling frequency and an accurate traveling-wave propagation velocity estimation are properly addressed. Two traveling-wave-based protective relays were implemented and evaluated in realistic real-time hardware-in-the-loop simulations considering the communication equipment between the relays, in which reliability and protection operating time could be assessed accordingly.

Overcurrent Protection in Distribution Systems with Distributed Generation based on the Real-Time Boundary Wavelet Transform

The protection system has been facing new challenges with the distribution systems with distributed generation (DG), which may be successfully accomplished through the combination of the existing protections, such as overcurrent protection, with modern protections based on emerging technologies. By using conventional and modern protection trends, the aim of this paper is to propose the overcurrent protection based on the boundary discrete wavelet transform. In real time, this transformation decomposes a signal in the boundary scaling and wavelet coefficient energy. Following the conservative trends of power system protection, the instantaneous and time-delay overcurrent elements (phase and neutral units) are reproduced in the wavelet domain by using the boundary scaling coefficient energy, providing similar performance in the fault detection, a faster trip, and less computational burden than the conventional overcurrent protection. Following the modern protection trends, the boundary wavelet coefficient energy provides real-time detection of the fault inception time in order to reduce the relay operating time and minimize the harmful effects of the faults. A distribution system with DG was modeled in a real-time digital simulator, and wavelet-based overcurrent relays were evaluated and compared to conventional overcurrent relays based on the Fourier transform in real-time simulations, and promising results were obtained.

A Method for Fault Classification in Transmission Lines Based on ANN and Wavelet Coefficients Energy

This paper proposes a novel method for transmission lines fault classification using oscillographic data. The scheme is based on the analysis of the current wavelet coefficients energy using an artificial neural network. In order to validate the proposed approach, both simulated and actual oscillographic data were used.