Explicit fault analysis is the basis of protection for the bipolar HVDC Line. The characteristics of the initial values of traveling waves under various internal fault conditions are investigated on the basis of the symmetrical component analysis. The criteria of fault classification and faulty-pole selection are put forward based on the zero- and positive-sequence backward traveling waves, and an integrated traveling wave-based protection scheme is proposed. The simulations based on real-time digital simulation show that the proposed scheme can detect faults rapidly, determine the fault type effectively, and select the faulty pole correctly.

Fault Analysis and Traveling-Wave Protection Scheme for Bipolar HVDC Lines

Microgrid is a distribution system composed of a set of micro-generators which are added to a network. One serious challenge facing a microgrid network is designing a proper protection scheme. This is because the fault current in a microgrid is constantly changing due to the presence of distributed generation (DG) resources at all levels of the distribution network and to the fact that they can operate in two islanding and normal modes. This makes the conventional methods inappropriate for microgrid protection. That is, new schemes should be developed for this purpose. This paper is a summary of studies recently carried out in the field of microgrid protection. Along this line, the structure and topology of microgrids are reviewed first. Afterwards, the protective challenges facing DG-equipped distribution networks are discussed. Then, the innovative methods proposed to solve these problems are analyzed. These methods can be divided up into six main categories: changing settings of protective devices at presence of DG units, disconnecting pertinent DG units when faults occur, creating a balance among different DG technologies, using fault current limiter, using smart transformers, and adaptive protection. In so doing, we consider the factors involved in selecting each method. The factors identified are microgrid type and topology, DG type, communication type and delay time, method of fault detection and analysis, relay type, fault type, method of grounding, and use of smart transformers in microgrid. It is hoped that this work will be useful to the researchers in the field of microgrid protection in finding relevant references and designing appropriate methods.

An overview of microgrid protection methods and the factors involved

Inverter-dominated microgrids impose significant challenges on the distribution network, as inverters are well known for their limited contribution to fault current, undermining the performance of traditional overcurrent protection schemes This paper introduces a new protection scheme based on the initial current traveling wave utilizing an improved mathematical morphology (MM) technology, with simplified polarity detection and new logics introduced for meshed networks and feeders with single-end measurement The proposed protection scheme provides ultrafast response and can be adapted to varied system operational modes, topologies, fault conditions, and load conditions Only low-bandwidth communication is required to achieve high-speed operation and adequate discrimination level in meshed networks Simulation in PSCAD/EMTDC verifies both the sensitivity and stability of the proposed protection scheme under different microgrid operational scenarios

/pdf/traveling-wave-based-protection-scheme-for-inverter-7mvosxpvgg.pdf

Traveling Wave-Based Protection Scheme for Inverter-Dominated Microgrid Using Mathematical Morphology

The development of modern protection functions is a challenge in the emerging environment of smart grids because the current protection system technology still has several limitations, such as the reliable high-impedance fault (HIF) detection in multigrounded distribution networks, which poses a danger to the public when the protection system fails. This paper presents the wavelet coefficient energy with border distortions of a one-cycle sliding window designed for the real-time detection of transients induced by HIFs. By using the border distortions, the proposed wavelet-based methodology presents a reliable detection of transients generated by HIFs with no time delay and energy peaks scarcely affected by the choice of the mother wavelet. The signatures of different HIFs are presented in both time and wavelet domains. The performance of the proposed wavelet-based method was assessed with compact and long mother wavelets by using data from staged HIFs on an actual energized power system, taking into account different fault surfaces, as well as simulated HIFs. The proposed method presented a more reliable and accurate performance than other evaluated wavelet-based algorithms.

Real-Time Detection of Transients Induced by High-Impedance Faults Based on the Boundary Wavelet Transform

In the few years, wavelet-based methodologies have been proposed as a good alternative for real-time fault detection. However, these methodologies usually fail to detect faults with overdamped transients and they are highly influenced by the choice of the mother wavelet, presenting time delay in the real-time analysis. By using the discrete wavelet transform (DWT) or the maximal overlap discrete wavelet transform (MODWT), the wavelet coefficient energy has been also used for fault analysis and presents the same drawbacks of the wavelet coefficient analysis. However, this paper presents a novel wavelet-based methodology for real-time detection of fault-induced transients in transmission lines, where the wavelet coefficient energy takes into account the border effects of the sliding windows. As a consequence, the performance of the proposed energy analysis is not affected by the choice of the mother wavelet, presenting no time delay in real-time fault detection, and the fault detection is scarcely influenced to the fault inception angle, fault resistance, and fault location, even if in critical situations where there are no fault-induced transients. The performance of the proposed methodology was assessed by using actual and simulated data. Some records were reproduced to be analyzed in real time with a digital signal processor.

Fault-Induced Transient Detection Based on Real-Time Analysis of the Wavelet Coefficient Energy

This paper presents a new approach that deduces the fault direction based on the traveling-wave directional principle. The algorithm by means of wavelet transforms decomposes the voltage signals and calculates the spectral energy at selected detail which allows detecting the fault and to choose the phase to make the slope change analysis. This analysis provides a clear indication of fault direction from the comparison of the slope change polarities of the voltage and current at selected phase during quite a short time. The algorithm, which belongs to the ultra-high-speed protecting relaying, is able to discriminate the direction for all kinds of faults and is not affected by the change of the fault angle inception.

Directional Traveling-Wave Protection Based on Slope Change Analysis

An approach to line protection that is based on fault characteristics extracted by means of wavelet transforms is presented. Analysis of the spectral energy of the phase voltage signals for different frequency bands enables faults to be detected, classified and faulted phases selected. The proposed approach points to the development of ultra-high-speed protective relaying and has been applied to a series-compensated line. The system has been simulated with MICROTRAN and the protection with MATLAB. The results show the feasibility of implementing this algorithm.

Fault detection, classification and faulted phase selection approach based on high-frequency voltage signals applied to a series-compensated line

This paper presents an adaptive noncommunication approach for line protections that are able to classify the fault as internal or external with respect to the relay protection zone for most of the faults in radial lines and for all faults in meshed networks. Basically, with a combination of the current traveling waves detected at the relay location due to fault and open switching operations with apparent impedance seen by relay, the remote breaker operation is detected and the faulted line is identified. The protection developed is selective and is not affected by power system oscillations. The system was simulated with the MICROTRAN, the results showing the feasibility of implementing this algorithm.

Adaptive noncommunication protection based on traveling waves and impedance relay

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Papers

Directional Traveling-Wave Protection Based on Slope Change Analysis

Fault detection, classification and faulted phase selection approach based on high-frequency voltage signals applied to a series-compensated line

Adaptive noncommunication protection based on traveling waves and impedance relay