A Review of Fault Diagnosing Methods in Power Transmission Systems

Transient stability is important in power systems. Disturbances like faults need to be segregated to restore transient stability. A comprehensive review of fault diagnosing methods in the power transmission system is presented in this paper. Typically, voltage and current samples are deployed for analysis. Three tasks/topics; fault detection, classification, and location are presented separately to convey a more logical and comprehensive understanding of the concepts. Feature extractions, transformations with dimensionality reduction methods are discussed. Fault classification and location techniques largely use artificial intelligence (AI) and signal processing methods. After the discussion of overall methods and concepts, advancements and future aspects are discussed. Generalized strengths and weaknesses of different AI and machine learning-based algorithms are assessed. A comparison of different fault detection, classification, and location methods is also presented considering features, inputs, complexity, system used and results. This paper may serve as a guideline for the researchers to understand different methods and techniques in this field

Novel methods for earth fault passage indication in non-effectively grounded electricity distribution networks

Electricity distribution networks are commonly subject to supply interruptions and outages caused by faults. This dissertation focuses on medium voltage distribution networks, which typically consist of primary substations having multiple feeders along which secondary substations are located. When a permanent fault occurs on a segment (the part linking two consecutive secondary substations) of a distribution feeder, the faulted segment needs to be identified and isolated. Identifying the faulted segment can be realized through fault passage indicators. This is a straightforward task when the fault type is a short circuit, as these types of faults involve large currents. However, faulted segment identification for earth faults in non-effectively grounded medium voltage distribution networks has remained a challenge as the earth fault current in those networks is typically relatively small. Therefore, the main objective of this dissertation was to develop novel methods for locating single-phase earth faults in medium voltage distribution networks and validating them through simulations and real system measurements. After comprehensive review of state-of-the-art approaches presented in the literature, the dissertation proposes innovative methods for earth fault passage indication aimed at non-effectively grounded urban or rural distribution networks with radial feeders. The proposed methods are underpinned by a theoretical analysis based on the symmetrical components of the currents on a distribution feeder under an earth fault condition. The comparison of the sequence currents collected from various measuring points on the network forms the backbone of the methods. For practical implementation, current measurements need to be transferred to a central location for processing and decision making, but this can be done without accurate time synchronization. The proposed methods were developed and verified through simulations and empirical data. This work is a product of close collaboration between academia and industry that enabled the validation of the proposed methods with the help of empirical data that was provided by system operators and relay manufacturers. The results obtained from simulations and field tests show the efficacy of utilizing sequence current quantities, in the manner proposed in this work, for identifying the passage of earth faults with fault resistances ranging from zero to several kilo-ohms. In practice, the methods are reliable as long as the current measurements are accurate enough.Sähkönjakeluverkoissa esiintyy vikoja, jotka aiheuttavat sähkönjakelun keskeytyksiä eli sähkökatkoja. Tämä väitöskirja käsittelee keskijänniteverkkoja, jotka koostuvat sähköasemista ja niiltä lähtevistä johtolähdöistä. Johtolähtöjen varrella sijaitsevat pienjänniteverkkoa syöttävät muuntamot. Kun jollain johto-osuudella (tässä ns. muuntamovälillä, joka yhdistää kaksi peräkkäistä muuntamoa) ilmenee pysyvä vika, viallinen johto-osuus on tunnistettava ja erotettava. Viallisen johto-osuuden tunnistaminen tapahtuu vianilmaisimien avulla. Viallisen johto-osuuden tunnistaminen on yksinkertaista, kun vikatyyppi on oikosulku, sillä oikosuluille ominaista ovat yleensä suuret vikavirrat. Haasteena on kuitenkin edelleen viallisten johto-osuuksien tunnistaminen maasulkutilanteissa ei-tehollisesti maadoitetuissa keskijänniteverkoissa, joissa maasulkuvirta on tyypillisesti hyvin pieni. Tämän väitöskirjana tavoitteena on ollut kehittää uusia menetelmiä maasulkuvikojen paikantamiseen keskijänniteverkossa ja varmentaa niiden toimivuus simuloinnein ja todellisesta verkosta saatujen mittausten avulla. Kattavan kirjallisuuskatsauksen jälkeen tässä väitöskirjassa esitellään innovatiivisia menetelmiä vikavirran reitin ilmaisuun jakeluverkkojen maasuluissa. Ehdotetut menetelmät tukeutuvat teoreettiseen analyysiin, jossa johtolähdön virrat maasulkutilanteessa on kuvattu symmetristen komponenttien avulla. Menetelmät perustuvat verkon eri pisteissä mitattuihin virran symmetristen komponenttien vertailuun. Käytännön toteutuksessa nämä mittaukset tulee siirtää keskitettyyn järjestelmään prosessointia ja päätöksentekoa varten, mutta tämä voidaan tehdä ilman tarkkaa aikasynkronointia. Ehdotettujen menetelmien kehittämisessä ja testaamisessa hyödynnettiin simulointeja ja kokeellista mittausdataa. Yhteistyö teollisuuden kanssa mahdollisti menetelmien toiminnan todentamisen hyödyntäen todellisista verkoista mitattua dataa, jota saatiin sekä verkkoyhtiöiltä että laitevalmistajilta. Simulointien tulokset ja mittaukset todellisessa verkossa tehdyistä testeistä osoittavat, että virran symmetriset komponentit toimivat hyvin vian paikannuksessa kun vikaresistanssi on nollan ja muutaman tuhannen ohmin välillä. Käytännössä menetelmien luotettavuus riippuu virran mittauksen tarkkuudesta.fi=vertaisarvioitu|en=peerReviewed

Intermittent earth fault passage indication in compensated distribution networks

An intermittent or restriking earth fault is a special type of earth fault that is common mostly in compensated cable networks. A great deal of effort has gone into protection against this type of fault. However, locating this fault has not received much attention. Therefore, there is a need to have a reliable method for locating this fault to repair the damaged cable. In this paper, the principles of a new method developed for locating transient intermittent earth faults on distribution networks are presented. The proposed method employs negative and zero sequence currents, and no voltage measurement is required, which means the proposed method has the potential to reduce cost when implemented in practice. It is intended mainly for typical intermittent earth faults in cable distribution networks where the typical fault resistance is in the range of a few ohms. Real data obtained from practical field tests is used to explain the phenomenon. A series of disturbance recordings obtained from field tests validate the proposed method.©2021 Elsevier. This work is licensed under a Creative Commons Attribution 4.0 License. For more information, see https://creativecommons.org/licenses/by/4.0/ This article has been accepted for publication in a future issue of this journal, but has not been fully edited. Content may change prior to final publication.fi=vertaisarvioitu|en=peerReviewed

Recent Developments and Challenges on AC Microgrids Fault Detection and Protection Systems–A Review

The protection of AC microgrids (MGs) is an issue of paramount importance to ensure their reliable and safe operation. Designing reliable protection mechanism, however, is not a trivial task, as many practical issues need to be considered. The operation mode of MGs, which can be grid-connected or islanded, employed control strategy and practical limitations of the power electronic converters that are utilized to interface renewable energy sources and the grid, are some of the practical constraints that make fault detection, classification, and coordination in MGs different from legacy grid protection. This article aims to present the state-of-the-art of the latest research and developments, including the challenges and issues in the field of AC MG protection. A broad overview of the available fault detection, fault classification, and fault location techniques for AC MG protection and coordination are presented. Moreover, the available methods are classified, and their advantages and disadvantages are discussed

Measurements, Models, Systems and Design

531 s.

Comprehensive STATCOM Control For Distribution And Transmission System Applications

This thesis presents the development of a comprehensive STATCOM controller for load compensation, voltage regulation and voltage balancing in electric power distribution and transmission networks. The behavior of this controller is first validated with published results. Subsequently, the performance of this STATCOM controller is examined in a realistic Hydro One distribution feeder for accomplishing the compensation of both mildly and grossly unbalanced loads, and balancing of network voltages using PSCAD/EMTDC software. The STATCOM voltage control function is utilized for increasing the connectivity of wind plants in the same distribution feeder. The thesis further presents a frequency scanning technique for simple and rapid identification of the potential of subsynchronous resonance in induction generator based wind farms connected to series compensated lines, utilizing MATLAB software. This technique is validated by published eigenvalue analysis results. The voltage control performance of the developed comprehensive STATCOM controller is then demonstrated for different scenarios in the modified IEEE First SSR Benchmark transmission system for mitigating subsynchronous resonance in series compensated wind farms using industry grade PSCAD/EMTDC software

Dynamic Phasor Modeling of Type 3 Wind Farm including Multi-mass and LVRT Effects

The proportion of power attributable to wind generation has grown significantly in the last two decades. System impact studies such as load flow studies and short circuit studies, are important for planning before integration of any new wind generation into the existing power grid. Short circuit modelling is central in these planning studies to determine protective relay settings, protection coordination, and equipment ratings. Numerous factors, such as low voltage situations, power electronic switching, control actions, sub-synchronous oscillations, etc., influence the response of wind farms to short circuit conditions, and that makes short circuit modelling of wind farms an interesting, complex, and challenging task. Power electronics-based converters are very common in wind power plants, enabling the plant to operate at a wide range of wind speeds and provide reactive power support without disconnection from the grid during low voltage scenarios. This has led to the growth of Type 3 (with rotor side converter) and Type 4 (with stator side full converter) wind generators, in which power electronics-based converters and controls are an integral part. The power electronics in these generators are proprietary in nature, which makes it difficult to obtain the necessary information from the manufacturer to model them accurately in planning studies for conditions such as those found during faults or low voltage ride through (LVRT) periods. The use of power electronic controllers also has led to phenomena such as sub-synchronous control interactions in series compensated Type 3 wind farms, which are characterized by non-fundamental frequency oscillations. The above factors have led to the need to develop generic models for wind farms that can be used in studies by planners and protection engineers. The current practice for short circuit modelling of wind farms in the power industry is to utilize transient stability programs based on either simplified electromechanical fundamental frequency models or detailed electromagnetic time domain models. The fundamental frequency models are incapable of representing the majority of critical wind generator fault characteristics, such as during power electronic switching conditions and sub-synchronous interactions. The detailed time domain models, though accurate, demand high levels of computation and modelling expertise. A simple yet accurate modelling methodology for wind generators that does not require resorting to fundamental frequency based simplifications or time domain type simulations is the basis for this research work. This research work develops an average value model and a dynamic phasor model of a Type 3 DFIG wind farm. The average value model replaces the switches and associated phenomena by equivalent current and voltage sources. The dynamic phasor model is based on generalized averaging theory, where the system variables are represented as time varying Fourier coefficients known as dynamic phasors. The two types models provide a generic type model and achieve a middle ground between conventional electromechanical models and the cumbersome electromagnetic time domain models. The dynamic phasor model enables the user to consider each harmonic component individually; this selective view of the components of the system response is not achievable in conventional electromagnetic transient simulations. Only the appropriate dynamic phasors are selected for the required fault behaviour to be represented, providing greater computational efficiency than detailed time domain simulations. A detailed electromagnetic transient (EMT) simulation model is also developed in this thesis using a real-time digital simulator (RTDS). The results obtained with the average value model and the dynamic phasor model are validated with an accurate electromagnetic simulation model and some state-of-the-art industrial schemes: a voltage behind transient reactance model, an analytical expression model, and a voltage dependent current source model. The proposed RTDS models include the effect of change of flux during faulted conditions in the wind generator during abnormal system conditions instead of incorrectly assuming it is a constant. This was not investigated in previous studies carried out in the real-time simulations laboratory at the University of Saskatchewan or in various publications reported in the literature. The most commonly used LVRT topologies, such as rotor side crowbar circuit, DC-link protection scheme, and series dynamic braking resistance (SDBR) in rotor and stator circuits, are investigated in the short circuit studies. The RTDS model developed uses a multi-mass (three-mass) model of the mechanical drive train instead of a simple single-mass model to represent torsional dynamics. The single mass model considers the blade inertia, the turbine hub, and the generator as a single lumped mass and so cannot reproduce the torsional behaviour. The root cause of sub-synchronous frequencies in Type 3 wind generators is not well understood by system planners and protection engineers. Some literature reports it is self excitation while others report it is due to sub-synchronous control interactions. One publication in the stability literature reports on a small signal analysis study aimed at finding the root cause of the problem, and a similar type of analysis was performed in this thesis. A linearized model was developed, which includes the generator model, a three mass drive train, rotor side converter, and the grid side converter represented as a constant voltage source. The linear model analysis showed that the sub-synchronous oscillations are due to control interactions between the rotor side controller of the Type 3 wind power plant and the series capacitor in the transmission line. The rotor side controls were tuned to obtain a stable response at higher levels of compensation. A real-time simulation model of a 450 MW Type 3 wind farm consisting of 150 units transmitting power via 345 kV transmission line was developed on the RTDS. The dynamic phasor method is shown to be accurate for representing faults at the point of interconnection of the wind farm to the grid for balanced and unbalanced faults as well as for different sub- synchronous oscillation frequencies

Synchrophasor Assisted Efficient Fault Location Techniques In An Active Distribution Network

Reliability of an electrical system can be improved by an efficient fault location identification for the fast repair and remedial actions. This scenario changes when there are large penetrations of distributed generation (DG) which makes the distribution system an active distribution system. An efficient use of synchrophasors in the distribution network is studied with bidirectional power flow, harmonics and low angle difference consideration which are not prevalent in a transmission network. A synchrophasor estimation algorithm for the P class PMU is developed and applied to identify efficient fault location. A fault location technique using two ended synchronized measurement is derived from the principle of transmission line settings to work in a distribution network which is independent of line parameters. The distribution systems have less line length, harmonics and different sized line conductors, which affects the sensitivity of the synchronized measurements, Total Vector Error (TVE) and threshold for angular separation between different points in the network. A new signal processing method based on Discrete Fourier Transform (DFT) is utilized to work in a distribution network as specified in IEEE C37.118 (2011) standard for synchrophasor. A specific P and M classes of synchrophasor measurements are defined in the standard. A tradeoff between fast acting P class and detailed measurement M class is sought to work specifically in the distribution system settings which is subjected to large amount of penetrations from the renewable energy

Multilevel Converters: An Enabling Technology for High-Power Applications

| Multilevel converters are considered today as the state-of-the-art power-conversion systems for high-power and power-quality demanding applications. This paper presents a tutorial on this technology, covering the operating principle and the different power circuit topologies, modulation methods, technical issues and industry applications. Special attention is given to established technology already found in industry with more in-depth and self-contained information, while recent advances and state-of-the-art contributions are addressed with useful references. This paper serves as an introduction to the subject for the not-familiarized reader, as well as an update or reference for academics and practicing engineers working in the field of industrial and power electronics.Ministerio de Ciencia y Tecnología DPI2001-3089Ministerio de Eduación y Ciencia d TEC2006-0386

Use of STATCOM in wind farms with fixed-speed generators for grid code compliance

The increasing penetration of wind energy into power systems has pushed grid operators to set new requirements for this kind of generating plants in order to keep acceptable and reliable operation of the system. In addition to the low voltage ride through capability, wind farms are required to participate in voltage support, stability enhancement and power quality improvement. This paper presents a solution for wind farms with fixed-speed generators based on the use of STATCOM with braking resistor and additional series impedances, with an adequate control strategy. The focus is put on guaranteeing the grid code compliance when the wind farm faces an extensive series of grid disturbances