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Condition monitoring of circuit-breaker (CB) operating mechanisms is one the most important aspects of predictive maintenance. This paper proposes a contact force monitoring scheme for 10 \sim 35-kV vacuum CB. With specially designed force sensors and a signal-processing method, we can accurately find the instants of contact touch and separation. With the indirectly measured contact touch-and-separation instants, we can measure the opening speed, closing speed, and open gap over the travel of each phase. The accuracy of our online monitoring scheme is compared with the conventional offline methods that can directly obtain the instants of contact touch and separation by measuring the connectivity of the contacts. The results show that the accuracy of the scheme proposed in this paper is satisfactory and it can meet the engineering requirements of online condition monitoring of CBs. By introducing a set of new force sensors, some additional information that is useful for overall condition assessment of CB operating mechanism can also be extracted; this will help us to find new ways to improve our CB condition monitoring systems. [ABSTRACT FROM AUTHOR]

This paper investigates on a new concept for very-fast transient overvoltages (VFTOs) attenuation in gas-insulated switchgear (GIS). The concept, first introduced by the authors in this paper, involves modification of the GIS disconnector contact system in order to dissipate the VFTO energy in damping elements placed inside the GIS busbar conductor. The concept is an alternative to the state-of-the-art method where magnetic rings are placed in the space between the GIS conductor and the enclosure. The proposed arrangement has no impact on the damping element on the dielectric design of the GIS busbar, and it highly reduces the impact on the GIS thermal design. This paper presents analyses which show feasibility of the concept, through 1) principles which govern voltage conditions inside the GIS busbar and 2) full-Maxwell finite-element method electromagnetic simulations of VFTO attenuated with the use of the proposed concept. [ABSTRACT FROM PUBLISHER]

On transmission lines where switching surges are not mitigated with closing resistors and/or surge arresters, high-speed reclosing on a line with trapped charge will produce high overvoltages that have been measured above 3 p.u. Careful simulations of these switching events using available electromagnetic transient (EMT) programs consistently produce significantly higher voltages than the measurements. This indicates a phenomenon present on the line that acts to reduce the switching surge magnitudes but is not typically modeled. This paper aims to identify the required simulation practices in reproducing the field measured overvoltages in EMT simulations and investigates the sensitivity of results to modeling approaches and electrical parameters. Field measurements from a switching surge test of a 230-kV line without surge mitigation have been used for model comparisons. Variations in frequency-dependent line modeling, ground resistivity, skin effect, shunt conductance, parallel lines, and source-side detail have been tested in an unsuccessful attempt to decrease the difference between the field measurements and the higher simulation overvoltages. It is demonstrated that even though the pattern of the transient voltage waveforms can be reproduced very well using frequency-dependent line models, the magnitude of the maximum overvoltage is significantly overestimated unless the effect of corona is considered. Two types of corona models are tested, and both demonstrate that corona is the primary factor that allows the simulations to correctly reproduce high peak overvoltage measurements. [ABSTRACT FROM AUTHOR]

This paper presents the work carried out by the IEEE Working Grou[ on field-measured overvoltages and their analysis for validating power system component models to be used in switching transients studies. The work uses measurement data obtained from field tests performed by Bonneville Power Administration in June 1995 where switching overvoltages were measured on one of its 230 kV lines. This paper includes a description of the switching tests and the main results derived from field measurements. Details of the switching procedures that were followed to calibrate component models used to match field-recorded waveforms can be found in the Part II paper. [ABSTRACT FROM AUTHOR]

The objective of this paper is to present a 126-kV/40-kA–2500-A single-break vacuum circuit breaker (VCB) and its type test results based on the IEC 62271-100: 2006 and GB1984-2003 standards. A single-break 126-kV vacuum interrupter (VI), with a pair of 2/3 coil-type contacts, is used in the 126-kV VCB. The external insulation of the VI is provided by SF6 at 0.1 MPa. A spring-type operating mechanism is used to provide a closing velocity of 1.15 m/s, which is an average velocity for 4 mm before the moving contact mates with the stationary contact. The opening velocity within 20 mm, which is 1/3 of a full contact stroke of 60 mm, is 3.5 m/s. Two kinds of test circuits are used in the type tests to verify the making and breaking capabilities of this 126-kV VCB prototype. One is a direct test circuit for test duty cycles, such as out-of-phase making and breaking test duties, that is, OP1 and OP2; capacitive current switching test of class C1, that is, CC1/LC1 and CC2/LC2. The other is a synthetic circuit, used for tests, such as the terminal fault test, the short-line fault test, the double earth fault test, and the electrical endurance test of class E2. The dielectric tests of a 230-kV/1 min power frequency voltage withstand test and a 550-kV lightning impulse voltage withstand test were used to verify the dielectric withstand performance of the VCB. Experiment results presented in this paper showed that the 126-kV/40 kA–2500 A single-break VCB passed the type tests according to IEC 62271-100 and GB1984-2003. [ABSTRACT FROM PUBLISHER]

Maintenance management—as a part of the asset management policies—plays a vital role in enhancing the reliability of the electricity distribution system (EDS). The electric utility companies devote a considerable effort to allocate their financial resources to critical parts of the system, to achieve higher efficiencies. In this paper, a practical method is proposed for reliability-centered maintenance budgeting. The proposed method determines the optimal maintenance actions and their execution times in EDS feeders. The objective is to minimize the total reliability cost, including: the total customer interruption cost and total energy not supplied cost. Moreover, four cases are considered to explore the performance of the proposed maintenance method, including: the conventional EDS, the EDS equipped with remote-controlled switches (RCSs), maintenance budgeting and time allocation for the conventional EDS, and maintenance budgeting and time allocation for the EDS equipped with RCSs. The proposed reliability improvement approaches are applied to bus number two of the Roy Billinton test system, as well as a real scale distribution network followed by discussions on the obtained results. [ABSTRACT FROM PUBLISHER]

The current interrupting capability of a load break switch (LBS) depends on many design parameters, such as contact and nozzle geometry, contact movement, and gas flow. For developing more compact gas blow LBSs for air, it is necessary to find design recommendations where each parameter is addressed individually. In this paper, a current interruption test switch is built for this purpose. The interruption tests are conducted with a directly powered high-voltage circuit. The result shows the minimum gas flow required for current interruption for various basic nozzle geometries and at different contact positions. The study is particular relevant for the 24 kV/630 A class, and it is shown that 0.3 bar upstream pressure appears to be a threshold value for successful interruption. Some conclusions are also applicable for other medium-voltage ratings. An LBS should be designed so that at least one current zero crossing comes outside the nozzle when the switch is still blowing with full strength. [ABSTRACT FROM PUBLISHER]

This paper shows that there is great potential for saving money when reconfiguring distribution systems at an optimal frequency. Studies are conducted on hourly, daily, weekly, monthly, and seasonal reconfiguration plans, based on the 8760 hourly loads of a year. Switches that actively participate in the reconfiguration process are first identified. These sectionalizers are substituted by smart (remotely controlled) switches. According to the results, two economic indices: total savings and return on investment are used to determine the optimal switching frequency. Numerical simulations are conducted on three distribution systems including one with 119 buses that is commonly used as a benchmark for reconfiguration of large-scale distribution systems. The results reveal that there exist large potential gains on frequent switching reconfiguration. Therefore, detailed studies must be carried out to determine the benefits of the dynamic reconfiguration for particular distribution systems. [ABSTRACT FROM AUTHOR]

This paper presents a new concept and approach for topology control and switching in distribution systems by extending the traditional circuit switching to laterals and single-phase loads. Voltage unbalance and other key performance indicators including voltage magnitudes, line loading, and energy losses are used to characterize and demonstrate the technical value of optimizing system topology on a per-phase basis in response to feeder conditions. The near-optimal per-phase topology control is defined as a series of hierarchical optimization problems. The proposed approach is applied to IEEE 13-bus and 123-bus test systems for demonstration, which included the impact of integrating electric vehicles (EVs) in the test circuit. It is concluded that the proposed approach can be effectively leveraged to improve voltage profiles with electric vehicles, the extent of which depends on the performance of the base case without EVs. [ABSTRACT FROM AUTHOR]

This paper aims at evaluating the methods of multiclass support vector machines (SVMs) for effective use in distance relay coordination. Also, it describes a strategy of supportive systems to aid the conventional protection philosophy in combating situations where protection systems have maloperated and/or information is missing and provide selective and secure coordinations. SVMs have considerable potential as zone classifiers of distance relay coordination. This typically requires a multiclass SVM classifier to effectively analyze/build the underlying concept between reach of different zones and the apparent impedance trajectory during fault. Several methods have been proposed for multiclass classification where typically several binary SVM classifiers are combined together. Some authors have extended binary SVM classification to one-step single optimization operation considering all classes at once. In this paper, one-step multiclass classification, one-against-all, and one-against-one multiclass methods are compared for their performance with respect to accuracy, number of iterations, number of support vectors, training, and testing time. The performance analysis of these three methods is presented on three data sets belonging to training and testing patterns of three supportive systems for a region and part of a network, which is an equivalent 526-bus system of the practical Indian Western grid. [ABSTRACT FROM AUTHOR]

A novel temperature monitoring system for gas-insulated switchgears (GISs) based on surface-acoustic-wave (SAW) sensing is proposed in this paper. Compared with the existing systems, this system has several unique advantages, such as being wireless, passive, and at a proper cost with continuous monitoring. First, an accurate SAW temperature sensor is designed for the GIS conductor, where epoxy encapsulating and loop antennas are adopted in the SAW sensor to prohibit the potential partial discharge of the sensor itself. After that, a multifunctional reader antenna is developed, which can measure the conductor temperature and partial discharge by the time-division multiplexing technique. Experiments are carried out to examine the accuracy and response speed of the SAW sensors, and the results indicate that the uncertainty of the contact temperature measurement is smaller than 10 ^\circC. Moreover, the insulation level and anti-interference ability are demonstrated based on experiments carried out on a 126-kV GIS. At last, temperature monitoring performance of the developed system is investigated by changing the current in the 126-kV GIS conductor. The experiment results prove that the developed system can meet the requirement of temperature monitoring in GIS. [ABSTRACT FROM AUTHOR]

Subsynchronous resonance (SSR) damping in fixed-speed wind turbine generator systems (FSWTGS) by using two series flexible ac transmission system (FACTS) devices, the thyristor-controlled series capacitor (TCSC), and gate-controlled series capacitor (GCSC) are studied in this paper. The former is a commercially available series FACTS device, and the latter is the second generation of series FACTS devices using gate turnoff (GTO) or other gate-commuted switches. The GCSC is characterized by a fixed capacitor in parallel with a pair of antiparallel gate-commuted switches enabling rapid control of series impedance of a transmission line. It is shown that the SSR damping with a GCSC is limited to changing the resonance frequency, in comparison with a fixed capacitor, which may not be adequate to damp out the SSR. Therefore, a supplementary SSR damping controller (SSRDC) is designed for the GCSC. Moreover, it is proven that the GCSC equipped with a well-designed SSRDC can effectively damp the SSR in FSWTGS. In order to verify the effectiveness of the GCSC in SSR damping, its performance is compared with the TCSC, which is an existing series FACTS device. In addition, time-frequency analysis (TFA) is employed in order to evaluate and compare the SSR time-varying frequency characteristics of the GCSC and TCSC. The IEEE first benchmark model on SSR is adapted with an integrated FSWTGS to perform studies, and extensive simulations are carried out using PSCAD/EMTDC to validate the result. [ABSTRACT FROM PUBLISHER]

This paper presents an economic study to find the switches that should participate in a switch upgrade plan, based on the results of reconfiguration. The traditional reconfiguration problem trend considers only one loading condition (mostly maximum demand), in order to find the optimum reconfiguration. However, as the distribution loading condition has hourly and daily variations, the optimum configuration continuously changes. Consequently, considering only one loading condition might lead to inefficiency of the results. In this paper, daily load curves of different types of distribution consumers, during various types of days (weekdays and holidays) and seasons (summer and winter), are used to obtain the best reconfiguration hours during a day. Then, genetic algorithm (GA) is used to obtain the optimum configuration during each time interval. The objective function applied to GA consists of loss and energy not supplied. The switches that contribute to reconfiguration should be remotely controlled in order to have the capability of immediate mode alteration. In order to evaluate the feasibility of automated switch installation, the benefit-to-cost ratio is calculated. The entire procedure is applied to a test distribution system, and the results are discussed in this paper. [ABSTRACT FROM AUTHOR]

This paper evaluates the abilities of fast tap-changer topologies by using insulated-gate bipolar transistors to mitigate flicker generated by the ac electric arc furnaces, based on technical and economic criteria. The design problems derived from the very high powers and currents involved have been solved to a preliminary industrial level. The operation of the best resulting topology is verified on a real 80-MVA arc furnace with a dedicated graphical-mathematical multilevel simulator developed to perform short- and long-term tests. Selected pattern windows of the arc voltage, taken from exhaustive logs of electric variables of a real 80-MVA furnace during a complete meltdown process, have been loaded into the simulator. This novel simulation strategy enables the testing of the proposed compensator under reproduced “real working conditions” with several degrees of flicker severity. The simulator includes an IEC flicker meter capable of checking the flicker level online at any point in the installation. The simple open-loop and closed-loop control tests confirm the new tap changer as a fast and economical competitor to other arc furnace compensators. It manages 16% of the furnace system power at a subcycle or supercycle tap changing rate (between 0 and 10 changes per half cycle), as required. This fast switching capacity reduces the compensating time to the very limited values imposed by the L/R time constant of the furnace installation. [ABSTRACT FROM AUTHOR]

For lack of the appropriate global distribution of dc currents, the conventional suppression method to suppress dc bias based on capacitive dc blocking device (BD) redirects current to the ground as much as possible, which predisposes to the exceeding neutral current of other transformers in the regional power grid and leads to the contradiction between the power grid corporation and other public enterprises. Therefore, this paper presents a flexible suppression method for dc bias based on a novel dc-bias suppression device. First, a current balancing device (CBD) based on adjustable parallel resistances is designed. The mathematical model for global optimal switching of CBDs is established by a field-circuit coupling method with the equivalent resistance network of an ac system along with the location of substations and ground electrodes. The optimal switching scheme to minimize the global maximum dc current is obtained by gravitational search algorithm. Based on the aforementioned work, we propose a suppression strategy considering electro-corrosion of metal pipelines. The effectiveness and superiority of suppression methods are verified by comparative case studies of the Yichang power grid. [ABSTRACT FROM PUBLISHER]

This paper investigates a new family of converters for high-power transfer between dc buses with different voltage levels. The proposed converters achieve high-voltage dc-dc conversion without an intermediate ac conversion stage. Three converter circuits are investigated, all based on the use of a common switching cell module. The first is a step-down converter, the second is a step-up converter, and the third is an inverting step-up/downconverter. For each converter, the structure is presented, its operation principle is explained, and the design equations are derived. A comparative analysis between the converters is carried out to highlight the merits and limitations of each topology. [ABSTRACT FROM PUBLISHER]

The measurement of partial discharge (PD) using ultra-high frequency (UHF) method is considered an effective approach to monitor the online condition of the equipment, which is used to facilitate the detection of incipient defects in gas-insulated switchgear (GIS). In this paper, in order to assess the severity of PD defects using UHF method, the actual 220-kV GIS were subjected to experimentation. The PD was measured simultaneously by using the UHF method and the IEC60270 measurement technique. The combined measurement has been carried out on different defects in PD test cells, including the floating metal, metallic protrusion, and void in epoxy resin. The inner coupler installed in the GIS tank, and the outer coupler placed outside the spacer, are used to measure the UHF signal. The relationship of the apparent charge and the amplitude of the time-domain signal, and the integral energy from 300 MHz to 1.6 GHz of the signal induced by PD in GIS are analyzed thoroughly. In this way, the severity of PD can be quantified using the UHF signal. In addition, to verify the sensitivity of the UHF detection method, a pulse generator with a rise time of about 500 ps is designed. The GIGRE method for the verification of sensitivity, which is used worldwide, is applied in the experiment. The results of the pulse generator experiment are compared to the results produced by the actual discharge sources, and several possible approaches of improving this method are proposed. [ABSTRACT FROM PUBLISHER]

Insulation monitoring is crucial to personal safety and equipment operation in the power distribution system. Recently, with the rapid development of distributed generators, the three-phase voltage-source PWM converter (VSC) is widely used as the bidirectional interface between the dc microgrids and the distribution networks. This paper presents the relationship between the response of insulation monitoring device (IMD) and the neutral-point voltage deviation (NPVD) of VSC, by analyzing the disturbances of the switching function and the dc-side insulation balancing. Then, a method of detecting the NPVD for grid-connected VSC is proposed, based on the dc signal injection and the Duffing oscillator. Furthermore, the proposed method takes the mean and spectrum of the neutral-point voltage as the primal characteristics. Thus, the dc signal injection is adopted to detect the mean of the neutral-point voltage, and the Duffing oscillator is adopted to determine the frequency disturbance of the neutral-point voltage, respectively. The test result confirms the existence of the neutral-point voltage deviation and verifies the availability of the proposed method. Hence, the proposed method could be used to improve the response of IMD. [ABSTRACT FROM AUTHOR]

Preinsertion resistors (PIR) are used in combination with circuit breakers to absorb switching transients and come into effect during the “closing” operation of the breaker. It is mainly used for rated voltages equal to or higher than 420 kV for line lengths above 200 km. Although it is an important component, power testing of complete PIR is very complicated and not well defined. Therefore, an attempt has been made in this paper to provide alternative test methods for power testing of PIR without compromising its important parameters. Due to high energy requirements and limitations of the test laboratory, a multipart testing of PIR is necessary to prove its thermal capability and dielectric behavior. Before proceeding with the complete PIR test, the critical parameters of PIR, such as mechanical insertion time, rate of decay of dielectric strength of the interrupter, and PIR switch, etc., should be verified with testing. These test procedures are also explained in detail along with a method to theoretically evaluate electrical insertion time for different network conditions. The series PIR configuration for the metal-enclosed \mathrmSF6 system has been considered in this paper. [ABSTRACT FROM AUTHOR]

This paper presents a method for determination of breakdown voltage characteristics (BDV) of a gas-insulated switchgear (GIS) disconnector. The method is applicable for modeling very fast transient overvoltages that are generated during the disconnector opening and closing operations. The method is based on full-scale measurements, as typically performed during the disconnector development and/or type tests. The method is first presented in a simplified, illustrative setting, and then applied for the full-scale measurement results obtained for an 1'100 kV disconnector design. The BDV determined is then applied for two 1'100 kV test setups as recently reported for the Wuhan (China) station. Selected test cases are simulated, analyzed, and validated with the use of the multispark modeling approach, with two BDV characteristics implemented: the nonlinear BDV obtained with the method presented here applied for the measurement results on the example 1'100 kV disconnector, and the linear BDV reported in the literature for the 1'100 kV disconnector used in the Wuhan GIS station. [ABSTRACT FROM PUBLISHER]

This paper proposes an algorithm for determining the optimal composition which means number of links and section switches in a feeder and placement of automatic switches in a distribution automation system (DAS). A DAS is configured by automatic switches and reclosers on a power distribution line. The composition and placement of switches affect the operational applications of a DAS. More switches lead to better DAS operation but also to increased cost and maintenance. Thus, this paper proposes an approach to determining the optimal composition and placement of automatic switches. Additionally, the proposed algorithm is developed considering various system topologies in a real field. The algorithm was tested on an example power distribution system with eight-feeders and on a real power distribution system operated by KEPCO in Young-Deung-Po and Jeju, South Korea. [ABSTRACT FROM PUBLISHER]

This paper describes a modified phase-shifted carrier-based pulsewidth-modulation (PSC-PWM) scheme for modular multilevel converters (MMC). In order to reduce the average device switching frequency, a reduced switching-frequency (RSF) voltage balancing algorithm is developed. This paper also proposes a circulating current suppressing controller (CCSC) to minimize the inner circulating current in an MMC. Based on the double line-frequency, negative-sequence rotational frame, the three-phase alternative circulating currents are decomposed into two dc components and are minimized by a pair of proportional integral controllers. Simulation results based on a detailed PSCAD/EMTDC model prove the effectiveness of the modified PSC-PWM method and the RSF voltage-balancing algorithm. The proposed CCSC not only eliminates the inner circulating current but also improves the quality of the converter ac output voltage. A simple loss evaluation demonstrates that the RSF voltage-balancing algorithm and the CCSC reduce the converter power losses. [ABSTRACT FROM AUTHOR]

The severe insulation breakdown on one medium-voltage (MV) switchgear led to a complete blackout of Taipower's 3rd nuclear power plant on March 18th, 2001. This has been one of the most serious incidents during the past 30 years of Taipower's nuclear generation and while the cause of the event was a combination of design, maintenance, and equipment aging issue, it is apparent that repeated switching operation on the extra-high-voltage (EHV) side eventually caused this severe insulation breakdown on MV switchgear. Very-fast transient overvoltage (VFTO) is the phenomenon of transient overvoltage generated during switching operation characterized by a very short rise time of 4 to 100 ns. Prior research on this topic focused on VFTO's impact on the EHV side of the transformer and this paper presents the field measurement result together with long-duration multiple-restrike simulation for the VFTO transferred from the EHV side to the MV system through the power transformers. It is shown that this VFTO can be as high as 7 times the rated line-to-ground peak voltage and the maximum VFTO often occusr neither at the first nor at the last strike due to the superposition of restriking voltage on top of oscillation voltage created by prior strikes. [ABSTRACT FROM AUTHOR]

This paper develops a frequency-dependent analytical representation for a multilevel cascaded converter, with fundamental frequency switching. The gain and phase angle are studied with the firing angle as a parameter, where the converter is subjected to oscillatory excitation at a range of frequencies. This paper presents analytical formulae for a single cell and for a generic cascade multilevel converter where the number of cells is a parameter. Also, the formula for fundamental frequency studies is separately developed. The equivalent capacitance concept is introduced and its convergence to a constant value for high frequencies is demonstrated. The analytical formulae are tested against detailed digital simulation and good matching is reported. The formulae developed in this study will be of particular importance in studying interactions between a multilevel STATCOM and the host ac grid (similar to harmonic resonance) and in studying converter transient responses. [ABSTRACT FROM AUTHOR]

This paper presents a new method for online real-time detection and classification of voltage events in power systems. The method proposed simultaneously uses the results obtained in the application of the discrete wavelet transform and an extended Kalman filtering to the voltage waveform. Wavelet analysis is used for detection and estimation of the time-related parameters of an event and the extended Kalman filtering is used for confirmation of the event and for computation of the voltage magnitude during the event. The paper presents different experimental results showing the improved performance of this combined approach. [ABSTRACT FROM AUTHOR]

A VSC-MTDC (multi-terminal dc) system consists of Voltage-Source Converters (VSCs) connected to a dc network at their dc terminals. The MTDC is most vulnerable to a dc fault which paralyses all the VSCs until the default is cleared. As dc circuit breakers are expensive, this paper proposes a solution based on extinguishing the dc fault current by opening all the ac-circuit breakers (ac-CBs) which the VSCs are already equipped with on the ac-sides. However, it is necessary to identify which dc line is the faulted line (in case it is a permanent fault) so that it can be isolated by fast dc switches (which are much more economical than the dc circuit breakers), prior to restoring the MTDC system by re-closing all the ac-CBs. This paper presents the handshaking method, which locates and isolates the faulted dc line and restores the MTDC without telecommunication. [ABSTRACT FROM AUTHOR]

This paper presents a method to determine the relative location of a switched capacitor bank using voltage and current waveforms recorded at a single measurement point. The hypothesis states that a switched capacitor bank downline from the monitoring location will have opposite polarity in grad [Vϵ (t)] and grad [Iϵ (t )], while a switched capacitor bank upline from the monitoring location will have an identical polarity in grad [Vϵ (t)] and grad [Iϵ (t)], where grad [·] is the gradient or slope of voltage and current traces immediately after the switching instant. The method is valid for both wye-and delta-configured capacitor banks. This paper proves the hypothesis using principles of electric-circuit theory, and demonstrates its efficacy using simulated and actual capacitor energizing events. [ABSTRACT FROM AUTHOR]

This paper presents the design of the power section of a 25-kV, 50-Hz, 10-MVAr single-phase static var compensator (SVC) for railway applications. It is based on a third harmonic filter, on a low-pass filter for harmonic reduction, and on a saturable reactor connected in series with the thyristor-controlled reactor. Harmonic filtering is the crucial aspect of the system because of the very stringent limitations imposed on the harmonic current generation due to railway signaling requirements. The effectiveness of this innovative solution in reducing the grid harmonic current injection is shown in the paper and the advantage, in terms of system efficiency, is underlined. The system was successfully constructed and installed at the end of 2002, and the commissioning will be completed during 2003. [ABSTRACT FROM AUTHOR]

A hybrid system, comprising a line commutated thyristor high-voltage direct current (HVdc) converter and a static VAR compensator, is proposed in this paper for the connection of networks with no synchronous generation to a main grid. The proposed system combines the robust performance and low capita! cost and power toss of a line-commutated HVdc converter, with the fast dynamic performance of a voltage-source-converter (VSC)-based transmission system. The paper describes the principles and control strategies of the proposed system. PSCADIEMTDC simulations are presented to demonstrate the robust performance and to validate the proposed system during various operating conditions such as black-start, variations of load or generation, and ac fault conditions. [ABSTRACT FROM AUTHOR]

An advanced solution for the bypass protection of a series compensation system in arc furnace plants is presented in this paper. It is based on high-power light triggered thyristors (LTTs). In this paper, after a description of the application, the thyristor bypass design is presented with the analyses of the most peculiar aspects and interesting technological solutions. The paper also re- ports some experimental results and the comparison with the wave- forms obtained by the numerical simulations. [ABSTRACT FROM AUTHOR]

Internal arc fault tests are important for ensuring the safety of medium-voltage metal-enclosed switchgears. Since these tests are conducted at full scale, the costs of the test objects as well as the high-power laboratory are significant. This paper presents an experimental study to clarify whether such tests can be simplified by downscaling. Tests with volume and energy downscaled to 1/3 and 1/10, respectively, were performed on a single-phase arrangement with air as the insulating gas. The test results showed that the internal pressure rise caused by the arc can be reproduced well using a smaller compartment and lower current. The potential damage caused by the exhaust of the hot gas escaping through the pressure-relief openings is more challenging to predict from small-scale tests. [ABSTRACT FROM PUBLISHER]

Nanocrystalline magnetic rings have been experimentally proven for effective damping of very fast transient overvoltages (VFTOs) in gas-insulated switchgear (GIS). The application of any damping solution in a specific GIS setup (rated voltage, GIS arrangement) requires simulation-based design, which, in turn, requires reliable models with proven accuracy in demanding high-frequency and high-current VFTO conditions. This paper presents a new model of a magnetic ring, employing full frequency-dependent characteristics of the ring's complex impedance, as well as the dedicated approach on modeling the saturation effect of the material magnetization characteristics. The saturation effect is modeled by a bypassing branch, activated at a certain saturation current value calculated according to the specific magnetic material properties and for the VFTO main frequency component. The model was implemented in Electromagnetic Transients Program simulation software and validated experimentally in a full-scale 550-kV GIS test setup. The validation proved the applicability of the model for the assessment of VFTO damping effectiveness with the use of nanocrystalline magnetic rings and, thus, for the design of a particular magnetic-based damping solution in a specific GIS setting. [ABSTRACT FROM PUBLISHER]

With smart fault indicators (SFIs) being widely deployed in distribution networks, availability of SFIs statuses and their current measurement provides an opportunity to locate distribution system faulted line sections in real time. However, the integrity of SFIs data together with complex fault scenarios poses a challenge for fault diagnosis, especially with the presence of distributed generators (DGs). To solve this issue, this paper proposes a new method based on mixed integer linear programming (MILP) for identification of the faulted line sections using incomplete and incorrect SFIs statuses. By minimizing the discrepancy between the expected SFI statuses and the available evidence at the distribution operating center, the proposed approach is able to handle complex fault scenarios with multiple faults and failures or malfunctions of SFIs. When DGs are present, the current measurement of SFIs and their statuses are jointly used. The result is a robust algorithm for detection of faulted line sections of distribution systems with DGs in real time. In addition, a new technique is proposed to convert nonlinear logical constraints into a linear combination of decision variables. The resulting linearity of the developed optimization model ensures its optimality. Simulation results based on a utility feeder demonstrate the effectiveness of the proposed approach. [ABSTRACT FROM AUTHOR]

Future multi-terminal dc networks are envisioned for the large-scale integration of renewable energy sources into today's power systems. An essential aspect for the reliable operation of these systems is the fast and selective dc-side fault handling and separation of faulted lines. The objective of this paper is the development and evaluation of a multi-terminal dc protection strategy based on fault-blocking converters (e.g., full-bridge based modular multi-level converters) and high-speed switches. Both a suitable fault control and a new high-speed switch design for a fast separation of faulted dc lines are elaborated. The novel concept is intended to reduce the requirements on the high-speed switches compared to dc circuit breakers and to ensure a fast restoration of the active power transmission capability, as well as the dc voltage. The fault-clearing strategy is analyzed using electromagnetic transient (EMT) simulations under variation of the fault location, type, and resistance. The investigations are carried out in a cable-based multi-terminal HVdc system with full-bridge modular multi-level converters in symmetrical monopole configuration. [ABSTRACT FROM AUTHOR]

In Nordic countries, distribution networks are traditionally unearthed and increasingly compensated. For such networks, switching their neutral point to the earth is practically applied through a resistor for better selectivity functions of earth faults. In this paper, the neutral switching and, consequently, an arrival time of the aerial mode traveling wave reflected from the fault point are utilized to accurately determine the earth fault distance. A concept to create traveling waves is implemented by earthing the neutral via a controlled thyristor that provides a short period of high fault current and produces traveling waves to estimate the fault distance. Much higher transient signals are generated by earthing through an opposite charged capacitor. A capacitor-resistor divider is utilized to measure the reflected surge over a heterogeneous distribution feeder. An adaptive setting is proposed for stamping the arrival surge. The results provide evidence of the efficacy of the proposed fault distance estimation. [ABSTRACT FROM AUTHOR]

Controlled switching technology operates circuit breakers at the minimum arcing time for short-circuit current interruption. However, there is no report to reveal a relationship between the short-circuit current interrupting capability with the minimum arcing time and the opening velocities of vacuum interrupters. The objective of this paper is to reveal a relationship between the short-circuit current interrupting capability with the minimum arcing time and the opening velocities of vacuum interrupters. A 40.5-kV fast vacuum circuit breaker prototype was built up which was equipped with a commercial 40.5 kV–31.5 kA vacuum interrupter and it was driven by an electromagnetic repulsion mechanism. It provided an average velocities ranging from 2.5 to 5.5 m/s. A total of 50 times of 40-kA short-circuit current interrupting tests were carried out in a synthetic circuit. Test results showed that the minimum arcing time of successful interruption decreased with the increasing of the average opening velocity. The minimum arcing gap was determined as 1.8 mm and it kept as a constant as the average opening velocity increased. The experimental results also showed a relationship between the arc energy density and the arc extinguishing gap, which acted a linear boundary between the successful and failure short-current interruptions. [ABSTRACT FROM AUTHOR]

This paper provides an effective misalignment fault diagnosis method of the gas-insulated switchgear (GIS) disconnector. Relationships between contact forces and the surrounding magnetic field in various mechanical assembly conditions were studied by the 3-D electromagnetic-mechanical coupled finite-element model and physical experiments. First, spring deformation and contact forces on individual contact elements were obtained by mechanical field analysis. Holding springs were modeled by equivalent elastic rings during analysis. Second, the magnetic field around the GIS disconnector was obtained by electromagnetic-field analysis. Contact resistances on contact interfaces were modeled by cylindrical bridges, which use mechanical contact forces as parameter inputs. Physical tests have been carried on the prototype GIS disconnector with various artificial misalignment faults. In different situations of misalignment faults under ac current, surrounding magnetic flux densities were measured by the Hall sensor array. Calculated and measured results have the same trend that the mechanical misalignment fault could change distributions of contact forces then make distortion of currents and the surrounding magnetic field. Magnetic-field behaviors of the GIS disconnector with different mechanical assembly conditions were studied. The results show that the deviation of magnetic flux density becomes larger while reducing holding spring stiffness, decreasing movable conductor insert depth, and increasing the movable conductor docking angle. [ABSTRACT FROM AUTHOR]

The expected abolishment of SF6-gas in medium-voltage switchgear has prompted a search for replacements for the switch types that depend on SF6 to obtain the required capability, reliability, compactness, and cost. Ablation of polymers can enhance the arc-quenching capabilities in certain electrical switch designs. Several aspects, like electric arc plasma composition, gas flow, and wall stabilization, must play together to obtain successful interruption. In this paper, open and closed switch geometries and two nozzle materials [polypropylene (PP) and polytetrafluoroethylene (PTFE)] are studied in medium-voltage interruption experiments. Fundamental differences in the arc-quenching process for PP and PTFE are shown. In the case of PTFE, the current interruption performance depends on gas flow resulting from the pressure built up under the high-current period. In the case of PP, the gas flow plays a lesser role for the arc-quenching capability as the interruption capability is large even in an open design with no forced gas flow around current zero. Current chopping happens a few tens of microseconds before voltage zero crossing; thereafter, a remnant conductance in the contact gap is observed, lasting for up to several milliseconds. This can be explained by an arc-to-glow transition in the presence of hydrogen. [ABSTRACT FROM AUTHOR]

The popularity of underground cables to replace overhead lines is increasing. This is partly a consequence of the requirement for better reliability and supply security. In some countries, the authorities have set maximum interruption durations for distribution system operators to steer the operators to avoid the use of overhead lines. However, although faults are typically of a rare occurrence in underground cable networks, they cannot be completely avoided. Since the fault repair process in an underground cable network is time consuming, the distribution network should be meshed, and the rate of disconnecting switches should be high enough. However, this is not always possible or economically feasible and, therefore, other opportunities to restore the electricity supply should also be considered. This is especially the case for branch lines without a backup option. Yet, the power should be restored in a reasonable amount of time, which emphasizes the significance of an appropriate switch placement strategy and reserve power planning. This paper proposes a methodology to analyze the costs of different reserve power strategies and to optimize the reserve power arrangements. The reserve power strategies under consideration are the application of reserve power cables and reserve power generators and looping of the existing branch lines. [ABSTRACT FROM PUBLISHER]

An effective measure to mitigate a shunt capacitor caused harmonic resonance is to add a C-type damping unit in series with the capacitor. If there are multiple switchable capacitors, each of them requires a C-type damping unit. The cost and space requirement for implementing these changes, therefore, increase with the number of switchable capacitors. In view of this disadvantage, a scheme that allows multiple switchable capacitors to share a common damping unit is proposed in this paper. The damping unit is designed in such a way that it will provide adequate damping for all possible on/off combinations of the capacitors involved. In addition and proven methodically, the design method can further guarantee resonance free for all possible network impedance conditions. Performance and usefulness of the proposed scheme has been demonstrated through comparative studies on actual capacitor application cases. [ABSTRACT FROM PUBLISHER]

The alternate arm converter (AAC) is an emerging fault-tolerant multilevel converter topology from the same family of multilevel converters as the modular multilevel converter (MMC). Due to the alternate operation of the converter arms, energy balancing in the AAC is not continuous, but restricted to small time intervals. This paper develops a gradient-based current control and energy-balancing method for the AAC. The proposed strategy enforces the dynamic limits on the redundant submodules (SMs) during the overlap period and allocates effectively the maximum available number of redundant SMs to control the circulating current. The choice of the gradient as the circulating current control parameter improves the energy regulation capability of the AAC, and the enforcement of dynamic limitations avoids distortions of the output voltage. Results from an AAC-based HVDC converter model derived from the CIGRE benchmark MMC system demonstrate that the proposed strategy delivers improved energy control and balancing with good harmonic performance compared to existing current control methods for the AAC while also maintaining zero-current switching of the director switches of the AAC arms. [ABSTRACT FROM AUTHOR]

The facility to save multiple setting groups (SGs) within digital overcurrent relays (OCRs) is to adapt the active setting of the relays to the current topology of the power network. However, the number of available SGs is much lower than the possible topologies of the network, so this facility is usually applied to a few local changes in the network. This paper aims to extend the application to a complete set of topologies. A proper index is introduced and applied with a k-means clustering technique to classify the topologies into some clusters, whose number is equal to the number of SGs. Then, for every topology cluster, the optimal settings are calculated and saved in the OCRs as a distinct SG to be activated by changing the topology to any member of the cluster. Applying this technique to OCRs of the IEEE 14-bus test network and a 63/20kV substation verifies its effectiveness on reserving coordination for all topologies and reducing the relays’ time dial setting. Using available communication links, this technique can be implemented by making a computer network between substations of the power network without needing to interact with the control center. [ABSTRACT FROM AUTHOR]

Switching operation of the disconnector in gas-insulated switchgear (GIS) results in very fast transient overvoltage in GIS pipes. In a smart substation, this process induces disturbance voltage on the port of the intelligent component fixed on GIS pipes or placed in the local cabinet nearby, which then may lead to the failure of the equipment. The experimental results of the port disturbance voltage during the switching operation via a 1100 kV test circuit are first reported in this paper. The test arrangement, including both 70 opening operations and 70 closing operations, had been performed. The influences of different grounding schemes of cable shield on port disturbance had been investigated. Three different cases of the terminal load had also been considered: open circuit, short circuit, and 50 Ω. Over 100 000 micro-pulses had been extracted from the disturbance voltage waveforms. The waveform characteristics including peak voltage, rise-time, oscillation frequency, and decaying had been obtained by statistical analysis of these micro-pulses. Furthermore, the differences between measured waveforms and the IEC 61000-4-18 immunity test standard waveform had been discussed. [ABSTRACT FROM PUBLISHER]

The modular multilevel converter (MMC) is one of the most potential converter topologies for high-power/voltage systems, specifically for high-voltage direct current (HVDC). One of the main technical challenges of an MMC is to eliminate/minimize the circulating currents of converter arms while the capacitor voltages are maintained balanced. This paper proposes a model predictive control (MPC) strategy that takes the advantage of a cost function minimization technique to eliminate the circulating currents and carry out the voltage balancing task of an MMC-based back-to-back HVDC system. A discrete-time mathematical model of the system is derived and a predictive model corresponding to the discrete-time model is developed. The predictive model is used to select the best switching states of each MMC unit based on evaluation and minimization a defined cost function associated with the control objectives of MMC units and the overall HVDC system. The proposed predictive control strategy: 1) enables control of real and reactive power of the HVDC system; 2) achieves capacitor voltage balancing of the MMC units; and 3) mitigates the circulating currents of the MMC units. Performance of the proposed MPC-based strategy for a five-level back-to-back MMC-HVDC is evaluated based on time-domain simulation studies in the PSCAD/EMTDC software environment. The reported study results demonstrate a satisfactory response of the MMC-HVDC station operating based on the proposed MPC strategy, under various conditions. [ABSTRACT FROM AUTHOR]

Gas-insulated switchgear (GIS) plays an important role in power systems, not only because it is maintenance free and has less of an influence on environmental and industrial conditions, but also due to its low space requirements and high reliability. In order to monitor the online condition of GIS and diagnose existing defects, the ultra-high frequency (UHF) methods are widely used for detecting partial discharge (PD) owing to its sensitivity and anti-interference capability. In this paper, five types of typical PD sources are designed and fabricated to imitate the defects in GIS online. In order to distinguish different types of PDs, some feature parameters from the UHF signals are extracted and discussed. Generally, the conventional phase-resolved PD (PRPD) and pulse-sequence analysis methods are adopted to discriminate PD sources. However, sometimes it is not convenient to employ these methods because of the absence of phase information. In this research, nine feature parameters realized by processing the UHF pulse magnitude sequence q and time interval sequence \mit\Deltat are introduced. The parameters can represent exactly the physical characteristics of different PDs. Based on these parameters, a new approach is developed through which pattern classification of PD can be achieved effectively without employing the phase information of the applied voltage. The clustering results obtained by performing statistical product and service solutions indicate that there is evident difference in the characteristic coefficients. [ABSTRACT FROM AUTHOR]

Capacitor switching transients are harmful to the capacitor and the switching device. For reducing these transient phenomena, this paper proposes a symmetrical structure transient limiter (SSTL). The proposed SSTL can automatically provide high impedance at the instant of capacitor energization, and, thus, the switching transients can be effectively suppressed. After the restriction, owing to the compensation of all power losses caused by the diodes and reactors, the SSTL acts as a short circuit during the steady state and, thus, has no effect in the circuit. As a result, the capacitor voltage and current waveforms will not be distorted. Moreover, due to the freewheeling effect in the SSTL, no transient overvoltage will appear across the switch contacts at the instant of capacitor de-energization even though the reactors are inserted into the circuit. Theoretical analyses of the proposed SSTL for the energization state, steady state, and de-energization state have been completely carried out. Also, the selections of the related components are depicted. Finally, the experimental results obtained using different methods of capacitor switching verify the feasibility and performance of the proposed SSTL. [ABSTRACT FROM AUTHOR]

Automation can significantly enhance substation reliability by speeding up service restoration. Although much research works has been done in reliability assessment of substation control systems, there are still several aspects that need to be considered in automated substation reliability evaluation. The impacts of automation system on substation reliability indices have not been comprehensively covered in the literature so far. This paper aims at presenting a comprehensive technique to quantitatively assess the reliability of the automated substations. The technique is based on the event tree methodology and the concepts of conditional probability technique. A step by step evaluation procedure is presented using a typical substation automation architecture known as simple star. The proposed technique is applied to some conventional substation configurations to examine the effectiveness of the technique and also to examine the level of reliability improvement achieved by automation. Furthermore, different sensitivity analyses have been carried out for both automatic switching action and a specific automated substation. The proposed strategy is easy to implement and suitable to analyze for an automated substation reliability with arbitrary automation architectures. Also, automated substation reliability assessment tools can be developed in detail, and can be catered to the specific needs of substation design. [ABSTRACT FROM AUTHOR]

Continuity in power supply for the consumers is a permanent concern from the utilities, pursued with the development of technological solutions in order to improve the performance of network restoration conditions. Using remotely controlled switches corresponds to one possible approach to reach such an improvement and gives some convenient remote resources, such as the fault detect, isolation, and transfer loads. This paper presents a methodology implemented in a computer programming language for allocation of these devices in electric distribution systems based on the analytic hierarchical process (AHP) method. The main contributions focus on considering the impact of installing remotely controlled switches in the reliability indices and the AHP decision-making algorithm for the switches allocation. The effectiveness of the proposed algorithm is demonstrated with case studies involving actual systems of the AES Sul utility located in Southern Brazil. [ABSTRACT FROM AUTHOR]

In this paper, a new method is proposed that can be used to discriminate faults from switching transients. The method is primarily intended for use in systems where fast fault detection and fast fault clearing before the first peak of the fault current are required. An industrial system, in which high short-circuit power is desired but in which high short-circuit currents cannot be tolerated is an example of such a system. A phase-locked loop (PLL) is used to perform the discrimination. Computer simulations have been performed and it has been demonstrated that the output of the PLL is completely different for a fault compared to a switching transient. This difference can be used for discrimination between a fault and a switching transient. [ABSTRACT FROM AUTHOR]