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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]

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]

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]

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]

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]

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]

In this paper, the commutation and switching mechanisms between the operating low-voltage (LV) switch and parallel external branches are presented. Experiments for the limitation of electric arc energy during inductive current interruption were performed for three scenarios: 1) for standalone operated switch (base case), 2) for passive method of arc energy limitation (widely applied RC branch connected in parallel to operated switch), and 3) active method of electric arc energy limitation (current commutation into the external semiconductor branch controlled by the microprocessor system). A typical three-phase electromechanical LV switch with double arc quenching chamber was selected as the tested object. The following parameters were investigated: electric arc resistance, electric arc power, electric arc energy, as well as power and energy generated at the external branch connected in parallel to the operating switch. Measurements were performed for current interruption in a single-phase circuit. In addition, observations of a burning electric arc in the quenching arc chamber were registered by an ultraspeed camera (for two cases: base case and hybrid switching). [ABSTRACT FROM AUTHOR]

A simple gas-blow switch, consisting of an axisymmetric tulip/pin contact and a cylindrical polytetrafluoroethylene (PTFE) nozzle, has been used for empirical studies of medium-voltage load current interruption in air. Only the thermal phase of the interruption is considered. Based on the results of more than 3000 interruption tests, a logistic regression model has been developed to describe the relationships between the switch design and test circuit parameters, and the current interruption capability. The most important design recommendation is that the inner diameter of the nozzle should be only slightly larger than the pin contact. The upstream overpressure needed for successful interruption increases as a polynomial function of degree 0.5–1 with the rate of rise of recovery voltage and of degree 2-3 with increasing current. [ABSTRACT FROM PUBLISHER]

A multiperiod network reconfiguration to meet the requirement of hourly hosting capacity under a minimal required number of switching operations, taking into consideration the uncertainty of renewable generation, is formulated as a nonlinear, nondifferentiable integer optimization problem with nonlinear equality and inequality constraints. A four-stage solution methodology, including an assessment stage, a time-partitioning stage, an optimization stage, and an evaluation stage, is developed to solve the constrained large-scale nonlinear integer optimization problem. A fuzzy C-means clustering algorithm is applied to partition the time period to facilitate the design of a minimum-number switching solution. A hybrid particle swarm optimization algorithm is developed to find an optimal network topology for each partitioned time period. The IEEE 123-bus case and a 1001-node system, three-phase and unbalanced, are used to evaluate the proposed method with promising results. [ABSTRACT FROM AUTHOR]

Active current injection circuit breakers (ACICBs), which utilize the mechanical switch and a parallel-connected precharged capacitor, have broad application prospects in future multiterminal dc grids. However, with the increase of system voltage, the precharged capacitor leads to the great cost and size being spent on the charging circuit and auxiliary commutating appliances. To address this shortcoming, an innovative dc circuit breaker (DCCB) based on a magnetic induction current commutation module (MICCM) is proposed. The influence of the main component parameters on the commutation performance is investigated by calculation, in which the self-, mutual, and stray inductances are involved. Besides, the validity of calculation is experimentally proved. Then, by applying the MICCM to the ACICB, the breaking characteristics of the ACICB are analyzed in detail. Finally, a 10-kV DCCB prototype is developed, verifying the feasibility of current commutation concept and the validity of simulated interruption results. Our studies show that a 10-kA bidirectional fault current can be interrupted successfully with a commutation duration less than 250 μs. [ABSTRACT FROM PUBLISHER]

A new bidirectional multilevel converter topology called the sparse modular multilevel converter suitable for high power ac/ac applications is presented. The proposed topology has fewer insulated-gate bipolar transistor switches and capacitors compared with conventional approaches. Moreover, a salient feature of the proposed topology is that more than half of the switches are operating in soft switching conditions, which considerably decreases the switching losses of the converter. The theoretical calculations and simulation results are provided to verify the feasibility of the proposed topology. [ABSTRACT FROM PUBLISHER]

Introducing distributed generation (DG) into distribution networks can affect the problem of optimal switch placement. A method for solving the problem of optimal placement of sectionalizing switches with a large number of DGs is presented. The primary objective is to minimize the total cost of achieving a certain level of reliability in the presence of DG. The problem is formulated using mixed-integer linear programming to determine the optimal number and location of sectionalizing switches. Allowing DG to operate in an island mode is also considered. The effectiveness of the proposed formulation is examined on a modified reliability test system. The presented results indicate that the proposed formulation can provide a global optimum solution for the problem of sectionalizing switch placement, while reliability, capital investment, and annual operation and maintenance costs are considered. Furthermore, DG can play a key role in providing a reasonable improvement in the reliability indices of the system. [ABSTRACT FROM AUTHOR]

Experiments were performed on two different ultra-high voltage gas-insulated switchgear test circuits to evaluate the mitigation performance of ferrite R2KB rings with very fast transient overvoltages (VFTOs). Significant decreases in the overshoot factor and the VFTO level were observed, although the steepness was not much improved owing to saturation. It was found that ferrite rings are more effective for VFTO mitigation at the source side than at the load side. Simulations were carried out with a new circuit model of the ferrite ring, and the simulation results were consistent with the experimental results. The method of drawing the contour plot of VFTO and very fast transient current in the time-space domain was proposed to facilitate the analysis. With this method, the principle of determining the optimal installation location of ferrite rings for the best mitigation performance was clarified. [ABSTRACT FROM AUTHOR]

Failure progression of metal oxide-based surge arresters in response to exposure to harmonics is modeled using the accelerated failure time model. Multistress accelerated ageing tests, with and without ac distorted voltage stress, are conducted on arrester samples sourced from different suppliers to obtain baseline and harmonic-factor logarithmic life and reliability functions. A maximum likelihood approach is taken to estimate the accelerated failure time model parameters based on the failure time data. The modeled harmonic-factor reliabilities prove metal oxide varistors life acceleration and show multiplicative failure progression of up to 41 times faster for a total harmonic distortion (THD) content of 8.52% in the applied voltage stress. [ABSTRACT FROM AUTHOR]

Internal dielectric strength of vacuum interrupters (VIs) is primarily determined by the macroscopic electric field strength and effective area on the electrode surfaces. While internal dielectric strength is usually not an issue for medium-voltage VIs ($U_{m}$ ≤ 52 kV), it requires special consideration when going to higher voltage levels. Generally, the vacuum breakdown is initiated by field emissions from critical enhancement points with higher electric field on a cathode. The most critical point of the macroscopic electric field in a VI is present at the front contact edge between the main contacts. A vapor shield of a VI is one component that determines the electric field strength and distribution. Its floating electrical potential can basically be determined by the geometry of the VI and its surroundings. Since the shield potential can change the maximum electric field strength at the front contact edge in the VI, it seems possible to increase the internal dielectric strength of the VI by giving the vapor shield a well-defined electric potential. The present study focuses on the possibility of electrical potential control of the vapor shield for increasing the internal withstand voltage of the VI. Basically, the potential control of the vapor shield can be realized by connecting a parallel capacitor network. This allows controlling the shield potential arbitrarily between H.V. potential and zero by changing the voltage division ratio. From the field calculation results for a 72.5 kV VI model, the maximum electric field strength can be reduced by up to 23.3% compared to a floating vapor shield. Dielectric withstand tests for the 72.5 kV VI with potential control to determine the internal breakdown voltage with positive impulse voltage were carried out. The experimental results show that the breakdown voltage can be increased by 11.2%, by setting the vapor shield potential to one-third of the applied voltage. The increase in the breakdown voltage of the VI can be explained by the relaxation of the electric field on the critical point as a result of the decrease in the potential difference between cathode and vapor shield. [ABSTRACT FROM AUTHOR]

Switching overvoltages on busbars occur during the operation of circuit breakers and disconnectors in power plants and substations. The transient electromagnetic interferences arising from the switching surges may cause disturbances in sensitive electronic devices in low-voltage control circuits and may induce voltages on other busbars grounded for maintenance. To suppress the effect of electromagnetic interferences properly, it is useful to predict surge phenomena and design effective protection methodologies. The finite-difference time-domain (FDTD) method, which is a full-wave numerical approach, has become an effective tool for analyzing surge phenomena in a 3-D arrangement. In this study, first, we propose techniques for applying the FDTD method to the switching surge analysis of an extremely high voltage air-insulated substation. Second, using the proposed techniques, we calculate voltages induced on a grounded busbar due to a restrike at a disconnector during its operation in a 500 kV air-insulated substation and compare the calculated results with measured results for validation. [ABSTRACT FROM AUTHOR]

In substations, buswork, insulators, and supporting structures are subjected to electromagnetic forces caused by short circuits. The current industry design standard of practice is to apply the maximum instantaneous short-circuit force to the structure and perform simple static structural analysis to calculate supporting structure member. However, it is well known that this may be overly conservative since the applied forces and the response of the structure are dynamic in nature. To quantify the dynamic effects, full-scale short-circuit testing was performed on a typical 138 kV disconnect switch stand. The switch stand was instrumented with fiber optic strain gages and subjected to a variety of fault conditions. Extensive dynamic finite element analyses were performed on the subject structure, which were validated with the test data. The results confirm the reduced dynamic response of the structure. With further analyses, it is anticipated that a generalized quasi-static design methodology that considers dynamic response can be developed to replace the present short-circuit design approach. [ABSTRACT FROM AUTHOR]

This letter presents a cost-effective technique for partial-discharge testing of medium-voltage (MV) cables using a combined ac and damped ac (DAC) voltage. The combined ac and DAC voltage is generated by a conventional variable-frequency resonant test system and two high-speed switches. An experimental study and on-site test are performed to validate the proposed technique. [ABSTRACT FROM PUBLISHER]