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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]

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]

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 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]

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]

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]

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]

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 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]

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]

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]

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]

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]

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]