Switching Overvoltages Research Articles

Исследование энергетических характеристик устройства компенсации реактивной мощности с регулируемой индуктивностью в электротяговой сети на экспериментальной установке

Objective: Checking the theoretical provisions of the possibility of controlling the reactive power of an adjustable inductance compensating device. Testing and optimizing the algorithm of the reactive power regulating device. Assessing energy effi ciency of the device. Checking stability of the device in transient modes. Suggesting methods to improve stability of the system. Conducting a harmonic analysis of current and voltage curves obtained as a result of physical modeling, developing ways to suppress higher current and voltage harmonic. Methods: The scheme of the experimental setup was built, the electrical element base was selected, the measuring instruments used were determined, the experimental stand was assembled. Curves of changes in current, voltage, active and reactive power were taken on the physical model for operating modes without a compensating device, with an unregulated and adjustable compensating device. The change in current for critical transients is analyzed. To evaluate the fi ltering of higher harmonics of current and voltage by a compensating device, oscillograms were taken in operating mode with a load and after adding a diode bridge to the electric locomotive circuit, and their harmonic analysis was performed. Results: The adjustable device provides reactive power compensation in the load range of no less than 90 %. Additional measures are required to lower the active resistance of the compensating device reactor. The use of a reactor connected in series with a capacitor reduces the switching current and overvoltage in the device. The compensating device can operate in the mode of a broadband fi lter of higher harmonics. Practical importance: A physical model of an alternating current traction network with a reactive power compensating device and a controlled variable inductance has been created, which makes it possible to analyze both instantaneous and long-term processes in the traction network.

Energy Storage System Control Strategy for Restraining Overvoltage Caused by Switching Non-Load Power Transmission Lines

During the switching operation of the non-load power transmission lines, the undisired switching overvoltage issue is inevitable, causing grid voltage oscillations, waveform distortion and other phenomena at the end of the non-load power transmission lines, and even lead to the insulation breakdown, all above phenomena probably make the power transmission failure. To avoid the above harmful cases, the formation mechanism of the undisired switching overvoltage issue caused by switching non-load power transmission lines is first analyzed in detail. Based on this mechanism analysis, the energy storage system (ESS) based overvoltage suppression method and corresponding ESS voltage command synthesis algorithm are developed. The method can quickly and effectively restrain the voltage change rate and reduce the voltage difference between the initial value and the steady state value of the power transmission lines, so that the line voltage during the switching operation can be kept within the safety limit range. Finally, a simulation model was built by using MATLAB/Simulink software, and the simulation results verified the effectiveness of the proposed overvoltage suppression strategy.

Effect of shield placement for transient voltage mitigation due to switching surges in a 33/11 kV transformer windings.

This study presents an investigation on the effect of shield placement for mitigation of transient voltage in a 33/11 kV, 30 MVA transformer due to Standard Switching Impulse (SSI) and Oscillating Switching Impulse (OSI) surges. Generally, the winding and insulation in transformers could experience severe voltage stress due to the external impulses i.e. switching events. Hence, it is important to examine the voltage stress and identify the mitigation action i.e. shield placements in order to reduce the adverse effect to the transformer windings. First, the resistances, inductances, and capacitances (RLC) were calculated for disc type transformer in order to develop the winding RLC equivalent circuit. The SSI and OSI transient voltage waveforms were applied to the High Voltage (HV) winding whereby the transient voltages were simulated for each disc. The resulting voltage stresses were mitigated through different configurations of electrostatic shield placements. The resonant oscillations generated due to switching surges were analysed through initial voltage distribution. The analyses on the transient voltages of the transformer winding and standard error of the slope (SEb) reveal that the location of shield placement has a significant effect on the resonant switching voltages. The increment of the shield number in the windings does not guarantee optimize mitigation of the resonant switching transient voltages. It is found that the voltage stress along the windings is linear once a floating shield is placed between the HV and Low Voltage (LV) windings of the disc-type transformer under the SSI and OSI waveforms. These findings could assist the manufacturers with appropriate technical basis for mitigation of the transformer winding against the external transient switching overvoltage surges.

Study on Laminated Bus Bar for High-pulse Power Converter Module

Aiming at the problems of high switching overvoltage of power semiconductor devices and unbalanced current of parallel power devices in high-pulse power converters, this paper proposes a laminated bus bar of symmetrical path on the basis of the theoretical analysis and key points of laminated bus bar. The finite element simulation software was used to analyze the stray inductance of laminated bus bars. The actual stray inductance and overvoltage of the converter commutation circuit were measured by single pulse experiment. The results show that the laminated bus bar of symmetrical path can effectively reduce stray inductance, suppress switching impulse overvoltage and improve the current balance of the parallel power devices. It is of great significance to analyze the performance of laminated bus bar of symmetrical path, and it can be used for high-pulse power conversion technologies.

Statistical Switching Overvoltage Studies of Optimized Unconventional High Surge Impedance Loading Lines via Numerical Laplace Transform

The development of a revolutionary design for transmission lines was recently introduced by shifting phase configurations and sub-conductors into “unconventional” arrangements that were geometrically optimized to maximize natural power. The objective of this paper is to study the electromagnetic transients that result from the simultaneous and sequential line energization and re-energization of the previously developed unconventional high surge impedance loading (HSIL) lines. Statistical switching overvoltage (SSOV) studies are performed using a frequency domain method based on the inverse numerical Laplace transform. Compared to a conventional line, all unconventional HSIL line designs studied in this paper lead to very similar surges for long line lengths (400 km) and similar values for short line lengths (100 km), indicating additional advantages of these lines. The use of a frequency domain method for SSOV studies offers enhanced accuracy, simulation flexibility, and substantially lower computational burden compared with traditional time-domain methods.

Research on switching overvoltage suppression of 35 kV shunt reactor

In recent years, a number of equipment abnormal events caused by operating overvoltage have occurred during the interruption of 35 kV shunt reactors, which jeopardizes the safe and stable operation of the grid. In order to explore the mechanism of operating overvoltage when 35 kV shunt reactor is cut off and the effect of various suppression measures, this paper carries out simulation analysis and research, mainly considers several factors to the effect of overvoltage, such as bus outlet, circuit breaker switching position and overvoltage protector.

An experimental analysis of DC magnetic blowout high-speed circuit breakers’ parameters

High-speed circuit breakers (HSCB) used in DC circuits are one of the basic elements of overload, short-circuit and electric shock protection. Such breakers are used in transport (trams, trolleybuses, subways and railways) in electric power supply facilities and in vehicles. The performance and capability of limiting the current depend on the HSCB design and solutions applied in it. The circuit parameters, particularly its inductance also affect the performance. Additionally, each DC breaking in the RL circuit is accompanied by overvoltages whose level depends on the circuit parameters and breaker design. The paper discussed the process of direct current breaking by magnetic blowout high-speed circuit breakers and factors that affect the HSCB performance, i. e. opening time and arcing time. The influence of the circuit parameters and HSCB design on the value of arc voltage is outlined. The results of laboratory tests of 4 types of high-speed circuit breakers produced in Europe are presented. The test results were used to analyze the effect of current changes in the short circuit on the time of current breaking and the value of switching overvoltages – arc voltage. The results of simulation of the short-circuit breaking in the RL DC circuit made at the rate-of-rise of current in the circuit are presented. Based on the tests and simulations, the current breaking times, values of arc voltage generated in this process and arc energy that is acquired and dissipated by the arc chamber are determined. The objective of the tests and simulations was to answer the question whether it is possible to turn off direct current quickly without generating high arc voltage values – overvoltages in the circuit and how di/dt changes should be formed by a high-speed circuit breaker to achieve the shortest possible time with the lowest possible arc voltage and its lowest energy

Выбор средств защиты высоковольтного двигателя экскаватора на руднике открытых работ горно-металлургического комбината

Based on the results of conducting comprehensive studies of power consumption of the open-pit mine of the mining and metallurgical plant in high altitude conditions, the issues are considered related to ensuring safe operation of electric motors supplying excavators. Experimental studies were carried out in a 6 kV electric network, from which the excavators and drilling rigs are powered. The design schemes of sections of the electric network are given, the characteristic of the main equipment is provided. One of the problems in the operation of the excavators in high altitude quarries is a decrease in their productivity due to the need in periodical repair of the insulation of synchronous motor drive of the converter unit. The influence of switching overvoltages on the synchronous motors insulation integrity of the excavator is established. The scheme of a protective device is presented, which allows protecting the isolation of the excavator engine from atmospheric and internal switching overvoltages. The principle of synthesis of the surge suppressor is to determine the maximum amplitude of free component of the switching voltage and the corresponding frequency with the subsequent installation of the quenching spark gap and the shunt capacitance, calculated according to a certain amplitude and frequency. Therefore, the main measure providing protection of the insulation of the drive motor should be the suppression of overvoltage, which has a fundamental frequency of 8–8.2 kHz. The network transient in the open-pit electric circuit — a synchronous motor is investigated, and the parameters of the shunt capacitor are determined. It was found that the selected capacitor is capable of long-term operation in an electrical installation at a frequency of 50 Hz. In order to reduce the effect of additional capacitance on the frequency, it is necessary to install capacitors together with the arresters in a 6 kV input cell.

A Gliding Arc Microreactor Power Supply System Based on Push–Pull Converter Topology

The era of evolution in power electronic systems has led to a widespread displacement of power supplies operating at mains frequencies. Switched-mode power inverters offer possibilities incomparably higher than mains transformers. These trends have also entered into plasma technologies, including GlidArc plasma processing. The article presents the use of an inverter power supply for a miniaturized GlidArc. It is a demonstration of using a push–pull topology in an unusual application. A special part is devoted to parasitic phenomena in the inverter and the implementation of switching overvoltages as a way of improving the ignition parameters of the power supply. The results of the tests with a plasma reactor in air conditions as a process gas are also presented.

Controlled Shunt Reactor for UHVAC System Reactive Power Control

Background: In this paper, a novel technique for reactive power management of the Ultra High Voltage (UHV) lines having voltage level of 1200 kV line and above is suggested. The UHV power grid has to frequently face the problems associated with the power- frequency and switching over-voltages. Methods: The technique involves the use of three-phase UHV Transformers as a Controlled Shunt Reactor (CSR) in combination with the use of a fixed reactor. The performance of the UHV AC transmission line is studied using PSCAD software and working of CSR is evaluated. Results: Standard parameters of the proposed Wardha-Aurangabad 1200 kV transmission line in India are considered for simulation model. The use of CSR has been found to be effective in mitigating system problems. Conclusion: The system can be used for maintaining voltage profile, resulting in enhancement of the reliability of the UHV transmission system.

Bulk FDTD Simulation of Distributed Corona Effects and Overvoltage Profiles for HSIL Transmission Line Design

Power system load growth and transmission corridor constraints are driving industry activity in the area of high surge impedance loading (HSIL). Examples include compact structure design and uprating existing transmission lines. Recent research relating electric field uniformity to transmission line capacity and critical flashover voltage underscored the need for better overvoltage data to quantify insulation margins for HSIL design. To that end, this work extends the finite difference time domain (FDTD) method with distributed corona losses to transmission lines with bundled conductors. The model was adapted for practical use in high-volume statistical transient simulation and applied to an example 500 kV line. Transients included line energization and trapped charge reclosing. Overvoltage profiles and statistical distributions were generated from 9500 simulations obtained by random breaker close timing and variation in line length and altitude. Distributed corona losses reduced 98th percentile line-to-ground switching overvoltages by 4%–14% of nominal. The estimated line-to-ground switching surge flashover probability was 54%–80% lower with corona loss. Corona had less impact on line-to-line overvoltages, but the effects were still notable. Results highlight the importance of considering detailed overvoltage profiles and accounting for corona loss attenuation when seeking to carefully quantify insulation design margins.

Electromagnetic interference characteristics during switching operation in power distribution network

The disturbance problem caused by the transient electromagnetic field during high-voltage switching operation is the most typical. Electromagnetic interference can be coupled to the secondary circuit in a conductive and radiating manner, then, affects the reliability of the secondary-side circuit. The key to the simulation calculation of the operating switch overvoltage is the judgment and simulation of its opening and closing conditions. The arc current zero-crossing judgment signal, the arc extinguishing and reignition judgment signals are fused, and a control signal is recursively obtained for switching operation. By analyzing the transient process during switch operation, a simplified model for isolating and closing the no-load bus, an overvoltage calculation model, and a fast transient model for overvoltage time-frequency signals are established. The characteristics of the transient electromagnetic field generated when the no-load bus and the circuit breaker of the disconnector are charged to the no-load transformer are simulated. The mechanism of fast transient pulse group generated by switching operation is obtained. The maximum overvoltage amplitude generated during the disconnector’s switching, and the no-load bus is obtained by simulation. Comparing with the measured data, the laws of electromagnetic interference characteristics during switching operation in power distribution network are verified.

Modelling of Metal Oxide Surge Arresters in Simulation Software DYNAST

This paper describes the possibilities for mathematical modelling of gap-less surge arresters in simulation software DYNAST. This tool does not belong to standard modelling softwares in the field of electric power engineering. However, it may provide some key advantages when compared to more frequently used softwares such as EMTP-ATP and MATLAB-Simulink. Description of the metal oxide varistor modelling at temporary and switching overvoltages, fast-front states, and lightning strokes is presented. More information about the defined internal structure of surge arrester models and ways for implementing respective V-I characteristics are provided. To verify the correct behaviour of the models, both slow and fast overvoltage scenarios are simulated and evaluated.

Non-Contact Measurement and Analysis of Trapped Charge Decay Rates for Cable Line Switching Transients

During reclosure of 275 kV cable circuits used for voltage control, excessive overvoltages were observed on the network. Such events cause onerous and costly failures. Transient simulations have shown that the normal voltage on its own cannot generate such excessive switching overvoltages. Initial investigations by the network operator pointed towards trapped charge on the unearthed as the cause of the failures. Measurement of these trapped charge voltages and their slow decay without interfering with the charge has, to the author’s knowledge, not been done before in an operational substation. This work introduces a technique to measure trapped charge at a 275 kV substation using the Electrostatic Field Mill. Since the electric field is a proxy measurement of surface voltage, field mills can also be used to measure voltage. In this paper, an on-site substation measurement setup using an electrostatic field mill has been developed for the non-contact measurement of trapped charge voltage on a 275 kV underground cable circuit following switching operations at a National Grid substation. Results of field measurements within the substation and laboratory experimentation are discussed. It is demonstrated that with adequate calibration, achieved by using the known pre-switching power frequency steady state voltage, the slowly decaying DC voltage caused by the cable trapped charge can be measured using this non-contact technique. The correlation between the instantaneous time constant and the relative humidity is also analysed.

Study of Transmission/Distribution Network With Large Number of Power Electronic Devices Using Hybrid Simulation

Power System Networks are generally regarded as the most complex structures ever built by humanity. In an interconnected power system, there are tens of thousands of buses, transmission lines, transformers, generators etc., and they work together in one large network to supply the necessary power to the human society. While the behaviors of the power system are subject to basic physical laws, such as the Kirchhoff Law where sum of all currents injected to a node is zero, to study or predict such behaviors turned out to be quite complex. Digital time-domain simulation tools have been extensively used in power system studies since 1960's. In many areas including transient stability analysis, switching over-voltage analysis, and power electronic studies, such simulation platforms have become the industry standard tools.

Single-phase ground short circuits in the 6–10 kV mains and electrical traumas in the coal mines

Introduction. This article provides analysis of electrical traumas and single-phase ground short circuits (SPGSC) in the 6–10 kV electrical systems in the period from 1995 to 2018. It has been shown that reduction in the number of SPGSC will improve electrical safety at coal mines. Research aim is to determine the interrelation between the indicated factors based on the statistical data in the 6–10 kV mains of coal mines according to SPGSC minor and moderate electrical traumas. Methodology. Coal production, development of single-phase ground short circuit and changes in numbers of injuries in the period from 1995 to 2018 have been analyzed making it possible to vividly and qualitatively estimate the dynamics of changes in coal output, the number of SPGSC, electrical traumas and determine the interrelation between these parameters. The discovered interrelation between SPGSC and electrical traumas allows to handle the problem of improving the electrical safety more seriously by means of reducing the number of SPGSC. Results. This article shows the main reasons of single-phase ground short circuit incidence depending on time. The article shows the main ways to lower the amount of single-phase ground short circuit in the 6–10 kV electrical systems of coal mines. Summary. Significant reduction in the number of single-phase ground short circuit in the 6–10 kV electrical systems and, as a consequence, reduction of electrical traumas at coal mines can be achieved by means of effectively limiting switching overvoltage, overvoltage in the mode of single-phase ground short circuit, reaching high selectivity of protection from ground short circuit and improving the quality of electrical energy, and limiting the overloading of electrical equipment and cables.

Electromagnetic Effect of an Alternating Current Traction Power Supply System with a High-Voltage Power Cord on Electrical Installations and Networks of Nontraction Consumers

In this paper, we ground a method for calculating switching overvoltages including the discharge of lightning currents into the contact network and into a high-voltage power wire (HVPW) to isolate the contact network in the power supply system with the HVPW. It was established that the protection of outdoor signaling, centralization, and blocking (SCB) devices from switching overvoltages in a power supply system with a high-voltage power wire (PSS HVPW) can be solved by connecting the reinforcement of the support foundations of the contact network to an extended artificial grounding conductor (GC) located under the ground and not connected to the rail track. The use of a GC, along with limitation of pulse overvoltages on the insulation of the contact network supports, solves the problem of ensuring reliable protection of the traction networks from short-circuit currents in the traction network. An algorithm for calculating the voltage of the zero sequence of phase voltages of overhead power lines (OPLs) with an isolated neutral relative to the ground when they are located in the zones of electromagnetic influence of the PSS with the HVPW was developed. Due to the electrical effect of the HVPW voltage, the induced voltage in an OPL is shown to reach values ​​that significantly exceed the levels allowed by regulatory documents. An analysis of the obtained results indicates the feasibility of placing OPL wires on free-standing supports outside the reserved strip. The need for such a solution is also determined by keeping the HVPW voltage from entering the OPL wires, with their possible breakage.

Estimation of switching surge flashover rate of 1200-kV UHVAC transmission line considering switching overvoltage waveshape

The insulation of the power transmission system experiences stresses due to power–frequency voltage under normal operating conditions, temporary overvoltages at or near power–frequency and transient overvoltages arising either from switching operations and faults or from lightning discharges. However, in the insulation design of extra-high-voltage and ultra-high-voltage systems, transient overvoltages arising from switching operations and faults become the controlling factor. Insulation failure probability under switching overvoltages is the main impressive concern in the estimation of switching surge flashover rate. In this paper, a practical method is used to estimate the switching surge flashover rate of insulation under switching overvoltages generated during energization, re-energization, fault initiation and fault clearing of an unloaded transmission line, which considers the variable characteristics of the insulation strength of the transmission line according to the switching overvoltage waveshape. The results focus on the comparison between traditional and practical methods which considers the effect of the front time on the first 1200-kV UHVAC transmission line in India.

Prospect of voltage uprating of a conservatively designed EHV transmission line

Voltage uprating of existing overhead lines provide a useful method to tackle increasing power demands under present circumstances, where there is growing opposition to the construction of new power transmission installations. In the past, voltage uprating techniques have been applied to lines formerly intended to operate up to 275kV, but there is an incentive to examine the prospect of uprating lines of even higher voltages which have been designed conservatively with deterministic procedures. This paper explores the prospect of voltage uprating of an existing 500kV double-circuit overhead transmission line in Pakistan. The study includes statistical evaluation of line insulation under switching overvoltages, lightning and pollution together with assessment of corona effects and low frequency electric and magnetic fields. It has been shown that voltage uprating of the studied line to 735kV is achievable whilst satisfying performance criteria.

Probabilistic analysis of switching transients due to vacuum circuit breaker operation on wind turbine step-up transformers

Vacuum circuit breaker operation causes transient overvoltages that may lead to severe damages to transformer insulation. Since the parameters affecting these overvoltages have stochastic nature, a statistical analysis may provide detailed insight into the overvoltages from the point of view of insulation coordination applications. In this paper, a statistical analysis of the overvoltage variations of the step-up transformer during vacuum circuit breaker operation is conducted. Some variables, including switching angle, current chopping, high-frequency current quenching capability, and wind turbine power, are assumed as random variables. Besides, some indicators representing the switching overvoltage characteristics such as the amplitude, the number of restrikes, and the rate of rise are extracted. By performing a probabilistic analysis, the destructiveness due to switching overvoltages on typical transformer insulation can be investigated. The sensitivity of different surge protective devices and their effectivities are also analyzed and statistically evaluated. The applied methodology is very useful because of the stochastic nature of the switching overvoltages. In this work, the impact of protective equipment on each of the overvoltage indicators is analyzed. It is also found that considering only the amplitudes of transient overvoltages is not enough to draw conclusions about the safety of the transformer when exposed to frequent switching surges.