Switching Surge Research Articles

Switching Overvoltage Reduction Using Surge Arrester, for 400 KV-line Connecting Khoms and Gmmra Substations

Transient overvoltage in power systems is one of the most important issues to be considered for system stability. Switching surges is an important reasons that cause transient overvoltage. This paper presents a full study of the high-voltage line connecting KHOMS and GMMRA substations. The study utilizes the Alternative Transient Program (ATP) to compute the transient overvoltage due to switching surges (line closing and re-closing); as well as presenting the usage of surge arrester to reduce the upper limit of transient overvoltage. The results present the positive effect of using surge arrester switching element to limit transient overvoltage and keep it at certain level; in addition to damping the isolation in the voltage waveform.

N-doped β-Ga2O3/Si-doped β-Ga2O3 linearly-graded p-n junction by a one-step integrated approach

The p-n junction is the foundation building structure for manufacturing various electronic and optoelectronic devices. Ultrawide bandgap semiconductors are expected to overcome the limited power capability of Si-based electronic device, however, it is very difficult to achieve efficient bipolar doping due to the asymmetric doping effect, thereby impeding the development of p-n homojunction and related bipolar devices, especially for the Ga2O3-based materials and devices. Here, we demonstrate a unique one-step integrated growth of p-type N-doped (2¯01) β-Ga2O3/n-type Si-doped (2¯01) β-Ga2O3 films by phase transition and in-situ pre-doping of dopants, and fabrication of full β-Ga2O3 linearly-graded p-n homojunction diode from them. The full β-Ga2O3 p-n homojunction diode possesses a large built-in potential of 4.52 eV, a high operation electric field > 2.90 MV/cm in the reverse-bias regime, good longtime-stable rectifying behaviors with a rectification ratio of 104, and a high-speed switching and good surge robustness with a weak minority-carrier charge storage. Our work opens the way to the fabrication of Ga2O3-based p-n homojunction, lays the foundation for full β-Ga2O3-based bipolar devices, and paves the way for the novel fabrication of p-n homojunction for wide-bandgap oxides.

Experimental Approach for Reliability Analysis of Medium-Power Zener Diodes under DC Switching Surge Degradation

This study investigated the reliability of Zener diodes subjected to a gradually increasing DC switching surge amplitude with delay internals between surges to avoid thermal degradation from different manufacturers with similar specifications. The analysis involved applying occasional 3 ms direct current (DC) switching surges with a gradual increasing surge voltage, followed by a constant current test to verify device functionality for three different selected manufacturer 5.1 V Zener diodes. This experimental approach was used to identify the maximum surge current that each Zener diode could handle before failing to clamp the surge voltage at the specified Zener reference voltage. Statistical analysis revealed significant differences in the maximum average surge current between different manufacturers. The maximum average surge current findings just before failure were 1.98 A, 3.18 A, and 3.33 A, respectively, and associated 95% confidence interval ranges can be used as a reliable metric to compare Zener diode population reliability against occasional DC switching surges. The findings revealed variations in the DC switching surge current handling capabilities between Zener diodes from different manufacturers with similar electrical specifications. The statistically measured maximum average surge current just before device failure can be considered an effective metric to compare the reliability of Zener diodes against DC switching surge degradation.

Modelling of Low-Voltage Varistors’ Responses under Slow-Front Overvoltages

In this study, commercially low-voltage MOVs are exposed to switching surges to analyse and model the relationship between the number of surges and the MOV grain barrier height response. Repeated slow-front overvoltage transients are used to degrade the protective qualities of metal oxide surge arrester devices, affecting their reliability and stability. A total of 360 MOVs with similar specifications from three different manufacturers are degraded under switching surges at a constant temperature of 60 °C. The reference voltage and C-V characteristics of MOVs are measured before and after the degradation process to analyse the MOVs’ conditions. Grain barrier heights are determined from the C-V characteristics curve. An F-statistical analysis is then applied to analyse the effects of number of surges on the grain barrier height. The T-test is used to assess the statistical difference between the tested groups. Linear regression analysis is then applied to model the relationship between the number of surges and MOV grain barrier height. The results obtained show that the number of surges has a significant impact on grain barrier height. MOV grain barrier height is found to decrease as the number of surges applied increases. Regression models obtained for the tested MOV groups across all three manufacturers agree and indicate that the reduction in grain barrier height results from an increased number of surges. Regression coefficients of a developed model indicate that for one surge applied, the MOV grain barrier height decreases by 0.024, 0.055, and 0.033 eV/cm for manufacturers X, Y, and Z, respectively. Therefore, there is a linear relationship between grain barrier height and the number of applied switching surges.

Electromagnetic force distribution computations due to switching surge in disc-type winding

This manuscript discusses the computation of electromagnetic forces on a disc-type winding due to a standard switching impulse (SSI). First, the resistances, inductances and capacitances (RLC) of a 30 MVA, 33/11 kV disc-type distribution transformer were estimated to obtain the winding equivalent circuit. The transient voltage waveforms for each of the disc layers and corresponding resonances of the windings under the SSI were then obtained in time domains. Next, the axial and radial force distributions in the disc winding due to the SSI were computed. The forces on each disc layer and along the disc windings due to the SSI were computed based on the analytical and numerical methods via the finite element method (FEM) respectively. The non-uniform switching impulse voltage distribution results in non-uniform force distribution along the disc winding. The magnitude of the axially directed force on the disc winding is found to be higher as compared to the radially directed force.

Slew rate control of switching transient for SiC MOSFET in boost converter using digital active gate driver

This paper experimentally validates a fully digitalized active gate driver for suppressing the switching surge voltage of SiC MOSFETs in a boost converter. High-voltage power conversion systems are expected to adopt SiC unipolar power devices utilizing their high-speed switching capability. The high-speed switching operation causes the switching surge voltage in its switching transient. Active gate driving is a key technology for suppressing it. A fully digitalized active gate driver is particularly focused upon, which freely shaped the output gate-source voltage waveform by a multi-bit gate control signal. This driver achieves the dynamical control of the voltage/current behaviours of MOSFET in the switching transient by taking the Miller effect into account. It contributes to suppressing the switching surge voltage. This paper applies this digital active gate driver to a high voltage power conversion circuit. The switching surge voltage is experimentally suppressed by slew rate control with the digital active gate driver for various operating conditions. The results clarify the control strategy of the digital active gate driver for SiC MOSFET in a power conversion circuit.

전기저장장치용 SPD의 최적운용 평가 알고리즘에 관한 연구

Recently, ESS(energy storage system) for output stabilization of renewable energy source, peak demand management, frequency control, etc. is actively installed and operated. However, as the fire accidents are continuously occurred in ESS, the Korean government has presented the causes of fire accidents and countermeasures for safety enhancement through the public-private joint accident investigation committee, which recommends the installation of electrical protection devices such as SPD(surge protect device) and IMD(insulation monitoring device). However, it is reported that the capacity of SPD (USUBc/SUB, USUBp/SUB) installed and operated in each ESS site is different and improper due to the absence of installation regulations. When the inappropriate capacity of SPD is adapted at DC side in ESS, there are possibilities that the battery may be negatively affected as SPD cannot properly protect the battery from the lightning and switching surges. Therefore, this paper proposes an algorithm to calculate the appropriate capacity of SPD for the stable operation of ESS and performs the modeling of surge test device, which is composed of surge generator, SPD, battery, etc., using PSCAD/EMTDC, in order to evaluate operation characteristics of SPD for the lightning and switching surges. And also this paper implements surge test device which generates 3rd class combination wave for lightning surge and switching surges. From the simulation and test results based on the presented modeling and test device, it is confirmed that the SPD can safely protect the battery from the lightning and switching surges when the proper SPD calculated by the proposed algorithm is installed.

Protection for 330 kV transmission line and recommendation for Nigerian transmission system: a review

The transmission line is an integral part of the electrical power system; however, a fault has a negative impact on the system, like blackout, power loss, financial losses, and socio-economic impact. This fault occurs due to ageing conductors, lightning stroke, switching surge and human interference. We reviewed the protection scheme implemented in the Nigerian transmission network, which has challenges relating to the environment's terrain and a long-distance transmission line of about 20,000 km. The different approach of fault classification, detection and location was analysed and critically summarised. This review paper proposes a hybrid Artificial Neural Network and distance protection scheme that can automatically identify, locate, isolate, predict, correct faults, and real-time monitor and control the entire network. It can also detect the shortest possible trip time of 0.02 s and 0.03 s of line current and fault losses, respectively, during fault to avert damage on the line. However, this method has its challenges, such as the volume of data generated from load flow analysis, training time, and the total distance covered by the network. However, these can be averted by segmenting the entire network for easy evaluation and monitoring to achieve set goals.

Feasibility Evaluation on Elimination of DC Filters for Line-Commutated Converter-Based High-Voltage Direct Current Projects in New Situations

The line-commutated converter (LCC)-based high voltage direct current (HVDC) technology has been widely applied on long-distance and bulk-capacity power transmission occasions. Due to the terrible interferences in the vicinity of communication lines, DC filters (DCFs) are always installed to mitigate the interferences within acceptable levels for almost all in-service overhead line transmission LCC-HVDC schemes. With the rapid development of the communication technology, however, the anti-interference capability of the telephone system has been remarkably improved. Thus, the original purpose of employing DCFs has been virtually absent, and the necessity of the DCFs shall be re-evaluated in sufficient depth not only for new LCC-HVDC projects, but also in the case of refurbishment of older projects. To demonstrate this constructive topic, this paper carries out a commercial ±800 kV/8000 MW LCC-HVDC project as an illustrative example to analyze and discuss those crucial aspects, which may influence the LCC-HVDC stable operation and reliability after removing the DCFs. Then, the paper studies the harmonic voltage/current stresses of the DC equipment, the DC loop low-order harmonic resonances, and the overvoltage under the switching surge and lightning stroke. Finally, it is concluded that the DCF elimination mainly affects the harmonic steady-state stresses of the DC equipment, but has little influence on the transient stresses. For the refurbishment of older projects, the evaluation on the cost between the DCFs’ maintenance cost and the equipment modification is needed for the DCFs’ elimination. For new LCC-HVDC projects, the DCFs’ elimination or at least simplification may be a more economical and attractive alternative, thereby reducing the footprint and cost.

Operation Characteristics of Mechanical DC Circuit Breaker Combined with LC Divergence Oscillation Circuit for High Reliability of LVDC System

DC systems are modernly starting to come into the spotlight again due to the carbon-neutral policy, the development of semiconductor devices for power, and the increase in digital loads. We need to prepare in advance solutions to problems that may arise from fault currents due to transients for future DC power grid models. In the case of DC, there is no current zero-point because there is no frequency. Therefore, a large switching surge is generated when the circuit breaker cuts off the fault current. The possibility of insulation breakdown is greater than that of AC in severe cases. We consider power semiconductors or superconducting current limiters as an alternative. However, DC breaking cannot be safely achieved by itself. For reliable DC breaking, mechanical circuit breakers must be used with them. Among the mechanical shut-off methods, we adopted the divergence oscillation method. It has the biggest advantage compared to other methods in that it has a simple structure by composing passive elements and can artificially create zero current. In addition, it can be applied to a power semiconductor and a superconducting current limiter to perform a high-reliability cut-off operation. In this paper, we conducted simulation analysis by configuring the DC power grid and DC cut-off system through the PSCAD/EMTDC program. Results confirmed that the application of the LC divergence oscillation circuit can reduce the cut-off time and reduce the power burden of the mechanical DC circuit breaker (MCB).

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.

Circuit Breaker Performance Analysis

The problem of circuit breaking becomes complicated when voltages and currents in the range of kilovolt and kiloampere are involved. Circuit breaker (CB) is used in performing switching operations, and is a switch that can open live circuits. Circuit breakers are especially important in protective schemes where they have to interrupt fault currents, and isolate faulty section of the network. When the circuit breaker opens under fault condition many thousands of amperes pass through the contacts and the extinction of the arc and hence effective opening of the contacts of the CB are major engineering problems. When a circuit breaker opens, a high-frequency voltage, superimposed on the normal system voltage appears across the CB contacts. This voltage is known as transient recovery voltage (TRV) or restriking voltage, constituting a switching surge. Restriking delays arc quenching, and so it is detrimental to the circuit breaker as well as the entire system, since fault clearing may be delayed. This paper shows how resistance switching can be used to damp this surge and enable the CB to open before the magnitude of the voltage across the CB contacts reaches peak level, to prevent possible restriking of the arc.

Photo electric properties during streamer-to-leader transition in a long positive sphere–plane gap

In this work, a combined photoelectric detecting system is established using devices such as a photomultiplier, an electric field sensor based on optoelectronic integration, and a high-speed camera. The system is used to measure the instantaneous optical power, spatial electric field strength, and optical image during discharge of a 3-m-long sphere–plane gap under standard switching surge voltage of positive polarity. The test results show that the initial streamer of the 3-m-long sphere–plane gap can be divided into strong and weak ionization according to the rate of rise of optical power and electric field strength. Within the dark discharge period in the sphere–plane air gap, the intensity of the spatial electric field slightly jumps when the streamer-to-leader transition is completed, with an increase of about 162.59 kV/m. It is proposed to take the time when the intensity of the spatial electric field jumps in the dark discharge period as the criterion for the streamer-to-leader transition. The measured duration ta of the streamer-to-leader transition is calculated according to instantaneous optical power and spatial electric field strength. Based on the thermodynamic equilibrium equation, a Gallimberti simulation model for this streamer-to-leader transition is established. The duration ts for completing the streamer-to-leader transition is obtained according to the quantity Q of injected electric charges. By comparing the measured duration ta with the calculated duration ts of the streamer-to-leader transition, the rationality of the criterion is verified. The research results provide a basis for establishing an improved model for the inception of a leader in a long air gap.

Performance of Composite Outdoor Insulator Under Superimposed Direct and Switching Impulse Voltages

High Voltage Direct Current (HVDC) systems are increasingly being adopted around the world to integrate renewable resources, increase power transfer, and allow flexible grid operation. HVDC overhead lines play a critical role in this, and focus is needed on the research of composite outdoor insulators failure. In the case of a pole to ground fault of a bipolar scheme, the healthy pole experiences a slow transient overvoltage similar to a Switching Impulse (SI) superimposed on the operational DC voltage. However, there is no standard test for such voltage superimposition. This paper investigates the performance of a composite insulator stressed with such superimposition under dry and rain conditions. To determine the direct voltage influence on the flashover voltage, the results have been compared with the SI only case. Four different rain conductivities have been used in the test program because these insulators can be exposed to different acid conductive rain types, typical of industrialized environments. Both vertical and horizontal orientations have been studied. It was possible to conclude that, in most cases, the direct voltage pre-energization has a negative impact on the flashover performance. The increase in rain conductivity leads to lower flashover values, and the horizontal orientation outperforms the vertical configuration. Under these test conditions, the flashover voltages were all larger than a typical DC operational switching surge. Thus, in the case of pole to ground fault, the healthy pole failure risk appears to be low. However, further research is needed on higher voltages and polluted conditions.

Switching Surge Design of 1200kV UHVAC Transmission Line

With the increase in operating voltage of transmission system to transport large amounts of power to meet increased demand switching surges became governing factor in the insulation design of EHV and UHV systems. Insulation failure probability under switching surges that is switching surge flashover rate (SSFOR) is the main concern in the switching surge design of transmission lines. In this paper, SSFOR of 1200kV UHVAC transmission line under switching surges which are generated during energization of no-load transmission line is estimated.

A Study on Application of Recloser Operation Algorithm for Mixed Transmission System Based on Travelling Wave Method

Recently, the operation of a mixed transmission system has increased due to rapid urbanization and the purpose of a good view. Therefore, a proper protection scheme for a mixed transmission system is required. Generally, when a fault occurs on a transmission line, auto reclosing is performed for the purpose of improving the continuity of service by clearing the fault and restoring the power system. However, the auto reclosing scheme should be applied to a mixed transmission system carefully because the mixed transmission system involves underground cable sections. When a fault occurs in the underground cable section, it is mostly a permanent fault. If auto reclosing is performed on a permanent fault condition, it may cause excessive overcurrent and switching surge, which can generate a serious impact on the whole transmission system and even cause an explosion. Due to this, many utilities worldwide do not allow auto reclosing or only apply it very restrictively on a mixed transmission system based on their practice. However, there is no clear guidance or standard related to auto reclosing on a mixed transmission system. Therefore, in this paper, an application of a recloser operation algorithm is proposed. Based on the proposed algorithm, reclosers can work properly and protect the transmission system. To verify the proposed algorithm, simulations were conducted using the ElectroMagnetic Transient Program (EMTP).

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.

Mechanism Clarification of Switching Loss and Surge Voltage / Current Reduction with Active Gate Drive for System Reliability Improvement

The active gate drive (AGD) technique is payed attention as a switching technique which can reduced both of switching loss and surge voltage. So far, only switching loss and surge voltage of main switch have been discussed, and the reverse recovery characteristic of rectification diode has not been discussed. In addition, the mechanism of loss and surge reduction has not been clarified. In this paper, the influence of AGD on reverse recovery characteristics, and the mechanism of loss and surge reduction are discussed for system reliability improvement. As a result, the mechanism of loss and surge reduction is clarified.

An approach for controlled energization/re-energization of shunt compensated transmission lines

In Asia-pacific region, at Ultra High Voltage/Extra High Voltage (UHV/EHV) levels, the combination of Controlled Switching Device (CSD) and Circuit Breaker having Pre-Insertion Resistor (PIR-CB) is readily available in schemes such as tie circuit breaker used in One-and-a-Half-Breaker (OHB) scheme. Therefore, in this paper, a new strategy is presented using CSD with PIR-CB to mitigate the level of switching surge during energization/re-energization of Shunt-Compensated Transmission Line (SCTL). The proposed methodology requires lineside voltage measurement during the dead time of CB. The performance of the proposed methodology has been evaluated by modelling an existing Indian 400 kV, 400-km long SCTL using PSCAD/EMTDC software package. Moreover, its performance remains unaffected during wide variation in the length of the line, level of compensation, type of fault, duration of fault, fault inception angle, fault location, short circuit capacity of source, and inclusion/removal of Switching Arrestor (SA). At the end, comparative evaluation of the proposed methodology with the reported methodology clearly shows its effectiveness in terms of reduction in the level of the switching surge considering Mechanical Operating Time (MOT) scatter of the CB. The philosophy presented here can also be extended for discrimination between permanent fault & temporary fault and identification of fault type.

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.