Overvoltages In Systems Research Articles

Estimation of abnormal states in shunt capacitor banks using transient disturbance feature extraction

Shunt capacitor banks are essential for reactive power compensation, ensuring voltage stability, and reducing system losses. These banks consist of multiple units with components in series and parallel. A few component failures do not immediately affect the safe operation of the capacitor bank, but component breakdown can lead to voltage redistribution. Under combined factors such as system overvoltage and equipment aging, and others can trigger an avalanche effect causing capacitor breakdown, resulting in significant safety accident risks. Practical operation experience shows that partial component breakdown generates many transient disturbance signals. Quantitative analysis of these signals can detect capacitor bank anomalies early. This paper proposes the quantitative extraction of transient disturbance characteristics using the Prony algorithm and estimates the phase and number of capacitors that break down to judge capacitor anomalies. The simulation part verifies the theoretical analysis and detection algorithm’s correctness through numerical simulations and PSCAD (Power Systems Computer Aided Design) electromagnetic transient simulations. The numerical simulations consider different signal lengths, noise levels, attenuation coefficients, and oscillation frequencies. In the PSCAD simulation environment, verification models are built under varying sampling frequencies, numbers of breakdown components, signal lengths, and signal-to-noise ratios. These simulation results verify the accuracy of the detection algorithm under different conditions.

A fault ride-through strategy for accurate energy optimization of offshore wind VSC[sbnd]HVDC system without improved fault ride-through strategy of wind turbines

The transmission of offshore wind power through High Voltage Direct Current (HVDC) systems is an important way to utilization of offshore renewable energy. However, onshore AC grid faults can make it difficult to transmit the energy from offshore wind farms, resulting in HVDC system overvoltages. Existing solutions to this problem mainly include adding DC or AC energy-dissipation devices, adding communication systems, and improving the fault ride-through(FRT) strategy of wind turbines, which have issues with economics or reliability. Based on this, this paper proposes a device-free, communication-free FRT strategy, and the fault ride-through strategy of wind turbines does not need improvement. The exchange of active power between the AC side and DC side of the onshore MMC is calculated under grid-following and grid-forming control strategy. The reference value of DC voltage and offshore MMC capacitance energy are proposed at different control stages. Especially, the dynamically calculated offshore AC voltage reference values have been theoretically provided. This approach ensures that the HVDC system avoids over-voltage and effectively stores more energy. The effectiveness and correctness of the proposed scheme were verified through simulation on the RTDS platFform. This paper is of great significance to promote the development of offshore renewable energy and ensure the safe operation of offshore wind HVDC systems.

Application of artificial intelligence methods for determination of transients in the power system

Numerous factors, including sudden load reductions, switching transient loads, lightning strikes, and malfunctions of control devices, can result in overvoltage. Overvoltage can harm associated power supply components and result in insulation failure, electronic component damage, flashovers, etc. A machine learning technique called a "neural network" estimates computation results that depend on a lot of inputs. For a variety of reasons, neural networks have recently been used to manage and optimize the power system. This paper presents an artificial neural network (ANN)-based approach to determining overvoltages in power systems. To simulate overvoltages, many simulations were performed in Electromagnetic Transient Program (EMTP). Variations of parameters of interest that have an influence on overvoltages were made using JavaScript that was connected to EMTP models. The extraction of characteristic parameters from overvoltage waveshape is a demanding task, and it was conducted in MATLAB, as was a overvoltage classification methodology based on neural networks. Results were presented and discussed.

Generic security-constrained inertia emulation scheme for VSI-based DC system using supercapacitor

The large-scale grid integration of renewable energy source via a voltage source inverter (VSI)-based DC system results in a continuous reduction in system kinetic inertia, deteriorating grid frequency stability. To mitigate this problem, this paper proposes a generic security-constrained inertia emulation (SIE) scheme, which integrates an appropriately-sized supercapacitor (SC) bank with a VSI-based DC system via a bidirectional DC/DC converter. Inertial response provision is enabled by an SIE control loop developed for the DC/DC converter controller to adjust the SC voltage along with the grid frequency. It is further underpinned by adding an inertia adjustment algorithm to cope with potential security risks of VSI overcurrent and DC system overvoltage. The SIE scheme features a plug-and-play advantage without modifying the original system. The SIE controller parameter optimization is also carried out through the small-signal stability analysis. The effectiveness of the SIE scheme is evaluated using a modified IEEE 39-bus test system in the presence of generator outage and grid fault.

Analysis of influence of energy storage system parameters on HVDC commutation failure overvoltage

Overvoltage is a common fault in high voltage direct current (HVDC) transmission systems, which directly affects the safe and stable operation of the system. Energy storage system has been widely used in power system because of its fast response speed, high precision and bidirectional energy transmission. As a variable parameter, the low voltage traverse active power coefficient directly affects the overvoltage of commutation failure in HVDC system. In this paper, the influence of transient characteristics and energy storage parameters on commutation failure overvoltage of energy storage system connected to HVDC is analyzed. Based on PSASP simulation, combined with the actual characteristic setting parameters of a power grid in northwest China, the positive correlation between energy storage low-pass active power and transient overvoltage of HVDC system commutating failure is verified by dynamic trajectory sensitivity analysis, and the optimization space of HVDC energy storage system is expanded.

Modeling and Experimental Analysis of Overvoltage and Inrush Current Characteristics of the Electric Rail Traction Power Supply System

High-speed EMUs (electric multiple-units) frequently pass through the phase-separation zone during operation. Overvoltage generated during the operation of the vehicle-mounted circuit breaker has a long duration and high waveform steepness, which accelerates the service life of the vehicle-mounted equipment and is likely to cause insulation failures. For the above-mentioned problems, the operating overvoltage characteristics of high-speed EMU were obtained by traction substation-catenary-EMUs system (SCES) analysis and experiments, thus deriving the influences of the closed phase angle and the residual magnetism of the vehicle-mounted transformer on operating overvoltage. The results showed that the voltage phase of the catenary significantly affected the operating overvoltage, and the closed switching overvoltage was small at 0–40°, 140–210° and 320–350°. The voltage on the primary side of the vehicle-mounted transformer was 60.78 kV, with the transient impact of high-frequency oscillation overvoltage of 22.71 kV, and an initial period of oscillation of 0.01 ms. Then, the period became longer, and it took 0.5 ms for the high-frequency oscillation from attenuation to disappearance. Finally, a scheme of series reactance suppression devices was proposed to protect vehicle-mounted voltage transformers. This work is to provide data support for the insulation design and system protection of a traction power supply system.

Impact of steady state and impulse excitations on CuSO4 based memristor

The memristor technology will replace nonlinear resistor applications in suppression of power system overvoltages. A characterization study on Memristance is useful to predict current–voltage characteristics of memristors under different source voltages. A Liquid Memristor (LM) has been chosen in order to study its suitability as a nonlinear resistance for mitigation of an Instrument Transformer overvoltages. The motivation is to investigate the nonlinear property of LM under DC and AC supply voltages in terms of pinching nature and memristance. The simulation response of LM has been validated experimentally for steady state and impulse excitations. The LM is subjected to sinusoidal and triangular supply voltages at 50 Hz and verified for its pinched hysteresis. The response of LM satisfies the standard specifications for (1.2/50) μs lightning and (250/2500) μs switching impulse voltages. The nonlinear resistance of LM shows a varying response for DC voltage instead of single operating point. The memristance of LM is observed to be 1.5 mS under steady state voltage and varied up to 2.89 mS under impulse excitations. The study investigates the dynamic response of LM as a nonlinear system.

Action Law and Deterioration Characteristics of Trigger Cavity of Plasma-Jet-Triggered Air-Gap Switch

The switch-type controllable metal oxide arrester (CMOA) is a flexible method to depress deeply switching overvoltage of transmission system, and the switching time of the fast bypass switch in CMOA is less than 1 ms with the meet of engineering. The plasma-jet-triggered air-gap switch (PTAS) has obvious advantages for the above switch. However, the cumulative effect of increasing the trigger discharge times is prone to trigger failure of the PTAS. In this article, a platform about trigger lifetime of PTAS is established to study the action law and degradation characteristics. The results show that the plasma jet process is divided into three stages: rapid growth stage, stable development stage, and dissipation and decline stage. The peak plasma jet velocity is up to 1.7 km/s, and the shock pressure can reach 5 MPa. With the increase of trigger discharge times, the surface discharge channel of PTAS trigger cavity gradually degrades due to the arc ablation cumulative effect, the surface roughness and nozzle diameter increase, the plasma jet characteristic parameters decrease, and plasma jet ability is weakened. The ablation degradation of trigger cavity surface is characterized by “pore size increasing, pore connection, and gully penetration.” The plasma jet characteristics are consistent with three types of the trigger cavity insulating materials, namely, Poly tetra fluoroethylen (PTFE), PTFE +0.5% Cu powder, and PTFE +0.2% MoS2. The decay rate of plasma jet parameters for +0.5% Cu powder is the fastest. Adding 0.2% MoS2, the ac ablation ability is strengthened. However, the trigger discharge lifetimes of both +0.5% Cu powder and +0.2% MoS2 are lower than that of PTFE. PTFE has obvious advantages in gas-producing performance and ablation resistance ability. The research results provide theoretical guidance for improving the trigger performance of PTAS.

Analysis and Parameter Design of SiC-Based Current Source Inverter (CSI)

Current source inverters (CSIs) use inductors as the major component to store energy. Compared with voltage source inverters (VSIs), CSIs have two advantages: 1. They can avoid the converter failure caused by capacitor failures, and 2. The load current does not increase with load mutation or even short-circuit failure. Therefore, CSIs can be a promising technology for EV charging. However, the waveforms, parameter design procedure, and power efficiency are still unclear. Therefore, it is unclear if CSIs are suitable for EV chargers. This article derives the closed-loop equations of the critical components, including the inductor current waveforms and the voltage ripple. Especially, the load over-voltage phenomenon is derived and verified to further ensure the reliability of the CSI system. Based on the derived equations and reliability requirements, the parameter design procedure is proposed. The power efficiency of both the Si- and SiC-based converters are derived and compared to remove the barrier of applying CSIs in EV chargers in the industry. Our simulations and experiments verify the correctness of the system modeling, over-voltage phenomenon, and power efficiency. All the simulation files (using PLECS) and calculation files (using MATLAB) are attached for the readers to verify and/or further modify.

Research on dual-mode fault suppression strategy of AC isolation and current limiting based on hybrid MMC

Abstract The DC side fault of the high voltage DC transmission system based on modular multilevel converters high voltage DC (MMC-HVDC) is easily affected by the double influence of AC transient electrical quantity infeed and overvoltage and overcurrent, seriously threatening the safe operation of the power grid. Aiming at the problem above, a fault suppression strategy in dual mode of isolation and current limiting is proposed. Based on the half-bridge-full-bridge hybrid MMC, the fault transient mathematical model considering AC feed and sub-module switching feed is analyzed. AC isolation module with double conduction self-resistance structure and current-limiting control module is constructed, which can be adaptively adjusted to the system’s direct current parameters. The ±500 kV double-ended hybrid MMC system model is established to verify the scheme’s effectiveness. In addition, the influence of high AC modulation parameters on the suppression effect is investigated. PSCAD/EMTDC simulation results show that AC active and reactive power feed-in peaks are reduced by 388.69 MW and 119.82 Mvar, respectively, under dual-mode control. The peak value of DC overvoltage and overcurrent is reduced by 1211.53 kV and 22.5 kA, respectively, the fault self-clearing time is shortened by 43 ms, and the fault suppression effect is remarkable. In the high AC modulation ratio operating state, the modulation parameters are positively correlated with the AC power feed and negatively correlated with the overvoltage and overcurrent of the DC system. The research results provide support for the fault protection scheme of the hybrid MMC flexible and direct power grid.

Power grid practice of suppressing transient overvoltage of sending-end system by ultra high voltage direct current control parameters

The transient overvoltage off-grid problem of new energy in the sending-end network has become an important factor limiting the ultra high voltage direct current (UHVDC) transmission capacity. In this paper, the causes of transient overvoltage during the DC fault process is analysed firstly, then from the perspective of adjusting the reactive power consumption of the converter, taking the Qingyu UHVDC project in China as an actual simulation example, the influence of the DC control mode and current control parameters at the rectifier side on the transient overvoltage is deeply studied. Combined with the transient voltage evaluation results of the actual power grid, guiding suggestions for DC control strategies are given to improve the transmission capacity. The research results have important reference significance for improving the consumption of new energy and the transmission capacity of UHVDC projects.

Second-Order Cone Programming Relaxation of Stealthy Cyberattacks Resulting in Overvoltages in Cyber-Physical Power Systems

Deployment of photovoltaic generation in smart grids has introduced overvoltage problems. Cyberattackers can take advantage of this situation and cause intentional overvoltages in distribution systems using stealthy false data injections (FDIs). To protect distribution grids from these FDIs, the first step is to model cyberattacks that can cause overvoltages. An accurate nonlinear optimization model is developed for stealthy FDI cyberattacks that can result in overvoltages on targeted nodes in distribution grids without being detected by bad data detection algorithms. Compared to the existing research, which mainly focused on dc state estimation for transmission systems, the proposed model formulates cyberattacks that cause overvoltages using ac state estimation in distribution grids. The proposed nonlinear model is then approximated to a convex optimization model using second-order cone programming relaxation formulation to guarantee that a global optimum exists for the model. Several case studies are considered to validate the effectiveness of the proposed attack model. It is shown that by limiting the FDIs on targeted buses to 20% of their nominal load, multiple buses can experience severe overvoltages in a distribution grid.

Inclusion of Neutral Points in Measurement-Based Frequency-Dependent Transformer Model

Measurement-based wide-band black-box transformer models are well suited for simulation studies of high-frequency transients in power systems. The inclusion of neutral points in such models can be difficult when the model is required to simulate voltage transfer to windings with high-impedance loads. The difficulty arises because it is then necessary to include the small winding capacitive currents in the measurement and model extraction procedure, while at the same time the capacitances can be asymmetrical with respect to the winding ends. This paper introduces a new measurement procedure which can accurately capture the effect of such capacitive asymmetries. The procedure is demonstrated for a wye-wye connected transformer. The measurement and subsequent passive rational modeling results in two alternative models. The first is a four-terminal model with bonded high-voltage and low-voltage terminals, suitable for simulation of lightning overvoltages in distribution systems. The second is a full eight-terminal model, suitable for general purpose transient studies.

과도안정도 제약을 고려한 발전기 단자전압 최적 제어 방안에 대한 연구

In this paper, we propose a method to solve the system overvoltage problem without causing the transient stability problem under light load of the power system. The optimal voltage can be found by applying the operating voltage constraints and transient stability constraints to the existing optimization function which the minimizing losses is the objective function. The method of applying the transient stability constraint is divided into two steps. The first is to find the voltage range of the power plant that satisfies the transient stability. Next, the optimal operating voltage is calculated by considering the derived voltage range as the voltage range constraint of the generator of the optimization function. The calculated the optimal reference voltage of generators can solve the system overvoltage problem without impairing the transient stability in case of a power system light load situation. The effect of the proposed scheme was verified using a light load Korean power system.

Signatures of Transient Overvoltages in Low Voltage Power Systems in Tea Factories and Their Implications on Insulation Deterioration and Allied Power Quality Issues

Electrical equipment and supply cables demand a better quality of supply, with the recent advancements in integrated sensitive solid-state controls. Divergently, proliferated heavy inductive motors and some performance additions based on power electronics have introduced power quality issues to the network. Thus, this study mainly investigates the impact of switching transients generated by electromechanical machines in industrial power systems on insulation deterioration while taking transient overvoltages due to capacitor bank switching also to support. Transients with a high rate of rise are likely to catalyze the degradation of the insulation quality and break down the insulating material through ionization. These steeply passing overvoltage stresses let partial discharges ensue, which can attack the insulation over long service. To unveil this danger, 314 common-mode transient waveforms were measured in the electrical machines of five tea factories in Sri Lanka, in a 50 ms measurement window, taken in 55 measuring attempts. Most of the transients observed are in the form of a damped oscillatory waveform tailed by fast exponential collapse. That correlates to insulation degradation having a very steep rise as 30.04 V/ns, the highest at the withering section. When machines are heavily loaded, situations tend to generate transients with high amplitudes. There were transient bursts that spread as 426.3 ms, while 14 ns fast rise times were recorded from withering motors. Unlike electrical resonance and power-frequency overvoltages, electromagnetic switching transients last even less than 100 ms. To underline this, an analysis of the frequency domain of transients was also presented, which proves high density of high-frequency components reaching 107 kHz range. Accepting the fact that frequency and amplitude are always under the influences of innumerable dynamics, the observational evidence of the study endorses that electrical stress built by the transient nature of the factories reduces the life expectancy of electrical insulation.

Generator stator windings ground fault diagnosis for generator–grid​ directly connected system of floating nuclear power plant

For floating nuclear power plants, the internal power system adopts the generator–grid directly connected structure. Generator ground fault diagnosis enables the protective device to adaptively determine the generator tripping control mode based on the fault degree, and shorten the troubleshooting time by fault location. To accurately calculate the ground fault current under different system operating modes, a real-time grounding capacitance parameters calculation method without injection devices is proposed based on third harmonic voltage. Using the fault component principle, the ground fault current is calculated including the fundamental and the third harmonic components. Through fuzzy membership function, the ground fault degree function is established including the ground fault current and the system overvoltage. It comprehensively reflects the damage degree of both the generator operating security and the system insulation security. According to the 60° phase-band distribution characteristic of the stator windings, a fault coil location method based on the windings’ electric potential distribution characteristics is proposed. PSCAD/EMTDC simulation results show that the proposed method has high computational accuracy.

Harmonic Mitigation Using Passive Harmonic Filters: Case Study in a Steel Mill Power System

In this study, we mitigated the harmonic voltage in a power system that contained the roughing mill (RM) and finishing mill (FM) motor drives. AC/DC converter type RM drive is a non-linear, large-capacity varying load that adversely affects power quality, e.g., a flicker, voltage distortion, etc. The voltage drop can be compensated within a certain limit by using the proper capacity of a power capacitor bank. In addition, the voltage distortion can be controlled as per the guidelines of IEEE Std. 519 using the passive harmonic filter corresponding to the characteristic harmonics of the motor drive load. The passive harmonic filter can provide an economical solution by mitigating the harmonic distortion with a proper reactive power supply. However, at the planning level, attention should be paid to avoid system overvoltage that is caused by the leading power under light load conditions and also the problem of parallel resonance between the harmonic filter and the step-down transformer. In addition, when designing the filter reactor, the K-factor and peak voltage must be considered; the filter capacitor also requires a dielectric material that considers the harmonic peak voltage. The purpose of this study was to acquire a better understanding of the filter applications as well as verify the field measurement, analysis, and design of harmonic filters together with its performance.

Impacts of Lightning-Induced Overvoltage on a Hybrid Solar PV–Battery Energy Storage System

With increased electrical energy demands projected in the future, the development of a hybrid solar photovoltaic (PV)–battery energy storage system is considered a good option. However, since such systems are normally installed outdoors and in open areas, they are vulnerable to lightning strikes and may suffer from malfunctions or significant damage to sensitive components, which may result in a major breakdown and loss of revenue due to equipment replacement costs and inefficient operation. Thus, the objective of this paper is to investigate the effect of lightning-induced overvoltage on a hybrid solar PV–battery energy storage system, considering indirect lightning strikes nearby the system. The presented hybrid solar PV–battery energy storage system and lightning-induced overvoltage are modeled in Electro-Magnetic Transient Program-Restructured Version (EMTP-RV) software. The lightning-induced overvoltage is simulated based on a lightning waveshape of 10/350 µs using the Heidler expression, whilst the Rusck model is used to simulate the lightning-induced overvoltage. Different lightning current amplitudes (3, 19, and 169 kA), lightning strike locations (20, 50, and 100 m), and cable lengths (5, 10, and 20 m) are used to investigate the induced effects on the system and on the impulse withstand voltage of 6kV, as stated in MS IEC 60664-1 for solar PV–battery systems and inverters at the DC side. The results indicate that as the lightning strike distance increases from 20 to 100 m, the percentage of strikes exceeding the impulse withstand voltage reduces from 67% to 54% at 19 kA. At 169 kA, the impulse withstand voltage is exceeded by more than 100%, regardless of the strike distance (from 20 to 100 m). Furthermore, differences in cable length do not have much impact on the lightning-induced overvoltage due to the small voltage drop across the short cable length. This study provides useful information for PV systems owners and will be useful in assigning appropriate lightning protection schemes for PV farms.

Reactive Power Control Strategy for Inhibiting Transient Overvoltage Caused by Commutation Failure

The commutation failure (CF) is the most common fault in line-commutated high voltage direct current (LCC-HVDC) systems that may lead to the transient overvoltage in the sending-side system. In the worst condition, the CF may lead to large-scale wind turbine tripping. To resolve this problem, the mathematical relationship between the reactive power consumed by the rectifier and DC voltage, DC current is derived. Then, a transient overvoltage calculation method is proposed in this paper. Furthermore, the mechanism of transient overvoltage caused by the CF is analyzed; it is revealed that the reason for three times transient overvoltage is the rapid decrease of the reactive power consumed by the rectifier during the CF and the recovery period from the CF. This paper proposes a constant reactive power control (CRPC) to inhibit transient overvoltage of the sending-side AC system. The proposed CRPC can increase the reactive power consumed by the rectifier, reduce the exchange reactive power between AC and DC systems, and suppress the transient overvoltage. A simulation model in PSCAD serves to verify the proposed CRPC on the transient overvoltage suppression in the situation of different fault types, fault duration, fault severity and short circuit ratio (SCR).

Surge arrester operation investigation in low‐ and high‐current regions using MATLAB GUI: Implementing an educational goal for undergraduate students

AbstractMetal oxide surge arresters (MOSAs) have been widely used as protective devices against switching and lightning overvoltages in power electrical systems. MOSAs have dynamic characteristics in low‐ and high‐current regions. The unique model of MOSA, which is able to evaluate all the possible operating conditions of power systems, would surely be so complicated. Therefore, by the selection of an operating condition, the appropriate model of MOSA has been created. Many parameters affect MOSA performance in low‐ and high‐current regions. As a result, MOSA's performance under different operating conditions has been investigated by using a MATLAB GUI environment. To make a software environment to simulate MOSA performance in a high voltage laboratory, temperature variations influence on leakage current and its harmonic components under power frequency applied voltages and also the efficacy of impulse parameters variations on MOSA's residual voltage have been investigated. The designed graphical environment has been used by 40 electrical engineering students. The results showed that the use of the graphical environment had a great impact on the concepts' understanding of MOSA's performance.