Dimensioning of protection devices for medium voltage transformers and shunt reactors against very fast front voltages

This study's object is a relay protection scheme against damage to transformers (autotransformers) and 35–750 kV shunt reactors as a result of bushing insulation breakdown. The study investigates the possibility of improving the efficiency of the relay protection of transformer equipment (TrE). The task relates to the widespread application of outdated TrE protection schemes and devices that account for their high cost, low operational efficiency, and may even harm TrE. This paper reports the results of investigating current signals from the measuring terminals of bushings and formulates basic requirements for implementing modernized protection schemes based on microprocessor monitoring unit. The proposed protection scheme modernization demonstrates improved operational characteristics: increased safety for personnel and equipment, reduced probability of false trips, decreased weight and dimensions, as well as cost. These characteristics were achieved by using a microprocessor device, reducing the length of measurement circuits, excluding matching transformers from the scheme, applying coupling devices with protection circuit. The effectiveness of using software filtering of current signals based on the discrete Fourier transform algorithm has been proposed and proven for excluding influence currents on the resulting unbalance vector. The inexpediency of accounting for all, except the 1st harmonic, components of insulation currents was demonstrated. The normalized value of the unbalance, while using full signals, was 14%, instead of 1.15%. The results could be used to manufacture and operate relay protection schemes and devices against 35–750 kV TrE damage caused by breakdown of bushing insulation to improve the reliability of power facilities

Suppressing the Zero-missing phenomenon in 330 kV long cable transmission system equipped with shunt reactors

Abstract Partial discharge (PD) monitoring is critical for ensuring the safe and stable operation of transformers and shunt reactors. Developing a non-invasive PD monitoring method applicable to both offline and online scenarios can significantly enhance operational safety. Conventional bushing current transformers (BCTs), primarily designed for power-frequency current measurement, exhibit topological similarities to Rogowski coils commonly used for high-frequency current sensing. The authors have verified their high-frequency current sensing capability. Diagnostic PD test data from an ultra-high-voltage shunt reactor (returned to the factory due to acetylene generation) at an ultra high voltage(UHV)substation demonstrate that bushing CTs exhibit consistent variation trends with conventional high-frequency current transformers (HFCTs) installed at the core and clamping structures. The correlation coefficient R2 between the two exceeds 0.89, with matching phase-resolved partial discharge (PRPD) patterns and comparable signal-to-noise ratios to HFCTs. These findings validate the feasibility and advantages of utilizing BCTs for online PD monitoring in transformers and shunt reactors.

ABSTRACTWith the expansion of electric vehicle charging stations, renewable energy integration, and electrified subway systems, maintaining the balance between load and generation in distribution networks has become increasingly challenging. This imbalance can result in power losses, voltage instability, and additional operational costs for independent grid operators (IGOs). To address these issues, this paper proposes a novel mixed‐integer nonlinear programming (MINLP) model to enhance the performance and resilience of distribution systems. The model incorporates demand response, energy storage, a battery‐to‐subway (B2S) system, optimal control of on‐load tap changers (OLTCs) and step voltage regulators (SVRs), as well as various generation resources, capacitors, and shunt reactors. A multi‐objective, scenario‐based stochastic framework is employed to manage uncertainties from renewable sources. To solve the complex optimization problem, the Large‐Scale Two‐Population Algorithm (LSTPA) is applied, offering robust performance in large‐scale scenarios. Simulation results on a standard 33‐bus system demonstrate improved efficiency and reliability. Notable findings include a 50% increase in losses after the failure of three distributed generation units and a 35% emission rise following the outage of three renewable units. The proposed model ensures uninterrupted power delivery over a 24‐h horizon, regardless of load variations or generation disruptions, making it highly suitable for real‐time grid applications.

In each vibration source of shunt reactor, the winding vibration caused by Lorentz force should not be ignored. In this paper, the electromagnetic-mechanical coupling field simulation model was established based on the structure of disks and blocks of shunt reactor, and the simulation modeling method was verified by an actual reactor manufactured according to the scaled model. The vibration caused by the alternating Lorentz force acting on the winding was simulated and analyzed. The results show that the axial Lorentz force is symmetrical up and down, whose maximum values are distributed at the top and bottom of the winding, and the values approaches zero at about 1/6, 1/2, 5/6 height. The winding deformation and amplitude are mainly axial, and the overall distribution along the winding axis is M-shape. With the increase of the elastic modulus or the number of winding blocks, the axial amplitudes of disks show a downward trend, but the decline rate gradually slows down. In addition to vibration attenuation performance, the design of winding blocks should also consider the investment costs and thermal constraints. The research results could provide a basis for simulation and control of reactor winding vibration.

The paper investigates the dynamic behavior of a 220 kV mixed overhead-underground transmission line compensated with a shunt reactor, with a focus on the current zero-missing phenomenon and switching overvoltages. The zero-missing phenomenon, a condition in which the current through the circuit breaker fails to reach zero, can affect breaker operation and system stability, particularly in shunt-compensated systems. Key factors influencing this issue include cable length, cable configuration, reactive power compensation, and switching strategies. Using EMTP/ATP simulations based on a real grid model, the study evaluates various mitigation strategies for the zero-missing phenomenon, such as pre-insertion resistors, compensation ratios, and connections to high-power loads. Transient overvoltages on cable cores and sheaths during switching operations are also analyzed.

The increasing integration of distributed renewable energy sources (RES), energy storage systems (ESS), electric vehicle (EV) charging stations, and demand response (DR) mechanisms has significantly enhanced microgrid deployment. However, the operational complexity and vulnerability of islanded microgrids to disruptions, especially during renewable energy fluctuations, pose critical challenges. Existing approaches primarily focus on minimizing operational costs or emissions but fail to simultaneously address load curtailment, voltage stability, and resilience under uncertain conditions. In this paper, we propose a novel resilience-oriented energy and load management framework for island microgrids, integrating a multi-objective optimization function that explicitly minimizes load curtailment, energy losses, voltage deviations, emissions, and energy procurement costs while maximizing the utilization of renewable energy sources. Unlike conventional models that separately optimize demand-side management (DSM), distributed generation (DG), EV charging/discharging, and ESS scheduling, our approach incorporates a coordinated control strategy that jointly optimizes these elements alongside reactive power compensation devices such as capacitors and shunt reactors. To effectively solve this high-dimensional, nonlinear problem, we employ the Multi-objective Moth Flame Algorithm (MOMFA), an enhanced metaheuristic evolutionary algorithm designed to handle complex trade-offs between cost, reliability, and resilience. The superiority of MOMFA over conventional optimization techniques such as Genetic Algorithm (GA), Particle Swarm Optimization (PSO), and Grey Wolf Optimization (GWO) is validated through simulations on a realistic 33-node microgrid under various renewable energy outage scenarios. The results demonstrate that the proposed framework achieves a 60% reduction in voltage deviation, an 81% decrease in energy losses, and an 86% reduction in CO₂ emissions, while ensuring zero load curtailment, even under severe outage conditions. The proposed method offers a scalable, real-time implementable solution for microgrid operators seeking to enhance resilience against renewable energy intermittency and optimize energy utilization. This work significantly advances state-of-the-art microgrid energy management by providing a holistic, multi-objective, and resilience-driven optimization strategy.

Resonance and delayed zero-crossing effects in offshore facilities with variable shunt reactors

The 1000 kV dry-type air-core shunt reactor, as one of the key components of ultra-high voltage AC transmission systems, is still in the preliminary stage of research regarding its grading ring configuration. Aiming to reduce the maximum electric field strength of the reactor, this paper proposes a hybrid surrogate model that combines Radial Basis Function Neural Network (RBFNN) and the Kriging model to optimize the configuration of grading rings. First, the sparrow search algorithm is used to optimize the hyperparameters of the RBFNN. To enhance the surrogate model’s fitting accuracy further, the Kriging model is utilized to adjust the deviations produced by the RBFNN. The RBFNN–Kriging hybrid model demonstrates superior fitting accuracy compared to the standalone Kriging model, exhibiting enhanced statistical consistency between simulated and predicted values of maximum electric field strength. This improvement is quantitatively validated through reduced absolute errors and lower root-mean-square error metrics. After the optimization, the maximum electric field strength is substantially reduced, proving the effectiveness of the hybrid surrogate model. Consequently, the proposed method not only ensures the hybrid model’s fitting accuracy but also significantly reduces the reactor’s electric field strength, aligning with engineering application standards and providing a valuable reference for configuring grading rings for the 1000 kV dry-type air-core shunt reactor.

Cumulative Effect of Reignition Overvoltage Caused by Vacuum Circuit Breaker on Shunt Reactor Insulation in Offshore Wind Farm

The insulation of oil-filled power transformers, shunt reactors, and high voltage bushings may be affected by copper dissolution in the insulating oil and copper deposition on the paper insulation. Dissolved copper increases dielectric losses in the oil while copper deposition can significantly increase the conductivity of the paper insulation. The corrosion activity of transformer insulating oils has been shown to be accelerated by multiple factors such as temperature, oxygen, sulfur groups, passivators, and aging time. To date, there is a lack of studies that systematically design and quantify the effects of corrosion factors on the copper dissolution of transformer insulating oils or copper deposition on the surface of solid insulation (Kraft paper). Therefore, in this study, the effects of corrosion factors on the copper and sulfur deposition on the paper insulation immersed in transformer mineral oil (TMO) were investigated using two-level (2k) factorial design. The factors investigated in this study were: (1) oil temperature, (2) elemental sulfur concentration, and (3) aging time. Based on the results of the two-level factorial design, it is found that the oil temperature has the most significant effect on the surface resistivity, with a percentage contribution of 38.68%. A regression model was also developed in this study, and it is found that the model is adequate to predict the surface resistivity as a function of oil temperature, elemental sulfur concentration, and aging time, where the coefficient of determination (R2) and p-value of the regression model are 0.9694 and 0.0070, respectively.

Abstract Partial discharge is considered one of the main reasons for insulation degradation. To investigate the effect of suspended discharge on oil-paper insulation degradation under mechanical vibration, a test platform for suspended electrode-paper insulation degradation was constructed. Experimental studies were conducted under static and mechanical vibration conditions. The results showed that mechanical vibration promotes the development of discharge, alters the electrode gap, enhances the electric field intensity ahead of the electrode tip, and accelerates the degradation of oil-paper insulation. During operation, ultra-high-voltage shunt reactors experience continuous vibrations, which can lead to loosening and detachment of components, forming suspended potentials in insulating oil, thereby causing partial discharges.

When a 35 kV distribution network has the problem of insufficient reactive power, the input of a shunt reactor is a common compensation method. Vacuum circuit breakers are widely used in 35 kV distribution networks because of their superior arc extinguishing performance and convenient maintenance. However, in recent years, accidents involving vacuum circuit breakers breaking shunt reactors have occurred more frequently in China, such as high-frequency phase-to-phase short circuits, inter-turn burning losses, bus outlet short circuits, etc., which can cause serious damage and pose a greater threat to the safety of the power system. This paper focuses on the switching overvoltage generated by the vacuum circuit breaker cutting off the shunt reactor. Firstly, the mechanism of overvoltage generation is analyzed theoretically. It is concluded that the equivalent chopping current of the other two phases caused by the continuous reignition of the first open phase is the root cause of the high-amplitude interphase overvoltage. Based on the MODELS custom programming module in EMTP/ATP, according to the process of breaking and reigniting the circuit breaker, this paper uses Fortran language to compile the program and establishes a model of a vacuum circuit breaker, including power frequency current interception, high-frequency current, zero-crossing, breaking, and arc reignition modules. The vacuum circuit breaker is simulated for hundreds of continuous reignitions in milliseconds. Finally, a simulation study on the overvoltage suppression measures of a 35 kV shunt reactor is carried out. The comprehensive comparison of various suppression measures provides a reference for the reasonable selection of actual engineering conditions.

An Approach for Real Time Implementation of Charging of Shunt Reactor Using Point on Wave Technique with Variable Pre-Insertion Resistor

An adaptive single-phase auto-reclosing scheme based on the Hausdorff distance algorithm for transmission lines with shunt reactors

In electrical power systems, shunt reactors control excess reactive power, keeping voltage levels within acceptable limits. As shunt reactors play a crucial role in the operation of electrical systems, it is essential to ensure the use of modern and fast protection schemes for these devices. Furthermore, protection functions must be capable of identifying various fault conditions, including critical operating situations such as turn-to-ground and turn faults, involving only a few short-circuited turns. This paper proposes a comparative evaluation of protection schemes commonly employed by manufacturers to meet the requirements of different grid codes. Thus, the investigation encompasses restricted earth fault, directional, differential, and distance functions. The latter is typically cited as a backup protection function. To support the analyses conducted, an electrical power system with shunt compensation was modeled in the ATPDraw software version 7.3. Through this platform, various internal fault conditions were simulated, encompassing turn-to-ground and turn faults. This facilitated the analysis of the influence of parameters such as the leakage factor value and the number of short-circuited turns. Additionally, external fault conditions were evaluated, including cases involving Current Transformer (CT) saturation.

UHV (ultra-high voltage) by instant AC transmission system is accompanied by huge reactive power transmission. When the load drops sharply, it is easy to produce serious power frequency overvoltage, which is also defined as load rejection overvoltage. This paper makes an in-depth analysis from the perspective of voltage increase caused by instantaneous load unloading, and obtains the causes and key influencing factors of load rejection overvoltage. Taking the UHV AC transmission line of a practical project as an example, the suppression effect of the suppression strategy represented by the installation of opening resistance and shunt reactor on the load rejection overvoltage is analyzed. The simulation results show that the above method has an obvious inhibitory effect on load rejection overvoltage. Based on the optimal suppression principle, the optional interval range of the opening resistance and shunt reactor parameters are designed.

To meet the need for electrical energy in Indonesia, especially in DKI Jakarta, PT PLN (Persero) built the Muara Karang Combined-Cycle Power Plant (CCPP), which has daily start-stop facilities with a capacity of 500 MW and 500 kV extra high voltage overhead lines between Muara Karang – Duri Kosambi is 30 km long. In high voltage and extra high voltage transmission lines, channel filling appears where the receiving side voltage is greater or smaller than the sending side voltage. This research aims to design a shunt reactor for reactive power compensation that can overcome the problem of voltage differences. The modeling uses ETAP 20.0 software. The required shunt reactor value is 164.8 MVAR. There was a decrease in the reactive power produced at the Muara Karang CCPP plant by 157,878 MVAR due to installing a shunt reactor. So that it can improve the voltage drop on the load buses from Extra High Voltage Substation (EHVS) Duri Kosambi, with each having a voltage pu value on the Cengkareng GI bus of 92.52%, Duri Kosambi VVIP GI bus of 93.91%, Grogol Baru GI bus of 93.7%, and GIS Cengkareng at 94.25%. This can maintain reliability on the 500 kV Extra High Voltage Substation Muara Karang transmission line.

Offshore wind farms are increasingly being commissioned farther from shore, and high voltage alternating current (HVAC) transmission systems are preferred because of their maturity and reliability. However, as cable length increases, ensuring system stability becomes more challenging, making it essential to investigate shunt reactor compensation configurations and converter control strategies. This study examines three different shunt reactor compensation arrangements and two control strategies, grid-forming (GFM) and grid-following (GFL), across three cable lengths (80 km, 120 km, and 150 km). The systems were evaluated based on small-signal stability using disk margins for different active power operating points, and later for different short-circuit ratios (SCR) and X/R. The results demonstrate that the GFM is preferable for longer cables and enhanced stability. The most robust configuration includes a shunt reactor placed in the mid-cable with additional reactors at both ends of the cable, followed by an arrangement with reactors at the beginning and end. The GFM converter control maintained stability across all operating points, cable lengths, and configurations, whereas the stability of the GFL unit was highly dependent on active power injection and struggled under weaker grid conditions. Thus, for longer HVAC cables, it is necessary to employ GFM control units, and it is recommended to use shunt reactors at the cable start and end, as well as at mid-cable, for optimal stability.