Short-circuit Impedance Research Articles

Analytical Modeling of Short-Circuit Impedance of Square Foil Winding Phase-Shifting Transformer Based on Planar Energy Density Equivalence Method

Analytical Modeling of Short-Circuit Impedance of Square Foil Winding Phase-Shifting Transformer Based on Planar Energy Density Equivalence Method

Short-Circuit Impedance Analysis of HTS Traction Transformer With Flux Diverters Using Magnetic Energy Method

Short-Circuit Impedance Analysis of HTS Traction Transformer With Flux Diverters Using Magnetic Energy Method

A New Method of Transformer Short-Circuit Impedance Regulation Based on Magnetic Shunts

A New Method of Transformer Short-Circuit Impedance Regulation Based on Magnetic Shunts

Study on the Design of Valve Base Insulation and Power Supply Transformer for High-Voltage DC Circuit Breaker

Abstract High-voltage DC circuit breaker is a key piece of equipment to building DC power grids. DC circuit breakers need to support and isolate from high voltage to ground through valve-based equipment and use valve-based power supply transformer to continuously supply energy to high potential components, the electrical performance of these two equipment determines whether DC circuit breakers and DC networks can be operated safely and reliably. For this reason, this paper carries out the research on the insulation capability of the valve base and the performance of the power supply transformer, such as the design and simulation of electric and thermal fields, as well as the test program. Firstly, the insulation design and simulation study of the valve base as a whole is carried out, and the design optimization of the equipotential scheme of the top homogeneous tubular bus, diagonal pull insulator and hydroelectric pole is completed. Secondly, the design and simulation verification of the thermal field distribution of the energy-supply transformer, the overvoltage between the ends of the output windings and the optimization scheme, and the short-circuit impedance were carried out. Finally, the insulation performance of the valve base, the temperature rise of the energy supply transformer, the overvoltage simulation of the output winding and the short-circuit characteristics were tested. The results show that: after optimization, the maximum field strength of the homogenizer is 2.3kV/mm, and the overall maximum field strength of the valve base is 2.61 kV/mm on the diagonal insulator, and there is no pressure difference between the water circuit and the fittings using the three-pin vertically distributed hydropower electrode scheme; the temperature rise of the supply transformer in the simulation and the actual measurement is 27K and less than 30K; by means of the parallel connection of the MOV, the overvoltage of the output winding of the power supply transformer under voltage impulse is effectively reduced to -1.8kV; the measured short-circuit impedance of the power supply transformer is 69.5%. The optimized design of DC circuit breaker valve base and power supply transformer can operate safely, and effectively support the construction of DC circuit breaker and DC power network.

New Short-Circuited Coaxial Method Implementation for Complex Permittivity Measurement of Power Transformer Oils

The investigation into the dielectric properties of transformer oils has been a focal point in both historical and contemporary electric insulation technology as high-voltage applications have greatly benefited from the continuous research efforts in this field. The dielectric permittivity is one of the factors to be negotiated when discussing the electric insulation of any material. This work aims to showcase a new short-circuited coaxial cable method to evaluate the complex dielectric permittivity of palm, sunflower and rapeseed oil and review other previously used measurement techniques. Mainly, the test was performed using a sample holder that represents a short-ended coaxial cable filled with the test material which is connected to one port of a vector network analyser. The measurements of the input impedance for various oil samples were conducted at frequencies ranging from 1 MHz to 10 MHz. The technique uses the value of the input impedance which depends on the reflected signals from the test sample to the network analyser, consequently, the value of the dielectric permittivity and dielectric loss have been calculated using the short circuit impedance formula which involves numerical methods to get the results which shows that this method can be used as an alternative to investigate the oils insulation parameters as it provides smooth results for permittivity without any divergence, ensuring more reliable and consistent measurements as well as providing high accuracy in determining the permittivity of materials.

Evaluasi Instalasi Kelistrikan Pada Gedung Vessel Traffic Service Palembang

Electrical installation is one of the important elements in buildings. Safe electrical installations that comply with applicable safety standards can prevent electrical accidents. This research aims to evaluate the electrical installation in the Palembang Vessel Traffic Service (VTS) Building. Evaluation is carried out by measuring and calculating several parameters, namely: voltage and current values, current carrying capacity (KHA), circuit breaker (CB) size, short circuit impedance, grounding value. Quantitative research methods were used because this research aims to evaluate the electrical installation at the Palembang Vessel Traffic Service (VTS) Building. Evaluation is carried out by comparing the results of measurements and calculations with applicable standards. Based on the research results, it can be concluded that the electrical installations of the Palembang VTS Building generally meet safety requirements and comply with applicable standards. However, there are several recommendations that can be made to increase the safety of electrical installations, namely: The results of checking that the electrical current on the 7th and 8th floors is unbalanced must immediately identify the cause and repair the load group points so that the electrical load is evenly distributed so that power losses do not occur and result in damage to the existing electrical installation.

Online time series monitoring method of transformer based on seq2seq model

Abstract To monitor the operating conditions of transformers in real time and improve the monitoring accuracy of three-phase voltage, load current and power frequency of transformers, an online time series monitoring method of transformers based on the seq2seq model is proposed. The impedance, excitation current, secondary side voltage and excitation branch of the transformer are reduced to the primary side value, and the regulation coefficient of the transformer under no-load operation is calculated. By obtaining the short circuit impedance of the transformer, the short circuit impedance of the transformer is analysed. Using the coupling inductance model structure of single-phase double-winding and single-phase three-winding transformers, the parameter matrix of a single-phase double-winding transformer is established. According to the corresponding relationship between port electrical data and online monitoring information, the transformer coupling inductance model is constructed. The online time series monitoring process of the transformer is designed by using the seq2seq model, and the online time series monitoring of the transformer is realized. The experimental results show that when monitoring the three-phase voltage, load current and power frequency of the transformer, the monitoring errors are controlled below 0.5, 5 and 0.5%, respectively, which greatly improves the accuracy of online time series monitoring of the transformer.

Impact of Short-Circuit Impedance Model for Variable-Speed Wind Turbine Generators on Operation of Overcurrent Relays

This paper discussed different short-circuit impedance models for type 3 and type 4 wind turbine generators. IEC and IEEE-PES models are either simplified or they require additional data. The proposed model is given by a non-linear dependency of the short-circuit impedance and voltage on the medium voltage side of the unit transformer. Furthermore, the proposed model, as well as the constant impedance-based model were used for timing coordination of overcurrent relays in a radial 6-bus network. The obtained results show that the constant impedance-based model overestimates short-circuit currents. Consequently, selectivity of individual overcurrent relays might be questionable.

Impacts of Renewable Sources on Power Quality in Distribution Systems

This paper analyzes the influence of renewable sources (RS) on voltage quality in MV networks and summarizes problems considered of general interest relating to the power quality of dispersed generation. We are interested in voltage fluctuations, flicker, harmonic distortion, interharmonic distortion, and the effect of dispersed generation on ripple control signals. The influence of DG on voltage stabilization, line losses, and short circuit impedance are also investigated. A basic analysis of the possibility and effectiveness of using a parallel Active Filter (AF) to compensate for the constant-speed wind turbine (WT) flicker, reactive power, and terminal voltage variation is presented too.

Designing Parameters to Reshape the Inverter Output Impedance Based on the D-Split Method under Weak Grid Conditions

Novel energy generation technologies, such as high-permeability wind power and photovoltaic systems, exhibit inherent intermittency, randomness, and volatility. During periods of energy production from these sources, the impedance of the electrical grid frequently experiences significant fluctuations. Consequently, the grid manifests characteristics akin to a weak grid, highlighting the challenges associated with integrating renewable energy sources with variable output profiles. These fluctuations lead to a shift in resonance spikes of the LCL-type filter towards the lower frequency band, consequently impacting the stability of inverter grid connections. To mitigate this issue, the present study introduces a novel approach integrating the D-split method and a proportional–differential feedforward strategy. This combination aims to reshape the inverter’s output impedance, ensuring its consistent stability even amidst significant fluctuations in grid impedance. In this research, the optimal controller parameters for systems operating under robust grid conditions are initially determined. This selection process involves the application of the D-split method, supported by graphical visualization. Additionally, the amplitude and phase angle margin tester is employed while considering the system bandwidth as a limiting constraint. Moreover, accounting for the influence of grid impedance, the D-split method is reapplied to ascertain the most suitable values for the proportional–differential feedforward parameters. This adjustment aims to enhance the adaptability of the grid-connected inverter specifically in scenarios characterized by a weak grid. The hardware-in-the-loop (HIL) simulation results demonstrate that despite the presence of harmonics within the grid and a short circuit impedance ratio (SCR) of 3, the inverter maintains grid stability and effectively suppresses harmonics. Moreover, the total harmonic distortion factor (THD) of the grid-connected current remains below 5%.

Three-Phase Transformer Optimization Based on the Multi-Objective Particle Swarm Optimization and Non-Dominated Sorting Genetic Algorithm-3 Hybrid Algorithm

The performance of transformers directly determines the reliability, stability, and economy of the power system. The methodologies of minimizing the transformer manufacturing cost under the premise of ensuring performance is of great significance. This paper presented an innovative multi-objective optimization model to analyze the relationship between design parameters and transformer indicators. In addition, the sensitive analysis is conducted to exploit the interaction relationships between design parameters and targets. The reliability of the model was demonstrated in 50 MVA/110 kV and 63 MVA/110 kV prototypes, compared with the actual material usage, short-circuit impedance, and load loss, and the maximum error is less than 7%. Due to this problem having many optimization objectives and the high dimension of variables, a two-stage algorithm called MOPSO-NSGA3 (multi-objective particle swarm optimization and non-dominated sorting genetic algorithm-3) is presented. MOPSO is used to find non-domain solutions within the search space in the first stage, and the solution will be used as prior knowledge to initialize the population in NSGA3. The result shows that this algorithm can be effectively used in multi-objective optimization tasks and best meets the requirements of transformer designs that minimize the short-circuit deviation, operating loss, and manufacturing costs.

Experimental Study of the Dynamic Short-Circuit Withstand Capability of an 8400 kVA Power Transformer Specially Designed for Photovoltaic Applications

This article, besides offering data of great value for any designer of high-power short-circuits of special three-winding design, illustrates the correlation with the corresponding FRA measurements, validating this type of measurement. The frequency response measurements can provide data about the transformer’s status after it is put into service, its vulnerability in incipient states, and, particularly for this type of transformer, its insulation, which is the subject of high dielectric stress due to its invertor working regime. This article presents the behavior of a three-phase 8400 kVA medium-voltage step-up transformer (corrugated hermetic tank) specially designed for photovoltaic applications during short-circuit tests. This transformer, fed by two inverters, has two secondaries with elliptical windings (non-circular aluminum foil for LV windings and an aluminum conductor for HV windings). Various experiments were performed, including measurements of winding resistance, measurements of voltage ratio, measurements of short-circuit impedance and load loss on three tappings, measurements of no-load loss and current, a frequency response analysis, and short-circuiting. These experiments were performed to study the behavior of the transformer, which, in real life, is powered by photovoltaic inverters on the LV side that feed into the MV grid on the HV side, making it the interface between the photovoltaic inverter and the MV grid. An auxiliary supply transformer may be connected to the LV side. Given these elements, concerning both the importance and the particularities of the problem studied, we can say that this article represents a niche study on the guarantee of good functioning and safety in operation given the passing of the test to withstand the dynamic effects of short-circuiting.

A Mechanical-Electromagnetic Coupling Model of Transformer Windings and its Application in the Vibration-Based Condition Monitoring

Winding vibration leads to the oscillation of coils position and further affects winding's nonlinear stiffness as well as electromagnetic forces (EMFs). This paper establishes a winding Mechanical-Electromagnetic Coupling Model (MECM) where the coupling between stiffness coefficient and vibration, magnetic field and vibration are considered, and deploy it in the vibration-based condition monitoring. In this model, EMFs are obtained through the superposition of leakage magnetic field generated by each coil. A novel numerical analysis method is further proposed, which is capable of calculating the vibration response containing nonlinearity and electromechanical coupling, and the accuracy of the method is verified in experiments. Then, the numerical analysis method is used to quantitatively analyze the effects of Nonlinearity and ElectroMechanical Coupling (NEMC) on the vibration characteristics. The study demonstrates the law that NEMC intensity increases with vibration, and the NEMC is obvious especially under mechanical fault. To extract the vibration patterns, Nonlinearity-ElectroMechanical Coupling Coefficient (NEMCC) with amplifying NEMC effects is proposed to monitor the winding mechanical condition. The analytical method predicts the variation trend of the winding looseness condition curve, and laboratory experiments prove that the Mean Absolute Percentage Error (MAPE) is able to successfully identify different degrees of winding looseness faults. Compared with the short-circuit impedance (SCI) method, the MAPE value based on NEMCC has a stronger detection capability and higher sensitivity for winding mechanical faults. This paper lays a foundation for the numerical solution of vibration response and pave a way for winding mechanical condition monitoring.

Design, development, and testing of a 6.6 MVA HTS traction transformer for high-speed train applications

High-temperature superconducting traction transformers (HTSTTs) have the merits of small size and lightweight in comparison with their conventional counterparts. This article reports the development progress of a 6.6 MVA HTSTT operating at 65 K, including the design, testing, and system cooling. The introduction of flux diverters and an optimized winding design realized a short-circuit impedance higher than 43% and AC loss less than 3 kW. The insulation structure was designed to pass insulation tests specified in standard in China GB/T 25120-2010. An open cooling system with reduced pressure was developed, which realized the efficiency of the 6.6 MVA HTSTT above 99%. Before assembling the prototype transformer, we conducted tests for critical current and dielectric performance of the HTS double pancake coils (DPCs) used in high-voltage (HV) and low-voltage (LV) windings to verify the current-carrying and insulation performances of each DPC. Finally, we measured the critical current and no-load loss of the HTSTT prototype at 77 K. Test results showed that the mass of the transformer is 33% less than conventional transformers. At 77 K, the critical current of the LV winding and HV winding is higher than 700 A and 50 A, respectively. Moreover, the HTSTT on a no-load test reached the test voltage of 25 000 V and loss of 6 kW. In the next step, we will continue to conduct experimental research, and verify the feasibility of the HTSTT on the train, and develop a circulating cooling system, all meeting the commercial requirements of the HTSTT.

A novel protection strategy for DC microgrid considering communication failure

DC microgrid has become an important part of supporting “carbon peaking, carbon neutralization” and building a low-carbon energy system. However, the short-circuit current of the DC microgrid rises rapidly and has a great impact, threatening the normal operation of the DC microgrid. As the main protection strategy for removing short-circuit faults, current differential protection can quickly and selectively remove fault lines, but it depends on communication. In addition, a high impedance short circuit may also lead to the failure of the current differential protection strategy. To improve the quick action and sensitivity of DC microgrids protection strategy, a differential protection strategy based on the bus power gradient is proposed, and to further solve the problem of protection failure caused by communication failure or communication data loss, an improved composite strategy for DC microgrids considering communication faults is proposed. In the case of normal communication, the power gradient differential protection detects and removes the short-circuit faults; In the case of communication failure, the power gradient differential protection is blocked and local power gradient protection is started. The problem of protection strategy failure caused by communication failure was solved without adding measuring devices. Meanwhile, the power differential gradient changed more violently than the current or voltage during the failure, which improved the protection sensitivity. Finally, simulation and experiment prove the effectiveness of the proposed strategy.

Optimization design of short-circuit test platform for the distribution network of integrated power system based on improved K-means clustering

Short-circuit test platform can verify the correctness of the distribution network simulation model and the effectiveness of short-circuits protection. It is necessary to simplify the structure of the distribution network into a typical branch and build an equivalent test platform due to the system’s complexity. The equivalent system based on empirical classification has particular subjectivity and randomness, which will reduce the representativeness of the short-circuit test platform. Therefore, this paper adopts the improved K-means clustering algorithm to cluster the short-circuit impedance parameters from the typical short-circuit point of the distribution network to the power supply into different clusters. Each cluster center is used as the equivalent system’s characteristic impedance to realize the complex system’s simplification. The feasibility of the improved K-means clustering algorithm is verified by comparing the short-circuit simulation results with the original and the empirical classification equivalent system.

Short-circuit Impedance Calculation of 25 MVA Autotransformer with Tertiary Winding using FEM

In this article, the percentage of short-circuit impedance is calculated using the finite element method for a single-phase power autotransformer with tertiary winding. The autotransformer specifications are: 25 MVA, 230 kV, 60 Hz, three-legged core type. A detailed 3D model where mixed formulations in terms of scalar and vector potential and circuit coupling is used. This type of study is essential to design the autotransformer and guarantee the impedance value, and so the safety and operability of electrical power systems. To calculate the percentage of short-circuit impedance the voltage relationship between the short-circuit voltage and the nominal voltage is used. In addition, the magnetic energy storage technique is presented as another alternative to calculate this parameter. The results are validated with the data from the laboratory tests obtaining differences of less than 5%.

Modelling of multi-winding transformers for short-circuit calculations in the power system – Modelling accuracy and differences in equivalent circuits

The theory related to the modelling of two-winding and three-winding transformers is well known and widely used in short-circuit analysis. The simplest equivalent circuit, and at the same time accurate, used for the above-mentioned transformer units is the star diagram. For transformers with more than three windings, it is simplified as it does not account for all short-circuit impedances between the individual windings. Therefore, in order to more accurately model multi-winding transformers, e.g. four- or five-winding ones, apart from star diagrams, other equivalent circuits, such as complete polygons, star polygons or chain diagrams, should be used. Which equivalent to use depends on the required accuracy of the calculations. Some of the diagrams mentioned (complete polygons, star polygons) are accurate, but require access to detailed data that are sometimes difficult to obtain from manufacturers, and determining all the parameters of the scheme is laborious and time-consuming. The remaining diagrams (star or chain ones) are created on the basis of certain simplifying assumptions: they do not require all detailed data and it is not difficult to determine their parameters. The article presents and describes various equivalent diagrams that allow to model multi-winding transformers. On the basis of exemplary data, for a four- and five-winding transformer, their parameters were determined for each scheme and sample short-circuit analyses were performed, indicating the similarities and differences in the modelling method and their impact on the calculation results.

Fast and accurate evaluation method of commutation failure in line‐commutated converter‐based high‐voltage direct current systems considering probability characteristics

Line-commutated converter-based high-voltage direct current (LCC-HVDC) systems suffer from commutation failure (CF) when receiving-end AC grid faults occur, which is a major drawback and threatens the security and stability of power systems. This paper presents a fast and accurate evaluation method of CF for the LCC-HVDC systems, considering the CF probability characteristics. Firstly, based on the analysis of the CF probability characteristics from the view of short-circuit impedance, the CF tolerance index (CFTI) and CF vulnerability index (CFVI) are proposed to quantitatively evaluate the LCC-HVDC systems' risk of the possible- and inevitable-occurrence CF, respectively. Secondly, four factors, that is, commutation voltage, fault occurrence time, DC current and firing angle command, are considered to calculate CF evaluation indices (CFEIs) and identify the CF risk area boundaries based on the theoretical analysis. Moreover, the relationships among short-circuit impedance, fault position, and extinction angle are established based on the AC/DC decoupling method, which helps realize the decoupling of multi-factors affecting CF during fault. Compared to earlier methods, this evaluation method combines the advantages of the accuracy of the electromagnetic transient simulation method and the rapidity of theoretical derivation. Finally, the validity and accuracy of the evaluation method are verified in the CIGRE HVDC benchmark model and IEEE 39-bus system.

Modeling and Analysis of Asymmetrical Faults for Relay Settings in Electric Power Protection System Learning

This study examines the analysis of Asymmetrical fault, namely single-phase ground faults for e-jobsheet products based on Information and Communication Technology (ICT) or utilizing computer programs for study. A study of short-circuit faults in the electric power system, is used to solve problems in the field of reliability and protection. the electric power system, namely the handling of single-phase short-circuit faults to ground which, if not neutralized, cause equipment damage to the electric power system. Parameters from modeling and analysis of asymmetrical faults are used for setting the Ground Fault Relay or often known as the Ground Fault Relay (GFR). The research study begins with modeling the interconnection system in the form of a reactance diagram, then modeling it with the bus impedance matrix equation, to determine the magnitude of the short circuit impedance value on the diagonal matrix. Then calculate the fault current of a single-phase short circuit to ground. From these results it is determined to determine the amount of the relay setting. The results showed that the asymmetrical fault current was 3.0 Pu with a setting time value of 2,45 seconds. The results of the study are used for learning relay settings. The simulation program was validated by experts, with a very good category with an Aikensv index of 0.872.