Voltage Transformer Research Articles

Estimation of insulation overheating in Medium Voltage and Low Voltage conductors and transformers due to stationary disturbances

This paper presents a method to estimate the insulation lifetime reduction for Medium Voltage (MV) and Low Voltage (LV) conductors and transformers due to the presence of stationary power quality disturbances. Insulation aging can be accelerated by temporary increases of rms values of voltages and currents caused by stationary disturbances, i.e. harmonics. A short duration increase of rms values cannot cause a significant reduction of insulation’s lifetime, but its recurrent presence during long time periods will produce a cumulative effect. Currently available models for insulation aging are employed.

Verification tests of a novel ferroresonance detection technique

Ferroresonance is a complex electromagnetic phenomenon that affects voltage transformers. The appearance of the ferroresonant phenomenon provokes important oscillations that are responsible for serious thermal and dielectric overstresses, which may lead to catastrophic failures in the electrical power system. This paper analyzes the behaviour of a novel ferroresonance detection technique, based on artificial neural networks, through the results obtained in several verification tests conducted in a real voltage transformer.

Simplified Control Method for Unified Power Quality Conditioner (UPQC)

Unified Power Quality Conditioner (UPQC) for harmonic elimination and simultaneous compensation of voltage and current, which improves the power quality offered for other harmonic sensitive loads. UPQC consist of combined series active power filter that compensates voltage harmonics of the power supply, and shunt active power filter that compensates harmonic currents of a non-linear load. In this paper a new control algorithm for the UPQC system is optimized and simplified without transformer voltage, load and filter current measurement, so that system performance is improved. The proposed control technique has been evaluated and tested under dynamical and steady state load conditions using PSIM software. The laboratory prototype experimental results for shunt active filter part are given.

Implementation of a New Method for an Improved Voltage Dips Evaluation by the Italian Power Quality Monitoring System in Presence of VT Saturation Effects

The paper deals with a recent measurement improvement introduced into the Italian power quality monitoring system, concerning voltage dips detection and their proper evaluation in the presence of voltage transformer VT saturation phenomena. Saturation effects, essentially on network operated with isolated neutral, can give origin to “false” voltage dips, which can affect the on-line voltage monitoring during a few specific events (i.e. single line-to-ground faults). The “false dip” problem, on the other hand, can be considered negligible in compensated neutral networks. A new criterion has been developed in cooperation with the Polytechnic of Turin, based on the detection of a second harmonic component in the measured voltages, which, once provided with the proper setting parameters, can succeed in identifying “false” dips. The criterion effectiveness has been evaluated on field. The major advantage of the filter implementation in the monitoring system is that, from now on, network operated with isolated neutral could be considered quite similar to those operated with neutral compensation from the point of view of voltage dip performance.

Improved Kalman Filter Based Inverter Control for Reduction of Low Order Current Harmonics due to Isolation Transformers in Renewable Energy Sources

This paper is focused on the analysis of a Kalman filter performance when introduced in the current control loop of a distributed generation connection inverter. The idea is to use this kind of filter to reduce the harmonic content of the currents injected in the point of common coupling. The study has been performed by means of simulation using Matlab-Simulink and clearly demonstrates that this kind of control system can improve the response produced by the inverters. The elimination of certain well-known noisy harmonics introduced by an element such as the isolation low voltage transformer has been accomplished.

Research on the Method of Calculating Short-circuit Voltage for High-voltage Rectifier Transformer for Electrostatic Precipitation by Using the ANSYS Maxwell

Research on the Method of Calculating Short-circuit Voltage for High-voltage Rectifier Transformer for Electrostatic Precipitation by Using the ANSYS Maxwell

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.

Comparative the effect of distribution transformer coil shape on electromagnetic forces and their distribution using the FEM

Abstract During the normal life of the transformers, they are subjected to different electromagnetic stresses. One of these stresses is the electromagnetic forces resulting from the passage of short-circuit current in the transformer coils due to internal or external faults and may lead to the failure of the transformer when this electromagnetic force exceeds the threshold level. This work deals with the computation and analysis of leakage magnetic flux and electromagnetic forces when the worst-case fault (symmetrical short-circuit current) occurs in distribution transformer (DT) coils using the finite element method (FEM). The three types of DTs that were adopted in this work are similar in capacity and voltage transformation ratio (250 kVA and 11,000/416 V), but they are different in the shape of coils (oval, cylindrical, and rectangular coils). ANSYS software was used to build two-dimensional models of the three transformers, which were different in coil shapes and in the type of iron core. The objective of this work is to compare the effect of coil shape on the distribution of electromagnetic forces and their value, in order to find out which coil shape is the best to withstand electromagnetic forces when short-circuit current is passed in the coils. The results of the simulation of the finite element models were approximately equivalent to the results of the design calculations that depend on the classical method (the analytical method), but the FEM is more accurate, due to the accuracy of calculating the magnetic flux and its distribution, which cannot be calculated using the classical method. One of the most important contributions of this research is the analysis and calculation of electromagnetic forces for three types of DTs with different coils by applying the same design parameters to all the transformers. The research also contributed to determining the best coil shape by comparing simulation results, and it was found that transformers with cylindrical coils are the best to withstand electromagnetic forces due to the homogeneity of the cylindrical coil structure from all sides.

Analysis of harmonic characteristics of UHV AC / DC power network considering the influence of geomagnetic storm

The resultant harmonic effect of geomagnetically induced current (GIC) caused by geomagnetic storm has an impact on the safe and reliable operation of ultra-high voltage (UHV) AC / DC power grid in China, which in severe cases may lead to power grid breakdown or even large-scale blackout. Firstly, the harmonic effect model of converter transformer under the action of GIC is established based on the GIC calculation results of China's UHV power grid during the super-geomagnetic storm in November 2004. The harmonic voltage of transformer equivalent model port is described in phasor form. Secondly, the characteristic harmonic model of the converter is established based on the switching function modulation theory. By analyzing the working principle of the equivalent circuit of 12-pulse rectifier, the harmonic coupling model between DC magnetic bias harmonic voltage of transformer and converter is established, and the harmonic coupling characteristics of AC / DC power network under the action of GIC are analyzed. Lastly, the simulation model of ±800 kV UHV AC / DC transmission system in China is built by using PSCAD/EMTDC software as the simulation platform. The non-characteristic harmonic current and voltage on the AC side and DC side of the AC / DC power grid are calculated. The results show that the harm caused by GIC invading converter transformer is more serious than that caused by GIC invading UHV transformer. When both of them are invaded by GIC, the non-characteristic harmonics generated by mutual superposition and coupling have a greater impact on the power grid. The research results of this paper can provide a theoretical basis for space disaster prevention of UHV AC / DC power grid in China.

Ferroresonance phenomena in power systems

It is a known fact that the world's dependence on electrical energy is increasing day by day. The fact that electrical energy has some advantages over other types of energy, the increasing world population and changing living conditions can be considered among the reasons for this increase. This increase in dependence on electrical energy can be met by expanding existing facilities and establishing new facilities. In these studies, the transmission of electrical energy from the place where it is produced to the place where it is consumed poses important problems as the system expands. Some work is required to eliminate these technical and economic problems and to ensure stable operation of the system. These are problems that were not considered beforehand as the system grew. One of these problems is the ferroresonance phenomenon that occurs at the fundamental frequency due to the nonlinear magnetization characteristics of transformers. Ferroresonance is a resonance phenomenon that occurs in an electrical circuit containing an iron-core self-coil as a nonlinear element. This resonance manifests itself with sudden oscillations in the output size of the system caused by a small change in the amplitude or frequency of a magnitude applied to the input of the system. High voltage transmission lines are double-circuit lines that share the same pole. In special cases such as maintenance or malfunction of such a transmission system, one of the lines can be disconnected from the system and continue energy transmission with the other line. In the high voltage transmission line, the system may oscillate due to the stored energy in the magnetic field of the transformer inductance on the disabled line and the electric field of the line capacity. This oscillation disappears after a certain period of time due to iron losses and other circuit losses. When these losses are covered by the other transmission line, permanent oscillations and over voltages may occur at the transformer terminals. All these events are the negative effects of ferroresonance on transmission systems. In the energy transmission system, ferroresonance phenomenon occurs. Over voltages may occur in case of idle power transformers in star point/isolated networks. In medium voltage networks, ferroresonance occurs due to the melting of a fuse, the opening and closing of voltage transformers with one pole, and the dissymmetry that occurs as a result of a connection process. These negative effects caused by ferroresonance in the energy transmission power system are discussed in detail within the subject of this study.

Personal safety monitoring system of electric power construction site based on AIoT Technology

For the purpose of real-time monitoring the hazard information on the electric power construction site, a personal safety monitoring system based on Artificial intelligence internet of things (AIoT) technology is designed. After the system sensing layer collects the gas information of the construction site through the gas sensor, limit current oxygen sensor and DS1820B temperature sensor, the edge computing device of the edge layer directly stores its calculation in the database of the platform layer through the data gateway. The Artificial Intelligence (AI) analysis module of this layer invokes the monitoring data of the power construction site of the database, and uses the personal safety identification method of the power construction site based on artificial intelligence technology, to complete the abnormal identification of monitoring data and realize personal safety monitoring. In addition, the system is also equipped with a power-fail detection module, which can collect the working voltage through the voltage transformer and compare it with the mains power standard to judge whether there is a power-fail risk, so as to prevent the problem of threatening personal safety due to the power-fail of the energized equipment. After testing, the system can monitor the operation status of the construction site in real time to protect personal safety.

Retracted: Genetic Algorithm Integrated Fuzzy AHP-VIKOR Approach for the Investigation of W-Cut Insert Heat Exchanger for Cooling of Dielectric Fluid Used in Ultra-High Voltage Transformer

Retracted: Genetic Algorithm Integrated Fuzzy AHP-VIKOR Approach for the Investigation of W-Cut Insert Heat Exchanger for Cooling of Dielectric Fluid Used in Ultra-High Voltage Transformer

РАЗРАБОТКА КОМПЛЕКСНОЙ МЕТОДИКИ ОПРЕДЕЛЕНИЯ ТОКОВ ОДНОФАЗНЫХ ЗАМЫКАНИЙ НА ЗЕМЛЮ В РАСПРЕДЕЛИТЕЛЬНОЙ СЕТИ КАРЬЕРА

The paper discusses methods for determining single-phase ground fault currents in the quarry's electrical distribution network. The appearance of these short circuits in an electrical network with an isolated or compensated neutral leads to the appearance of significant overvoltages of undamaged phases at the time of the circuit and a decrease in the stability of the functioning of protection devices against single-phase ground faults. It has been established that oscillography is carried out to study the components of higher harmonics in the groundfault current, the network voltage, the neutral bias voltage, as well as to determine the time required to restore the voltage on the grounded phase to a normal value after disconnecting the ground fault. Methods for determining the current of single-phase earth faults by indirect methods are presented, corresponding measurement schemes are presented in the absence of natural unbalance voltage, without a voltage transformer, as well as at a certain value of natural unbalance voltage...

Medium voltage digital instrument transformer

Instrument transformers with digital output provides significant advantages, including those related to increased reliability of power system operation. With the appearance of digital instrument transformers, the topology of the measurement channel and the functional purpose of its components change. This paper considers some function migration examples from protection devices to the primary converter (digital current and voltage transformer). Combined digital transformers expand the application area of distance protection principles, increase the fault location accuracy, as well as improve sensitivity and speed of single-phase earth fault (SPF) protection in 6-35 kV networks.

Topology Synthesis of Hybrid On‐Load Tap Changer in Ultrahigh Voltage (UHV) Transformer with Fast Arcless Switching

Topology Synthesis of Hybrid On‐Load Tap Changer in Ultrahigh Voltage (UHV) Transformer with Fast Arcless Switching

Design and Characterization of a Combined Low Power Voltage and Current Instrument Transformer for Low Voltage Applications

Design and Characterization of a Combined Low Power Voltage and Current Instrument Transformer for Low Voltage Applications

Online Detection Method for Capacitor Voltage Transformer Measurement Error Adapted to Non-Stationary Random Processes

Online Detection Method for Capacitor Voltage Transformer Measurement Error Adapted to Non-Stationary Random Processes

A Novel Generation and Measurement Setup for the Characterization of MV Voltage Transformers From 9 kHz up to 150 kHz

A Novel Generation and Measurement Setup for the Characterization of MV Voltage Transformers From 9 kHz up to 150 kHz

Online Capacitor Voltage Transformer Measurement Error State Evaluation Method Based on In-Phase Relationship and Abnormal Point Detection

Online Capacitor Voltage Transformer Measurement Error State Evaluation Method Based on In-Phase Relationship and Abnormal Point Detection

Research on welding defect examination technique based on phased array ultrasonic for high voltage transformer oil tank welds

Oil tank of high voltage transformer plates. During welding and operation, defects such as incomplete fusion, incomplete penetration , air holes and cracks may be produced which influence the integrity and density of the welds and the whole tank. In order to test the integrity of the shell weld of high-pressure transformer box and ensure no leakage of transformer oil, the phased array testing technology is used to detect the defects of the butt weld of the transformer oil tank. The characteristics of weld defect detection under the condition of incomplete penetration were studied, and the sound beam accessibility, process selection principle and probe selection principle were theoretically analyzed. The test tests were carried out on the artificial samples of the butt weld of the transformer oil tank plate. The results show that the phased array can effectively detect the defects in the weld of transformer tank shell under the condition of incomplete welding, and the imaging results are intuitive and easy to judge, which can effectively evaluate the integrity of transformer tank weld. During the process selection, the probe-wedge combination with appropriate front distance and detection Angle should be selected according to the wall thickness, weld penetration depth and crown width of the transformer oil tank. During defects judgment, the interference of structure echo wave and incomplete penetration area should be considered. The assistant defect positioning analysis based on incomplete penetration is also suggested.