High Voltage Electrical Machines Research Articles

Electrostatic Field for Positive Lightning Impulse Breakdown Voltage in Sphere-to-Plane Air Gaps Using Machine Learning

Breakdown (BD) voltage is significant in high-voltage power electric machines. Currently, BD voltages are mainly predicted by the semi-empirical formula in strongly inhomogeneous electric fields. However, the equation could not be applied for electrodes with weakly inhomogeneous electric fields. In this paper, positive lightning impulse BD voltages are predicted in various sphere-to-plane air gaps using forms of machine learning such as support vector regression (SVR), Bayesian regression (BR) and multilayer perceptron (MLP). Unlike previous studies, a method is also proposed by introducing streamer propagation characteristics as new features and by removing electric field gradients as unnecessary features to find out how to reduce the feature dimension. The streamer propagation characteristics are suggested to reflect the possibility of a discharge process between electrodes. Predicted voltages from machine learning algorithms are compared with the experimental results and calculated voltages from the semi-empirical formula. Firstly, the predictions from each model agreed well with the datasets. New features were observed to be applied for machine learning algorithms and to be as important as known electrostatic features before discharge. Secondly, predicted BD voltages were more accurate than calculated voltages from the semi-empirical equation in strongly inhomogeneous electric fields. Predictions from each model also agreed well with the experimental results in weakly inhomogeneous electric fields. The prediction accuracy of SVR was better than those of BR and MLP. Machine learning algorithms were also shown to be applied for electrodes with a wide range of inhomogeneities, unlike a semi-empirical method. We expect that the suggested features and machine learning algorithms can be used for accurately calculating BD voltages.

Electrodynamic withstand and effects of short-circuit currents on high-voltage electrical equipment

The analysis of simplified expressions allows us to estimate the electrodynamic effects of short-circuit currents on the main elements of a power electrical station and substation, which include busbars, high voltage circuit-breakers, disconnectors, electrical machines and transformers. Examples of calculations of magnetic field induction, mechanical forces and pressures that determine the electrodynamic withstand of electrical equipment are given. Simplified qualitative calculations allow us to assess the impact of key parameters on the selection of appropriate elements and the possible range of their changes during the design, operation and modernization at the preliminary design stage.

Ensuring the reliability of turbogenerators on the basis of the control of discharge processes in the stator winding insulation

Issues related to the reliability of the electrical insulation system of high-load powerful turbogenerators with indirect gas cooling are considered and analyzed. The mechanisms of aging of the main components (main insulation, slot filling elements) of the insulation system under operating conditions exposed to electrical and thermal fields, and mechanical forces are studied. Modern ideas about the mechanisms of aging of main insulation and slot filling elements under the action of internal and external impacts (slot and spark discharges) are analyzed. The degradation of insulating materials during operation begins, first of all, in a weak local area of the main insulation, characterized by a large number of technological defects (cavities filled with gas), in which internal partial discharges occur. However, thermosetting insulation of high-voltage electrical machines can function normally throughout its lifetime in the presence of rather intense internal discharges. At the same time, no service life deterioration is observed due to the specific properties of modern main insulation, which contains a mica barrier. The greatest danger is posed by slot partial discharges (SPD) and vibration spark discharges (VS) that occur in the slot area of the stator winding. To reduce the intensity of these discharge processes, it is necessary to optimize the design of the anti-corona coating. On the basis of the performed analysis, a scheme was developed of the aging of the electrical insulation system of the stator winding of air-cooled turbogenerators. Based on the results of prototype tests, an estimated assessment of the "lifetime" of the electrical insulation system of the stator winding, developed using promising electrical insulating materials, was carried out.

About dielectric materials with high thermal conductivity for electrical insulation systems of high-voltage electric machines: a review of domestic and foreign literature

About dielectric materials with high thermal conductivity for electrical insulation systems of high-voltage electric machines: a review of domestic and foreign literature

Partial discharges location in power transformers using piezoceramic sensors

The detection and the spatial localization of partial discharges in high-voltage electrical machines are considered as an effective method in predictive maintenance that can provide valuable information on the health of the insulation system and allow to determine accurately the location of the risky insulation elements, which in turn will avoid any premature equipment’s deterioration by scheduling preventive maintenance action. After confirming in a previous published paper the efficiency of a new generation of piezoceramics sensors (high temperature ultrasonic transducers) to detect and characterize partial discharges, we are going to investigate, in this work, a second potential of this technology to locate the partial discharge sources by relying on its ability to detect acoustic signals emitted by partial discharge sources. We will present experimental results, demonstrating the effectiveness of these sensors to locate partial discharges sources and, we will also present an algorithm for calculating the partial discharge foci, based on the acoustic wave flight time.

Particularities of measuring partial discharges in stator windings insulation systems of high-voltage electrical machines

The purpose of the article is to provide potential tools that can make a significant contribution to the identification of partial discharges (PD). Different types of partial discharges occur in stator winding insulation and a few partial discharges may occur simultaneously. Internal partial discharges are electrical discharges that occur in voids in the insulation of the stator winding. In typical stator insulation systems that use epoxy bonded mica tapes, insulation degradation due to internal partial discharges is usually slow (many years or decades). External partial discharges (slot PD and surface PD in the end-winding) are more dangerous and lead to the destruction of the insulation in a short time (several months or years). Therefore, the identification of insulation defects is essential. The analysis of existing methods for identification of defects in the insulation of high-voltage electrical machines using the results of measuring the partial discharges characteristics is carried out. The advantages and disadvantages of each of the groups of identification methods are characterized. It is shown that among the models of knowledge representation in solving problems of diagnostics of insulation systems for high-voltage electrical machines, identification methods, including field tests using training samples, are among the most suitable ones. It is noted that detection of insulation defects and their identification cannot be carried out only by direct measurements of PD characteristics and other dielectric parameters (electrical resistance, dielectric loss, polarization index). For this, special computing programs based on pattern recognition methods should be used. Results are presented of identification of technological defects in the insulation of the stator winding at the stage of factory testing, obtained using the PD identification method developed by the authors

Capacitor Voltage Ripple Estimation and Optimal Sizing of Modular Multi-Level Converters for Variable-Speed Drives

This work deals with the sizing of submodule capacitors for modular multilevel converters (MMCs) used for variable speed drives for medium voltage and high voltage electric machines. Variable speed drives are required to run over a wide frequency range from zero to a few hundred Hz or even over 1 kHz. Under low frequency operation (<30 Hz), a large current ripple flowing through the MMC submodule capacitors will cause significant capacitor voltage fluctuation. This article proposes an optimal submodule capacitor selection method based on the common-mode voltage injection. The proposed sizing model includes two functions: 1) accurately estimating the capacitor voltage ripple based on the drive system parameters; and 2) identifying the minimum capacitance of the submodule capacitors based on the allowed maximum capacitor voltage fluctuations. Simulation and experimental results show that the error between the actual and estimated values of the voltage fluctuation is within 3% using the proposed model.

THE METHOD OF CONTINUOUS AUTOMATED RESISTANCE CONTROL OF HIGH VOLTAGE MOTOR INSULATION

Electrical machines are widely used in various branches of the national economy. In particular, electric motors are one of the main elements in electrical power generation systems. The electric machines used at this ensure reliable operation of individual power units and the entire power supply system in general. The reliability of engines’ operation is largely determined by the quality of its insulation, that is why the improvement of methods for controlling the isolation of high voltage asynchronous motors is an actual task.&#x0D; The aim of the research is to develop a method of continuous automated control of electric insulation condition in stator windings of an asynchronous motor basing on the analysis of experimental and industrial operation data making it possible to estimate the dynamics of changes in the main insulation parameters.&#x0D; The main elements showing reliability of high-voltage electric machines, applied electro-insulation structures, methods for controlling insulation resistance in a high-voltage electric motor are considered in the article. The research performed was based on the results of the experimental and industrial operation of the automated system of insulation control under working voltage at the real facility carried out by the group of companies «Energopribor» of the town of Cheboksary.&#x0D; The analysis of existing methods for insulation control is given, the scheme of insulation control by superpositioning test current with the frequency which is different from industrial one. The authors propose the method to estimate the dynamics of resistance changes in insulation of stator windings of the asynchronous motor, to reveal its approximation to the maximum permissible state in the process of operation and in reserve shutdown. Software modeling was carried out, the results of which correspond to the data of experimental and industrial operation.&#x0D; The results obtained during the research allowed to systematize the obtained experimental data, to modernize the hardware part of the diagnostic complex DUKAT-SCAD, to outline the criteria area for its applicability.

Study on the Measurement of Volt Ampere Characteristics of Silicon Carbide Stress Grading Materials

In order to optimize the design of the stress grading structure for the end-windings of high voltage (HV) electric machines, a suitable and convenient method for accurate measurement of Volt ampere characteristics became significant. In this paper, the volt ampere characteristics of the Stress grading coating (SGC) before and after impregnation were studied. The experiment found that the resistivity of SGC after the immersion paint was significantly improved. There were two orders of magnitude differences in resistivity before and after impregnation. For the sake of obtaining more accurate volt ampere characteristics of SGC after impregnation, a new method of pre electrode was proposed for the first time in this paper. The results showed that the current obtained by the method with pre electrode was larger and more accurate.

Artificial neural network based technique for energy management prediction

&lt;p&gt;The energy management of electrical machine is significant to ensure efficient power consumption. Mismanagement of energy consumption could give impact on low efficiency of energy consumption that leads to power wastage. This paper presents analysis of power consumption and electricity costing of the electrical machineries and equipment in High Voltage (HV) and Electrical Machine (EM) Laboratories at Faculty of Electrical Engineering (FKE), Universiti Teknologi MARA (UiTM) Shah Alam, Selangor, Malaysia. The electrical data are collected using Fluke Meter 1750. Based on the analysis, it is found that the estimated annually electricity cost for HV Laboratory and EM Laboratory are RM 392.00 and RM 3197.76 respectively. For prediction of energy consumption of the two laboratories, Artificial Neural Network (ANN) algorithm is applied as computational tool using feedforward network type. The results show that the ANN is successfully modelled to predict the energy consumption.&lt;/p&gt;

EFFICIENCY OF APPLICATION OF SEMICONDUCTIVE COATINGS FOR REGULATION OF ELECTRIC FIELD IN HIGH-VOLTAGE INSULATION OF ELECTRIC MACHINES

Introduction. Intensification of competition and the desire to reduce the cost of high-voltage electric machines due to a significant increase in the electrical and thermal loads of the electrical insulation system complicate the operation of anti-corona coatings on the insulation surface of the stator winding and increase the intensity of discharge processes, which significantly reduce the life of the insulation in case of failure of the coatings. Purpose. The analysis of the efficiency of alignment of the electric field along the insulation surface of the stator winding of high-voltage electric machines with semiconductor anti-corona coatings. Methodology. A method for calculating the electric potential distribution along the surface of the winding insulation during the use of semiconductive coatings providing alignment decrease the electric field and eliminating the appearance of moving discharges. The reliability of the calculations is confirmed by experimental studies of the potential distribution over the surface of the anti-corona semiconducting non-linear coating along the frontal part of the samples of the rod of the hydrogenerator for a linear voltage of 20 kV. Practical value. The proposed methodology for calculating the distribution of the electric field over the surface of the insulation and the anti-corona semiconductive coating can be applied to justify the length of the coating in the frontal part of high-voltage electrical machines depending on the electrophysical characteristics of the coating, electrical insulation, and thickness. The results of an experimental verification of the stability of the nonlinear properties of coatings during prolonged electrical and thermal aging of specially made coating samples are presented.

Применение метода контроля частичных разрядов в изоляции статоров высоковольтных электрических машин

Применение метода контроля частичных разрядов в изоляции статоров высоковольтных электрических машин

Suppression of an Electric Field and a Local Heat Generation With the Equivalent Circuit of Stator Coil End of an Inverter-Fed High-Voltage Electrical Machine

We have been developing the insulation design techniques based on an equivalent circuit to predict the voltage distribution of the stator coil end of high-voltage inverter-fed electrical machines. A new equivalent circuit was proposed by an additional modeling of cover insulation, the corona protection shield, and the measurement circuits to the conventional equivalent circuit for mains-fed electrical machines. The applicability of our proposed equivalent circuit was verified experimentally and it was confirmed that simulation results of voltage distribution agreed with experiment results with uncertainty of less than 10%. Furthermore, in order to suppress the insulation degradation caused by inverter surge, sensitive parameters to reduce electric field concentration and local heat generation were explored. The capacitance of insulation layer affects both electric field and local heat generation, and those effects are reduced by 17% and 9% by halving the capacitance.

Choosing Expert Evaluations of Diagnostic Tests of Electric Insulation for High-Voltage Electric Machines

This article provides the results of studying the influence of test voltage frequency on the dynamic parameters (dielectric losses and characteristics of partial discharges) of micaceous insulation of stator winding for high-voltage (HV) electric machines. The tests have been conducted using mockup samples of stator insulation with an artificial defect in the front area. It has been established that the low-frequency (0.1 Hz) test voltage increases the dielectric loss tangent and, at the same time, reduces the peak apparent charge of external partial discharges compared to the tests at power frequencies. The established ratios must be taken into account when choosing expert diagnostic evaluations during high-voltage electric-machine tests.

Vibration of high-voltage electric machines with rotors on rolling bearings

The paper presents an investigation of vibrational activity of electric machines due to high-harmonic vibrational loadings. It is shown that the vibrational loadings experienced by bearings may result in the interruption of their normal operation and even take them out of action. Therefore, the values of the vibrational speed-up leading to high harmonics are factors determining the admissible dynamic loading on the bearings. In the paper, an attempt is made to consider the factors which result in origination of high harmonics and to illustrate methods for their smoothing.

Low-Pass Filter for HV Partial Discharge Testing.

The most common cause of high voltage electric machine malfunction is an electrical failure of the insulation system due to extreme partial discharges activity. The paper discusses the methodology for the construction of a low-pass high voltage filter for partial discharge measurement. It focuses mainly on the shape optimization, using an analytical approach with subsequent verification using the finite element method. The experimental verification is given together with important conclusions.

Fiber Bragg Grating Sensor for Electric Field Measurement in the End Windings of High-Voltage Electric Machines

This paper reports proof-of-principle of an optical fiber Bragg grating (FBG) operating as an electric field sensor. The system is based on a semiconductor diode laser, emitting around 1577.5 nm that interrogates the fiber sensor around its maximum reflectivity point. The application of a strong electric field causes a small variation of the optical path length of the waveguide due to electrostriction and thus perturbs the grating peak reflectivity wavelength. Calibration and dynamic range tests are performed using a parallel-plate capacitor to create a variable electric field (1–100 kV/cm). A great potential is pointed out in view of possible field applications for voltage graduation in power generators.

Influence of ambient and test conditions on insulation resistance/polarization index in hv electrical machines - a survey

Ambient and test conditions can affect the analysis results of the insulation system testing in high voltage (HV) electrical machines. In this context, insulation resistance (IR) and polarization index (PI) are two common techniques for winding insulation assessment in offline mode. This paper investigates the influence of main parameters that affects IR/PI tests results. Temperature, humidity, and pressure are the wellknown environmental parameters which could affect dielectric parameters of insulation such as IR and PI. On the other side, test voltage level and voltage polarities connections are two prominent factors in sampling the resistance during the test. Moreover, the insulation resistance value depends on the type of fault and its severity. The variations of insulation resistance with considering the mentioned parameters are evaluated in this paper, to study the possible correlation between IR/PI and changes in other parameters. It was found that with taking the effective parameters into account, the accurate and reliable insulation test interpretation can be achieved in HV electrical machines. A comprehensive review of literature was done and industry experts were surveyed for their ideas and experience under a research project. The main results are summarized in this paper.

An analysis of the influence of microclimate on partial discharge activity in emissions of electric machines in the conditions of industrial operation – own research

Abstract The article presents the results of diagnostic measurements of partial discharge signal propagation from the winding insulation in electrical machinery, which were performed using an on-line method. This paper describes the results of experiments and the acquired experience in the monitoring of winding insulation in high power and high voltage electrical machines which are important in industrial production processes. The authors show the measurement techniques employed in their research. Representative measurement results are presented along with their analysis. The authors use an SKF monitoring systems to measure: vibrations, temperature, and humidity, as major factors affecting partial discharge activity in the from winding insulation of electrical machines.

Analysis of Inter-Turn Insulation of High Voltage Electrical Machine by Using Multi-Conductor Transmission Line Model

In this paper, the inter-turn insulation of stator winding is comprehensively discussed. An equivalent circuit model and a multi-conductor transmission line (MTL) theory are established for the inter-turn voltage evaluation under the switching-impulse voltage, respectively. The distributed inductances are calculated by using small-signal analysis in finite element method (FEM) and the ac resistances of coils are analyzed considering the skin effect. The distributed capacitances of the coils are determined by using both electric field FEM and analytic equations. The electric potential distribution of inter-turn is calculated by the above two methods. The incident and reflect voltages are calculated by using the MTL model. The electric field of inter-turn calculated by using the FEM is presented. The FEM is used for the calculation of the inter-turn electric field distribution. The position where the inter-turn insulation may be more prone to breakdown is determined according to the result. Finally, the impact factors of inter-turn insulation including insulation materials and positions of failure in winding are analyzed in detail.