Insulation Of Electrical Machines Research Articles

Effect of Environmental and Operating Conditions on Partial Discharge Activity in Electrical Machine Insulation: A Comprehensive Review

Electrical machines for transportation applications are subjected to harsh environmental conditions during their operations. Partial discharge (PD), which is one of the main reasons for insulation failure, is greatly affected by ambient conditions (i.e., temperature, pressure, and humidity). Countless efforts are made for a comprehensive understanding of the physics of PD under variable environmental factors. This paper aims to review recent works addressing temperature, pressure, and humidity impact on PD activity. The main content of the paper is organized into three sections dealing with each environmental factor. In every section, relevant publications are reviewed considering the type of samples tested, voltage waveform applied, mutual effects, and the most common PD modeling strategies used. The applicability of the PD measurements for PD risk assessment is also discussed. Based on the review, the current progress in understanding the environmental effects on the PD inception mechanism and PD characteristics is presented and discussed in detail, and future research trends in this field are outlined.

Effect of the repetition frequency and polarity of square wave voltage on the partial discharge of electric machine insulation for more electrical aircraft

Effect of the repetition frequency and polarity of square wave voltage on the partial discharge of electric machine insulation for more electrical aircraft

Исследование существующих методов сушки увлажненной изоляции тяговых электродвигателей локомотива

Objective: consider the issue of increasing the reliability of electric locomotive traction motors, which depends on various factors. This article examines the factor of the impact of climate conditions on the operation of a locomotive. All attention is paid to the relevance of research into methods for drying the insulation of traction motors at the present time. It has been proven over many years of work that the most vulnerable part of the engine is insulation. All methods that are aimed at solving the assigned problems are listed. The article describes the principle of operation and technology of processes in each of these methods. From the proposed methods, efficiency indicators are derived from the perspective of technical and economic results, and some of their advantages and disadvantages are also noted. The article is based on a comparison of various methods that are aimed at solving current problems associated with increasing the reliability of traction rolling stock. Statistics on traction motor failures over the past three years are presented, and the reasons for moisture in the insulation of electric locomotive power equipment are described. The main methods and methods for drying moistened insulation used in VSZhD locomotive depots are listed, and the characteristics of each method are given. Methods: the method of statistical data and analytical review of the current state of the process of drying the insulation of traction rolling stock was applied. Results: the article lists the studies, experiments and results that evaluate the existing methods and methods of insulation drying processes on rolling stock. An updated method of three-cycle drying of moistened insulation of electrical machines has been developed, which is based on the use of electric heating units and provides for oscillatory energy supply. The task has been set to solve the optimal methods for removing moisture from the insulation of traction motors of electric locomotives based on the use of the convective method. Practical importance: based on the conducted research, the possibility of using the proposed three-cycle method for drying moistened insulation of electrical machines has been confirmed, which allows reducing energy costs for repairs and the time of the insulation drying process.

Derivation of Ambient Enhancement Factors of Impregnated Twisted Pairs for Partial Discharge Risk Evaluation

Partial discharge (PD) is the main issue challenging the electrical machine (EM) insulation system for more electric aircraft (MEA) applications. Indeed, the trend of adopting higher DC link voltage and fast switching device further boost the risk of PD. Partial discharge inception voltage (PDIV) is mostly dominated by ambient conditions (i.e., temperature, pressure, and humidity), and their influence is accounted for through experimentally determined ambient enhancement factors. For non-impregnated windings, ambient enhancement factors are suggested by both IEC 60034-18-41 and recent literature. However, in many applications, EMs’ windings are often impregnated with resin to improve thermal performance, mechanical resistance, and electrical insulation. In this case, no indications of the enhancement factors for PD risk assessment are given. The ambient enhancement factors are experimentally determined in this paper to enable the PD risk evaluation for impregnated windings. These factors are obtained relying on an extensive PD investigation, where PDIV and partial discharge extinction voltage are measured under variable temperature, pressure, and humidity conditions. Finally, the tests are performed on different wire types and motorette samples to validate the applicability of the derived factors.

Combined Effect of Short Rise Time and Relative Humidity on the Partial Discharge Inception Mechanism in Rotating Electrical Machines Insulation

Combined Effect of Short Rise Time and Relative Humidity on the Partial Discharge Inception Mechanism in Rotating Electrical Machines Insulation

Исследование усталостного старения изоляции тяговых электродвигателей тепловозов при циклической нагрузке

Purpose: To analyze the processes of fatigue aging of the insulation of traction electric machines of locomotives under cyclic loads in operation. Methods: When solving typical problems of fatigue strength of insulating materials of electric locomotives, periodic loading cycles are used in the study. Results: The analysis of the processes of fatigue aging of insulation materials of electrical machines shows that the main parameters that increase the intensity of aging are the frequency and amplitude of the heating cycle. Thermomechanical stresses increase with rise of heating speed and temperature amplitude. Practical significance: Determination of the fatigue characteristics of the insulation material is very important when modeling its damage, which will increase the reliability of electric machines of modern locomotives at the stages of design, manufacture, modernization and operation.

Improved Modelling of PDIV Evolution Over Time Under Multiple Ageing Factors for Insulation of Inverter-Fed Electrical Machines

This article describes research to model PDIV evolution under multi-factor stressing of the insulation system of an electrical machine. An attempt is made to establish whether a change of PDIV could be used to predict remaining life. Twisted pairs are used as samples of electrical motor insulation. They undergo accelerated ageing by exposure to high temperatures and the constant influence of inverter-style square-wave voltage. The ageing process lasts between weeks and months during which PDIV is measured periodically. The dedicated method of PDIV measurement with inverter-style voltage is presented. The evolution of PDIV is successfully modelled using an Inverse Power Model – observation and modelling of PDIV evolution is a novelty in the field. The ageing tests are performed according to the Design of Experiment method. The evolution of the parameters of the model at different factor levels can be extrapolated from the model obtained.

Design of a multilink system for calculating high-frequency processes in electric machines with mesh windings

This study considers the design of a multi-link high-frequency circuit for calculating defective and defect-free insulation of mesh windings in order to increase the operational reliability of general-purpose electric machines. The object of research is mesh windings of electric machines. The problem to be solved: increasing the operational reliability of electric machines with general-purpose mesh windings by analyzing and modeling defects. The research results make it possible to model defects for the analysis of the state of insulation of electric machines with mesh windings. Special attention in the research was paid to induction motors with a worn-out resource, in particular, 4A80A4 UZ engine. The analysis includes phase-to-body capacitance, winding inductance, eddy current impedance, and winding impedance. Under the WN mode, a decrease in the impedance of the winding section from 3 % to the short-circuit mode was simulated; accordingly, the resonance frequencies for each case of 3 % were determined – 73990 Hz, short-circuit – 74450 Hz, as well as the corresponding input impedances 8938.7 and 8082.5. The corresponding voltage resonances and current resonances were also determined. Appropriate results were also given for the WG scheme. The results reported here relate to the design of the scheme and the research on the defects of the mesh winding. This contributes to the analysis of the state of insulation of mesh windings. The numerical data (resonant frequencies and input impedances) allow a better understanding of the behavior of windings in different states and degrees of defects. Given the research findings, it is possible to better identify and analyze potential defects in mesh windings, which in turn contributes to increasing the reliability of electric machines. The results of this study could be used in the field of diagnosis, service, and maintenance of electric machines with mesh windings

A review of silicon carbide MOSFETs in electrified vehicles: Application, challenges, and future development

AbstractCompared with silicon‐based Insulated Gate Bipolar Transistors (IGBTs), silicon carbide (SiC) Metal‐Oxide‐Semiconductor Field‐Effect Transistors (MOSFETs) are characterized by higher operating temperatures, switching speeds and switching frequencies, and are considered the next evolutionary step for future electric drives. The application of SiC MOSFETs in the field of electrified vehicles has brought many benefits, such as higher efficiency, higher power density, and simplified cooling system, and can be seen as an enabler for high‐power fast battery charging. This article reviews the benefits of SiC MOSFETs in different electrified vehicle (EV) application scenarios, including traction inverters, on‐board converters, and off‐board charging applications. However, replacing Si‐IGBTs with SiC MOSFETs introduces several new technical challenges, such as stronger electromagnetic interference (EMI), reliability issues, potential electric machine insulation failure due to high transient voltages, and cooling difficulties. Compared to mature silicon‐based semiconductor technologies, these challenges have so far hindered the widespread adoption of SiC MOSFETs in automotive applications. To fully exploit the advantages of SiC MOSFETs in automotive applications and enhance their reliability, this paper explores future technology developments in SiC MOSFET module packaging and driver design, as well as novel electric machine drive strategies with higher switching frequencies, and optimized high‐frequency machine design.

Development of insulation moisture level criteria as a result of technological progress in the maintenance system of oil-filled transformers

Transformers are critical elements of electrical networks and systems. The operational reliability of oil-filled transformers largely depends on the characteristics of the insulation, which is confirmed by the failure statistics. A number of factors affecting the insulation of electrical machines are identified, including excessive moisture, with its negative consequences outlined. The complexity and shortcomings of the use of traditional technologies for drying solid insulation are indicated, which focus on the search and implementation of the latest technologies in the system of maintenance and repair of transformers — automated insulation restoration systems (AIRS).Taking into account the development of technical progress in the field of service maintenance of transformers, the negative impact of moisture on the reliability, durability and overload capacity of electrical machines, especially those beyond their normal service life, a new look at the criteria for the moisture content of cellulose insulation is proposed. A review is made of the normative requirements for the moisture content of the insulation of oil-filled transformers of a number of Russian and foreign standards. On the basis of the Oommen equilibrium curves, the shortcomings of the lack of comparability of the humidity criteria for solid and liquid insulation in STO 34.01–23.1– 001–2017 and RD 34.45–51.300–97 are presented. It is proposed to single out several areas of the operational state of transformers in terms of “moisture content of solid insulation (paper)”. The optimal period for the use of AIRS has been determined.The AIRS technology is implemented in a TRANSEC module, which enables to carry out work under load, without adversely affecting predictive diagnostics. The design features of the TRANSEC module, the principle of operation, functional and design differences from standard transformer units – thermosiphon /adsorption filters — are outlined. The results of testing the TRANSEC technology in an existing electrical installation serviced by PJSC Rosseti are presented. Six months of trial operation of the TRANSEC module demonstrated the restoration of insulation characteristics on operating equipment without additional involvement of personnel. Besides, during the testing of the TRANSEC technology, the influence of oil temperature on the information content of the assessment of solid insulation parameters was confirmed. Proposals are formulated on the revision of industry documentation in the established part.

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.

Methods of Diagnosing the Insulation of Electric Machines Windings

The presented article concerns issues related to the diagnostics of the technical condition of the insulation of electrical machines. It discusses the importance of the operational supervision, maintenance and diagnostics of electrical machine insulation systems. The structure of the insulation system is presented and known solutions for making winding insulation are described. The negative impact of conditions and various exposures on the technical condition of the insulation system is described. Special attention is focused on the review of available diagnostic methods for insulating systems of electrical machines. These methods have been arranged in a systematic order according to the type of tests to be carried out.

Effects of Hydrothermal Aging on the Breakdown Voltage of Polyesterimide

Polymers have always played a big role in the insulation of electrical machines and have been the focus of several studies when they are subjected to different stresses. The humidity and temperature are the main constraints that degrade the insulating performance of the materials when they act together causing hydrothermal aging of the polymers. This study deals with the influence of hydrothermal aging on the breakdown voltage of polyesterimide which is known as one of the most important factors which define the electrical insulation performance of the polymer. The breakdown test was executed under AC and DC voltage. A statistical analysis of breakdown data was carried out using the two-parameter Weibull distribution. According to the findings, the breakdown voltage changes with aging time. Its rise is due to a polymer crosslinking by thermal action, causing a reduction of the mean-free path of charge carriers decreasing their mobility. The decline is attributed to the material plasticization after water penetration into the polymer matrix at the beginning of aging, which is a physical effect. Eventually, the chemical effect reflects the hydrolysis reaction, which destroys the hydrogenous links of the polymer. The breakdown voltage under the DC ramp is higher than that obtained under the AC ramp. The DC breakdown voltage depends on the polarity of the applied electrical field. The polymer degradation is characterized by a change in color and the crumbling of samples.

DIAGNOSIS OF INSULATION OF ELECTRIC MACHINES USING SWITCHING PROCESSES

Insulation of electric machines is the most vulnerable area in the reliability of operation and use of electric machines. Existing methods of insulation diagnostics do not provide quality testing of winding insulation of windings. The existing normative method provides for exceeding the rated voltage by only 30%, which can detect only multi-closed groups, so the pulse process is provided as a DC break that feeds the winding during testing and then analysis of the transient process indicating the level of defect and diagnostic system module, which can provide a system of planned and preventive repairs.

Thermomechanical voltages in the insulation of traction electric machines of locomotive

In recent years, the production of locomotives in our country has increased significantly. At the same time, a lot of efforts are made to increase the power, reliability and efficiency of their work. One of the key components of any locomotive is electric traction machines, which are usually designed to the limit in order to obtain maximum torque and power density in the limited space of the rolling stock. Previously, this problem was solved by increasing the electromagnetic properties of materials, thermal conductivity of insulating materials. However, this path has exhausted the possibilities for increasing the efficiency of traction electric machines. As the design of traction electric machines improves, their level of functionality, reliability and durability increases, electric traction systems become more relevant and important for reducing the cost of materials, maintenance and ensuring traffic safety. The insulation state of the windings of traction electric machines mainly determines their reliability and performance, affects the service life and the cost of maintenance. Therefore, when designing a traction electric machine, it is important to take into account all operational factors that determine the optimal service life of a locomotive. The article discusses the effect of thermomechanical stresses in the insulation of traction electric machines on their reliability and durability.

Numerical simulation of control process and operation stability predicting of traction motors

The article presents the results of numerical simulation of operation modes of AC traction electric motors and the diagnostic information processing in MATLAB Simulink. Predicting the stability of the electric traction motor of electric rolling stock in electric railway transport is an important practical task. Emergency operation of the traction motor can lead to a violation of the safety conditions of train traffic and serious injury-prone consequences. Most of the currently used diagnostic systems are developed on the basis of the use of the gammapercent aging resource of the insulation of electrical machines in accordance with the theory of probability. A significant disadvantage of using the elements of a traction motor as a predicted gamma-percent resource is that, as practice shows, the operating time of real elements of electric machines to the limit state is much higher. As a result, when using the strategy of maintenance and repair on the basis of operating time, using the theory of probability, leads to a significant underutilization of the individual resources inherent in them in the design and production of most products. To reliably predict the residual life of the traction motor elements, it is necessary to perform its complete technical diagnostics. The most reliable methods for diagnosing and predicting the individual residual resource of traction motor elements in operation are statistical methods based on an objective assessment of its technical condition at the current time. The measurement and computing technologies available today have made it possible to use many previously studied physical phenomena in traction motor diagnostics systems, as well as to search for new diagnostic parameters.

Autonomous tracking of partial discharge pattern evolution based on optical flow

Measurement of partial discharges (PD) is one of the key indicators of high voltage insulation integrity. They long term effect may lead to insulation deterioration and breakdown. This paper presents a novel technique for autonomous tracking of partial discharge image sequence evolution. The approach is based on motion detection utilizing optical flow algorithm. The goal of the presented research was to automate pattern analysis, leading towards intelligent PD diagnostics. Experiments have been performed on various classes of PD images representing monitoring sequence, partial discharges in stator bars representing electrical machine insulation, effect of harmonics and development of corona phases. Optical flow based detection was successfully applied to the sequence of PD images. Presented approach of autonomous tracking of partial discharge pattern evolution based on optical flow may be especially suitable for monitoring applications, however it can be also applied to off-line diagnostics. Motivation to apply motion analysis to a PD pattern is based on the conviction and direction of future autonomous AI-supported partial discharge diagnostic systems.

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

New device for the quality control of the high-voltage electrical insulator

During the operation of high-voltage electrical equipment, its insulation ages, its properties deteriorate, and the electrical strength decreases. To avoid sudden breakdowns of insulation and maintain the necessary level of reliability of high-voltage electrical equipment, the state of its insulation must be periodically monitored. The device described in the article is intended for preventive testing and diagnostics of heterogeneous high-voltage insulation of electric machines, power oil transformers and cables with paper-oil insulation. In particular, the integral assessment of high-voltage insulation aging, its humidification and remaining operational life can be based on the use of the absorption phenomenon (the accumulation of internal absorbed charge). Self-discharge and return voltage are measured to assess the insulation condition. A block diagram of the device for monitoring the electrical insulator quality is given as well as the formulae for determining the spent and remaining operational life of the tested insulation. The proposed device will increase the operational reliability of high-voltage electrical equipment.

Physical and electronic model of studying infrared radiator for drying wending insulation

During a long shutdown of the motors, the insulation quality of the windings of asynchronous motors deteriorates due to moisture. This requires additional costs for drying the insulation of electrical machines. The signs and possible causes of malfunctions of electrical machines, as well as methods of drying insulation, are studied: Drying by external heating, Drying by heating from an external source, Convective drying, Drying by induction loss, drying using light emitters. Drying using infrared radiation is the mildest method and helps to maintain the quality of the insulation. The movement of moisture in the layers of insulating windings occurs according to the laws of heat-mass exchange, that is, heat and moisture are simultaneously transferred. In this case, heat is transferred from more heated layers to less heated layers and at the same time promotes moisture transfer. A physical and electronic model was developed to study the effect of infrared radiation on the drying process of insulation of electrical machines. The main factors influencing the process under consideration are the power of the radiation sources and the supply voltage, that is, the temperature changes in the layers of the insulated windings were studied depending on the change in the power of the emitters and the supply voltage. The created model was investigated according to the main features corresponding to the real process (even the geometrical dimensions coincide). An indispensable condition for physical modeling is the strict geometric similarity of the model and nature, as well as the equality of the corresponding similarity criteria in them.