Detecting insulation defects in electrical machines’ multi-turn windings based on analysis of transient electromagnetic processes

PurposeThe thermal management of electrical insulations poses a challenge in electrical devices as electrical insulators are also thermal insulators. Diamond is the best solid electrical insulator and thermal conductor. This can lead to a paradigm change for electrical machine winding and lamination insulation design and thermal management. The paper introduces these techniques and discusses its effect for the design of electrical machines and its potential consequences for electromagnetic analysis, for example, in multi-physics modelling. The diamond winding insulation is patent-pending, but the diamond enriched lamination insulation is published for the benefit of the scientific community.Design/methodology/approachThe windings of electrical machines are insulated to avoid contact between the coil and other conductive components, for example, the stator core. The principle of using mica tape and resin impregnation has not changed for a century and is well established to produce main insulation on a complex conductor shape and size. These insulations have poor heat-conducting properties. Similarly, the insulation of laminated steel sheets comprising the stator and rotor restrict heat flow. Diamond-based insulation provides a new path. Increased thermal conductivity means reduced temperature rise and the reduced thermal time constants in multi-physics simulations and system analysis.FindingsThe largest benefit of a diamond-based core insulation is in electrical machines in which the losses are conducted axially to the coolant. These are machines with radial ducts and effective cooling in the end regions. The main benefit will be in reducing the number of radial ducts that positively affect the size, production costs and the copper losses of the machine. The increased thermal conductivity of the diamond insulation system will reduce the thermal constants noticeably. These will affect system behavior and the corresponding simulation methods.Originality/valueDiamond insulation can lead to a paradigm change for electrical machine winding and lamination insulation design and thermal management. It might also lead to new modeling requirements in system analysis.

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

In this paper, a method for detecting broken rotor bar and stator winding fault in a low voltage squirrel-case induction motor using an air-gap flux variation analysis is proposed to develop a simple and low cost diagnosis technique. To measure the leakage flux in radial direction, a radial flux sensor is designed as a search coil and installed between stator slots. The proposed method is able to identify two kinds of motor faults by calculating load condition of motors and monitoring abnormal signals those are related with motor faults. Experimental results obtained on 7.5kW three-phase squirrel-cage induction motors are discussed to verify the performance of the proposed method. Induction motors are widely used electrical machines, for their simplicity of construction and reliability. However, they are subject to failures those may be due to production processes or operating conditions. These unexpected failures cause severe damages in industrial processes. Motor reliability working group have announced that percentage failure in induction motors is typically: stator related (38%), rotor related (10%), bearing related (40%), and others (12%) (1). Recently, many researchers have studied diagnosis techniques to predict motor failures at their incipient stage and decide proper replacement time of induction motors. Most of them are focused on the failure prediction method using abnormal signals of failure patterns of motors from current and vibration signals (2)- (4). Although vibration and current analysis are the most powerful methods for diagnosing motor faults, their sensors are occasionally difficult to install where the environment of industrial field is in poor condition. In addition to this installation problem, there are many low priced low voltage induction motors in the field. Therefore, the diagnosis technique should be easy to install their sensors and low cost comparing to the price of motors. This paper proposes a method for detecting broken rotor bar and stator winding fault in a low voltage squirrel-cage induction motor using a radial flux sensor to develop a simple and low cost diagnosis technique. The sensor is designed as a search coil and installed between stator slots during motor production to measure the leakage flux in radial direction at the air-gap. The proposed method consists of a calculating load condition, finding abnormal signals and monitoring those signals related with motor faults to indentify two kinds of motor failures. To demonstrate the performance of the method, experimental results obtained on 7.5kW three-phase squirrel-cage induction motors are discussed.

Low-voltage induction motor is one of the most widely used types of electrical machines. Today more and more end users demand reliable and energy efficient electrical machines as an extra feature. Design and applying of control systems for improving energy efficiency must be in correlation with reliability requirements; it is necessary to fetch out the changing operation conditions that can lead to unexpected failures, and to prevent them. This paper describes the influence of insulation defectiveness on winding insulation system reliability in PWM based regulation applications. Currently, the influence of technological defects in the winding insulation on its reliable operation in motor being part of the variable frequency drive has not been thoroughly studied. The relevance of this research is determined by the need to study the “healing” of winding insulation through defects by the impregnation, and its influence on the mean time to failure. The study results will permit to give recommendations for improving the reliability of low voltage windings and subsequently the reliability of induction motors fed by PWM invertors. The study was carried out using a test technique adapted to variable frequency drives and applied to insulation system “varnish — enamelled winding wire”. The experimental results are presented and the main findings are discussed.

In normal operation, the thin turn (or interturn) insulation in windings of rotating machines experiences relatively small electrical stress. However, under certain conditions, e.g., switching operations, the turn insulation may experience very large electrical stress. The turn insulation, if weak, may fail under such conditions. Many of the groundwall failures in machines are suspected to have initiated from a turn insulation failure. Hipot tests are used to test the groundwall insulation. This often leads to suggestions that surges (with sub-microsecond rise time) should be used to test the turn insulation in machine windings. However, the detection of a turn insulation failure in a single coil in a tested complete winding is difficult. The consequent risks involved in surge testing of the turn insulation in a complete machine winding are emphasized and reiterated in this paper. Tests using both single surge generators and repetitive surge generators are illustrated.

The increasing of world population, forced human beings to produce clean energy, more creative solutions have been developed to use the energy with most efficient way. Researches on this topic still working today. Nowadays, new electrical machines are invented and the currently used ones are being continue to be improved. In industry, if a survey is made according to use of electric motors, it will be seen that, induction motors used in industry average eighty percent. When viewed from the efficiency and energy quality of the interconnected system, increasing efficiency of induction motors will provide advantages for the production, transmission, distribution systems and the network. On the other hand, Permanent Magnet Synchronous Motors (PMSMs) have not windings on rotor core and much more efficient than induction motors. In this way PMSMs will save the company from spending unnecessary energy. For this reason, in this study, an industrial conventional type squirrel cage induction motor (SCIM) has been converted into a permanent magnet synchronous motor (PMSM) for improve the overall efficiency. For improving the efficiency in design and production, induction motor’s stator core will not change. Only squirrel cage rotor core of induction motor will change with PMSM in rotor design production stage. As a result of this conversion, various electromechanical parameters have changed and improved. Electromechanical modification process has been provide better energy density and power density for this motor. As a result of the research, the cost of modification process will be amortized in usage. In this way, conventional type induction motor (IM) that dominates the vast majority of the industry is converted into PMSM, it is seen that energy efficiency and energy quality will increase.

PurposeThe purpose of this paper is to elaborate the method and algorithm for the analysis of electromagnetic and thermal transients in a squirrel cage induction motor.Design/methodology/approachThe paper presents the special software for transient finite element (FE) analysis of coupled electromagnetic‐thermal problems in a squirrel cage induction motor. The software has been prepared and is successfully applied in the design of special squirrel cage motors, e.g. the motors working in cryogenic conditions. A time‐stepping FE method and transients analysis of an induction motor has been applied. The nonlinearity of the magnetic circuit, the movement of the rotor and the skewed slots have been taken into account. The results of computations have been compared with measurements.FindingsThe method presented and the elaborated specialised software for FE analysis of electromagnetic and thermal transients are used to determine the dynamic performance of the squirrel‐cage induction motor. The results of simulations compared with measurements confirm the adequacy of this approach to the analysis of coupled electromagnetic‐thermal problems.Research limitations/implications3D effects have only been taken into account by quasi‐3D techniques (e.g. the multi‐slice for the skewed rotor slots).Practical implicationsThe software developed can be useful in the analysis and design of squirrel cage motor, especially motors working in cryogenic conditions.Originality/valueThe paper offers appropriate software for transient analysis of coupled electromagnetic and thermal problems in squirrel cage motors with skewed slots.

Since the insulation of windings in electric machines has comparatively low temperature limits, the problem of cooling these machines with the most economical use of material becomes one of major importance. The design of such machines from a temperature standpoint is usually based on tests of a previously made similar machine or else is of the ``cut arnd try'' type where such tests are not available. The predetermination of the operating temperature depends a great deal upon the rate at which the heat losses can be liberated from the ventilating surface to some cooling fluid such as air, which is considered in this paper. Some data are available regarding this rate of heat dissipation with forced air convection currents; a comparison of the various results published, however, shows them to be inconsistent. The purpose of this paper is to submit additional information that should be of value to the industry and that will also explain some of the inconsistencies in the past tests. Extensive experimental tests were made regarding the rate of surface heat transfer with air flows of various velocities for radial and axial ducts. The influence of shape, size, cross-section, condition of surface, mean temperature, and other factors were investigated. The most important factor found was that this rate of heat transfer was not constant along the air flow path but that its value varied from point to point along the duct.

Since the insulation of windings in electric machines has comparatively low temperature limits, the problem of cooling these machines with the most economical use of material becomes one of major importance. The design of such machines from a temperature standpoint is usually based on tests of a previously made similar machine or else is of the “cut-and-try” type where such tests are not available. The predetermination of the operating temperature depends a great deal upon the rate at which the heat losses can be liberated from the ventilating surface to some cooling fluid such as air, which is considered in this paper. Some data are available regarding this rate of heat dissipation with forced air convection currents; a comparison of the various results published, however, shows them to be inconsistent. The purpose of this paper is to submit additional information that should be of value to the industry and that will also explain some of the inconsistencies in the past tests.

Electric machines for civil aircraft must have high reliability. However, the harsh operating environment will challenge the machines' insulation system. For electric machines in aircraft, thermal aging is the main reason for insulation deterioration and result in the failure of the electrical machine. Partial discharge (PD) is an essential indicator in evaluating the insulation damage. This paper aims to clarify the PD characteristics of the machine winding before and after thermal aging for aircrafts. It firstly established a thermal aging platform and used a PD measurement circuit to study the behavior of the PD inception voltage (PDIV), phase-resolved PD (PRPD), and PD magnitude before and after thermal aging. The insulation capacitance (IC) of machine windings with different aging stages is also tested and compared with PD characteristics. Results show that thermal aging will decrease the PDIV of winding insulation and PD magnitude increases exponentially after thermal aging.

Detection of low-level electrical winding faults in Squirrel Cage Induction Motor (SCIM) is prime importance in Electric Vehicle (EVs). This analysis is carried out to predict flux distribution inside and outside of SCIM using Finite Element Analysis (FEA). In FEA, time domain analysis is performed to determine flux at the instant of fault with respect to time whereas steady state analysis will not give such a results. Flux distribution provides significant information about the behavior of SCIM. For analyzing the leakage flux in the surface vicinity of SCIM a 15kW machine is chosen. The analysis indicates magnetic flux distribution and ideal location of flux sensor. From FEM model, leakage flux on the surface of SCIM is captured and exported to MATLAB for health monitoring. Fuzzy rule base is developed for mapping the flux with health monitoring of SCIM used in Electric Vehicle (EV). Continuous health monitoring of the machine is captured by fuzzy controller and displayed in EV or vehicle monitoring centre.

The direct torque control strategy of squirrel-cage induction motor using three-level neutral point clamped inverter is presented. The strategy used for controlling the torque of induction motor includes the change in applied voltage to the squirrel-cage induction motor .The variable voltage is provided with the help of look up table to the inverter. It is observed that the torque ripples are much in three-level inverter as compared to three level ineverter. This is because of the high dv/dt ratio of the output voltage of inverter. The current ripple produces torque ripples in steady state. The performance of motor in transient state and steady state are shown. The parameters of machine are given and the controlling strategy is performed using MATLAB/Simulink software. The control strategy is simulated on a 5 hp SQIM drive with three-level insulated-gate bipolar transistor (IGBT) inverter in MATLAB/Simulink software.

EVs (Electric Vehicles) have been rejuvenated over the last decades while the motor drive technologies are still evolving. This paper provides a review of electrical motor drive technologies used in EV applications, with a performance comparison of candidate machines and their drive topologies. EV applications demand high efficiency, high torque density, high reliability, and wide speed range while reducing weight, complexity, total costs and environmental impact. In the literature, DC (Direct Current) motors, IMs (Induction Motors) and PM (Permanent Magnet) motors can be generally found in marketplace whilst RMs (Reluctance Motors) have been researched for some time and are nearing commercial availability. This paper evaluates the performance of these four main types of electrical motor drives for EV propulsion applications using analytical methods. PM motors may offer the best performance in terms of torque density and compactness but the cost is the highest (primarily dominated by rare-earth permanent magnets), limiting their widespread application in mass production EVs. DC motors have their own merits but suffer from limited power density and necessity for maintenance. Induction motor drives are a mature and proven technology. In particular, squirrel-cage IMs are robust, reliable and inexpensive, striking a balance between system cost and complexity, power density and extended speed range. Reluctance motors can provide a good torque density and cost effective EV drive solutions. Their drawbacks can also be overcome by the use of power electronic converters and advanced control strategies. Induction and reluctance motor drives are well suited for cost sensitive mass production EV applications. Looking to the future, increased hybridization may be a way forward in industry which combines attractive features of different electrical machines and control algorithms and still offer much promise in performance and total cost. At last, reliability study on EVs requires historical information and driving patterns, demanding research expertise in eco-sociology, human behaviors as well as human-machine interface.

This book is concerned with circuit simulation using National Instruments Multisim. It focuses on the use and comprehension of the working techniques for electrical and electronic circuit simulation. The first chapters are devoted to basic circuit analysis. It starts by describing in detail how to perform a DC analysis using only resistors and independent and controlled sources. Then, it introduces capacitors and inductors to make a transient analysis. In the case of transient analysis, it is possible to have an initial condition either in the capacitor voltage or in the inductor current, or both. Fourier analysis is discussed in the context of transient analysis. Next, we make a treatment of AC analysis to simulate the frequency response of a circuit. Then, we introduce diodes, transistors, and circuits composed by them and perform DC, transient, and AC analyses. The book ends with simulation of digital circuits. A practical approach is followed through the chapters, using step-by-step examples to introduce new Multisim circuit elements, tools, analyses, and virtual instruments for measurement. The examples are clearly commented and illustrated. The different tools available on Multisim are used when appropriate so readers learn which analyses are available to them. This is part of the learning outcomes that should result after each set of end-of-chapter exercises is worked out. Table of Contents: Introduction to Circuit Simulation / Resistive Circuits / Time Domain Analysis -- Transient Analysis / Frequency Domain Analysis -- AC Analysis / Semiconductor Devices / Digital Circuits

Due to topological changes in dual stator induction motor and high cost of its fabrication, it is convenient to replace the squirrel cage rotor with a composite sheet rotor. For an experimental machine, the inner and outer stator stampings are normally available whereas the procurement of rotor stampings is quite cumbersome and is not always cost effective. In this paper, the equivalence between sheet/solid rotor induction motor and squirrel cage induction motor has been investigated using layer theory of electrical machines, so as to enable one to utilize sheet/solid rotor in dual port experimental machines.