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The source-to-wheel efficiency of today's electrified vehicles already far surpasses the efficiency of strictly gasoline vehicles. As sources of electricity become cleaner and more efficient, and as gasoline becomes more scarce, the need for transporation electrification is increasingly economically and environmentally driven. The automotive industry primarily makes use of permanent magnet synchronous machines (PMSMs) and induction machines (IMs), the latter has the cost advantage of containing no rare earth metals. This thesis studies two different induction motors for electrified powertrain applications using a novel optimization algorithm to create efficiency maps and compare the efficiencies of the two motors. Induction motors are difficult to banchmark due to their complicated control schemes. Each point in their operating range can be achieved with an infinite number of current/slip combinations and therefore has infinite potential efficiencies. The proposed algorithm limits the number of simulations needed to benchmark an induction machine, and provides a clear and unbiased way to compare machines based on losses at their most efficient current/slip combinations over their entire operating range. The proposed algorithm is able to calculate losses within 5% error of simulation values for both machines. The first motor studied makes use of stranded windings and geometry parameters from the Tesla Motors patents. The efficiency map created has a peak efficiency of 96% and corresponds closely to an efficiency map for a similar motor found in literature. The second motor makes use of copper bar windings, which are easier to manufacture and have lower material costs. Bar windings, typically have lower resistance and stator copper losses at low speeds, but higher effective resistance and stator losses at high speeds due to eddy effects. The motor modelled was intended simply to compare the stranded and bar windings, and to see the advantages and disadvantages. For this reason, no other changes are made to the winding layout or motor geometry, including changes that would reduce the eddy effect. The resultant efficiency map has a peak efficiency of only 90%, performing worse than the stranded wound motor across most of its operating range. At very low speeds, under 1000 rpm, the efficiency of the bar wound machine is better than that of the stranded machine. The bar wound machine also has the advantage of being over 80\% efficient everywhere. The author suggests that future research focus on applying the proposed benchmarking algorithm to stator bar motors designed to limit eddy effects. Strategies include changing the slot opening shape, increasing the number of stator bars, and moving the stator bars away from the air gap. / Thesis / Master of Applied Science (MASc)

The ideal squirrel cage motor should have a varying rotor resistance; large at standstill, and decreasing as the speed rises. Overseas - designed high impedance rotors try to fulfil these conditions - mostly used are double cage rotors and die cast aluminium rotors. However, in the South African coal-mining industry these rotors recorded high rate failures with heavy financial losses. As a result, the need for an alternative rotor type that was able to comply with basic conditions ignored before appeared on the market: • Higher reliability with extended life expectancy • Lower total ownership costs • Easy re-manufacturing with components available on the market • Specific performance stability at competitive price. Over the years, only two principles were tacitly accepted in designing squirrel cage rotors: 1. For a single cage rotor, in a circumferential direction around the rotor the squirrel cage bars are placed in the same cylindrical shell, with the same shape and same conductivity. 2. For a double cage rotor, the same rule as above applies; however, in the radial direction, the bars have different shapes and typically different conductivities. The Invention is based on a new principle, i.e. "in a circumferential direction around the squirrel cage rotor, squirrel cage bars may have different conductivities and same shapes, or different conductivities and different shapes”. Mixed Conductivity Fabricated Rotors (MCFR) are designed and manufactured based on this new principle, and are able to withstand the harsh South African mining conditions. Since patented, the invention has been materialised in a set of special rotors powering continuous miners of a reputable coal-mining house, which was spending about R5 million annually on replacing specific imported die cast aluminium rotors only. Fully complying with the above-mentioned basic conditions, the patent offers a large variety of technical and economical advantages, increasing mining processes efficiency beyond expectations. The thesis describes the MCFR's design adaptability by altering the rotor design to meet the demands of a specific engineering application as a base line of drives design. The patent is part of the new South African trend of increasing processes efficiency. It offers large possibilities of designing dedicated motors with a positive impact on the South African economy. Some socio-economical advantages are worthy of considerable study: • Being locally manufactured, the MCFR may reduce the country's economical dependence. • Requiring no special expertise, the MCFR can be produced in any quantity and size without excessive investment. • The MCFR offers an alternative option (product interchangeability) on the market as well as sound competition (with export potential). • The patent ensures business sustainability conditions which diffuse financial constraints on motor manufacturers and end-users during the re-capitalisation process (very loaded in South African economic and industrial environment). / Thesis (Ph.D. (Electrical Engineering))--North-West University, Potchefstroom Campus, 2007.

Student Number : 0004041J - MSc dissertation - School of Electrical and Information Engineering - Faculty of Engineering / Slip energy recovery (SER) drives are used extensively in industry as they offer cost effective speed control of large wound rotor induction motors. The biggest disadvantage associated with the use of SER drives is the vulnerability of the rotor circuit converters to power system disturbances such as voltage dips. The failure of converters as a result of voltage dips is a problem associated with the use of these particular drives. The aim of this research is to better understand the stresses on rotor circuit converters as a result of voltage dips at the terminals of the motor. The rotor transients developed by a wound rotor induction motor are investigated for a range of three phase and single phase voltage dips. Simulations conducted in the Alternative Transients Program (ATP) supplement measurements conducted on a simplified SER circuit. The results confirm that voltage dips cause significant stresses on the converters in the rotor circuit. Good correlation was obtained between simulated and measured results. This work allows for a better understanding of the response of wound rotor induction motors to voltage dips and identifies the threat that voltage dips impose on the SER rotor circuit converters.

Thesis (Ph.D. (Electrical Engineering))--North-West University, Potchefstroom Campus, 2007.

Accurate assessment of the electromagnetic excitation forces and the vibration behaviour of stators is essential to arrive at a suitable design for quiet operation of an electrical machine. These electromagnetic forces are produced on the surfaces of the stator and rotor along the air-gap periphery. The physical mechanisms underlying the production of the electromagnetic forces, and the characteristics of the ensuing vibrations are described in this thesis. <p>In this thesis, comprehensive analytical methods are developed for the determination of the radial electromagnetic forces in squirrel-cage and wound-rotor induction machines. Various magnetic fields are generated due to the distribution of the windings in slots, the slotting of the stator and rotor surfaces, and the magnetic saturation of the iron. The air-gap fields are determined using the permeance method by expressing the MMF and the air-gap permeance as waves. <p>In the analyses, the mutual interactions between the stator and rotor are incorporated. Asthe load increases, these interactions become prominent and influence significantly the nature of the air-gap field. Their effects on the electromagnetic forces are discussed from the perspective of the production of vibrations. Extensive investigations were conducted on a 7.5 kW squirrel-cage induction motor and a 70 kW wound-rotor induction motor to verify the validity of the analyses. The comparisons made between the experimental and the analytical results prove the general validity of the analytical methods. <p>Conclusions are drawn with a view to determine the actual role played by the harmonic air-gap fields on the production of the electromagnetic forces and the ensuing vibrations. In the course of these investigations, an experimental set-up which is particularly suited for the measurement of magnetic fields, magnetic forces, resonant frequencies, vibrations and noise was developed. A fundamental study on the vibration behaviour of electrical machine stators using an experimental modal-analysis is presented in the thesis. Modal-analysis is a process of forcing a structure to vibrate predominantly at a selected resonance. In order to achieve this, distributed electromagnetic forces are used.<p>Detailed investigations were conducted on the stator models of a 120 hp induction motor to study their vibration behaviour, and to critically examine the damping present in them. The physical interpretations of the results given in the thesis would help in acquiring a better understanding of the vibration behaviour of stators in relation to the problem of electromagnetic acoustic noise in electrical machines. This work was supported by the National Sciences and Engineering Research Council of Canada through grant no. OGP0004324.

Recent research has demonstrated the use of electrical signature analysis (ESA), that is, the use of induction motor currents and voltages, for early detection of motor faults in the form of embedded algorithms. In the event of multiple motors energized by a common voltage bus, the cost of installing and maintaining fault monitoring and detection devices on each motor may be avoided, by using bus level aggregate electrical measurements to assess the health of the entire population of motors. In this research an approach for detecting commonly encountered induction motor mechanical faults from bus level aggregate electrical measurements is investigated. A mechanical fault indicator is computed processing the raw electrical measurements through a series of signal processing algorithms. Inference of an incipient fault is made by the percentage relative change of the fault indicator from the “healthy” baseline, thus defining a Fault Indicator Change (FIC). To investigate the posed research problem, healthy and faulty motors with broken rotor bar faults are simulated using a detailed transient motor model. The FIC based on aggregate electrical measurements is studied through simulations of different motor banks containing the same faulty motor. The degradation in the FIC when using aggregate measurements, as compared to using individual motor measurements, is investigated. For a given motor bank configuration, the variation in FIC with increasing number of faulty motors is also studied. In addition to simulation studies experimental results from a two-motor setup are analyzed. The FIC and degradation in the FIC in the case of load eccentricity fault, and a combination of shaft looseness and bearing damage is studied through staged fault experiments in the laboratory setup. In this research, the viability of using bus level aggregate electrical measurements for detecting incipient faults in motors energized by a common voltage bus is demonstrated. The proposed approach is limited in that as the power rating fraction of faulty motors to healthy motors in a given configuration decreases, it becomes far more difficult to detect the presence of incipient faults at very early stages.

The ideal squirrel cage motor should have a varying rotor resistance; large at standstill, and decreasing as the speed rises. Overseas - designed high impedance rotors try to fulfil these conditions - mostly used are double cage rotors and die cast aluminium rotors. However, in the South African coal-mining industry these rotors recorded high rate failures with heavy financial losses. As a result, the need for an alternative rotor type that was able to comply with basic conditions ignored before appeared on the market: • Higher reliability with extended life expectancy • Lower total ownership costs • Easy re-manufacturing with components available on the market • Specific performance stability at competitive price. Over the years, only two principles were tacitly accepted in designing squirrel cage rotors: 1. For a single cage rotor, in a circumferential direction around the rotor the squirrel cage bars are placed in the same cylindrical shell, with the same shape and same conductivity. 2. For a double cage rotor, the same rule as above applies; however, in the radial direction, the bars have different shapes and typically different conductivities. The Invention is based on a new principle, i.e. "in a circumferential direction around the squirrel cage rotor, squirrel cage bars may have different conductivities and same shapes, or different conductivities and different shapes”. Mixed Conductivity Fabricated Rotors (MCFR) are designed and manufactured based on this new principle, and are able to withstand the harsh South African mining conditions. Since patented, the invention has been materialised in a set of special rotors powering continuous miners of a reputable coal-mining house, which was spending about R5 million annually on replacing specific imported die cast aluminium rotors only. Fully complying with the above-mentioned basic conditions, the patent offers a large variety of technical and economical advantages, increasing mining processes efficiency beyond expectations. The thesis describes the MCFR's design adaptability by altering the rotor design to meet the demands of a specific engineering application as a base line of drives design. The patent is part of the new South African trend of increasing processes efficiency. It offers large possibilities of designing dedicated motors with a positive impact on the South African economy. Some socio-economical advantages are worthy of considerable study: • Being locally manufactured, the MCFR may reduce the country's economical dependence. • Requiring no special expertise, the MCFR can be produced in any quantity and size without excessive investment. • The MCFR offers an alternative option (product interchangeability) on the market as well as sound competition (with export potential). • The patent ensures business sustainability conditions which diffuse financial constraints on motor manufacturers and end-users during the re-capitalisation process (very loaded in South African economic and industrial environment). / Thesis (Ph.D. (Electrical Engineering))--North-West University, Potchefstroom Campus, 2007.