Ewen Ritchie

Comparative investigation of diagnostic media for induction motors: a case of rotor cage faults

Results of a comparative experimental investigation of various media for noninvasive diagnosis of rotor faults in induction motors are presented. Stator voltages and currents in an induction motor were measured, recorded, and employed for computation of the partial and total input powers and of the estimated torque. Waveforms of the current, partial powers p/sub AB/ and p/sub CB/, total power, and estimated torque were subsequently analyzed using the fast Fourier transform. Several rotor cage faults of increasing severity were studied with various load levels. The partial input power p/sub CB/ was observed to exhibit the highest sensitivity to rotor faults. This medium is also the most reliable, as it includes a multiplicity of fault-induced spectral components.

Condition monitoring of wind generators

This paper focuses on the experimental investigation for incipient fault detection and fault detection methods existing in the literature suitably adapted for use in wind generator systems using doubly fed induction generators (DFIGs). Three main experiments (one for stator phase unbalance, one for rotor phase unbalance and one for turn-to-turn faults) have been performed to study the electrical behaviour of the DFIG. The article aims to provide wind generators with further documentation for an advanced condition monitoring system, in order to avoid undesirable operating conditions and to detect and diagnose incipient electrical faults.

A dynamometer performing dynamical emulation of loads with nonlinear friction

A dynamometer capable of emulating linear, nonlinear and discontinuous loads for rotating systems is described. The controllable load is produced by a servo drive system. Applications for the dynamometer are steady state load tests and dynamical load tests with linear, nonlinear or discontinuous loads for testing of electrical machines in variable speed drive systems. The configuration of the dynamometer is presented, together with simulation models and simulation results. The simulated torque and speed time responses show that the dynamometer tracks the required torque with a high degree of accuracy, for both linear, nonlinear and discontinuous loads.

Design Considerations of Permanent Magnet Transverse Flux Machines

Permanent magnet transverse flux machine (PMTFM) is well known for its high torque density and is interested in various direct-drive applications. Due to its complicated 3-D flux components, design and design optimization of a PMTFM is more difficult and time consuming than for radial flux electrical machines. This paper addresses two important design considerations for PMTFM - the influence of permanent magnet leakage flux, which plays an important role in the determination of machine output torque, and the leakage inductance. A new simple method to provide a quick estimation of the armature leakage inductance is proposed, avoiding use of complicated 3-D equivalent reluctance network model to estimate the circumferential armature leakage flux component, and the pole face fringing flux component. Analysis results are supported by 2-D, and 3-D finite element (FE) analysis results, and measurement results on a prototype surface-mounted PMTFM.

Calorimetric measuring systems

This paper discusses the calorimetric measuring system. The calorimetric principle is one of the most promising methods for accurate power measurements. A calorimetric wattmeter provides a useful tool for use in the developments of new, energy-efficient, electrical components for industrial and consumer products. Power measurements can be performed with an accuracy of 0.2% of full-scale deflection using the proposed calorimetric measuring method.

Model of stator inter-turn short circuit fault in doubly-fed induction generators for wind turbine

The doubly fed induction generator (DFIG) is an important component of wind turbine systems. It is necessary to identify incipient faults quickly. This paper proposes a complete simulation model of DFIG in wind turbine about inter-turn short circuit fault at stator windings, which is based on multi-circuit theory. A detail analysis about simulation results is presented, especially about short circuit current. By analysis, the apparent 150 Hz, 450 Hz and current phase angle difference are taken as fault features and the fault phase also can be detected by phase angle difference. Both simulated results and experimental results of emulated inter-turn short circuit fault by paralleling a resistance with phase A are carried out. They verify the preceding analysis results. Moreover, their coincidence certificates this model is good and simulation results of inter-turn short circuit fault are correct.

Determination of mechanical resonances in induction motors by random modulation and acoustic measurement

Acoustic noise emission from PWM-VSI inverter driven induction motors is a well-known problem. The generated noise depends mainly on two factors: the harmonic content of the supply voltage waveform; and the mechanical resonance frequencies of the induction motor. It is necessary to know the mechanical resonances to optimize the switching scheme of the inverter to reduce the noise emission. Measuring the resonance frequencies is normally a laborious process. This paper introduces a new method for estimating the mechanical resonances from acoustic noise measurements. Employing random modulation of the output voltage of the inverter, the voltage spectrum can be spread over a wide frequency range. Using the spectrum analysis of the measured acoustic noise, the resonances can easily be estimated as the dominant frequencies of the acoustic noise spectrum. The method was tested on a 2.2 kW induction motor at no load and full load. Some of the mechanical resonances of the motor at no load were calculated by the Holzer method. The calculations showed good agreement with the sound measurements. The influence of the fan cowl was investigated and it is concluded that this is an important factor in the acoustic noise emission. Finally, it was observed that new mechanical resonances appeared when the induction motor was loaded by a pump drive system, and they were estimated by the measurement technique. >

Calorimetric measuring systems for characterizing high frequency power losses in power electronic components and systems

High frequency power losses in power electronic components and systems are very difficult to measure. The same applies to the efficiency of high-efficiency systems and components. An important method to measure losses with high accuracy is the calorimetric measuring system. This paper describes two different calorimetric measuring systems, one for power losses up to 50 W and one for power losses up to 1500 W. These differ in size and also the systems which can be analysed. The basic concept of calorimetry is discussed and the overall performance of the two systems is specified. Methods to calibrate such systems are proposed and different applications of the systems are given. Two practical examples end the description of the research. It is concluded that such systems have a relative long time-constant but they are accurate and useful for precise power loss measurement.

Preliminary comparison study of drive motor for electric vehicle application

With the development of electric vehicles, increasing attention is paid to the selection of motor type for a specific vehicle application. Candidate drives include induction, reluctance, permanent magnet and transverse flux motor types. Calculations for these four machine types have been done to suit EV applications. In this paper, an analytical method is employed to extend these calculation results to general cases. The transverse flux machine (TFM) is taken as the reference machine and compared with the other types of machines by describing the main differences between them. Thus, the main characteristics of each machine type may be compared. In the paper, the TFM provides the best power and torque density at low speed with high efficiency, and seems suitable for EV application.

New low cost structure for dual axis mount solar tracking system using adaptive solar sensor

A solar tracking system is designed to optimize the operation of solar energy receivers. The objective of this paper is proposing a new tracking system structure with two axis. The success strategy of this new project focuses on the economical analysis of solar energy. Therefore it is important to determine the most cost effective design, to consider the costs of production and maintenance, and operating. The proposed tracking system uses a new solar sensor position with an adaptive feature.