Stjepan Stipetic

Measurement of Excitation Winding Temperature on Synchronous Generator in Rotation Using Infrared Thermography

A new measurement method for infrared (IR) surface temperature measurement of excitation winding in rotation is presented. The method is experimentally verified on a 400-kVA salient pole synchronous generator. This method uses an industrial IR thermometer which represents an alternative to expensive fast IR thermometers or cameras. The target application of this method is the determination of the dynamic limit in the P-Q diagram of a synchronous generator due to excitation winding overheating. The measurement error model which shows the way how to minimize measurement error has also been derived. The effect of the interpolar surface can be cancelled if the IR thermometer is positioned at a certain angle with respect to the machines main axis. Digital temperature sensors have been mounted on the rotor to measure the excitation winding surface temperature for comparison.

Analytical Wideband Model of a Common-Mode Choke

This paper presents an analytical model of a common-mode choke suitable for accurate calculation of the choke impedance over a wide frequency range. The model consists of lumped parameters (resistances, inductances, and capacitances) related to individual turns of the coils wound on the core. It takes into account the mutual interactions between the turns and the core with respect to their inductive and capacitive links. The variation of the core permeability and losses with frequency up to 100 MHz is also included. The open-mode impedance characteristic calculated analytically for a VAC 6123x425 single-phase common-mode choke shows very good agreement with the 3-D finite-element model and the measured characteristic from 150 kHz up to 30 MHz, thus confirming the accuracy of the model over a wide frequency range.

Influence of winding design on thermal dynamics of permanent magnet traction motor

This paper presents summarized electromagnetic and thermal design of interior permanent magnet motor for a low-floor tram TMK 2200. Motor geometry is optimized for maximum torque density using differential evolution algorithm. The influences of winding configuration on power losses and thermal transients in the motor during one driving cycle of the tram have been analyzed. The results indicate that an optimal number of turns per slot and parallel paths can be found to yield minimum temperatures in various parts of the motor considering the intermittent character of the load.

Optimization in design of electric machines: Methodology and workflow

This paper presents an overview of methodology for usage of mathematical optimization procedures e.g. optimization algorithms to achieve optimal design of an electrical machine. A special care must be taken in order to handle parameter definition, boundary constraints, constraint functions, model feasibility and computationally expensive calculation such as finite element analysis. Variants of workflows using different approaches to optimization are presented.

Scaling laws for synchronous permanent magnet machines

This paper defines the scaling laws for synchronous permanent magnet machines which include three separate procedures: rewinding, axial scaling, radial scaling. The derivation of scaling relations is based on the requirement that the magnetic fields in the scaled model should be the exact images of the fields in the referent model. The exact equations for the various parameters (torque, power, losses, mass, resistance, inductance) of the machine are derived using the three scaling factors, one for each scaling procedure. The equations are numerically validated using the state-of-the-art finite-element software.

Small-Signal Calculation of Common-Mode Choke Characteristics Using Finite-Element Method

This paper presents a finite-element (FE) method approach to calculation of the common-mode choke (CMC) impedance over a wide frequency range. The proposed method involves a 3-D electrostatic FE calculation of each turn-to-turn and turn-to-core capacitance, and their usage as electric circuit lumped parameters in the 3-D time-harmonic magnetic FE calculation of the CMC impedance. It also takes into account the variation of the nanocrystalline core permeability and losses with frequency up to 100 MHz. The proposed methodology is used for calculation of the common-mode, open-mode, and differential-mode impedance characteristic for single-phase and three-phase CMC. Results are compared with measurements.

Centrifugal fan design for permanent magnet synchronous motor in a traction application

The requirements of high torque density and high efficiency, which are particularly pronounced in electric traction applications, often result in substantial thermal loading of electric machines for driving trams, electric multiple units (EMU) or electric cars. Permanent magnet synchronous machines are suitable candidates for traction applications due to their inherently high torque density and high efficiency. At the same time they are sensitive to temperature rise, especially in permanent magnets, highlighting the need for implementation of efficient cooling system. The performance of the cooling system and its ability to remove heat directly affect the attainable torque and efficiency of the electric machine. In this paper, the selection and sizing of the cooling system for an interior permanent magnet motor designed to drive a low-floor tram is presented. The procedure for selecting the basic dimensions of the centrifugal fan according to the analytical formulas in combination with computational fluid dynamics (CFD) analysis are explained. In addition to the geometry of the centrifugal fan itself, the geometry of the passive system components (e.g. air flow router) which have a significant impact on the performance of the cooling system, are also considered. The results of computer aided CFD analysis, which is taken as a benchmark of system performance in the design stage of the cooling system, have been confirmed with measurements on the machine prototype.

Calculation of efficiency maps using scalable saturated flux-linkage and loss model of a synchronous motor

This paper proposes the application of analytical scaling laws on existing saturated flux-linkage and loss models for synchronous permanent magnet and reluctance machines. This scalable model is used for fast and accurate calculation of efficiency/loss maps and can also be used for drive cycle analysis including energy consumption. The scalable model is verified by comparison with existing state-of-the-art efficiency map and drive cycle analysis software. The main usage of these rapidly scaled created efficiency maps is in optimisation of the motor size to meet given traction motor drive cycle performance and requirements.

Multi-objective optimization of electric vehicle powertrain using scalable saturated motor model

This paper presents a methodology for optimal sizing of the electric powertrain based on vehicle level objective functions. The design variables gear ratio, rated torque and rated speed of the motor are size dependant on the objective functions energy demand over a driving cycle, powertrain mass, and high speed gradeability. Multi-objective optimization handles these conflicting objective functions simultaneously and produces the Pareto-optimal solutions in both objective function and design variable domains. The novelty of the proposed approach is the utilization of analytical scalable saturated flux-linkage and loss motor model which is used for fast and accurate calculation of drive cycle energy consumption and motor mass. The concept is demonstrated on an example of in-wheel motor electric powertrain with four synchronous permanent magnet outer rotor machines.

The analysis of the infrared excitation winding surface temperature measurement on a synchronous hydro-generator in rotation

Excitation winding temperature is used for determination of the dynamic limit in the P-Q diagram of a synchronous generator. The surface temperature of an excitation winding can be measured by an infrared (IR) thermometer. Due to rotation, the IR thermometer absorbs thermal radiation from the excitation winding on the salient pole and from the interpolar space as well. These two surfaces can have different temperature or emissivity, which both affect the amount of the thermal radiation radiated towards the sensor of the IR thermometer. Irradiation read by the sensor is therefore the average irradiation of a rotating rotor. This irradiation results in the temperature that differs from the pole surface temperature. The difference depends on the interpolar space size, emissivity and temperature. The effect of the interpolar space can be cancelled if the IR thermometer is positioned at a certain angle with respect to machines main axis. Temperature sensors have been mounted on the rotor to measure the excitation winding surface temperature for comparison.