Circulating currents in the parallel stator conductors of electrical machines
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Helsinki University of Technology |
Diplomityö
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Date
2005
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Sähkömekaniikka
Mcode
S-17
Degree programme
Language
en
Pages
55
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Abstract
Present-day high-speed induction machines typically rotate within the speed range 25 000 - 50 000 rpm. For a two-pole machine, the supply frequency is within 420 - 8S0 Hz. This frequency is high enough to eddy-current problems, and the special attention is to be paid on the stator conductors embedded in the stator slots. Using thin conductors, the diameters of which are smaller than the penetration depth of the magnetic field, reduces the eddy currents. However, this means a large number of parallel filamentary conductors and brings a new problem. The thin filamentary conductors should be distributed evenly in the slots, otherwise different electromotive forces will be induced in them and circulatory currents flow between the filamentary conductors. Measuring the filament currents in some high-speed machines has shown that significant circulating currents exist. The aim of the proposed MSC thesis is to develop a numerical method for studying the circulating currents in the stator winding. The existing finite element codes of the Laboratory of Electromechanics require some modifications to handle this problem. A finite element mesh should be generated to the stator slots, which allows distributing the filamentary conductors in the slots in a statistical manner. The large number of conductors connected in parallel must be handled in the circuit equation of the FEM code. After these modifications, the current distributions will be obtained for the statistically distributed conductors and some methods for reducing the circulating currents will be studied. Key words: circulating currents, parallel conductor, stator winding, high-speed machine, finite element method.Description
Supervisor
Arkkio, AnteroKeywords
circulating currents, kiertovirta, parallel conductor, rinnakkaiset johtimet, stator winding, staatorikäämi, high-speed machine, suurnopeussähkökone, finite element method, elementtimenetelmä