Electrical generator or motor structure – Dynamoelectric – Rotary
Patent
1993-10-01
1995-03-28
Stephan, Steven L.
Electrical generator or motor structure
Dynamoelectric
Rotary
310197, 310210, 310216, H02K 126, H02K 128, H02K 1716
Patent
active
054020263
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
The present invention relates to a rotor for a shortcircuited alternating current motor, and having a pack of circular rotor blades fixedly mounted on a shaft, the plates have, uniformly around the peripheral edges thereof, a number of recesses which, when the plates are packed, form generally axially extending rotor slots, and each rotor slot includes a first recess or cavity whose peripheral edge forms a closed contour and which accommodates a conductor radially inwards of the mantle surface of the rotor, the peripheral edge of said first recess has a concavity which faces towards said peripheral edge, and a second recess which forms a radially extending slot which extends from a point close to the concavity and out towards said peripheral edge, and a bridge is formed between the first recess and the second recess.
A rotor of this kind is known from U.S. Pat. No. 5,155,404. This known construction is intended for variable frequency operation, wherein the said first recesses are filled with conductors, whereas the second recesses form air gaps. The surfaces between the recesses form an iron bridge to which the major part of the circumferential magnetic leakage field passes, and where damping of the harmonic overtones from the current source can be achieved and the losses generated by said overtones therewith decreased, as a result of saturation effects.
It has long been known to provide short-circuited AC-motors with double rotor slots, in the form of so-called double squirrel-cage rotors. This affords an improved torque curve at high starting torques and the starting current is also slightly lower than in the case of normal so-called single squirrel-cage rotors.
SUMMARY OF THE INVENTION
An object of the present invention is to reduce the cost of rotor manufacture. The manufacture of such motors for different purposes, which although being predominantly the same may be intended for normal sinusoidal operation (mains operation) or for variable frequency operation, has hitherto necessitated the use of a large number of rotor plate punches. More specifically, another object of the invention is therefore to enable one and the same punch tool to be used for rotor plates which are to be used for motors intended for frequency changing operation and for rotor plates which are to be used for motors that are intended for normal sinusoidal operation.
The external measurements of such motors are standardized, so that some thirty dimensions may be involved in powers ranging from 1 to 1000 kW. Since many types of rotor and stator may be needed for each such dimension, it is obvious that the number of punch tools required is also large. When it is necessary to provide separate punch tools for motors that are intended for frequency changing operation, which at present represents a small percentage of the total production but which is steadily increasing, it is evident that the number of tools required will increase considerably. A reduction in the number of tools required Would therefore afford considerable economic advantages. Furthermore, the number of punched plates needing to be stored can be halved, which again improves the economy.
Another object of the invention is to provide a rotor slot or groove which can be filled completely with electrically conductive material by aluminium casting. In the case of motors intended for use with variable frequency, however, only a part of the rotor slot is filled and the other part of the slot is filled with air, in which case improved cooling can be achieved in accordance with a particular embodiment.
These objects and advantages, together with other advantages, are achieved in accordance with the present invention with a rotor of the aforedescribed kind which has the characteristic features set forth in the characterizing clause of the following claim 1.
When the inventive rotor is provided with an electrical conductor in only one of the recesses of respective slots, the same advantages are obtained as those obtained wi
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International Search Report; No. 9101026 8 Apr. 1991.
Gertmar Lars
Rydholm Bengt
Sadarangani Chandur
Zinck Jens P.
Asea Brown Boveri AB
Haszko D. R.
Stephan Steven L.
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