Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
1997-12-01
2001-07-03
Tamai, Karl (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C336S208000, C029S605000, C140S092100, C140S092200, 24
Reexamination Certificate
active
06255756
ABSTRACT:
BACKGROUND OF THE INVENTION
Eddy current losses tend to exceed the I
2
R losses in high speed, high power switched reluctance machines as will be utilized for internal jet-engine starter-generators. These machines are characterized by a low number of turns per phase made from rectangular, hollow conductors with outside dimensions of typically 0.090 inch by 0.125 inch or larger. These conductors are exposed to high magnetic fields which change amplitude very rapidly at a rate of typically more than 1000 Hz. the electrical losses in the conductors, generally called I
2
R losses, are much larger than the losses calculated by multiplying the square of the rms value of the winding current times the DC resistance of the conductor. These additional losses are due to eddy currents induced by the rapidly changing magnetic field in the solid walls of the conductor. Normally these eddy current losses are between 10 to 800% of the DCI
2
R losses. However, in high speed, high power switched reluctance machines, the additional losses due to the eddy currents can be a multiple of the DCI
2
R losses. Applying the same machine type to an internal starter/generator, the power rating and the fundamental frequency can readily be higher than for an external starter generator, potentially resulting in very high eddy current losses.
High eddy current losses introduce a number of challenges. For example, the cooling required by the high eddy current losses challenges the conventional cooling system for which standard engine lubrication oil is used. Also, the adverse impact on efficiency of the system becomes rather significant with high eddy current losses.
It would be desirable, then, to be able to reduce the eddy current losses in internal starter/generator arrangements.
SUMMARY OF THE INVENTION
The present invention provides for loss reduction by specific stator coil placement and winding arrangement. In the prior art, the first turn of the winding of the coil is directly on top of the second turn in the inside layer of the coil. With the coil configuration of the present invention, the first turn is moved to the outside, over the second layer; the wire, after completing the first turn, then returns to the inner layer. The winding arrangement according to the present invention provides major eddy current loss reduction/prevention compared to the conventional winding arrangement, without any significant weight and size impact.
In accordance with one aspect of the present invention, a stator coil winding arrangement comprises an inner layer and an outer layer which define two layers of the coil. A first turn of the inner layer is moved radially outward, out of the inner layer to be in a vertical plane with the outer layer, parallel with the inner layer and a subsequent turn of the inner layer is positioned over the inner layer.
In the drawings as hereinafter described, a preferred embodiment is depicted; however, various other modifications and alternative constructions can be made thereto without departing from the true spirit and scope of the invention.
REFERENCES:
patent: 1451374 (1923-04-01), Rogers
patent: 3802066 (1974-04-01), Barrett
patent: 3851830 (1974-12-01), Barthalon
patent: 4131988 (1979-01-01), Finegold
patent: 4668544 (1987-05-01), Takahashi
patent: 4684867 (1987-08-01), Miller et al.
patent: 4967464 (1990-11-01), Stephens
patent: 5376851 (1994-12-01), Lipo et al.
General Electric Company
Hess Andrew C.
Tamai Karl
Young Rodney M.
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