Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
2001-06-29
2003-05-27
Waks, Joseph (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S198000, C029S596000
Reexamination Certificate
active
06570290
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to single phase or polyphase electrical machines, and more particularly, to single layer interspersed concentric stator winding patterns for turbine generators and construction assemblies of SLIC windings.
BACKGROUND AND SUMMARY OF THE INVENTION
The fundamental elements common to a dynamo-electric machine or generator are a stator and a rotor. The stator includes a plurality of slots which are angularly and equally displaced along it's inner periphery. The rotor has one or more pairs of rotor magnetic poles which are created by permanent magnets or by a current carrying winding, or both. A current carrying winding is placed in the stator slots so as to create magnetic pole pairs on the stator which equal the number of rotor pole pairs. This winding is referred to as a stator winding. The stator for an ac machine can be wound for one or more phases (typically three). The peripheral span of one rotor pole or stator pole is called the “pole pitch”.
Stator windings are generally differentiated as single layer windings or two-layer windings. Lap windings and concentric windings are generally known with respect to coil arrangements in three-phase armature windings. Concentric windings have been used on single phase fractional horsepower motors. Concentric windings, however, are rarely used on larger horsepower polyphase machines (ac). Concentric windings are typically used for stator windings on single phase fractional horsepower motors (ac) and for field (rotor) windings for turbine generators (dc).
In a lap winding, coils having substantially similar configurations and peripheral spans are placed one upon the other (typically in a two-layer arrangement) in a sequence, and laid in the slots of a stator core. Thus, electrical characteristics of each phase are balanced since the coils have similar configurations and winding resistances for each phase.
In concentric windings, a plurality of coils having different peripheral spans are laid in the stator core slots such that the coils are distributed to lie concentrically about a pole center. Nested coils are generally located in adjacent slots in prior approaches.
A traditional “concentric” or “chain” wound stator winding is one in which a phase winding includes a finite number of “nested” coils which are centered on the axis of the phase winding. The coils each have one or more turns of electrically conductive material (usually copper) which are interconnected in series with each other to form what is termed a “phase group”. The interconnection of the coils in the “phase group” is made so that current will always flow in the same “sense” in each coil (either always in clockwise direction or always in counter-clockwise direction when viewed radially from the machine axial centerline).
To reduce harmonic content in the stator winding terminal voltage waveform and in the resultant stator winding magnetomotive force (MMF) waveform, usually a second “phase group” of coils is located one pole pitch away from the first “phase group” and is connected with the opposite “polarity” or opposite “sense” from the first “phase group” of coils. If the machine has more than two poles, then an additional phase group is added for each pole with connections made to reverse the polarity or current sense at each successive pole from that of the previous pole. The phase groups for the phase winding can then be carefully interconnected either in series, parallel, or series-parallel configurations via external conductors known as “phase connections”. In addition, both conductors at the ends of the now interconnected phase winding are brought outside of the machine by additional phase connections so as to interconnect with an external power system.
In a traditional concentric winding, the “nested” coils in a “phase group” include an innermost short span coil which spans a smaller fraction of a pole pitch which is contained within longer span coils, each of the coils are progressively larger in span by two stator slots. The outermost coil in the nest usually spans a full pole pitch. The conductors of the phase winding of a traditional concentric winding are always located in “adjacent” stator slots. Most of the concentric windings in which alternating current (ac) flows have continuously wound phase windings. In other words, the phase winding coils are wound from continuous strands of conductors and no joints are made in the conductors except at the ends of the phase groups.
Polyphase concentric windings have additional phase windings identical to the first phase winding, but displaced on the periphery of the stator from the first phase winding by an angular span which is dependent on the number of phases and number of poles. The most common type of polyphase machine is the three-phase machine. In a three-phase machine, the second phase winding is physically displaced from the first phase winding by (120)(2)/Np degrees, and the third phase winding is physically displaced from the first phase winding by (240)(2)/Np degrees where “Np” represents the number of poles on the machine.
In single phase or polyphase rotating machines, one of the design considerations is the reduction in higher order harmonic magnitudes in the resultant stator winding MMF waveform. This is one of the desirable considerations of the present invention. The following description provides some background information on stator winding MMF for concentric windings. For example, consider a 2-pole, three-phase machine for analyzing the case of a dc (direct) current flowing through a single coil of a phase group. Further, assume that the coil spans a full pole pitch of the machine. If the coil MMF, represented an (Y-axis), is plotted as a function of the peripheral angular span of the inner surface of the stator core, represented an (X-axis), the MMF waveform would appear as a rectangular waveform having equal positive and negative amplitudes about a horizontal X-axis. In addition, the angular span of the positive half of the waveform would be identical to that of the negative half of the waveform. Each half of the waveform is determined to span one pole pitch.
Considering the case of another coil in the same phase group, except that this coil spans a small fraction of a pole pitch. Further, assuming that the dc current in this coil flows in the same “sense” as in the full pole pitch coil. The MMF for this coil would also be rectangular in shape, but is different from that of the full pole pitch coil. The fractional pitch coil has a positive amplitude which is larger than the negative amplitude about the horizontal X-axis. In addition, the angular span of the positive portion of the waveform would only be within the confines of the coil span. The negative portion of the waveform would span the remainder of the stator periphery outside of the fractional pitch coil span.
Similar logic may be applied to other fractional pitch coils within the phase group except that the positive and negative amplitudes would be different and the angular spans of the positive and negative portions of the waveforms would be different, due to the different span of each of these coils.
The second phase group of coils on the adjacent pole would have similar waveforms except that they would be displaced from those of the first phase group by one pole pitch. In addition, the waveforms of the second phase group would be “inverted” (mirror image about the horizontal X-axis) from those of the first phase group because the second phase group is connected with opposite polarity or opposite current “sense”.
The combined or resultant MMF waveform of all the nested coils in the phase winding may be determined by summing the MMF contribution of each coil at every point on the inner periphery of the stator core. A stair stepped pattern above and below the horizontal X-axis would result for the case of dc current in the phase winding. This stair-stepped “space” pattern resembles a sinusoidal waveform. A Fourier Series Analysis may be made of the resultant phase winding MMF pattern in
General Electric Company
Nixon & Vanderhye P.C.
Waks Joseph
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