Patent Application
20060284511
The present technique relates generally to the field of electrical machines, which includes electrical motors and generators. More particularly, the present technique relates to the dissipation of heat in such electrical machines.
Electrical machines, such a motors and generators, are commonly found in industrial, commercial, and consumer settings. In industry, such machines are employed to drive various kinds of devices, including pumps, conveyors, compressors, fans, and so forth, to mention only a few. In the case of electric motors and generators, these devices generally include a stator, comprising a multiplicity of stator windings, surrounding a rotor.
By establishing an electromagnetic relationship between the rotor and the stator, electrical energy can be converted into kinetic energy, and vice-versa. In the case of alternating current (ac) motors, ac power applied to the stator windings effectuates rotation of the rotor. The speed of this rotation is typically a function of the frequency of the ac input power (i.e., frequency) and of the motor design (i.e., the number of poles defined by the stator windings). Advantageously, a rotor shaft extending through the motor housing takes advantage of this produced rotation, translating the rotor's movement into a driving force for a given piece of machinery. Conversely, in the case of an ac generator, rotation of an appropriately magnetized rotor induces current within the stator windings, in turn producing electrical power.
During operation, conventional motors and generators produce heat. The physical interaction of the machine's various moving components may produce heat by way of friction, and electrical current passing through the windings in the stator and rotor produce heat by way of resistive and inductive heating, for example. If left unabated, excess heat may degrade the performance of the machine, reducing efficiency, for instance. Worst yet, excess heat may contribute to any number of malfunctions, leading to system down time and, in certain instances, requiring maintenance and/or replacement. Undeniably, reduced efficiency and increased malfunctions are undesirable events that may lead to increased costs.
Unfortunately, traditional electrical motors and generators—particularly Totally Enclosed Fan Cooled (TEFC) assemblies—house the stator core within a frame assembly, placing an intermediate structure between the stator core and the surrounding environment and, thus, decreasing the efficacy of applied convective cooling techniques. For instance, cooling airflow produced by a fan does not come into contact with the outer peripheral surface of the stator core, but instead travels over the surrounding frame assembly. Because it is an intermediate structure, this frame retards the efficacy of the cooling airflow with respect to the stator core.
There is a need, therefore, for improved techniques for cooling electrical machines, such as motors and generators.
In accordance with certain exemplary embodiments, the present technique provides an electrical machine that has enhanced cooling features. The exemplary electrical machine includes a plurality of stator laminations, each stator lamination having a plurality of fins extending radially outward with respect to the stator lamination. When assembled in an electrical machine, the plurality of stator laminations cooperates to define a stator core. Cooling airflow generated by a fan, for example, is routed over the outer peripheral surface of the stator core: The stator fins improving heat dissipation in the electrical machine.
As an exemplary embodiment, the present technique also provides a stator lamination having a plurality of protrusions that at least partially define the outer periphery of the stator lamination. The protrusions increase the length of the outer periphery than if the stator lamination were generally circular or polygonal in shape. Advantageously, this increased length translates into an increased surface area for the outer surface of a stator core that employs the exemplary stator laminations, in turn improving the efficacy of convective cooling of the stator core.
The foregoing and other advantages and other features of the present technique will become apparent upon reading the following detailed description and upon reference to the drawings in which:
Turning the figures,
The exemplary machine 10 includes a stator core 12 capped at opposite ends by drive-end and opposite drive-end endcaps 14 and 16, respectively. Advantageously, the exemplary endcaps 14 and 16 include mounting and transportation features, such as the mounting flanges 18, as well as heat dissipation features, such as the endcap cooling fins 20. The stator core 12, which defines the central, peripheral portions of the machine 10, also includes protruding stator cooling fins 21 (see also
The tight fit and close tolerances between the assembled stator core 12 and endcaps 14 and 16 prevent the ingress of containments into the interior of the machine 10. Specifically, the exemplary machine 10 presents a Totally Enclosed Fan Cooled (TEFC) construction, as is defined by the National Electrical Manufactures Association (NEMA) and as is appreciated by those of ordinary skill in the art. In other words, the exemplary endcaps 14 and 16 and stator core 12 cooperate to present a assembly that is resistant to, but not sealed from the ingress of contaminants. It is worth noting, however, that those skilled in the art will appreciate in view of this discussion that a wide variety of motor and generator configurations may employ the cooling techniques outlined herein, and the present technique is not limited to TEFC's.
To effectuate cooling, the exemplary machine 10 includes a cooling assembly 24 disposed on the opposite drive-end of the machine 10. This cooling assembly 24 includes a shroud 26 mounted to the opposite drive-end endcap 16 and a fan 28. The shroud 26 directs air drawn in through vents 30 toward the drive end of the machine 10, thus directing airflow over the peripheral surfaces of the stator core 12 and endcaps 14 and 16, to cool the machine 10. It is worth noting, however, the cooling may be effectuated by an independent blower unit as well as by ambient air traveling over the peripheral surfaces of the stator core 12, particularly the cooling fins 21.
As is best illustrated in
To induce rotation of a rotor 34 located in the stator core 12 if the machine 10 is acting as an electric motor—alternating current is routed through windings 36 disposed in the stator core 12. The stator windings 36, of which only the end turns are shown in
Routing electrical current from external power source 38 through the stator windings 36 creates electromagnetic relationships with the rotor 34 (particularly with the conductor bars 41 extending axially through the rotor 34) that cause rotation of the rotor 34, as is appreciated by those of ordinary skill in the art. A rotor shaft 42 coupled to the rotor 34 also rotates in response to rotation of the rotor 34. Through the rotor shaft 42, torque may be transmitted to any number of drive machine elements. Rotation of the fan 28 is also driven.
Rotation of the rotor 34 within the electrical device is facilitated by drive-end and opposite drive-end bearing assemblies 44 and 46, respectively. Each bearing assembly 44 and 46 includes an inner race 48 that circumscribes the rotor shaft 42, an outer race 50 in abutment with the corresponding endcap 14 or 16, and a ball bearing 52 disposed between the inner the outer races. When seated in its appropriate endcap, the inner race 48 of each bearing assembly rotates in conjunction with the rotor while the outer race 50 remains stationary and seated. Advantageously, a lubricant disposed about the ball bearing 52 reduces friction within the bearing assemblies 44 and 46 and improves operation of the electrical machine 10.
Turning to
When assembled, the stator laminations 33 cooperate to present a number of features and attributes. For example, the stator laminations 33 cooperate to define a central chamber 56 that extends axially thought the stator core 12 and in which the rotor 34 (see
Turing to
Each stator lamination 33 includes a through-bolt receiving aperture 61 located on a stem portion 63 of the stator lamination 33. Advantageously, it is believed that placing this receiving aperture 61 on the stem portion 63 improves the structural integrity of the assembled stator core 12. Each stator lamination also includes a central aperture 62 sized to receive a rotor 34 (see
By way of example, in a 60 hp TEFC motor assembly with a stator lamination stack (i.e., stator core) length of 12 in., it is believed that that winding temperature rise can be reduced by 17.1° C. in comparison to a traditional assembly having a stator core disposed within a frame. For a 75 hp TEFC motor assembly with the same 12 in. lamination stack length, it is believed that a 17.2° C. reduction in temperature can be obtained. The following table summarizes believed improvements obtained through the present exemplary embodiment.
While only certain features of the invention have been illustrated and described herein, many modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.
