report on modern specialty motors design.

Assingnment 4.

modern specialty motors design




Definite and special-purpose motors .

INTRODUCTION.
Definite-purpose motors handle specific applications and have well-established NEMA standards. They are produced in high volume, and are low in cost when compared to general-purpose motors with the same ratings.
To apply a definite-purpose motor for a duty other than that for which it was intended must be carefully considered. Modifications can be made easily and inexpensively. Other modifications may require special tooling, increasing cost. The electrical characteristics of the motor must be checked very closely against the load. Testing the motor with the application is recommended.
Instrument motors: Instrument motor definitions vary with users and manufacturers of motors. Generally, an instrument motor is a precision motor with fractional or subfractional horsepower ratings. Sizes range from 1/2 to 3/4hp units.
Gearmotors: A gearmotor consists of a gear-reduction unit with an integral or flange-mounted rotor. The main advantage of a gearmotor is that the driving shaft may be coupled directly to the driven shaft. Belts, pulleys, chains, or additional gearing to step down motor speed are not needed. Also, coupling or belting of a motor to a separate speed-reducer unit is eliminated.
Torque requirements: Starting and running torques are considered separately because starting characteristics of the motor and gearing differ. Applications needing high breakaway torques require careful selection of the motor because split-phase, polyphase, capacitor-start, and brush-type motors have large starting torques.



APPLICATION
Applications with high inertias should be analyzed by the gearmotor manufacturer. This problem is critical with self-locking right-angle gearmotors. Since rotor and load are rigidly connected by the gear train, both must stop in the same time. In severe cases, momentary power failure may be all that is necessary for a high inertial load to destroy the gear train.
Overhung loads are applied to the output shaft of the gearmotor whenever the gearmotor is connected to the applications requiring cams, belts, or gearing. Applications requiring cams, hoisting drums, or switches at the output shaft can also cause very high overhung loads on gearhead bearings.
It is inherent with gearmotors that overhung load capacity decreases as the delivered torque increases. This reduction is caused by internal gear-reduction forces. In small fhp gearheads, reducer bearings may be fully loaded by the reactions resulting from rated torque. Under these conditions, no additional overhung load may be placed on the output shaft.
When the overhung-load capacity of a gearmotor is too small, it may be possible to obtain oversize shafts and bearings. A third or outboard bearing is sometimes used to support the end of the driveshaft. However, it is extremely important that this bearing is properly aligned to prevent excessive shaft and bearing loads. Thrust loads are most severe with vertical-shaft units and gearmotors driving a lead screw or axial actuating device. It is often less expensive to specify a heavy-duty unit rather than extensively modify a normal-duty unit when loads are excessive.
Toothless motors: Some motors can be made with toothless armatures, thanks to powerful modern magnets. Coils are wound and assembled outside the motor, then inserted and secured as a unit in the armature.
Toothless construction provides more space for armature coils and provides higher current ratings. Iron losses are cut by 50%, and armature inductance approaches that for cup motors. Toothless motors do not cog at low speed. And because coil insertion is easier, motor diameters can be smaller.
In toothless motors that use ceramic magnets, flux density in the air gap is much lower than in conventional motors. The low density results from the large air gap, an inherent characteristic of toothless construction.
Toothless motors equipped with rare-earth magnets, however, operate at high flux densities. These motors contain magnets that are about the same length as the air gap. With this relationship, rare-earth magnets operate at flux levels that are close to the magnet's maximum energy product.

special-purpose motors design

EXAMPLE

This example as meet all the above standards(ISOS ,NEMA)

With this in mind, UL did not write the new standards to be more stringent, but instead to accomplish three tasks:
1. To address new and emerging motor and motor-control technologies that were either not addressed or envisioned when the requirements were first written.
2. To clarify and to remove identified ambiguities from the existing standards so that manufacturers more clearly understand all of the requirements and their intent.
3. To provide alternatives. There is not just one way to build a motor, and, similarly, there should not be just a single way to meet the intent of a safety requirement.
Where the legacy of standards consisted simply of UL 1004 – Electric Motors and UL 2111 – Overheating Protection for Motors, the new standards are written as a more functional family that better categorize and organize requirements for specific types of rotating machines. This family scheme should be very familiar to those who are accustomed to IEC Standards. The new motor series of standards now has the following:
UL 1004-1 – Rotating Machinery: This contains requirements common to all rotating machines.
UL 1004-2 – Impedance Protected Motors: This contains requirements specific to this design.
UL 1004-3 – Thermally Protected Motors: This contains requirements specific to motors protected by any one of five different technologies of thermal motor protector devices.
UL 1004-4 – Electric Generators: This contains requirements for component electric generators, sometimes called generator heads.
UL 1004-5 – Fire Pump Motors: This contains requirements unique to that specific application.
In addition, there are three pending standards to further define requirements and further expand the family of motor standards. These include:
Electronically Protected Motors: This will address both BLDC (electronically commutated) motors as well as conventional motors protected by electronic circuitry.
Servo and Stepper Motors: This contains requirements specific to these very specialized motors.
Inverter Duty Motors: This contains requirements specific to the evaluation of motors intended for variable-speed drives or other non-sinusoidal AC supplies.
This family of standards architecture enables UL to build on a continuum of more focused requirements for the various types of rotating machinery. The segregation of the various standards also avoids the result of an enormous, unintelligible document. All of that should shed some light on how UL is addressing the first of the three reasons for introducing a family of standards. Regarding the second goal, it is a given that everyone tries to write standards that are crystal clear and intuitive. Unfortunately, as standards age and numerous revisions are appended, rearranged and tacked on, the original intended clarity inevitably suffers. Eventually, a complete rewrite is required to restore the intended precision, transparency, and user friendliness. As for the third goal, it remains important to understand that the intent of any requirement should be to provide more than one solution to a problem. Inflexibility in the consideration of alternatives simply stifles innovation and creativity in both motor design and appliance design. As noted, UL does not envision its role as the “Safety Police” throwing up barriers, but rather as colleagues of manufacturers desiring to bring safer products to market faster.