API St 547 pdf download.General-purpose Form-wound Squirrel Cage Induction Motors—250 Horsepower and Larger
1.3 UNUSUAL SERVICE CONDITIONS
Unusual service conditions should be brought to the atten- tion of those responsible for the design, manufacture, applica- tion, and operation of the motor. Among such unusual conditions are: a. Exposure to: 1. Combustible, explosive, abrasive, or conductive dust. 2. Dirty operating conditions where the accumulation of dirt will interfere with normal ventilation. 3. Nuclear radiation. 4. Abnormal shock, vibrations, or mechanical loading from external sources. 5. Abnormal axial or side thrust imposed on the motor shaft. 6. Altitude or ambient temperature outside the range cov- ered in 1.2. 7. Reciprocating or positive displacement loads. b. Conditions under which the variation from rated voltage or frequency, or both, exceeds the limits given in NEMA MG 1. c. Conditions under which the ac supply voltage is unbal- anced by more than the limits given in NEMA MG 1. d. Operation at speeds other than rated speed. e. Operation from solid-state or other types of adjustable fre- quency/adjustable voltage power supplies for adjustable speed applications. f. Load inertia greater than and/or starting conditions more severe than given in NEMA MG 1. g. Vertical mounting. Note: A round bullet ( • ) at the beginning of a paragraph indicates that either a decision is required or further information is to be pro- vided by the purchaser. This information should be indicated on the data sheets (see Appendix A); otherwise it should be stated in the quotation request or in the order.
1.4 DIMENSIONS AND STANDARDS
1.4.1 Both the SI and U.S. Customary system of units and dimensions are used in this standard. Any data, draw- ings, or hardware (including fasteners) related to equip- ment supplied to this standard shall use the U.S. Customary system. 1.4.2 This document recognizes two different systems of standards for the manufacturing and testing of electrical motors: the North American ANSI, IEEE, and NEMA stan- dards; and the international IEC and ISO standards. The North American standards are the base documents. When specified by the purchaser, the corresponding international standards are acceptable for use as alternatives; however, this must not be construed that they are identical to the North American standards. The selection of which system of stan- dards to be utilized shall depend upon the machine’s applica- tion and site location. Note: The purchaser should be aware that specific requirements con- tained within corresponding standards may differ.
2 Basic Design
2.1.1 Motors shall be rated on a continuous-duty basis. The output rating shall be expressed in power available at the shaft at the specified speed, frequency, and voltage. Note: Motors should be applied within their rating based on a ser- vice factor of 1.0. In those applications requiring a prolonged over- load capacity, the use of a higher power rating is recommended to avoid the reduction of insulation and bearing life associated with operation above the 1.0 service factor. 2.1.2 Unless otherwise specified, the A – weighted maxi- mum sound pressure level of the motor shall not exceed 85 dBA at any location at a reference distance of 3 ft (1 m) with motor operating at no load, full voltage, rated fre- quency, and sinusoidal power. The measuring and reporting of sound pressure level data shall be in accordance with NEMA MG 1 Part 9. 2.1.3 The motor and all of its auxiliary devices shall be suitable for and in accordance with the area classification sys- tem specified by the purchaser on the data sheets. Auxiliary devices shall be listed or certified where required in accor- dance with the area classification system specified.