API STD 541
Form-Wound Squirrel Cage Induction Motors - 250 Horsepower and Larger
|Publication Date:||1 January 1995|
1.1.1 This standard covers the minimum requirements for all form-wound squirrel cage induction motors above National Electrical Manufacturers Association (NEMA) 440 frame sizes (nominally 250 horsepower and larger) for use in petroleum industry services.
This standard may be applied to adjustable speed motors and induction generators with appropriate attention to the specific requirements of such applications. For adjustable speed applications, proper selection of the motor and drive are required to avoid the following conditions:
a. Motor RMS current exceeding the continuous sinusoidal nameplate rating due to excessive voltage harmonics or improper volts/hertz levels.
b. Excessive winding temperature due to insufficient cooling, excessive torque levels, improper volts/hertz levels, and increased losses due to harmonics.
c. Insufficient motor accelerating torque at reduced speeds due to insufficient volts/hertz levels or limitations in the drive's momentary current capacity.
d. Increased noise levels due to increased fan noise (above base speed), excitation of mechanical resonances, or magnetic noise caused by supply source harmonics.
e. Mechanical failure of the motor or coupling due to the torque pulsations, operation at or near mechanical resonances, or excess speed.
f. Winding failures due to repetitive high amplitude voltage spikes created by the drive system.
g. Damage to the motor and drive due to improper application of power factor correction capacitors.
h. Higher motor temperatures that may limit application in Division 2 hazardous areas.
i. Shaft voltages/currents due to harmonics that may cause bearing failure.
Note 1: A round bullet (•) at the beginning of a paragraph indicates that either a decision is required or further information is to be provided 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.
Note 2: A square bullet (▪) at the beginning of the paragraph indicates additional requirements for special purpose motors. Special purpose motors are motors that drive high-inertia loads, vertical motors that support high-thrust loads, motors that are part of a complete train requiring vibration sensitivity criteria, motors that operate in abnormally hostile environments, or motors that drive critical unspared equipment.
• 1.1.2 When the motor is specified as special purpose on the Purchaser's Induction Motor Data Sheets (Appendix A), the paragraphs that are marked with square bullets (▪) shall also apply. Where a paragraph includes both a round and square bullet, that paragraph shall apply when the motor is specified as special purpose, or when indicated on the data sheets, if the motor has not been specified as special purpose.
1.1.3 This standard requires the purchaser to specify certain details and features. In order for this standard to be meaningful as an aid to procurement, the purchaser must complete the data sheets in Appendix A.