API St 547:2005 pdf download.General-purpose Form-wound Squirrel Cage Induction Motors— 250 Horsepower and Larger
2.2.1 VOLTAGE AND FREQUENCY
The standard 3-phase voltage ratings are: a. 60 Hz: 2300 V, 4000 V, 6600 V and 13200 V. b. 50 Hz, 3000 V, 3300 V, 6000 V, 6600 V and 10000 V. Dual voltage motors are acceptable only for 2300/4000 V ratings. Note: When motors supplied under this standard are to be applied on a non-sinusoidal source and/or an adjustable speed application, the manufacturer should be consulted to determine if the motor will operate successfully over the required speed range. Refer to NEMA MG 1 Part 30. Proper selection of the motor and drive is required to avoid the following conditions: 1. Motor rms current exceeding the continuous sinusoidal nameplate rating due to excessive voltage harmonics or improper volt/hertz levels. 2. Excessive winding temperature due to insufficient cooling, excessive torque levels, or improper volt/hertz levels; and increased losses due to harmonics. 3. Insufficient motor accelerating torque at reduced speeds due to insufficient volt/hertz levels or limitations in the drive’s short- time current capacity. 4. Increased noise levels due to increased fan noise (above base speed), excitation of mechanical resonances, and/or magnetic noise caused by supply source harmonics. 5. Mechanical failure of the motor or coupling due to torque pulsations, operation at or near mechanical resonances, or excess speed. 6. Winding failures due to repetitive high-amplitude voltage spikes created by the drive’s carrier frequency and motor feeder cable system. 7. Damage to the motor and drive due to improper application of power factor correction capacitors or harmonic filters. 8. Higher motor temperatures that may limit application in Divi- sion 2 or Zone 2 hazardous (classified) locations. 9. Shaft-to-bearing voltages/currents resulting from common mode currents flowing through stray system capacitances to ground via the bearings. These currents are induced from the ASD’s high rate of change (dv/dt) of output voltage. 10. Extended operation at slow speed.
2.3 WINDING AND INSULATION SYSTEMS
2.3.1 Stator windings shall have an epoxy base, vacuum pressure impregnated, nonhygroscopic insulation system, including lead and coil connections. Bus bars shall also be insulated. As a minimum, the insulation system shall meet the criteria for Class F insulation listed in NEMA MG 1 or IEC 60034-1 as applicable. The allowable temperature rise above ambient, 40°C (104°F), shall not exceed that listed for Class B insulation. For ambient temperatures above 40°C the allowable temperature rise shall be reduced by the amount equal to the temperature above 40°C, so as not to exceed the total temperature limits (ambient, rise and hot spot) for Class B insulation.