Standard Motor Catalog
Section TR Technical Reference Guide
POLYPHASE OR SINGLE-PHASE POWER DEFINITION A power system can be either single-phase or polyphase. Figure 4 illustrates single-phase power, which is most commonly found in homes, rural areas and in small commercial establishments. A polyphase power system consists of two or more alternating currents of equal frequency and amplitude but offset from each other by a phase angle. Figure 5 illustrates a three phase power system having phases A, B, and C. Each phase is offset by 120 degrees, 360 degrees being the span of one complete cycle.
50 HZ OPERATION OF 60 HZ MOTORS General Electric standard motors rated at 60 HZ may be successfully operated at 50 HZ at reduced voltage and horsepower as shown in the following table: Table 3 Motor Rated 60 HZ Voltage 50 HZ Operational Voltage Rating (±5%) 230 190 200 208 460 380 400 415 575 475 500 - De-rate factor .85 .90 1.00 • Rated Hp at 50 HZ = Nameplate Hp x De-rate Factor • Allowable voltage variation at de-rated Hp = ±5% • Select motor overload protection for 60 HZ amps and 1.0 Service Factor • Motor speed = 5/6 nameplate rated speed • Service Factor = 1.0 60 HZ motors intended for use as shown above should be ordered as 60 HZ motors with no reference to 50 HZ operation. DUAL FREQUENCY Motors that require 50 HZ and 60 HZ operation of the same motor are non-NEMA defined motors and will be nameplate as such. When this is a motor requirement, it must be specified with the order. Some of our stock motors are nameplated 50/60 HZ and others can be re-rated; refer to technical support or EliteNet. VARIABLE FREQUENCY OPERATION Motors are available for use on variable frequency inverters of various types: 1. VVI is a square wave inverter in which voltage and frequency vary in proportion (constant volts per HZ). 2. PWM is a pulse width modulated inverter and the same as the VVI type except pulses are varied in time to simu late a sine wave. 2a. IGBT is a pulse width modulated inverter using a bipolar transistor for higher switching speeds. This technology provinces a cleaner resolved sine wave on a carrier frequency above the audible range. 2b. Vector control 3. CCI is a constant current inverter, which utilizes a square wave current supply as opposed to voltage. When applying a motor for use with a variable frequency drive, see section on special applications (For more details, refer to page TR.50).
Figure 5: Three-phase Power
For motors, an advantage of three-phase power is simpler construction which requires less maintenance. Also, a more powerful machine can be built into a smaller frame and will generally operate at a higher efficiency than single-phase motors of the same rating. MOTOR OUTPUT RATING SPEED The speed at which an induction motor operates is dependent upon the input power frequency and the number of electromagnetic poles for which the motor is wound. The higher the frequency, the faster the motor runs. The more poles the motor has, the slower it runs. The speed of the rotating magnetic field in the stator is called synchronous speed. To determine the synchronous speed of an induction motor, the following equation is used: 60 x 2 x Frequency Synchronous Speed (RPM) = Number of Poles Actual full-load speed (the speed at which an induction motor will operate at nameplate rated load) will be less than synchronous speed. The difference between synchronous speed and full-load speed is called slip. Percent slip is defined as follows: Synchronous Speed - Full Load Speed Percent slip = Synchronous Speed (x 100) Induction motors are built having rated slip ranging from less than 5% to as much as 20%. A motor with a slip of less than 5% is called a normal slip motor. Motors with a slip of 5% or more are used for applications requiring high starting torque (conveyor) and /or higher than normal slip (punch press) where, as the motor slows down, increased torque allows for flywheel energy release.
Data subject to change without notice. 02/23 • www.gemotorswolong.com
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