Polyphase Induction Motors
About two-thirds of the electric power in the U.S. is consumed by motors, with industrial three-phase motors above 5 HP (7 kW) being by far the bulk of that load. They are linear loads and therefore don't contribute to harmonics. They are, however, the major contributor to reduced Displacement Power Factor, which is a measurement of the effective use of system capacity.
Measurements
1. Voltage unbalance
Voltage unbalance should not exceed 1-2% (unless the motor is lightly loaded). Why such a small number? Voltage unbalance has a very large effect on current unbalance, in the neighborhood of 8:1. In other words, a voltage unbalance of 1% can cause current unbalance of 8%. Current unbalance will cause the motor to draw more current than it otherwise would. This in turn causes more heat and heat is the enemy of motor life, since it deteriorates the winding insulation.
Helpful Information About Treadmill Motors
Treadmills are not all the same, and one of the ways they differ is in their motors. This does not mean the treadmill motor is the only thing you should consider when making a purchase, but it is a factor you will want to look into.
Continuous Duty Treadmill Motors
If you've been looking into treadmills, you've probably learned that it's important to buy a model with a continuous duty motor. What exactly does that mean? Well, a continuous duty motor is aptly named, because it can run continuously without being damaged. An intermittent motor must stop to cool down and most can only run between five and sixty minutes. You wouldn't want to stop after only a few minutes, which is why a continuous duty motor is the most suitable for powering a treadmill.