Page 191 - Power Quality in Electrical Systems

Chapter
12

Electric Motor Drive

Equipment

In this chapter we discuss issues related to the use of electric
motor drive equipment, specifically equipment, operation and
protection for induction motors.

Electric Motors
Every industrial, commercial, or residential facility utilizes electric
motors, ranging from a fractional horsepower motor for a cooling fan to
thousands of horsepower in a motor for a plastic extruder. The power
for these motors is either supplied from the utility line or from power-
electronic inverters in adjustable speed drive (ASD) systems. They are
all susceptible to power-quality problems—for example, line-voltage
disturbances. In this chapter, we will address the vulnerabilities of both
induction motors and ASDs, as well as methods to reduce their vulner-
ability to these problems.

Induction Motors
Induction motors provide mechanical power to a wide range of domes-
tic, commercial, and industrial loads, ranging from refrigerators to
machine tools. These motors operate from single-and three-phase power
sources, are controlled by starters, and are usually protected by fuses
and thermal overload devices, as shown in Figure 12.1 [12.2]. The motors
operate essentially at constant speed unless powered by an inverter in
ASDs. As such, the induction motors are subject to all of the voltage dips,
interruptions, unbalance, and harmonics that characterize poor power
quality. For information on induction motors, see [12.4].

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