THE POWER OF THREE

摘要

Three-phase motors are used in many industrial applications to control loads such as pumps, compressors, valves, conveyors and other motor-driven devices. They are efficient, relatively simple in design, and capable of a high starting torque compared to single-phase motors. Smaller and typically less expensive than single-phase motors with comparable ratings, three-phase motors also may tend to last longer than single-phase motors with the same power rating. Many loads driven by a three-phase motor simply require the motor to turn on and off in order for them to perform their required function (figure 1). One such load would be an industrial fan, which only needs the motor to rotate in one direction in order for air to circulate. A compressor is another example of a three-phase load where the motor simply needs a connection to a three-phase AC network in order to perform its desired function. These applications typically use a simple three-phase solid-state relay, contactor or motor starter to switch power to and from the motor.