A Novel Approach to Determining Motor Load

Abstract

Properly sized electric motors are essential if industrial plant efficiency is to be optimized and energy costs minimized. Because of the difficulty in making power measurements on three phase motors, loading is rarely, if ever, checked. A simple indication of motor load can be achieved by measuring operating speed because speed and load are almost linearly related. The decrease in motor speed from no load conditions, referred to as slip, can be determined with a non-contact, optical tachometer. Field measurements of motor slip were conducted at a textile plant to quantify motor load conditions. To verify the relationship between operating speed and load, measurements of motor power consumption on a representative number of motors were also conducted. The results of the motor survey, including number of motors, size, and load, are summarized in this paper along with an estimate of the savings from replacing oversized motors.