On Site Efficiency Measurements for Electrical Motors is Possible and Easier than Thought

Abstract

The replacement of existing electrical motors by efficient ones is always a mat­ter of controversy, because the efficiency of installed motors is usually unknown. On site, it is extremely complex to measure the variables required by the testing standards.

In order to estimate on site the electrical efficiency of an installed motor, three basic methods, not considered by the testing standards, have been proposed to Chile’s main copper company, which is committed to promoting and implement­ing energy efficiency practices and technologies. It should be mentioned that this company consumes around 5,000 GWh per year, with motors consuming around 70% of the total. These methods provide results precise enough to ensure that adequate evaluations can be carried out to justify the replacement of an installed electrical motor.

The method considers separate evaluations of the no load losses, the stator losses, the rotor losses and the stray losses. For example, iron loss calculations are based on the measurement of input power for delta and star stator connections. The rotor losses are measured using the on load power input and the speed meas­urement. Finally a dynamic measurement of the efficiency is presented.