The Efficiency of Electric Motors: Definition and Improvement Methods

A motor is a machine that generates internal forces via the interaction between winding‑produced magnetic fields and electric current, thereby converting electrical energy into mechanical energy. When this process runs in reverse, mechanical energy is transformed into electrical energy — a function fulfilled by a generator. The operating principle of electric motors is built primarily upon electromagnetism.

What Is the Efficiency of Electric Motor

The efficiency of an electric motor, denoted by the symbol η, refers to the ratio of motor output to motor input. It serves as a key metric for evaluating motor performance, calculated as the quotient of shaft output power over input power. The mathematical expressions are shown below:

Efficiency of electric motor = motor output power / motor input power or η = output / (output + losses)

Zero‑loss machinery does not exist in practice. For this reason, the output power of an electric motor is invariably lower than its input power.

How to Boost the Efficiency of Electric Motor

Losses emerge within electric motors throughout the energy‑conversion process from electricity to mechanical power. Typical loss categories include resistive losses, friction‑induced mechanical losses, core magnetic‑dissipation losses, plus extra losses related to component material properties. Practical measures for raising the efficiency of electric motor are listed as follows.

Heat Dissipation

The motor frame offers mechanical shielding for internal windings and provides mounting bases for installation. More critically, it dominates thermal management: it conducts internally‑generated heat out to the outer frame surface, where forced airflow from the fan accelerates heat dissipation and cuts thermal losses.

Stator

As a core assembly for large synchronous motors, the stator accounts for roughly 60 % of total system losses. Enlarging the mass of stator windings brings down winding resistance and suppresses such losses. High‑efficiency electric motors adopt stator windings with around 25 % more copper content than standard‑efficiency counterparts.

Rotor

Rotor losses represent the secondary loss source, largely determined by motor slip magnitude. Lower slip is required for loss mitigation, which can be realized by upgrading rotor electrical conductivity. Copper material with superior conductivity is heavily adopted; modern die‑casting copper technology enables mass‑production of copper rotors.

Lubrication

Recommended lubrication service intervals depend on motor rated speed, bearing dimension, grease grade and operating temperature rise. Proper lubrication practices are essential. Never mix different grease formulations even with similar constituent elements. Grease incompatibility will degrade the working performance of permanent‑magnet electric motors.

Laminated Steel Sheets

Substitute low‑cost carbon steel with silicon‑alloy laminated steel sheets to mitigate hysteresis loss and steel saturation, so as to reduce core losses. Further suppression of magnetic‑flux density and core losses can be achieved by thinning lamination sheets and extending lamination stacking length.