Understanding the Efficiency of Motor and How to Improve It

What Is the Efficiency of Motor?

The ratio of the output of a motor to its input is called the efficiency of motor and is expressed by the symbol "η". This is the factor that describes the performance of the motor. It is the ratio between the output power and the input power on the shaft and can be written as:

Efficiency of motor = motor output power / motor input power

or

Efficiency of motor = η = output / (output + losses)

There is no such thing as a machine without losses. Therefore, the output value of a machine is always less than the input value.

How to Improve the Efficiency of Motor

Electric motors incur losses during the conversion of electrical energy into mechanical energy, including resistive losses, mechanical losses due to friction, losses due to the dissipation of magnetic energy in the core, and different losses depending on the type of material used. The following are some methods or techniques that can be used to improve the efficiency of motor.

Heat Dissipation

The function of the motor frame is to provide mechanical protection for the windings. It is also responsible for the interface through which the feet are mounted. The motor frame plays a vital role in its thermal performance as it is responsible for transferring the heat generated inside the motor to the surface of the frame where the air blown by the fan will promote heat dissipation. This will reduce heat loss and improve the efficiency of motor.

Stator

The stator, which is the main component of a motor, is responsible for 60% of the losses. To reduce these losses and improve the efficiency of motor, the mass of the stator winding must be kept large, as the increase in mass will reduce the resistance. High-efficiency motors contain 25% extra copper compared to motors designed for standard efficiency models.

Rotor

Rotor losses are also considered to be a secondary source of losses caused primarily by the degree of slip displayed by the motor. In order to reduce these losses and improve the efficiency of motor, the slip must be reduced, which is achieved by increasing the electrical conductivity of the rotor. Copper must be used in large quantities because of its high electrical conductivity. But the copper must be die-cast, as processes have recently been developed for die-casting copper.

Lubrication

The lubrication interval is a function of the rated speed of the motor installation, the bearing size, the type of grease, and the temperature rise. Therefore, care must be taken when applying the lubricant. Do not mix grease types, even if they use the same elements. If another type of grease is used in the application, this will directly affect the performance and efficiency of motor.

Stacked Sheets

Reduce the effect of hysteresis and saturated steel by using steel with a small amount of silicon in the laminations instead of low-cost carbon steel. In this way, core losses can be minimized, improving the efficiency of motor. Flux density and core losses can be further minimized by reducing lamination thickness and increasing lamination length.