Premium efficiency is an engine design standard which seeks to improve carbon dioxide emissions, reduce overall consumption of power, and decrease the environmental impact of electric motors. According to the worldwide standard, a premium efficiency motor is the highest grade of performance, labeled as IEC IE3. This grade is given to those motors that exceed the highest levels of expectations of supplied power to output power. The standard to qualify as a premium efficiency motor runs on a sliding scale, depending upon the number of kilowatts produced by the motor.
When considering the efficiency of an electronic motor, the ratio of power usable at the shaft of the motor is compared to the amount of electrical power being used to run the motor. Much like the gas-powered motor in a car, where the horsepower rating of the engine does not represent the actual amount of horsepower which makes it to the drive shaft to turn the wheels, no electrical motor runs at 100% efficiency; there are always friction and drive train losses as the power moves through the engine. In electric motors, these losses come from resistance in the coil, losses to the magnetic iron core, and losses in the slip rings and rotor bars.
Once the efficiency is calculated as a ratio, it can also be expressed as a percentage. For example, an electric engine which has an efficiency ratio of 5:1 — a situation where 100 units of power going into the engine would result in only 20 units of power actually powering the motor — would have an efficient rating of 20%. To contrast that against the standards required of a premium efficiency motor, a motor which produces roughly 75 kilowatts of power must equal or exceed a 95% efficiency rating to be considered a premium efficiency motor. That is a fairly high bar to meet.
The percentages required to qualify as a premium efficiency motor are not uniform across the board; they vary depending on the amount of power generated by the engine. The general rule, however, is that the higher the power output of the engine, the more efficient it must be to quality as a premium efficiency engine. Whereas an engine producing 0 to 50kW of power requires an efficiency between 90% and 95%, an engine producing 200kW of power requires well over a 95% efficiency rating for the International Electrotechnical Commission (IEC) IE3 award.