UNDERSTANDING HIGH EFFICIENCY - ELECTRIC MOTORS

UNDERSTANDING HIGH EFFICIENCY


A major misconception in the marketplace is that the purchase/installation of High Efficiency motors will automatically contribute to energy and cost saving.

There are various ratings of High Efficiency been offered by motor suppliers from Standard Eff 3 , Eff2 & Eff 1. ( Each individual company might have their own efficiency brand / name).

Generally however motor suppliers will quote their particular Efficiency standard in accordance with a International recognized standard. ( CEMEP – European ; EPACT – USA ; MEPS – Australia ).

It is generally accepted that a High Efficiency 2 motor with regards Efficiency, Power Factor and cost is the most economical and widely accepted standard of High Efficiency motor currently in use in the world today.

The added cost implication of between 30% to 45% to increase from a Efficiency 2 to Efficiency 1 motor compared to the minimal improvement in efficiency has prevented Industry in Europe and

other industrialised countries to implement Efficiency 1 motors as standard.

( Attached : ABB UK article – What is wrong with High Eff motors )

CONSIDERATIONS PRIOR TO CHANGING TO HIGH EFFICIENCY MOTORS MOTOR MANAGEMENT PLAN

It is imperative that a concise plan incorporating the identifying of motor loads, hours of

operation, critical motors, maintenance and repair is in place, prior to uniformly replacing

existing standard motors to high efficiency motors. MOTOR LOADING

Motors operate at their highest efficiency between about 65% and 100% of their full-rated

load, dropping off sharply in efficiency below 50% loading.

It is generally accepted that about one-third of motors in the field are so oversized that they

operate below 50% of rated load most of the time. Motors operate at their peak efficiency if

they are sized correctly for the load that they will drive. Oversized motors not only operate

inefficiently, but they also carry a higher first cost than correct sized units. They can also

contribute to reduced power factor, which may result in increased electricity costs and poorer

utilisation of the power systems.

HOURS OF OPERATION

Hours of operation is a critical factor in determining the replacement or purchase of High

Efficiency motors. Motors with more operating hours use more electricity and cost more

to operate. Standard motors operating above 4000 hrs / year (ie.167 days x 24 hrs/day)

should be considered for future replacement with high efficiency motors.

HIGH EFFICIENCY POWER FACTOR

Power factor for High Efficiency motors are generally equal or lower than standard motors

( Eff 3 ). The lower power factor can be corrected by applying the correct power factor

correction. ( One must take both Efficiency & Power factor data into consideration when purchasing a High efficiency motor)

MOTOR RANGE BEST SUITED FOR REPLACEMENT

Research has shown that smaller kilowatt motors have the best benefit & gain in motor

efficiency. CEMEP high efficiency tables show the most effective range to be the following :

2 Pole - 1.1kW to 90kW

4 Pole - 1.1kW to 90kW

On larger motor efficiency the difference between Eff 3 , Eff 2 & Eff1 is small & the gain can be relatively insignificant.