Motor Efficiency

Electric motors consume 64 percent of the electricity produced in this country. Although they are generally efficient, motors are often run at lowered efficiency because the motor size is not matched to the horsepower requirements of the task.

Motors frequently drive variable loads such as pumps, hydraulic systems and fans. In these applications, motor efficiency is often poor due to operation at low loads.

The operating cost of a motor over its lifetime is many times its purchase price. For example, a 100 horsepower AC induction motor costs approximately $5,000, yet will use as much as $35,000 worth of electricity in a year. Small improvements in efficiency can therefore generate significant savings in energy costs.

Here are some suggestions on how to improve electric motor efficiency:

Loading. Since motors run most efficiently near their designed power rating, it is good practice to operate between 75 percent and 100 percent of full load rating. The National Association of Electrical Manufacturers (NEMA) publishes guides for selecting motor design types for particular tasks. Motor manufacturers are another good source of information on proper selection of motors.

Voltage Balance. Proper power supply is essential for achieving rated performance of a motor. Unbalanced three-phase voltage affects a motor's current, speed, torque and temperature rise. Equal loads on all three phases of electric service helps assure voltage balance while minimizing voltage losses.

Maintenance. Regular maintenance helps minimize loss from friction and heat and extends motor life. Lubrication and cleaning should be performed periodically. Motors should also be checked for proper ventilation, mounting bolt security and load change application.

Consider Energy Efficient Motors. They can improve efficiency from three to eight percent. Heavier copper wire, higher core-steel grade, thinner core laminations, better bearings and reduced windage design add up to better efficiency. And even though initial cost is higher payback can be very short, especially for motors that are in constant use.

Electronic Variable Speed Drives (VSDs) control the speed and torque of an AC electric motor by varying the frequency and voltage of the electricity supplied to the motor. They replace inefficient, energy robbing speed controllers such as belts and pulleys, throttle valves, fan dampers and magnetic clutches.

• VSDs have many advantages.
  • No friction loss because there are no moving parts percent.
    
  • Instant and precise control of equipment speed - one VSD can control multiple motors.
    
  • Gentle startups and gradual slowdowns reduce motor stress.
    
  • Small size makes them ideal for retrofit.
    
  • Energy savings up to 20 percent
• VSDs and Versatility
  VSDs save energy in pumping applications such as in municipal water systems, chemical and petrochemical industries, pulp and paper industries and food industries. They also save energy when applied to air handling and ventilation systems.
• Putting VSDs on the Line
  VSDs provide precise, efficient speed control in conveyor systems used in the food, paper, automotive and consumer goods industries. They're also used in crushers, grinding mills, rotary kilns, presses, rolling mills and textile machinery.
• Living in Harmony
  All variable speed drives with power switching devices generate harmonics. When installing VSDs, pay particular attention to the harmonics generated and their potential effect on other facility operations.