MRO Magazine

7 steps toward electrical motor efficiency


Industry

July 5, 2010
By PEM Magazine

Question: Dear Ken, I work in an industry that employs hundreds of electrical motors that are not slated for exchange with an energy efficient version any time soon. What can I do in the meanwhile to ensure maximum motor efficiency, and lowest energy cost

When North American electrical motor systems account for 23 percent of all energy consumed, and electrical consumption constitutes 98 percent of a motor’s lifetime cost, it pays to ensure that motors run as efficiently as possible. To ensure maximum efficiency at the lowest energy cost, there are seven simple steps we can take:

• Step 1: Sizing. To work efficiently, a motor must be sized correctly in accordance with its operating load requirements. Oversize motors perform adequately, but will still use too much electricity under normal operation. Inversely, under-size motors can labour under load and draw more energy. If the equipment still retains its original design specification, refer to the equipment manual to ensure the correct motor is employed. If modifications have taken place, or no literature is available, confer with your local motor supplier’s engineering department for assistance.

• Step 2: Balance. Any reputable new motor should come with its drive shaft balanced. However, this may not be the case for an inexpensive off shore example, or rebuilt motor. Unbalanced motor shafts are noisier and vibrate more requiring more energy to operate. Check your motor’s balance using vibration-analyzing equipment, or have it certified independently by your local motor shop.

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• Step 3: Alignment. Correct alignment between the drive shaft and the driven shaft is paramount. Misalignment presents in two forms: 1) Angular, in which the shafts line up centre to centre, but do not align in a straight line, and 2) Offset, in which the shafts do not line up centre to centre. Both conditions place tremendous stress on the driver and driven bearings and couplings, assuring rapid wear and considerable increases in motor energy consumption. Laser alignment is inexpensive and the most accurate alignment method.

• Step 4: Soft Foot. Often missed during the alignment process is a check for soft foot condition. Soft foot is a condition set up when one of the motor base feet is not as flat as the others, resembling a table with a short leg. Soft foot can also be encountered when the motor base grout is not flat or square. Both conditions are easily remedied with precision shims and correct tie-down bolt torquing. Soft foot causes vibration that eventually loosens bolts, causing the motor to vibrate excessively and increase energy consumption. Most laser alignment equipment is set up to detect soft foot condition. 

• Step 5: Lubrication. Learn how to lubricate motor shaft bearings correctly. The tendency to grossly over lubricate motor bearings is mainly due to the simple act of neglecting to undo the grease drain plug, allowing the grease to pass by winding seal into the motor winding causing massive overheating, premature failure and excessive energy consumption.

• Step 6: Cleanliness. The simple act of regular motor cleaning ensures no thermal blanket caused by dirt build up, allowing the motor to cool as designed and use energy more efficiently.

• Step 7: Maintain the driven system. Simple maintenance of the driven systems will significantly reduce motor loads and increase energy use efficiency, which can include:
• ensuring drive belts and chains are tensioned regularly and correctly;
• using matched drive belts on multiple belt systems;
• when replacing worn chains, always replace sprockets at the same time;
• lubricating drive chains regularly;
• if coupled to a gearbox, ensuring the gearbox lubricant is the correct viscosity;
• ensuring the driven component is balanced and lubricated regularly; and
• when aligning with direct coupling, using the less expensive non-flex style that require and force accurate alignment techniques. p


For more information on implementing asset maintenance and energy management programs, contact Ken Bannister at (519) 469-9173 or by email at kbannister@engtechindustries.com.