Our previous article discussed that motor-driven systems use 25% of all electricity in the United States, and that the purchase price of a motor is only 2% of its life cycle cost. Energy costs can be controlled by careful selection and operation of these electric motor systems.
According to the U.S. Department of Energy's 2002 Motor Systems Market Opportunities Assessment, most facilities are lacking in established motor management policies.
- More than 90% of motor decisions are made at the facility level
- Only 11% of companies have written motor specifications
- Only 12% of companies have written motor rewind specifications
- 24% of facilities have not addressed energy issues
Upgrade existing motors
Historically, we have looked at upgrades from standard motors to motors with higher efficiency, called NEMA Premium efficient motors. This is easy to do because the new motors are simple bolt-in replacements. Any motor operated continuously in production or in a commercial building is a candidate for replacement, offering savings up to 6%. Savings on a typical motor-driven industrial pump are shown as:
|50 HP 4 pole operating costs
|NEMA Premium efficiency
|$1,630 x 20 years = $32,600
Continuous operation at $0.10 kWh.
Based on the 50 hp motor shown above with 90.7% efficiency, a significant savings will occur with replacement using a NEMA Premium motor. In many states, the utility might offer a rebate incentive to ensure that a premium motor would be used instead of an EPAct-level motor.
Repair or replace
When a motor fails, a repair or replace decision must be made. Many companies use a 50-50 policy on repairs. If the motor repair cost is more than 50% of the cost of a new motor, it is not repaired. If the motor is less than 50 hp, it is not repaired. Based on the electric and repair costs in various areas, these might be a bit different.
In the case of the pump system above, the motor can be rewound at a cost of $1,200-$1,400. Replacement of the motor with a new EPAct motor would cost about $1,945 and a new premium motor would be $2,800. These are approximate costs and might be a bit lower in certain areas. Here is where things can get complicated.
- A new motor at $2,800 is more than twice the cost of a $1,200 repair, so the rule would suggest a repair. This can also be done from a maintenance budget without need to get capital approval.
- The utility will offer a $3/hp rebate (WI Focus on Energy as an example) = $150
- The premium motor can save $1,630 per year at today’s energy cost of $0.10 per kWh.
- Using an energy-savings program with the above numbers, the payback for the premium motor is 16 months.
Repair and new motor specifications
When a motor is repaired, it should be done to an industry standard established by the Electrical Apparatus Service Association (EASA), called ANSI/EASA AR100-2006 Recommended Practice for the Repair of Rotating Apparatus. Service shops that follow this practice will repair the motor and restore it to its original efficiency without damaging the core steel. A poor repair results in a less-efficient motor that operates at a higher temperature, leading to early failure. The analysis from the failed motor can be used to indicate that a motor needs a better level of environmental protection, different bearings, better maintenance, or any number of items that might reduce downtime or eliminate premature failure.
Facilities also should establish standards for any new motors purchased. Any industrial-grade motor should be specified with NEMA Premium efficiency, which will result in lower electrical usage. Depending on where the motor is used in the facility, the enclosure (open or enclosed fan-cooled) and level of environmental protection should be correctly specified for long use without failure.
John Malinowski is product manager of AC & DC motors for Baldor Electric Co., Fort Smith, Ark., Contact him at (479) 648-5909 and [email protected].