Legislation and Standards
Techniques to make motors more efficient are well known. However, it can be seen that the steps to make a more efficient machine are not necessarily in the best interest of either the machine manufacturer or purchaser. It can also be seen that in some instances, Standards could in the past have been said to hinder the development of new, more efficient designs.
The standard that covers the design, construction and operating limits of induction machines is NEMA MG1.
NEMA is the National Electrical Manufacturers Association, a US group which represents electrical equipment manufacturers. MG-1 is the standard for motors and generators. Canadian motors also follow MG-1.
NEMA MG-1 sets minimum performance values, (e.g. start, pullup, pullout torque, efficiency) and also mechanical constraints. Motors are grouped by frame size and all motors of a certain frame must have the same external dimensions, bolt hole locations etc. The standard also specifies the following classifications
- TEFC: Totally Enclosed Fan Cooled
- TENV: Totally Enclosed Natural Ventilation
- ODP: Open, Drip-Proof
The benefit of the standard is that the consumer knows what they are buying, independent of the manufacturer. This allows easy comparison between brands based on cost. e.g. all 5 Hp motors will be the same physical size and shape and in the event of failure one motor can be replaced by another from a different manufacturer without the need to redesign the mounting points, bolts etc.
At times, Standards have limited the incentive to develop higher efficiency designs. As a result, Governments have mandated legislated improvements over MG-1 (MG-1 was re-written to reflect the legislation. Canada was one of the first jurisdictions to legislate for higher efficiency, introducing standard CSA 390, which mandated a step change in motor efficiency. This was followed in the US by NEPACT legislation, which duplicated the Canadian efficiency limits, resulting in a common North American standard on efficiency.
NEMA has recently (2004) introduced an extension to MG-1 to introduce efficiency standards for "premium" efficiency motors. The premium efficiency motors program allows manufacturers to develop, and consumers to purchase, motors at a higher efficiency than the minimum set by legislation.
Standards specify motor design and performance parameters, allowing consumers to make informed choices about the motors they are buying. At times, the reluctance of industry to improve standards has required legislators to force changes and impose minimum standards. Due to the relationship between efficiency and motor cost, this is not usually in the best interest of motor manufacturers. Manufacturers have recently pro-actively announced extensions to the standard to enable higher efficiency motors in the marketplace.