There are three major motor efficiency standards, namely pre-EPAct, EPAct and NEMA Premium. Each standard has a comprehensive set of guidelines, written under the US Department of Energy (DOE).
Rewinding or Replace
One of the very first decisions engineers are faced with upon motor failure is whether to rewind or replace it. Factors that play an important part in this decision include:
Replacement is mostly preferred in case of pre-EPAct motors as greater savings can be made through installation of NEMA Premium motors. However, in case a NEMA Premium motor fails, the lines become blurry.
In the past, rewinding motors was often assimilated with lesser efficiency, but today that is no longer true. It is even possible to improve the motor’s efficiency through rewinding, so it can’t be ruled out.
Due to the complexity, the extent of improvement should be consulted with an expert.
The decision becomes easier for custom motors, as they take longer times to replace and cost greater as well. However, for motors that follow non-custom standards of efficiency, replacement is often better due to efficiency gains.
The frequency of operations of a motor also plays a great role in making this decision. The calculations are complex, fortunately the Department of Energy provides a free software, i.e. MotorMaster+ that helps in making the rewind/replace decision based on the amount of time the motor runs.
A common misconception is that the procurement of a NEMA Premium motor would deliver optimum efficiency, irrespective of the application. Note that when trying to boost savings, the factor of “sizing” gains paramount importance. If the new motor is oversized, the energy savings would be minimized by the initial cost. Correctly sizing a motor is necessary as overloaded motors are prone to overheating while underloaded motors can waste energy.
Two of the most important factors which affect sizing any type of load are:
Determining the speed is usually a straightforward process, and requires only the design specifications; the latter however is not so simple. Conducting a motor survey is a great way to make sure the replacement motor is correctly sized.
The process involves:
Conduction of a motor survey may seem like a complex task; however, it is one that is necessary to maintain optimum performance. Before skipping this vital step, keep in mind that the energy usage accounts for more than 95% of a motor’s cost!
Interested in learning more on how you can keep your motor operating properly?
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