In East Texas, a perennial question in maintenance circles is whether it’s best to repair or replace an electric motor that fails. For most plant engineers and maintenance staff, experience attests to the reliability of standard efficiency motors that have been repaired or rewound using industry best practices.
Repair also can cost far less than replacement, especially if the motor has special features. But some decision makers opt to replace failed energy efficient motors (NEMA Premium models in particular) because they’ve “heard” these motors can’t be repaired without a loss of efficiency. So, what’s the right answer?
It turns out that the decision to repair, rewind or replace a failed energy efficient motor is not always so simple and straightforward as you may have heard. Motors convert input power (electricity) into useful (mechanical) work, and in the process some energy is always lost–to heat, friction and windage. To improve motor efficiency manufacturers must therefore find ways to reduce these losses.
Interestingly, though, they did not change the raw materials or production methods with the advent of higher efficiency (EPAct) motors, or with the introduction of the NEMA Premium models. Instead, they achieved efficiency gains through design changes.
Compared with standard efficiency motors, for example, some higher efficiency models have longer stator and rotor cores to reduce core losses, and more copper wire area in the windings, which decreases copper losses. Totally enclosed, fan-cooled (TEFC) designs use the smallest fan that can keep the windings within the design temperature limit to minimize the power diverted to windage. Read More
