Very good question. The prevailing view among many facility
managers is that it is cheaper to repair failed motors larger than 15
horsepower (hp) than to replace them. Although this is usually true in terms of
first cost, the best economic decision for a given motor is not quite
so straightforward. When all the relevant factors are considered,
replacement with an energy-efficient motor makes economic sense in many
situations. We recommend that you read this excellent article from
Minnesota Energy Resources.
Another thing to recognize is that a rewound motor is less efficient
than a new one. Each time a motor is rewound, you lose in the region of 1% of
its previous efficiency.