Replacement of Variable Speed Drives happens due to a number of different reasons.  Find below a list of these reasons.   

Existing equipment should be replaced with an AC Drives system when:

• The existing DC motor nears the end of its lifespan;
• Power factor and distortion are an issue, such as when the DC motor has a poor power factor when running below base speed, or when you’re paying a penalty or need to add a power factor correction, or when there’s an IEEE 519 requirement;
• The motor is small, perhaps less than 200 hp, so the money difference becomes insignificant given the many benefits that will be gained with an AC Drive system; and
• The machine can be out of service for a longer period of time.

DC Drives systems should be upgraded when:

• You want to save money, as when the DC drive replacement costs less than AC system replacement throughout the HP range;
• The existing DC motor is in decent shape, and spares are readily available; and
• Your situation requires fast upgrade with minimal downtime.