The dollars lost from the inefficiencies the latter is likely to cause can be enormous. What's more, you probably can recover the cost for this relatively inexpensive retrofit in less than twelve months. To show you how to justify this capital expenditure, let's make a few reasonable assumptions and derive a few rules of thumb. You can then plug in the values for your plant and see how you would fare if you made the switch to solid state. Motors are rated based on their output power.
Efficiency typically is defined as output divided by input.
Energy costs are computed based on the input power to the converter. The horsepower into the DC motor is the same as the horsepower out of the converter. To see how these rules pan out, let's apply them to a 100 hp M-G set application. A plant is operating two shifts. Some caveats, of course, go with this example.