Replacing large motors purchased and installed 20 to 30 years ago is often a difficult undertaking as frame sizes are smaller and new models do not fit onto the old bases. A custom-engineered adaptor plate is now available to allow a smaller frame to fit on the existing base, simplifying large motor interchangeability.

“Many of the large motors operating in South Africa – in the larger size ranges of 400 kW to 500 kW and over – were manufactured according to the North American NEMA specifications – in inches,” explains Zest WEG sales specialist HV motors Floris Erasmus. “If they are replaced by a motor made to IEC specifications – in millimetres – the size of the frame will be different.”

The dimensions of motors have generally become smaller over time, as efficiencies have improved. The result is that the frame size of a new replacement motor – whether NEMA or IEC – will invariably be smaller than that of the older units.

“The implication of this dimensional change is significant for customers, as it can become costly to adapt or replace the carefully constructed base,” he says. “These large motor bases have been designed to handle heavy weights and considerable torque – often in excess of 10 000 Nm. To remove this and build another of the correct size is usually time consuming and expensive.”

There is also the height of the shaft to consider, he adds. Ideally, owners want their replacement motor to occupy the same footprint in their factory, mine or workshop as it occupies a specific place to power the required operation.

“Smaller dimensions also mean that the shaft height may be too low,” says Erasmus. “Fortunately, a well-designed base plate can generally accommodate this change as well.”

He highlights that Zest WEG will conduct the necessary measurements on the existing old motors and supply a specially machined, fit-for-purpose adaptor plate. This will allow the new motor to fit on the existing old base and ensure a fairly hassle-free installation for the customer. Parent company, WEG’s state-of-the-art facilities in Brazil, India and Portugal manufacture large motors and can also supply the adaptor plate, ensuring that there is a perfect match.