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Easing the headache of large motor interchangeability

WHEN companies look at replacing large motors which were purchased and installed 20 to 30 years ago, they often find that frame sizes are smaller – which means the new models do not fit on the old bases.

The good news is Zest WEG has the answer: a custom-engineered adaptor plate which allows a smaller frame to fit on the existing base. According to Floris Erasmus, sales specialist HV motors at Zest WEG, this solution overcomes the problem without requiring any physical changes to the base.

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

Also, he says, 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 says. 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 that manufacture the large motors can also supply the adaptor plate, ensuring that there is a perfect match.

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