ABB claims that some motor manufacturers are selling high-efficiency Eff1 motors which actually deliver Eff2 performance. A Finnish university performed tests for ABB which measured the efficiencies of four Eff1 motors from an unnamed rival manufacturer and found that only one motor exceeded the efficiency allowed in the tolerance bands of the IEC 34-2 standard. One of the machines — a 200kW model — was found to be below the Eff1 band, delivering the performance of an Eff2 motor.

The tests were part of campaign that ABB is mounting to persuade motor buyers that an Eff1 rating does not necessarily signify a well-made motor.

"The belief is that if you pay a higher price for a higher efficiency motor, that certification also indicates high quality and high reliability," says Steve Ruddell, ABB`s general manager for motors and drives in the UK. "This is just not the case. Our experience shows that there are some motors which achieve Eff1 status at the cost of significant drawbacks. These manifest themselves in many ways — increased running temperatures and excessive noise being a couple of examples."

If a motor is running too hot, it is likely to fail prematurely, and Ruddell believes that such failures are costing users "thousands of pounds".

Ruddell points out that Eff1 is easy to achieve in all but the smallest motors, simply by increasing the amount of copper in the slots and by using smaller air gaps. He suspects that some manufacturers are claiming efficiencies near the top of the allowed tolerance band, while producing machines with efficiencies at the bottom of the band — or even outside it.

Poorly designed motors will often run at temperatures that can degrade their winding insulation and their bearing grease. Ruddell claims that ABB has measured motors with surface temperatures as high as 140°C (as shown in the thermal image above), whereas a well-designed motor running at full speed and load can operate at 60-80°C.

The two main reasons for motors failing are winding breakdowns and bearing failures. "We believe that many of these winding and bearing failures are the direct result of motors running too hot," Ruddell says.

"You may be told that your bearing has run dry," he continues. "While in some instances this may be down to a poor re-greasing regime, it is also possible that the motor was simply too hot and the grease degraded prematurely."

He says that a 10°C rise in operating temperature can halve the life of epoxy insulation, while cutting the operating temperature by 10-15°C can double the working life of bearing grease.

Ruddell suggests that motor catalogues should include a "reliability factor", possibly based on the sum of the efficiency and the operating temperature rise.

Another indicator of poor design can be noise levels. Hot-running motors need larger cooling fans, and larger fans mean more noise. Motor manufacturers quote noise levels in their catalogues and, according to Ruddell, these figures can give an indication of whether a motor running at a high temperature.

"If, say, a 200kW motor is showing a 77dB level against one showing a 70dB rating, the 7dB increase in noise equates to the motor being about four times noisier," he says. "This should set alarm bells ringing."

As well as campaigning for motor buyers to be given more useful data on machine performance, ABB is trying to develop simple methods for measuring motor temperatures.

Ruddell emphasises that his concerns apply mainly to motors running continuously in critical applications. "Not all motors need to be ultra-reliable," he concedes. "For a motor running for two hours a day, its temperature is less important." But for continuous-duty machines, reliability is paramount.