- 08 August 2005 -

Motors to reduce running costs

Motors form a significant part in the running costs of any pump system. Not only do motors rack up energy costs, downtime and repairs can all add to the final bill. Steve Ruddell, general manager drives & motors ABB Limited, looks at the differences between energy efficient motors, as labelled by the EU, and argues the case for paying for quality.

The simplest and most fruitful approach to reducing the running costs of pumping operations can be summed up in just four words - invest in quality motors. First, paying a bit extra up front for energy-efficient, reliable motors will cut energy bills. This is no mean feat when the US-based Hydraulic Institute suggests that 90 % of the total cost of owning of a pump lies in the energy it consumes over its lifetime. Furthermore, there are fundamental reasons why high-quality, energy-efficient motors tend to be more reliable, reducing the need for expensive repairs and the potentially huge expense of downtime.

The right choice

The trick is not to be tempted by so-called bargains. Some motors with similar specifications can cost twice as much as others. But motors normally consume their own capital cost in energy after just 30 days of continuous operation, in which case the initial purchase price soon pales in comparison to the running costs. Cheap motors are normally less efficient, so they produce more waste heat and all that energy ends up on the electricity bill of the end user.

The European Union has introduced labelling to make it easier than ever to make an energy-efficient choice. For AC motors between 1.1 and 90 kW, the EU now requires manufacturers to label motors according to efficiency. The labels run from EFF3 (the least efficient) to EFF1 (the most efficient).

The difference in the energy efficiency offered by two motors may seem slight, but even a few percentage points will soon add up. The difference in efficiency between a high-efficiency EFF1 motor and a standard EFF2 motor can be as much as six per cent. This can offset the additional cost of an EFF1 motor compared to an EFF2 motor in less than 12 months of continuous operation and will continue to save money over its operational life.

The main reason that it is the more expensive motors that tend to be more energy efficient is that 55% of the cost of a motor lies in the materials. This means that it is not possible to make significantly cheaper motors just by cutting back on sales, marketing or distribution - a cheaper motor is typically going to be built from cheaper, lower quality materials. Today's market for motors is very competitive, so the opposite also holds true: A manufacturer of more expensive motors won't last long without providing a genuinely superior product.

Cheaper motors are less durable, typically falling way short of the 20 years possible life expectancy with high-quality versions. Some might argue that if you could buy a motor cheaply enough you could replace it more often and still be better off. But the cost of downtime soon surpasses any initial savings. Indeed, downtime costs many companies as much as a new motor every five minutes.

A case in point

For example, Imerys Minerals in Cornwall has entered an agreement with ABB to supply motors and drives to its UK plants in a bid to save downtime costs of up to £10,000 per hour.

Extraction and processing is a 24/7 continuous process, using high pressure water systems in the quarries. Imerys is the largest user of motors in the South West, employing more than 5,000 motors and over 27 MW of installed power driving pumps and handling systems for the extraction of two million tonnes of china clay per annum. The company makes extensive use of condition monitoring and failure mode analysis since any motor failure can lead to extended downtime.

Quality and delivery problems from their previous suppliers prompted Imerys to look for a new supplier of motors and drives. ABB motors and drives were ultimately selected on the basis of mechanical build quality, reliability and energy efficiency.

Dave Constance, Electrical Manager for Imerys, says: "In our experience of running motors we have never come across a motor as reliable as these from ABB. They are well designed for the harsh environment we work in, with better protection against ingress of dust and water and improved cooling. The drives work well in the wet and harsh environment found in our quarries and are well protected against ingress of water or slurry, which could otherwise cause expensive damage and downtime.

"We didn't take what we were told at face value. We examined motors and drives from a number of manufacturers and conducted compatibility tests to see if they were suitable for our environment. We stripped the motors down to look at how easy they were to maintain and how this would affect the running costs. Efficiency tests were also an important part of our investigation. For all criteria, ABB came out on top."

Lifetime cost of ownership is important to Imerys and so getting the maximum time between maintenance sessions was vital. The company made suggestions to improve the sealing on a motor bearing to reduce its maintenance needs and ABB altered the design of a casting to accommodate this as part of its policy of continuous improvement based upon customer feedback.

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