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Case Studies - Variable Frequency Drives

Staggering energy savings prove value of professional audit

Over 80% saving in the running cost of paint plant motors is being achieved by a Coventry-based vehicle body panel manufacturer following the installation of ABB AC drives.

“We were cynical at first about the huge savings that were being claimed,” says Pat O’Sullivan, Facilities Manager for Mayflower Vehicle Systems, which manufacturers body panels for, among others, Aston Martin and MGF cars. “We believed that anyone suggesting up to 80% saving had probably loaded the product price to cover it.

“But a SEAchange energy audit of the paint plant by ABB Drives Alliance Partner, Sentridge Control, revealed that the 30kW phosphate/ alkali rinse pumps – used in the nine stage pre-treatment system – needed the motors for just over two minutes of its eight minute duty cycle. In addition, the motors were running for 10 hours per day.

Unlike AC drives, the existing star-delta starter arrangement meant that the motors could not be turned on and off quickly to meet the rinse pumps duty cycle, without severely damaging the motors windings and bearings.

“Due to the ABB ACS 600 and Comp-AC drives, we have now been able to change our control strategy such that today we have cut the running costs of these pumps by 87.9% – even greater than the original 84%,” says O’Sullivan. “The additional benefit is that the cost savings are immediate.”

Such were the projected savings that the management of Mayflower committed $30,000, which had not been budgeted. The money was used for the purchase and installation of six drives for the phosphate and alkali rinse, chemical and soap pumps and a further 11 drives for other pumps and cooling tower applications ranging from 2.2 kW to 55 kW. The investment is expected to yield a return in less than 12 months. This will be seen in a direct reduction in Mayflower’s energy bill. O’Sullivan explains: “Sentridge had one compelling phrase: “Do you want to save $98,000 off your electricity bill? Can you afford not to?”

Other savings have resulted from reduced maintenance. For example, the 11 kW soap pump was throttled manually to achieve 3 bar, but the valve would regularly work loose. Using PID control on the AC drive, that now controls the pump, not only avoids the manual valve adjustment, but, provides a faster more reliable control method.

Mayflower’s motivation for the energy audit had been two-fold. Firstly there was the Climate Change Levy (CCL), a government energy tax that came into force on April 1st this year. Secondly, Mayflower has implemented the environmental management system standard, ISO 14001 and as such is driven towards meeting its environmental targets, which includes a significant reduction in CO2 emissions.

But such are the savings achieved using the ACS 600 and Comp-AC drives, that according to O’Sullivan, any additional saving that can be made from the CCL such as through Enhanced Capital Allowances, is a bonus. “Until Sentridge visited us, we had found the information available on Climate Change confusing and unclear. We were struggling to understand just how it applied to us. We wanted to save money and quickly”

Sentridge Control’s SEAchange energy audit is a systematic examination of key pump and fan applications that include the monitoring of energy consumed both before and after the change to AC drives. So confident were Sentridge about the results that the audit would achieve, the company loaned an ABB drive to Mayflower to test its findings.

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