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Update your drives for best performance

28 February 2012

Are you getting the best from your drives? Replacing them with more modern products that offer better efficiency and more capable software could transform your process and save even more energy. Neil Ritchie reports

More and more companies are getting the message about variable-speed drives (VSDs) and the energy and process benefits they can bring. Your organisation or facility may well be one of them. But, are you getting the most out of your drives?

It has been estimated that 40 percent of new drives are bought as replacements for VSDs bought within the past 25 years. Some companies are obviously looking at their existing drives and wondering if they could do better.

The answer is probably yes. Today’s drives technology is much more efficient than those introduced in the 1980s. These early drives had a typical efficiency of about 80 percent, while today’s drives are often in excess of 90 percent.

Users of old drives also miss out on energy saving features such as flux optimisation, a software algorithm which automatically provides the motor with the optimum voltage for any operating speed and load. This can save up to 10 percent more energy in pump and fan applications.

There is also the possibility of updating software to run the process itself more effectively and efficiently, leading to savings in operational or maintenance costs. 

With some manufacturers’ products, spare parts become increasingly difficult to find once the drive has reached a certain stage in its product lifecycle. ABB has developed a product lifecycle management model that provides proactive service for maximising availability and performance. This model provides not only optimum support to end-users but also a smooth transition to a new drive when the service life of the current drive ends.

When assessing an application for drive replacement, it is always best to treat the application as a new installation and base calculations on the present torque requirement of the load. Parameters may have changed while the old drive has been in operation and the conditions that dictated the original sizing of the drive may no longer be valid. Moreover, in the past, drives were often ten percent oversized compared with what would be the norm today.

But how do you go about upgrading your drives? How can you be sure you will get the right one for your needs? Reputable drives manufacturers have tried and tested processes in place to help companies choose the best drive for their application. Take ABB as an example. Working with its ABB Drives Alliance network, the company can assess a site and application and make recommendations. And using dedicated software, it can enter the details of its older drives and determine the best new replacement drive for an application.

This process may involve an energy appraisal. ABB’s 50 strong Energy Appraisal Team provides companies with a free, no obligation energy appraisal to determine which applications would most benefit from a new unit., and long experience has led to the development of a set of tools that equips each team member for any eventuality.

A camera is carried  to capture images of each process, a torch to make sure no detail is missed, a tape measure to determine the exact space needed to fit a new VSD and an energy meter to measure the before and after energy use of a particular motor driven application. It even features a telescopic mirror used to get into the difficult areas where motors are often located, so that they can get to the motor nameplate data.

Let the savings flow
An example of the energy saving benefits that can be achieved is demonstrated by a project for Anglian Water Services (AWS). With help from ABB it has saved a total of over £2.7m on energy costs across a hundred of its sites.

Part of the programme was identifying opportunities to replace existing drives with newer, more efficient versions. The viability of energy savings was proven by monitoring the existing system for a period of time, then installing one of ABB Drives Alliance’s hire drive fleet and monitoring again. This ‘try before you buy’ method helped prove to AWS that the proposed upgrade would achieve the savings predicted.

Sky high savings
A similar programme produced 50 percent savings at Manchester Airport. Working with members of the ABB Energy Appraisal Team, as well as ABB Drive Alliance member Quantum Controls, Manchester Airport carried out extensive trials on air handling units (AHUs) 48 and 49, which serve the Terminal 1 check-in hall. Terminal 1 is some 50 years old and the normal practice at the time was to oversize motors. By installing the latest ABB IE2 high efficiency motors and resizing them to a more suitable frame size, energy savings of five percent can be realised.

ABB drives for HVAC were also installed on the two AHUs used in the trial. To prove the savings, Manchester Airport’s Engineering Team installed permanent half hourly energy meters and monitored the results over a six month period. By reducing the set point frequency from 50Hz to 40Hz, it was shown that savings of 50 percent could be made with no noticeable change in the air flows provided by the AHUs.

Eventually, the project involved replacing motors in 110 AHUs with 220 ABB drives for HVAC and 220 IE2 high efficiency motors, throughout the airport’s terminals 1, 2 and 3.
Annual savings for the high efficiency motors and inverter drive elements of the scheme were calculated at 4,000MWh, which saves around 2,200 tons of CO2 a year.

Cutting the waste
An illustration of how the capabilities of modern drives can improve a process is a project for Severn Trent Water (STW) that is saving the company around £100,000 per year on energy costs. STW was suffering low flow rates on its dry well flow pumps, with typical rates being less than 400 litres per second against a design of 550 litres per second. ABB Drives Alliance member Sentridge suspected the problem was due to ragging of the pumps and reversed the flow of selected pumps to prove this.

The original installation had four direct-on-line pumps and two pumps controlled by VSDs. One of the drive controlled pumps was a duty pump while the other was used to assist as pumping requirements demanded.

Reversing the pumps had allowed them to achieve higher flow rates for short periods of time. One of the direct-on-line pumps achieved 550 litres per second compared with the 325 litres per second achieved previously, while one of the VSD powered pumps achieved 575 litres per second, compared with 390 litres per second.

To solve the problem permanently, Sentridge suggested installing 75kW ABB industrial drives on all the pumps, each equipped with ABB anti-jam software, part of its intelligent pump control (IPC) software suite. An add-on to ABB industrial drives, IPC contains all the common functions needed by water and waste utilities, industrial plants and other pump users.

With increased energy saving potential and improved control features, modern VSDs can offer a significant improvement in the operation of pump and fan driven applications over their forbears. It could be high time to take a long hard look at your own drives and see what improvements you could make.

Neil Ritchie is with ABB Limited


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