Surgery
Question
In what ways can drives help reduce pump running costs?Answer
Geoff Brown, Drive Applications Consultant, ABB Limited 
Variable speed drives can help reduce pumping system running costs in many different ways. Energy is the largest part of the running cost. With a drive, it is easy to control so that your pumps are not running at higher speed or for longer hours than needed.
The cost of unexpected downtime and lost production is a very significant part of the lifecycle cost and can rival the energy costs. Variable speed drives cut maintenance and repair costs not only of the pump, by reduced water hammer effects, less stress on the electrical supply, minimized risk of cavitation and by offering redundancy. It also reduces the cost of maintaining the associated valves as it reduces wear.
Water hammer is caused by rapid changes in flow. These flow changes are followed by rapid pressure transients that can damage pipes, pipe supports and valves, causing leakage. Variable speed drives allow you to gradually ramp the acceleration at a safe rate to avoid hammering.
Less stress on the electricity supply is achieved by soft-starting the pump motor, giving much lower peak current than direct-online starting.
Cavitation occurs whenever the static pressure drops below the liquid vapour pressure, causing bubbles to collapse with a very high impact force. This force causes surface damage inside the pump. With a variable speed drive, it is possible to monitor the pressure of the incoming pipeline and take steps to avoid cavitation.
Redundancy can be offered by using parallel pumps. If one pump fails, the remaining pumps can continue uninterrupted. During normal duty, the load can be shared between the pumps to achieve the most energy efficient operation. You can also control the running times of each pump to get service breaks at the most convenient times.
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Email: enquiries@gb.abb.com
Web: www.abb.co.uk/energy