Electrical Power & Protection


Saving energy and water

January 2012 Electrical Power & Protection

Omron’s solution for right-sizing pump applications.

According to Omron, when engineers select a pump for an application most opt for a built-in safety factor. However, this safety factor leads to system inefficiencies when over-pressure or high flow rates are encountered. Traditionally, the way an over-pressure problem is handled is to throttle back on the valve to lower the pressure in the system. This solves the pressure problem, but the motor and pump are still running at full speed (akin to driving a car with your foot on the brake).

Omron solves this problem through the use of its variable speed drive units, which allow users to control system pressure and flow by varying the speed of the pump motor, thus eliminating the need to throttle a valve.

A closed loop system is installed in order to achieve water and power savings. The closed loop is obtained by installing a pressure measuring sensor in the system that gives feedback directly to the VSD, allowing it to maintain a constant desired pressure by automatically controlling pump speed to compensate for changing system dynamics.

An example of the system at work: if a pivoted system that requires two bar pressure at the end of a pivot starts moving uphill, the pressure sensor will call for more flow and the motor will automatically speed up to maintain the two bar pressure. Likewise, if the pivot starts moving downhill, the motor will decrease its speed dropping the flow to maintain the system pressure. Power is saved over the time the motor is running below full speed i.e. for every 10% speed change, the power changes by 27% as it is proportional to the cube of the pump speed.

An added benefit of this approach is the reduced starting current when compared to on-line and star-delta techniques. Also, acceleration and deceleration curves are controllable, which eliminates mechanical strain on the system during start-up reducing wear in the pump and motor. Water hammer is eliminated by controlling the deceleration.

For more information contact Terry McIntosh, Omron Electronics, 086 066 7661, [email protected], www.industrial.omron.co.za



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