Pump drive saves energy


Traditionally, pumps are started 'DOL' or direct on line. By that we mean when there is demand for (example) water, the operator throws a switch or closes a contactor and the pump turns on. When the demand is met, the pump is turned off. This is relatively simple; however, it causes wastage electrically because every time the motor is switched on it sees an 'inrush current'.

It also offers little flexibility because the pump is either flowing at a fixed rate or not - and sometimes variable flow (or pressure) is required by the user. To offer a variable flow rate, an oversized pump is used and then valves are introduced into the system to restrict flow. Unfortunately, this makes the overall system efficiency far, far worse - the pump is working at 120% load but the flow is restricted by a semi-closed valve.

For some time now, pump manufacturers and system integrators have used PI Control in conjunction with a variable-speed drive (VSD) to ensure the pump only works as hard as it needs to - and, in turn, realises significant gains in system efficiency. A pressure or flow transducer (sensor) is fitted into the pipe work of the system. This transducer then sends a signal back to the VSD and the drive uses a PI calculation to respond to the actual events in the system. The P in PI stands for proportional or the amount of response and the I stands for integral or the time of the response. The beauty of PI Control is both sides of the calculation can be set up individually to give a high response quickly, or a little response slowly, or any combination between. This offers the system integrator great flexibility. It also saves considerable money via energy efficiency as the pump is only working as hard as it needs to in order to meet demand and best of all once a PI control loop is set up the whole process is automated.

The downside of a PI Control loop is it can be a little confusing and difficult to set up depending on the application. This is where selectable vector drives can offer flexibility for variable speed industrial process applications such as pumps.

The Bonfiglioli Vectron ACT 201 and 401, for example, combine good hardware design with the flexibility of macro configuration-based software control. The ACT series of drives is equipped with a PI control loop. The application of flow or pressure control is via the Technology Controller which can be set up to behave in different ways depending on the specific application, such as indirect flow control, maintain filling level in tank, etc independently of the proportional and integral values. This is done by data set switching and will allow up to four distinct operating characteristics all remotely switchable.

The benefits are immediately apparent for manufacturing and food and beverage processing, for example, where different inputs are required for different stages of the process. The same could be said for pumps responding to seasonal demands - and even differences between night and day - such as the pumps used on heating, ventilation, air conditioning and refrigeration equipment.

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