In modern industry, one of the most highly utilised form or rotating machine (after the electric motor) is the pump. As a result, pump control is a huge business and also one driven by efficiency gains to streamline process control and also save the end user money.
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 it’s 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 per cent load but the flow is restricted by a semi-closed valve. We have extra motor and pump losses and now we add valve looses. In all, not a good outcome for the pump, the energy consumption or the end-user.
Technology, as always, comes to the rescue. 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.
Essentially how it works is we fit a “pressure” or “flow” transducer (sensor) 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 huge amounts of 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 outstanding flexibility for variable speed industrial process applications such as pumps.
The new Bonfiglioli Vectron ACT 201 and 401, for example, combine award-winning hardware design with an unparalled flexibility of macro configuration-based software control. The ACT series of drives is equipped with a PI control loop (in fact PI controls many aspects of the ACT drives but this is an article for another day!). For the application of flow or pressure control and to differentiate us from the pack, we call it a Technology Controller and it offers a few subtle differences.
Firstly is we can set the Technology Controller 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 in a wide range of industrial, commercial and domestic buildings.
Perhaps the simplest way to illustrate the benefits is to think of the ACT working in conjunction with an irrigation pump, for which you could set up four distinct operation points for each of the years four seasons (summer, autumn, winter and spring all demand different amounts of water for plant growth) and then simply switch them over when you needed to. We can further expand on this with the ability to assign a number of “fixed reference” channels or points per each individual data set that will tell our drive to react in a different way to the same signal from our pressure transducer. From this we could have a day and night pump behaviour for each of the four seasons all from the one Variable speed drive and a simple transducer.
Such flexibility can be very powerfully efficient and extremely commercially competitive across a wide range of industrial and process control applications ranging from manufacturing to mineral processing and water treatment and conservation.
Setting up of the system is very simple with the ACT because we have designed the software to be diagnostic as well as operational. The user will know the performance of the pump in terms of desired pressure (in the example of a constant pressure variable flow system which is very common) and they input this data into the drive. The system integrator will also know the characteristics of the installed transducer and we can then use these two fixed and known values to set up the system.
The customer simply increases the speed of the pump using the VSD until he reaches his desired pressure (read either from the drive or from an external pressure meter), they then use the VSD to visualise the value that is actually been returned from the transducer and they simply enter this into the fixed reference set point of the VSD and that’s it, the drive will maintain that pressure or operating point by automatically adjusting the motor/pump speed to the changing values measured in the pipes…very simple and very quick and of course it can be fine tuned by individual adjustment of the Proportional Value and Integral time.
Remember the benefit is the process, once set up, is automatic and also will save the user considerable amounts of money in the terms of efficiency gains as the pump only works as hard as it has to. In these days of mandatory efficiency levels in electric motors measured in single digit figures, a saving of up to 40 per cent when using PI control VSDs and pump sets can only make sense.
Quickly and easily setting the system up using the ACT and Technology Control can only bring further benefits to the market.