A control system based on CC-Link has integrated eleven boreholes in the West Jutland region of Denmark so that the on-demand water supply can cope with the increasingly variable daily demand brought about by the growth in tourism.
Rural West Jutland has long been a magnet for tourists, but a concerted promotional effort has built visitor numbers to the point where tourism is now an important part of the regional economy. However, this means that the population varies considerably between the winter and summer, and water demand can be as low as 1500 cubic metres per day or as high as 5000 cubic metres per day.
The existing supply system was based on five remote boreholes deep in the local forest and a main pumping station 1.2km away. Each borehole was 100m deep and could supply up to 30m3/hr. The control system, installed in the 1970s, was electromechanical and had no provision for remote monitoring, which made it expensive to maintain. It was therefore decided to sink another six boreholes and to upgrade the control system.
One of the first technical issues to address was the highly distributed nature of the system, and this lead to the decision to use CC-Link, which can be used over extended distances with either standard cabling or optical fibres.
CC-Link (Control & Communication Link) is a field network system that processes both control and information data at high speed to provide efficient, integrated factory and process automation. The dual functionality leads to a significant reduction in cabling, and CC-Link is an 'open' system with many manufacturers making compatible control equipment.
Because West Jutland is very flat, lightning strikes are common. These can lead to transients in communication signals, so fibre-optic cabling was selected and repeater stations located at key points in the network.
The master control installed at the central pumping station was a Mitsubishi Q-series PLC (programmable logic controller). This is connected to the fibre-optic network through Wago I/O modules that monitor a range of sensors and switches at each borehole.
Two major advantages of the new control system are that it monitors itself constantly and it has high-level diagnostic capabilities to determine the cause of any problems that are encountered. Furthermore, it uses predictive diagnostics, monitoring parameters such as ground water level and critical bearing temperatures to identify potential problems early. This has reduced the running costs and maintenance costs considerably, despite the expansion of the system.
In normal operations, two, three or four boreholes feed the system, each working on a staggered two-hour duty cycle before another borehole takes over. As demand increases, more boreholes can be brought on line, although it only rarely goes above six working at once. All but one of the boreholes are fitted with a CC-Link controlled variable-speed drive on its main pump so that flow can be trimmed to match demand, and extraction is shared evenly over the system.
Additionally each borehole is individually tested one night every month. This is done automatically over the CC-Link communications, putting the hole through a pre-defined 30-minute routine that tests all its associated equipment and measures the water output.