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Climate change and its consequences are a matter of growing concern. Increasing precipitation causes increasing water flows and several Swedish towns have experienced flooding. Kristianstad is surrounded by water, and Sweden's lowest point (2.4 metres below sea level) is in thisarea. To protect the city from flooding, the municipality is investingaround 22 million Euros in dykes and pump stations over the next years to 2011.
The threat of flooding
Kristianstad is largelybuilt on seabed that was reclaimed in the 1860s. Nearby flows the River Helge, which is linked to a canal system passing through the city and discharges into Lake Hammarsjön. The river has a large catchment area and flows slowly through a flat landscape. All this combines to create a high risk of flooding.
Kristianstad faced a serious threat atthe beginning of 2002, when large quantities of rain and melt water resulted in record high water levels. The River Helge reached 2.15 metres above sea level, compared with the average figure of 0.38 metres. Itwas obvious that the old dykes would not hold. There was a risk thatthe hospital would be flooded, supplies of electricity, heat and watercut off and schools and homes put under water.
Dykes and pumpsto protect the city
The Rescue Service and the municipality's C4 Teknik water and sewage department fought the water for six weeks. Pumps were operating at high pressure and a pressure bank was built in record time to reinforce the dyke. It was completed just as the waves began to wash over the edge. The rescue action was successful: only one park was submerged.
Longer-term measures are now being taken. In view of climate change, the municipality is playing safe by protecting itself against water flows three times as great as those in 2002. A total of 22 million Euros is being invested in flood defence works and pump stations up to 2011. Funds have been sought from the Swedish RescueServices Agency, which can contribute up to 80% of this amount.
"Wecurrently have five dyke pump stations in operation, with a total capacity of 14,000 litres per second," says Lennart Hermansen, Works Manager at C4 Teknik. "Their job will be to pump water from the canal outinto the River Helge when there is a risk of flooding."
Systemsthinking yields the best solution
Södra Dämmet is one of the pumpstations, and a total of 1.6 million Euros has been invested in it. Malmberg Water has supplied all the mechanical equipment, such as pumps,pipes, sluice gates and grilles. The company has also carried out theconstruction and installation of these. Project Manager Patrik Almlöfstresses the importance of systems thinking in coming up with a solution:
"To find the most cost-effective control, you need to take account of what the pump curve looks like and what the load variations are. In this case, the Emotron FDU variable speed drive was chosen. Thismeans we also know we will get reliable delivery and good technical support."
Emotron FDU controls the pumps
The canal system isintended to maintain a water level of 0.6-0.9 metres above sea level.When the water reaches 0.9 metres, the Emotron FDU variable speed drive starts one of three submersible pumps, each with a capacity of 1,000litres per second. When the first pump has reached its capacity limit, the next one will start.
A range of measures has been employed for extra relia-bility. There are change-over switches so that all pumpscan be started directly, and they can also be operated manually. Thepressure sensor is backed up by a rocker, and a mobile reserve power plant can be connected. GSM technology is used for remote monitoring ofthe pump station.
Energy saving paid for investment
The plan was to install softstarters to reduce the start current. Speed control was not needed. In the end, the chosen solution was three 75 kW variable speed drives. The option of reducing both start current and power was decisive. By lowering the frequency, the current was reduced from 100 A to 50 A, while capacity only fell from 1,000 litres to 800 litres per second. Energy consumption has been reduced and operation is optimized at all times.
"We are finding more and more advantages with the variable speed drives," says Lennart Hermansen. "It was a more expensive solution than we'd planned initially, but it's paid for itself through the energy we save."
Use of variable speed controls spreading
C4 Teknik is now introducing variable speed control in more plants to increase the efficiency of monitoring and alarm functions,thereby reducing the need for manual supervision. This also levels out the load in sewage treat-ment plants with large variation in demands, reducing wear on equipment. Water treatment works are next in line.
"There'll never again be a water treatment works without variable speed control," says Lennart. "We avoid water hammer that cause pipe damage and leaks. The reduced maintenance and longer pump lifetime morethan compensate for the higher cost of investment. And the customers get more even water pressure in their pipes."
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