Reliable power when it matters most

When Fredericia Spildevand og Energi A/S, Denmark’s second largest sewage plant and the largest public industrial treatment plant, needed one of the transformer stations to be replaced at,

Bredenoord was contacted to ensure that the plant’s power supply would not be interrupted during the replacement work. Shutting down the plant for the several days required for the maintenance was simply not an option, as both residents and businesses need to be able to drain their rainwater and wastewater at all times of the day, all year round. The challenge was clear: to ensure excellent and stable operation at all times, during both normal weather conditions or an outright downpour.

The plant receives ten million cubic metres of rainwater and wastewater annually, corresponding to the annual water consumption of 420,000 residents. In addition to the sewage plant, Fredericia Spildevand og Energi A/S services and maintains a 1,000-kilometre long pipeline network with 38 overflow structures with outlets to recipients, aquatic environments and bodies of water, as well as 50 economising basins, 100 rainwater basins and 140 pumping stations throughout the municipality of Fredericia.

In addition, Fredericia Spildevand og Energi A/S use surplus sludge to produce energy and heat that supplies electricity to several hundred houses in the area.

The quality of the equipment is extremely important because it is a complete treatment plant that depends on three generators and the peak load can be enormous.

Important task

If rainfall and wastewater cannot be transported through the sewer system or the treatment plant does not have the capacity to receive the water, this will ultimately result in overflows and flooding, leading to pollution of the local environment. When replacing an old and worn-out transformer station at the treatment plan it was therefore essential that the power supply to the plant was maintained. Otherwise this project would result in an outage at the plant, with the risk of interrupting the transport and treatment of wastewater from residents and companies in the municipality of Fredericia.

So, comprehensive planning was initiated to ensure that Fredericia Spildevand og Energi A/S could secure the power supply using other sources. This work was tasked to Per Tandrup Dejgaard, an engineer at Fredericia Spildevand og Energi A/S, and the solution was to rent two twin sets of 500 kVA each and a large 1,250 kVA genset from Bredenoord.

There were strict requirements for the equipment, which had to be powerful enough to handle the operation of the treatment plant, both in a normal situation and during heavy rainfall.

"The quality of the equipment is extremely important because it is a complete plant that depends on three generators, and the peak load can be enormous," says Per Tandrup Dejgaard. “The largest pump has a nominal power of 110 kW. Denmark's second largest treatment plant cannot be shut down and allow untreated water to discharge into the Little Belt.”

Extensive capacity tests

The task required close coordination between Fredericia Spildevand og Energi A/S and Bredenoord to ensure the power supply during the replacement of the transformer station. The approach taken was successful, thanks to the comprehensive capacity tests carried out by Bredenoord prior to the actual replacement work. In these tests, Bredenoord simulated the loads on the generators at Fredericia Spildevand og Energi A/S by providing the generators with incremental load steps. This way the client knew the size of the voltage dips that could be expected when the pumps were switched on and off. The capacity test showed that the generators were fast enough to adjust themselves.

In addition to the functional requirements, the leased equipment aligned with Fredericia Spildevand og Energi A/S’s strategy to optimise energy for its own processes and reduce its own energy consumption, as the twin sets are more energy efficient. This is because a twin set consists of two generators that are connected together, with one providing power in the most energy-efficient performance mode and the other on standby, ready to take over or assist when needed. This ultimately benefits both the environment and the climate.

The delivery and setup of the leased equipment went according to plan. Five days were allocated for the entire task and this deadline was not exceeded. On Monday, the first of three trucks left Bredenoord and headed towards the treatment plant in Fredericia. On Tuesday, the actual replacement of the transformer started and on Thursday the work was completed, so that the treatment plant could be reconnected to the power grid. On Friday, the equipment from Bredenoord was packed for pickup.

In addition to the generator plants themselves, Bredenoord supplied 1,800 meters of cables, as well as fuel tanks for the generators. These fuel tanks were equipped with tank monitoring to allow Bredenoord, in collaboration with the fuel supplier, to ensure the operation of the generators 24/7.

Fredericia Spildevand og Energi A/S had a clear success criterion for the replacement of the transformer station at the treatment plant: the replacement had to take place without disrupting operation. They succeeded in upholding this criterion, so the company was able to treat wastewater as usual without any overflow – thanks to the successful collaboration with Bredenoord’s experts.