High accuracy with heavy elements

Building high-voltage substations is precision work. Especially the concrete foundations of the electricity fields require tight dimensions with low tolerances. Van Dijk Beton knows all about that. The Groot-Ammers-based company supplies precast foundation beams, cable ducts and shear walls for several of TenneT's high-voltage substations, including the one in Zevenhuizen. 

Van Dijk Beton is one of the companies chosen by construction consortium SC&M as preferred supplier for a number of high-voltage substations. "Our core business is precast with a specialization in larger elements," says Henk Schaap, commercial director at Van Dijk Beton. "For example, we supply piers for the portals of the Department of Public Works and shrapnel walls for the transformation stations; these are precast walls that ensure that in the event of a transformer explosion, the pressure of the explosion is diverted vertically as much as possible, thus limiting the consequences of an explosion." For the station in Zevenhuizen, Van Dijk Beton supplied a special type of shrapnel walls as well as the foundation beams and all the cable ducts with associated covers. "A total of almost four thousand tons of precast elements are involved."

The basis of the power fields is formed by a grid of foundation beams. Schaap: "A high degree of accuracy is required here. It involves 500 beams of 3 to 7 meters long that are partly cross-linked and monolithic with the pile foundation and interconnected. Anchors must therefore connect properly. On this grid are placed the Mobriq elements that carry the steel superstructure. For Zevenhuizen, we delivered a total of almost three kilometers of foundation beams, accounting for 3,000 tons of precast concrete. In most elements, in addition to structural reinforcement, there is special earth reinforcement that is connected to the earth grid via earth plates."

Another important part of the high-voltage substation is the cable ducts located in the switching garden. "This too involves hefty numbers," Schaap said. "In all, we delivered 750 meters of cable trays. These are straight sections, corner elements and T-splits, obviously with matching covers. We supply these channel elements in various sizes and with a single compartment or in two- or three-compartment layouts. The lids can have different thicknesses, depending on the traffic load the gutter has to withstand locally."

A special delivery involved the shrapnel walls of high-voltage substation Zevenhuizen. These are in a U-shape around TenneT's two large transformers that convert high voltage to medium voltage. Schaap: "These walls ensure that any explosion goes upwards. Usually they are constructed with horizontal elements, but here we chose 6.5-meter-high vertical elements 2.5 meters wide. Each element weighs about 17.5 tons and 30 were needed to build the walls. They taper upward, which saves in concrete without compromising the protective function. In addition, the client requested walls with relief on the outside to add some aesthetic value. This was achieved by including a textured mat in the bottom of the mold. This relief is not up to the edge, as this makes the elements more vulnerable to minor damage. The wall elements are connected to the foundation via plug anchors. All gaines for pouring concrete are on the inside. This prevents the beautiful relief wall from being marred by capped spar pipes. Even on an unmanned high-voltage substation, you want it to look good."