Grid connection guidelines

Experiences with grid connection guidelines and the certification of Howden / KK&K-Steam Turbines


The ongoing energy transition is shifting power generation from a small number of large power plants to numerous decentralised plants. To ensure that grid stability continues to be guaranteed, uniform regulations have been established throughout Europe via Regulation EU2016 / 631. With the subsequent implementation of German national standards (VDE4110 and 4120) three different ways of proving the grid conformity of plants have been indicated: firstly, via a unit certificate for standard machines, secondly via a prototype process that also leads to a unit certificate and thirdly, individual machine verification procedures. Typically, certification is carried out by a third party. With these certification procedures, manufacturers and plant operators as well as network operators are confronted with new tasks. Additionally, especially with regard to customer- optimised, smaller steam turbines, the certification process also poses a commercial challenge.



Challenge: certification for small, individually-designed steam turbines

Steam turbines in the Howden-KK&K series have a relatively small output of up to 15 MW el. They are often used to increase steam utilisation and thus directly increase energy efficiency. Applications include pressure reduction in steam and (district) heating processes and the utilisation of residual steam for power generation. Often the actual steam process already exists and the turbine is added. To ensure the best possible utilisation, each Howden steam turbine is individually designed, as the processes are very specifically designed as well. Howden turbines are designed based on customer operating points, so no two turbines are alike. Howden turbines can be single- or multi-stage, and one or more steam extraction units are possible. Condensing turbines are often used for residual steam recovery. Howden’s own power and process controller allows one or more process variables, such as live steam pressure or exhaust steam temperature, to be individually controlled in parallel with mains operation. This high degree of optimisation and customisation for each individual customer means, of course, that there is no standard product.

The only possible way to obtain plant certification for individual turbines is the individual verification procedure. In this procedure, the machine is designed, the simulation model is created and then, during commissioning, the machine is tested and validated in its facility over several days for its electrical properties. Particularly for turbines with a connected load of less than 1 MW, the costs of certification in the individual verification procedure can amount to up to 30% of the machine costs. This is of course an economic barrier for many customers. In addition to the pure costs, the complexity of certification is another difficult point to clarify. The certification process introduced in Germany leads to an economic obstacle and thus to a slowed-down energy turnaround, as the energy feed-in becomes uneconomical due to residual steam generation.

In addition to the commercial aspects, two other major problem areas in particular can arise during certification: on the one hand, the technical design of the machine and on the other hand, the process of certification itself.


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