Although the Siemens Wind Power strategy is to use proven technology to the greatest possible extent, the ramp-up of any new turbine type inherently holds a number of risks. Testing is a key measure in minimizing these risks.
By Anne Korsgaard
The Siemens 6 MW wind turbine is the 32nd wind turbine product from Siemens Wind Power since 1980. But even with this track record and experience within the company, product testing is still a high priority.
The test program for the 6 MW turbine is first and foremost more elaborate than any test program Siemens has ever run, according to Henrik Stiesdal, Chief Technology Officer at Siemens Wind Power and one of the most experienced engineers in the wind industry:
"When developing a new wind turbine, we use as much proven technology as possible – but the ramp-up of technology can still create unforeseen challenges. That is why testing is so important at every single stage of development. Now that the gear box is no longer a weak point, we must direct our focus to rethinking, for instance, the surveillance systems. However, the most critical components are still the main bearings, generator, and transformer".
Main bearing test set-up that allows bending moment on the main bearing while the shaft is rotating. Photo: Siemens Wind Power
Considerable testing is done on the first prototype installed at an outdoor test site at Høvsøre on the windy west coast of Jutland, Denmark.
"At Høvsøre, we measure power curve, noise, safety systems reliability, and functionality. We do structural measurements and a large number of electrical tests, for instance grid simulation. There are 120 measurement points on the nacelle and blades to prove the design assumptions", explains Henrik Stiesdal.
Parallel testing saves time
Testing is carried out simultaneously at Siemens’ in-house test rigs and on the test site. The testing has a time overlap to ensure a safe ramp-up of the product. The basic idea is to do robustness tests like for instance Highly Accelerated Life Tests (HALT tests) on all primary components and systems before the product is ramped up big time and to do this simultaneously with the real-life testing being undertaken at the Høvsøre test site.
"We want to speed up the process in order to market our product as soon as possible. The results that we receive from the test site are channelled directly into the project and used to optimize the product. Thanks to the HALT methodology, with high acceleration and increased loads, we test the components and systems for a whole lifecycle within a few months.
The testing of a new wind turbine model like the 6 MW starts early in the process, beginning already when the technology development results in the first components and groups of components. Many tests have thus already been performed on the 6 MW.
"We have done a low-load test where we drive the entire nacelle using a 1.3 MW drive train as a drive unit. We have also carried out vibration testing, shaking the whole rear end of the nacelle to find the weakest point. Over the next months, we will test the generator on our performance test stand and do a back-to-back test of the entire structural system of the turbine. Using an extra generator as the drive unit, the whole drive train of the 6 MW is operated under extremely heavy loads. Parallel to all this, we test the prototype at Høvsøre",explains the CTO.
Drawing on extensive experience, the full test program will last approximately two years and will be performed at the Siemens test facilities in Brande and in Aalborg, Denmark.
Full-scale, realistic test facilities in Denmark
Measurements in the field as well as testing in in-house test centres is undertaken by the approximately 100 employees dedicated entirely to this area in Siemens Wind Power. It is commonly said that around 75% of design or engineering flaws are revealed by a combination of component and component group testing at the technology development stage and full-scale field testing of a prototype. This still leaves a significant number of the potential flaws remaining undetected until the product has been launched in significant numbers. This is the reason for Siemens’ emphasis on full-scale HALT testing parallel to prototype testing.
"We need good, realistic test sites with conditions that resemble offshore, for example for load cases. At Høvsøre, wind loads are very varied – the turbulens intensity varies from 8 to 15% depending on the wind direction - and the medium wind speed is around 8.5 m/s. These conditions can help accelerate the wind turbine test, says Henrik Stiesdal. He continues:
"However, we also know that thorough, realistic testing on a test bed simulating 25 years of operation will further reduce the risks of ramp-up. Experience has taught us that efficient and combined testing will pay itself back tenfold in saved repair costs".