Approved testing at Delta
Delta is one of the nine Danish GTS institutes (GTS is a Danish abbreviation of ‘approved technological service provider’). An approval from the Danish Ministry of Science, technology and development is required to get GTS status.
Test rigs at DELTA
1. Electromagnetic compatibility test rigs (EMC rigs)
The item is tested for the reaction to disturbances from lightning, flight traffic and all other kinds of electromagnetic noise, etc.
2. Climatic test rigs
The item is placed in test chambers with extreme heating, cooling, humidity, dust, salt mist or water spray plus testing for other types of corrosion.
3. Mechanical testing
The item is subjected to vibration, shocks, drops, impacts, pulling on cables etc.
HALT testing: the buzzword of testing
HALT is a methodology to challenge the upper limits of a component or group of components. It is utilized to find and correct weak points at a very early stage in the product development process and can improve the robustness of the product. A traditional thermo-mechanical HALT combining temperature and vibrational influences reveals three thirds of the flaws in a new design and is thus considered the most efficient way to assure quality. With a HALT test the upper limits of durability is tested; not the lifetime.
Although wind turbine companies put a lot of resources into developing their own test facilities, Delta test institute is not worried about business. Test methods are getting more and more complex. OceanWise takes the pulse of a business area that has been growing steadily over the past few years.
By Anne Korsgaard
At Delta test institute, an institute specializing in acoustic and electrical testing, they know something about what’s cooking in the renewable wind sector. Kim Albert Schmidt is a reliability consultant who advises and makes test programs for customers requiring independent testing of their products. He can see two main tendencies in testing for the wind sector.
"I see the number of combined tests increasing. There is a growing understanding of the fact that a component has to be submitted to simultaneous heat, cold, vibration etc. testing, whereas previously we would keep the influences apart", he explains and continues:
"Another tendency is that the manufacturers of wind turbines use test results and certificates as a marketing and sales argument when submitting their designs to the power utilities. This need for documentation and certification of the reliability and overall quality of products is where Delta is strong".
Setting up for electromagnetic testing in one of Delta’s large test rooms. Photo: Delta.
Challenges and opportunities
In a sector where the manufacturers seem to have discovered the advantage of testing in-house, it might be a challenge to keep an independent test business performing strongly. But this does not seem to worry Kim Albert Schmidt. Amongst other things, he sees big opportunities in teaching and training the manufacturers and sub-suppliers in the running of their test facilities.
"At Delta, we have the advantage of 70 years of experience with testing in areas as varied as bicycle lights, control systems, and wind turbines. One of the challenges for the manufacturers is to constantly have enough in-house test experience to choose the correct test methods, to make efficient test programs and to interpret the results. The test design is crucial in order to avoid underestimating the challenges facing a new product. Thus one of the great challenges for the industry is to assess in which areas it makes sense to do testing in-house and where it does not make sense".
The great focus on testing creates many new opportunities:
"The biggest opportunity that we have to seize right now is to take advantage of the high degree of professionalism in the sector. There is a basic interest in testing and an understanding of the major advantages, also financial, in discovering the teething problems in a product or component at an early stage of development. And I see it as a great advantage for the product’s quality that it is well tested. It makes sense and we still have a lot of testing to do e.g. in certifying products, as it becomes a parameter of competition to have documentation of quality".
Philosophy: the earlier, the better
The earlier in the development process the testing of a component starts, the easier and cheaper it is to correct and adjust it before it creates dependencies on other components or goes into serial production.
"For example, when we test the effect of components (that control the electricity in a wind turbine) it is highly effective to use the HALT testing methodology early in the production cycle because in this way we can give the product a sort of vaccination against childhood diseases. Typical flaws found in a HALT test may be overheating of the components in a nacelle due to lack of appropriate cooling or a print card losing components due to weak soldering points or poor component fixing that will show up in the vibration test", explains the reliability expert.
Thus the test philosophy at Delta is to carry out stress testing as early as possible. When it comes to ‘How to do it’, Delta has a number of test methodologies. For the Wind turbine industry, the following two strategies are the most commonly used:
- Weak-point testing in the form of Highly Accelerated Lifetime Testing or HALT. It is a fairly simple process: keep on increasing the stress until something stops working or breaks down. Improve the product on this weak point and continue the HALT with even higher stress levels and so on.
"Design Verification Testing (DVT). The product is tested up to a given set of minimum requirements in order to verify compliance. This is often performed according to recognized international standards such as IEC, ISO and EN. DVT can include testing of performance, environmental conditions and reliability".
The youngest sibling in the test family is the so-called Calibrated Accelerated Lifetime Testing or CALT. Kim Albert Schmidt explains:
"CALT was developed by General Motors back in 2004. Using this method we can find a good estimate of the actual lifetime within a few weeks of testing. Performing both HALT, DVT and CALT ensures and documents robustness: DVT can verify that the predefined set of requirements are met, but it cannot improve the robustness, whereas HALT can improve the robustness of a product, but cannot give a number for the lifetime, and CALT can give a figure for the expected lifetime, but cannot improve the robustness of the product".
Although a lot of the testing at Delta is performed on small items like electrical components and component groups, size does matter. The practical limit at the moment is a maximum mass of 1000 kg and maximum size of up to a couple of meters. When faced with the question of which test facility Kim Albert Schmidt would wish to have in one of his test centers, he answers with excitement:
"A giant shaker that could apply six degrees of freedom, he says and makes a short pause, and then I should also have a climatic chamber to put on top of it in order to offer combined vibration and climatic testing of whole nacelles, for instance. That would be awesome".