The Facts about Wind Power Pitch Control Accumulators, by the People who Know Figure 1: An Example of a Piston Accumulator from an Olaer Test Bench under Simulated Pitch Control Application Conditions


Product is shown after 1.1 million cycles.


Figure 2: Closed-loop System Prototype under Test in the Olaer Laboratory


Figure 4: The Olaer Wind Power Development Process with Bladder Accumulators


Application


Reliability assessment


Milking machine testing (patent pending)


Rotation 30 rpm


Oil volume displacement


MM FEM analysis: solicitation evaluation Application FEM analysis FEM = finite element modelling.


Figure 3: The Olaer Finite Element Tool in Action, Shown with One of Our Transparent Test Accumulators Modelling the Product in Rotation


Mounting Position and Packaging Space


We know that a poor mounting position will lead to premature product failure in bladder accumulators, as has been seen in earlier generations of wind turbines. However, working in co-operation with our OEM customers, it is now well-established practice on new turbines to mount the bladder accumulator parallel to the axis of rotation. Generally, the bladder accumulators are mounted in a ‘cartridge’ arrangement, which reduces connecting and supporting structure costs. This is now a ‘non-issue’.


We are tempted to say that mounting position is unimportant for piston accumulators but, as of today, there are not a lot of data available to validate this. We have heard some rumours from customers that there are some disturbing wear phenomena when piston accumulators are mounted parallel to the axis of rotation, but again we would stress that we do not have data to validate this.


if the product fails in the field in 10 years, we will find that in the laboratory within two months of testing.


This technology is only applicable to bladder accumulators and no such equivalent technology exists for piston types, which is one of the explanations for the lack of data on lifetime expectations.


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However, a much more significant issue is the geometry of the product. For the most commonly required size of 20 litre accumulators, the bladder accumulator is a very compact solution, as the diameter is 226 mm with a typical total product length of 895 mm.


In order to keep costs down and to avoid some regulation issues (e.g. to be outside American Society of Mechanical Engineers [ASME] regulations


MODERN ENERGY REVIEW – VOLUME 4 ISSUE 1


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