DESIGN AND TEST LOADS OF THE POLAR LOAD ENVELOPE FOR WIND TURBINE BLADES

Abstract

The new international guidelines for full-scale blade static tests introduced the polar load envelope to provide much more reliable loads. Because of the ambiguous description, the loads in the polar load envelope are prone to be misunderstood as constituent loads rather than resultant loads. To resolve this misconception, the misunderstood procedure along with the consequences induced by applying the misconception to designs and tests have been examined and contemplated. Recently, resultant loads based on the polar load envelope concept have frequently been applied in oblique directional loading tests to increase the reliability. If this is considered an extension of the polar load envelope, it is unreasonable to argue that selecting the oblique polar load is more defendable than the conventional method. When the limitations of the actual test are considered along with the principal direction and primary structures, the conventional method is still valid and sometimes more reliable than the resultant load application method. Thus, the polar load envelope should be generated by using whole resultant loads. And even though conventional test is valid as a mandatory test, arbitrary directional load that causes the minimum safety margin can be supplemented to increase the reliability.