10089_001.pdf - Load set calculation - ECN

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Load set calculation DOWEC 6MW H. Efdé The standard load cases apply to a rotorspeed of 11.84 rpm, the LTS (Low Tip Speed) load cases 10.36 rpm and the HTS (High Tip Speed) loadcases to 12.58 rpm. For this Low Lambda analysis load case 027LL was generated to assess the fatigue damage of a LTS turbine at a stochastic windspeed of 27 m/s (wished rotorspeed at 10.36 rpm). The occurrence of the load case is based on a Rayleigh distribution with a Vm of 9.2 m/s. The Pmean is the average generator power of the load case and is used to calculate the yearly production. The results of the load case calculations can be found on CD C45.04/01.03/03. The 1Hz equivalent fatigue tables can be found in Appendix H as well. 5.6.1 Cost of energy. The blade- and tower parameters and the annual production are taken into account for the calculation of the cost of energy. The annual production is calculated by ADAP using the occurance and mean power from table 18. The average gearbox torque could not be used, since the rotorspeed-shaft torque table differs per loadcase. Also extreme values are not available because the loadsets consisted only of fatigue loadcases. The results are presented in the table below. Table 19: Cost of energy Low Lambda control variations. Low Low Low Low Lambda 1 change in Low Lambda change in Lambda 3 change in Lambda 4 change in Lambda 5 change in 100% loadcase change cost 2 change cost change cost change cost change cost blade kNm % % % % % % % % % % Myb[i]-p[01] -18006.00 Eog50-12 n.a. n.a. n.a. n.a. n.a. 1Hz-Mxb[i]-p[01] 4483.82 all -1.72 -0.03 -0.71 -0.01 1.46 0.02 1.79 0.03 0.89 0.01 gearbox Mxn mean n.a. n.a. n.a. n.a. n.a. tower Myt[01] -281560.00 GrEog1Voc n.a. n.a. n.a. n.a. n.a. 1Hz-Myt[02] 2558.84 all -4.33 -0.14 -1.83 -0.06 0.73 0.02 3.95 0.13 0.32 0.01 total -0.16 total -0.07 total 0.05 total 0.15 total 0.02 annual production baseline LL1 change (%) LL2 change (%) LL3 change (%) LL4 change (%) LL5 change (%) MWh 3532.3 3511.4 -0.59 3528.4 -0.11 3429.4 -2.91 3422.4 -3.11 3427 -2.98 LL1 loadset, influence on cost of energy 0.42 LL2 loadset, influence on cost of energy 0.04 LL3 loadset, influence on cost of energy 2.76 LL4 loadset, influence on cost of energy 3.17 LL5 loadset, influence on cost of energy 2.92 Based on the simplified Low Lambda load sets and the cost of energy model, it can be concluded that only LL1 has a reasonable decrease in fatigue damage. But because the annual production is lower, the cost of energy increases. LL3 to LL5 even cause more fatigue damage than the baseline while production is lower than the baseline. R45.04/01.03/03 Stentec, 3-1-03 page 22
Load set calculation DOWEC 6MW H. Efdé 6 Conclusion. Based on the turbine description of ECN ref. [3] a PhatasIV load set has been generated. With the results of this final load set the components of the turbine can be checked by NEG Micon or ECN for ultimate and fatigue loads according to the IEC and DNV regulations. From the results of the load cases it is shown that the turbine behaviour is conform the load set description given by NEG Micon ref. [2]. But the extreme loads are not in accordance with the expectations. When table 10 is compared with ref. [13] it can be concluded that the maximum tower top tilt moment Myt[02] is 1.7 times higher than calculated statically. The highest tower bottom tilt moment Myt[01] is 2.5 times higher than expected. A possible cause for this large difference might be the ECN modelling that allows short generator overshoots while originally the 6MW was considered to be an absolute highest value. Key load cases are used to calculate DOWEC design variations. Of the most important parameters tables with extreme values and 1Hz equivalent signals can be found on CD C45.04/01.03/03. To make the large amount of data understandable, it has been used to calculate relative turbine costs and changes in cost of energy. It is shown that tower frequency and turbine control have the largest influence on the cost of energy. An increase or decrease in tower frequency of more than 0.1Hz, a lower tipspeed or the use of peak shaving will have a beneficial influence on the cost of energy of the 6MW DOWEC. R45.04/01.03/03 Stentec, 3-1-03 page 23
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