the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 30 Jul 2024
State-of-the-art efficiency determination of a wind turbine drivetrain on a nacelle test bench
Abstract. The efficiency of wind turbine drivetrains is a topic of great interest for both the wind energy industry and the academic community. With the developing maturity of this technology and the increasing pressures to reduce costs, the importance of drivetrain efficiency has grown. However, insufficient accuracy in torque measurement makes actually determining the efficiency of wind turbine drivetrains a very challenging task. In the project known as WindEFCY, state-of-the-art measurement and calibration instruments are used to determine the drivetrain efficiency of a direct drive wind turbine on the nacelle test bench called the DyNaLab. This paper discusses the test configuration applied for this work as well as the instrumentation of the measurement systems used. It further presents the results from two tests of different types to demonstrate the process of efficiency determination and the analysis of uncertainty. Within the paper’s scope of study, an uncertainty level of approximately 0.7 % is achievable when measuring drivetrain efficiency. Details and recommendations concerning data processing and uncertainty analysis are also given in the paper.
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RC1: 'Comment on wes-2024-70', Anonymous Referee #1, 13 Sep 2024
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General analysis:
The paper is a milestone in the recent discussions on the challenges involved in metrological traceability in the efficiency assessment of wind turbine drivetrains, one of the main international topics in the field, as addressed by the Euramet "WindEFCY" project.
This paper presents a sequence of tests involving the analysis of the energy efficiency of a drivetrain under different torque and speed settings, since these two quantities determine the input mechanical power, and the output result as electrical power. All relevant quantities and parameters involved are measured and metrological analysis of deviations and uncertainties is performed. Traditional (static) and new (dynamic) approaches are treated together to give the most appropriate interpretation and application of traceability.
The discussion and conclusion address the metrological realization of the work, highlighting mainly the measurement uncertainty of 0.7% and the relevant contributions of Pmech and Pelec.
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General recommendations:
Since the WES journal is not specifically addressing metrology experts, it is highly recommended that authors include a brief description of the main metrological terms. It does not need to be a glossary or anything like that, but including some extensive description in the body of the text is welcome.
Authors are also encouraged to consider whether it is better to create a dedicated section to describe the methodology. There is a jump from "Materials" to "Results", and part of the method is described within the results section.
The angular speeds applied during the tests are not mentioned in the text, but are identified as normalized. It would be good to have the nominal speeds (in rpm or/and rad/s) so that the reader can have an idea of the dynamics that are being addressed here.
In the Summary/Discussion/Conclusion, in addition to the uncertainty achieved, it is also important to give attention to the calibration method that is being developed, as it is written in the text "it is not always possible to reconfigure the test layout just for one test. Therefore, it is important to plan the test in advance and take all relevant factors into account". So, the method created is something that will be reproducible, even if different standard sensors are used in the future.
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Specific technical comments:
- In the abstract: Why focus on torque in the abstract, since other quantities are involved in the research and also generated important results?
- Improve the introduction to the WindEFCY project, since it is a kind of main reference to the article.
- In Section 4.1, the TTS is described as "manufactured by HBM and acquired by PTB". Harmonize the information that is contradictory to Section 1, where it is mentioned as "developed by PTB".
- In Section 4.1, text between lines 79 and 98: This whole procedure is very important to define the existing torque traceability. The suggestion is to open the description with more details, referring to previous studies that allowed this one to consider the extrapolation method as a consolidated approach.
- The expression of the uncertainty values should be more detailed with regard to the coverage factor, for example. Elements of DIN 51309, considered for the uncertainty assessment, should be better introduced, such as the classification parameters and the calibration case.
- Lines 124 and 125: I think that the concept to be achieved here is that of a Traceable Mechanical Power measurement, since there is torque and speed measured with known MUs.
Suggestion to calculate the combined uncertainties to find the "Pmech MU", as is done for the "Pelec MU"
- It is worth having a brief description of the acquisition system configuration. This is fundamental to understand the dynamic behaviors versus the static calibration chain. In addition, some minimal information about the calibrations should be harmonized (e.g.: Line 112 contains a comment about the digital filter used for angle calibration, but for torque this parameter is not mentioned)
- Lines 190 and 191: To enrich the article, it is important to look for sources of uncertainty within the 10-revolution package drive. In addition, the amplitude of the variation is important due to mechanical stresses and metrological parameters. One suggestion is to deepen the relationships between the evaluated hypothesis and the metrological parameters (e.g.: under a torque overshoot, can the transducer show any hysteresis? with speed variations, is there any considerable acceleration for the shaft?)
- In the Section Discussion, the text within Lines 258 to 264 is not clear. It is as if there were two PTB torque transducers. Is this correct?============
Specific editorial comments:
- Open some acronym explanation as the first time they are used (e.g.: PTB, WindEFCY, MU)
- Correct the description of PTB to National Metrology Institute, not Metrological...
- Revise Figure 1 to include identification of all relevant components, e.g., LAU and DUT are not identified
- Equation 1, there is no introduction to the variable Pmech in the text
- In Figure 2, identify and detail the components of the left and right image.
- Do not break lines to separate the units of their values (e.g.: in Section 4.1 "1.1 MN m")
- In Table 2, last column, the parameter is not "Pelec", but "Pelec MU"
- Revise and improve the detail of the captions for figures and tables
- Figure 6, there is no unit for PowerCitation: https://doi.org/10.5194/wes-2024-70-RC1
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