WP2:  Mechanical power measurement

The aim of this work package is to develop a transfer standard for mechanical power measurement consisting of a traceable torque and a traceable rotational speed measurement up to 5 MN m and 1600 min-1 respectively working in a timewise synchronised manner. To perform a traceable efficiency determination in test benches, a traceable mechanical power measurement with a target uncertainty below 0.5 % is required. A calibration procedure for mechanical power measurement will be developed.

Based on a survey among test bench operators, the requirements on tachometers to measure rotational speed will be specified. After investigating the physical principles of tachometers and their synchronisation possibilities with a torque transfer standard, a commercial tachometer will be acquired, calibrated and tested. To realise traceable torque measurement on both the LSS and the High-Speed Shaft, two torque transfer standards up to 5 MN m and up to 100 kN m respectively will be established through calibration. There is a growing need amongst calibration and testing laboratories to have traceable high torque and high rotational speed. This project will investigate up to 1600 min^-1, the influence of rotational on torque measurement using simulation methods validated by test data. A guide on the calibration procedure for traceable mechanical power measurement consisting of torque and rotational speed measurement will be prepared based on the findings in WP1. This guide will be enhanced by a practical execution of such a mechanical power measurement calibration in a test bench. Moreover, it will serve the traceable efficiency determination in test benches, which will be developed in WP4.

• Task 2.1 will develop a transfer standard and an appropriate procedure to calibrate the measurement of rotational speed traceably.
• Task 2.2 will establish a torque transfer standard to measure torque up to 5 MN m traceably.
• Task 2.3 will investigate the influence of rotational speed on torque measurement under alternating rotation conditions.
• Task 2.4 will implement a mechanical power measurement based on synchronised torque and rotational speed measurements.

WP3:  Electrical power measurement

The aim of this work package is to develop a metrological framework for the measurement of the electrical part of the whole nacelle as well as of individual parts (e.g. generator, frequency converter, auxiliary systems, filter etc.). This measurement will be used together with the mechanical power measurement from WP2. Therefore, it needs to be adequately synchronised. Furthermore, because of the relevant signals are rich in harmonics and interharmonics, the power measurement will have to be tolerant to these. It is current practice to measure up to the 50th harmonic of 50 Hz (i.e. 2.5 kHz) or the second harmonic of the switching frequency of the frequency converter (e.g. 5 kHz), whichever is higher. The measurement of this parameter will be made traceable. The electromagnetic environment of a nacelle test bench is challenging. It affects the behaviour of common measuring systems. Due to the size of a nacelle test bench, grounding is not trivial. The design and calibration of the measuring system needs to account for this.

• Task 3.1 will identify the requirement for electrical power measurement in test benches. Stakeholder Committee (especially nacelle test bench operators and the manufacturers contribute) will provide guidance and support.
• Task 3.2 will provide traceable electrical power measurement at the generators on test benches.
• Task 3.3 will provide traceable electrical power measurement at the frequency converter output on test benches.
• Task 3.4 will provide a good practice guide for performing electrical power measurement in test benches and calibrating systems available in test benches including an adequate synchronisation of the transfer standard and the measuring devices to be calibrated.

WP4:  Efficiency determination in nacelle test benches

The aim of this work package is to develop a practical and traceable procedure to determine the efficiency of nacelles and their components on large-scale test benches with an uncertainty of 1 %. To realise this, the mechanical and the electrical power measurement will be calibrated as devised in WP2 and WP3, combined and synchronised.

As a first step, a measurement procedure for the efficiency determination of nacelles and their mechanical as well as electrical components on test benches will be developed. This procedure includes load cycles based on the output of WP1 and a practicable evaluation approach including a measurement uncertainty model. As the measurements are rather complex and involve several different motor and nacelle test benches, detailed schedules for the campaign will be created in the beginning of this work package. To verify the quality of the test procedure developed, a downscaled test on a well-known motor test bench will be conducted. Its results will be compared to the results using a common direct and indirect efficiency determination according to EN 60034-2-1. For this test, the torque and the rotational speed transfer standard from WP2 and the reference electrical power measurement system established in WP3 will be deployed. Afterwards, the efficiency determination will be executed exemplarily on different full-scale test benches for the wind energy sector via mechanical power measurements on both the High-Speed Shaft (HSS) and the Low-Speed Shaft (LSS) and electrical power measurements at various points to determine the efficiency of entire nacelle and single electrical components. The efficiency determination via the LSS will be implemented using two distinct nacelle test benches to analyse the dynamic effects on the result caused by the load application system: one with a hydraulic and the other one with a hexapod load application system. All gained knowledge will be collated in a standardised guideline for traceable efficiency determination with a large focus on the practicability for test bench operators and wind turbine manufacturers and their suppliers. As different partners and different measurement equipment comes together to ascertain the efficiency and alteration of the efficiency should be observable, the measurement equipment must be well synchronised. The test bench owner must supply different GPS based time synchronisation signals or an accurate local network-based protocol. Experience shows that different measurement systems rely on different time synchronisation signals, which normally makes converters necessary. The functionality and cooperation must be planed, organised and tested. This is relevant for all the three measurement campaigns.

• Task 4.1 will develop a direct and an indirect efficiency determination procedure for devices on test benches including an uncertainty model.
• Task 4.2 will perform a preparatory small-scale test of direct and indirect efficiency determination.
• Task 4.3 will execute an efficiency determination via the HSS of a test bench.
• Task 4.4 will implement an efficiency determination via the LSS of a nacelle test bench with a servo hydraulic load application system.
• Task 4.5 will implement an efficiency determination via the LSS of a nacelle test bench with a hexapod load application system.