May 2019

Precision sensor technologies are not only proving their value during the production and testing of wind turbines, but also in the real time condition monitoring of operationally active onshore and offshore wind farms, says Chris Jones, managing director of Micro-Epsilon UK. Sensor solutions A range of unpredictable events such as lightning, stormy weather and rough seas can have serious consequences on a wind turbine, potentially resulting in defective rotor blades, tower movements or, in the worst case scenario, complete failure or collapse of the wind turbine. This is why wind turbines require 24/7 monitoring. The rotor towers of wind turbines weigh dozens of tonnes. Their average rotor diameter is now 110m, with average hub heights now 130m. If such equipment fails, a high financial cost is incurred. Cranes and other machines are typically unavailable at short notice. Offshore wind farms, in particular, are not easily accessible at any time of day or night. Due to wear and the complexity of assets, in addition to environmental influences, there are also a number of possible problems such as shaft issues, gear faults, gear wheel wear, material fatigue, imbalance, temperature differences, lubrication faults and bearing clearances, which do not only impede smooth operation but might also involve other subsequent or secondary damage. Predictive Maintenance plays an essential role here. Proactive monitoring based on precision sensor technology has already begun to be used in the production process of wind turbines and continues in test rigs and in the real-time monitoring of turbines during operation. Worn parts or deviations in coupling ring. This leads to the determination of the load profile. Monitoring the measured values is required in order to avoid unnecessary wear of couplings, bearings and shaft seals or, in extreme cases, serious damage to the wind turbine. Eddy current sensors allow measurements to be carried out in different directions – in the axial, radial and tangential axes. Some suppliers offer temperature- compensated versions that provide high measurement stability, even in strongly fluctuating ambient temperatures. The sensors are factory-calibrated for ferromagnetic and non-ferromagnetic materials, which eliminates the need for field calibration of the sensor. Compared to inductive switches and sensors, eddy current sensors provide a higher bandwidth and so are suitable for precise detection of high speed movements. Gap measurements in bearings Hydrostatic bearings are used in wind turbines. The task is to monitor the gap size between the bearing surface and the shaft. In the lubricating gap is an oil film, which prevents direct contact between the bearing surface and the shaft. In the case of a malfunction in the hydraulics, the oil pressure can rise and, in extreme cases, the gap will close. This would lead to damage of the bearing and in turn to a possible turbine failure. Therefore, our sensor is mounted horizontally to the bearing shoe. It measures through the oil film and the plant bearing Process, Controls & Plant Focus on: Sensors & Measurement production can now be recognised before catastrophic damage occurs. Therefore, it is possible to intervene long before the parts fail or tools begin to wear out. Not only can current asset conditions be documented, but trends and changes in measurement data can be analysed and evaluated. Maintenance becomes predictable and sudden failure or downtime of these large plants is reduced to a minimum. Innovative sensor solutions are now available that enable reliable measurements and targeted evaluation of critical data. This sensor technology helps customers by preventing repairs, reducing failures, reducing costs and helping to predict maintenance cycles. Compared to manual inspection where differences can depend on a person’s tiredness and changing mood, sensors can provide high precision, reliable, repeatable measurement results 24/7, 365 days per year. Offset measurement of the coupling ring Above 100m, huge wind loads act on the rotor blades, housing and tower. Therefore, gearbox and generator have an elastic bearing. This is why couplings in wind turbines must balance the relative movement of the gearbox and generator. When measuring the offset of the coupling ring, non-contact eddy current displacement sensors can be used to determine the distance, while measuring onto the metallic 30 | Plant & Works Engineering www.pwemag.co.uk May 2019

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