CONDITION MONITORING BLADEcontrol
BLADEcontrol is a system that continuously monitors the condition of the rotor blades on wind turbines and immediately signals to the operator and/or the machine control of problems such as structural blade damage, ice build-up or lightning damage. What’s more it can keep track of the history of the blades condition to offer an on-going forensic trail of wind turbine performance.
ANALYSIS AND MONITORING The system performs an analysis of the natural oscillation frequencies of the turbine blade which change when the blade is damaged or has a greater dynamic load, such as when ice forms. The frequencies of a rotor blade can vary within a typical range of up to around 350 Hertz. This distribution of frequencies is essentially the fingerprint of the blade.
Distinctive frequencies arise when ice is formed due to the ice on the rotor blade being heavier causing a slower oscillation. These specific frequency peaks are easily visible on a monitor. Structural damage is visible within the low frequency range, whilst minor damage is only visible within the higher frequency range. For example, slight rotor blade damage, such as multiple trailing edge cracks will not affect the spectrum between 0 Hz and 50 Hz but visible changes are noticeable between 150 Hz and 250 Hz.
TECHNICAL DETAIL
The system works via the attachment of accelerometer sensors (multi-dimensional piezo-electric accelerator sensors), which are glued directly into the rotor blades. A data collector in the hub converts the analog, measured oscillations into digital values and transmits these from the hub into the nacelle via WLAN. The digital data is then interpreted by the embedded processing unit.
The data is recorded online and evaluated in detail in the embedded processing unit in real time. If, at any point, an extreme event occurs, such as serious damage to the blades or ice on the rotor blade, the control system is immediately informed that the system is to be stopped. A further benefit is that as the blades are being monitored locally even when stopped as there is still wind blowing over them, the system can perform an auto re-start when all ice has cleared. This obviously removes the need for an engineer to visit the turbine and also keeps lost power generation to a minimum
DIFFERENTIATION AND PAYBACK In terms of maintenance work, BLADEcontrol can differentiate between small, non-threatening edge cracks and major structural damage. This allows for the introduction of a planned maintenance schedule rather than a reactive schedule.
Calculations suggest that a control system could generate a payback period of less than two years by early detection of repairs, lower insurance costs, savings on maintenance costs and reduction in unnecessary downtime leading to higher yields. For many wind farm operators there is also the added benefit of peace of mind that their expensive asset is in top condition and fully operational.
Bosch Rexroth
Click to view more info = Click to view video 1 = Click to view video 2
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www.windenergynetwork.co.uk
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