This week: Vibration sensors in wind power plants

In many cases, this enables more extensive damage to be avoided and the value of the system to be maintained.
One important physical measurement variable which has to be recorded to protect the system is the vibrations which occur during operation, primarily in the gondola or in the mast. If these vibrations are excessively strong, the entire system is detrimentally affected. Cracking or even fractures may occur in the mast due to the acceleration forces which arise.
Causes may include transmission or bearing damage, which is typically able to generate vibrations of 10 to 50 Hz. Or the rotor is out of balance (e.g. due to icing). In this case, the frequencies which cause the system to vibrate lie in the range from approx. 0.1 Hz to 15 Hz.
These vibrations and oscillations have to be determined as part of a wind power plant's vibration monitoring in order to cause the control system to shut the system down or halt it in the event that relevant limit values are exceeded.
TWK-ELEKTRONIK has developed the NVA65 vibration sensor for applications such as this. The MEMS acceleration sensor which is used registers the vibrations in a frequency range from 0.1 Hz to approx. 60 Hz. With a high-performance 32-bit controller, this frequency range is subdivided into several bands using high-order digital band-pass filters in order to separate the different causes of the vibrations. Uninteresting interference frequencies are filtered out. The sensor measures on two axes, i.e. the acceleration which occurs in each direction on the x–y plane is continually registered and output as an analogue signal (4 … 20 mA) or CANopen respectively. Either with x and y separated or as the geometrical sum (s=sqrt(x²+y²)).


Integrated limit value relays serve as warning or stop relays. If the accelerations in the defined frequency ranges exceed specific values, these switch and generate an alarm or cause the system to shut down.
The relevant limit values can be parameterised by the customer using the CANopen interface.
If the NVA65's internal monitoring of various functions and components discovers a fault, the integrated fault relay outputs a signal to the system's control system. The relay outputs are galvanically separated from each other.
All of these functions are accommodated in a compact aluminium or stainless steel 1.4404 housing. This has dimensions of 100 mm x 65 mm x 42 mm and offers protection type IP 67.
As it is tailored specifically to the requirements of wind power plants, this device is an inexpensive alternative to the usually over-dimensioned and therefore expensive devices available on the market. Thanks to its electronic and very compact design, it is also superior to the bulky mechanical devices.