A context that comes into play twice. On one hand, the availability of a wind turbine should be high. This means very few turbine or sensor system failures and low maintenance effort with few repairs. On the other hand, turbines are increasingly being equipped with safety sensor systems. The Germanischer Lloyd guidelines additionally underscore this development. Certified safety components are therefore increasingly being used in wind turbines – e.g. with SIL2 certificate.
TWK has been supplying the wind energy sector with products for over 30 years and was involved from the word go. Thanks to this experience and acquired knowledge, the company has not only developed numerous devices but also a feel for which products are suitable for this industry. For some time now, TWK has also been offering safety sensors that meet the increasing requirements. The product portfolio now encompasses a range of SIL2-certified sensors.
The electronic switching cam encoder of the NOCN/S3 CANopen models is a good example. In many cases, it replaces a mechanical switching cam encoder with integrated rotary encoder. The electronic switching cam encoder is more compact and easier to operate and adjust. System adaptations can be carried out electronically and do not have to be implemented mechanically - through various gear wheels, for instance. The cams' switching points are accurate down to the bit level, a characteristic that is not achieved by a conventional switching cam encoder. As the cam switches have to meet specific safety requirements in many applications, SIL2 certification is indispensable. The customer is provided with a device that transfers a safe rotary encoder position and speed (via CANopen Safety) and which has two integrated switching contacts to register end positions. The relay contacts are galvanically separated and can switch both DC and AC voltage up to 60 V. They are suitable for the safety chain.
One example: the gondola of a wind turbine is tracked accordingly as the wind direction changes so that the rotor is always positioned vertically to the wind direction. Only this enables optimal use of the energy contained in the wind. However, the gondola cannot turn infinitely in one direction, as the lines that feed the generated electricity into the grid would otherwise become twisted. After approximately 3 revolutions in the same direction, the gondola is therefore stopped by the switching cam encoder and turned back to 'zero'.
Besides the safe design of the hardware and software that is required in any case, the switching contacts are also polled directly via a controller to guarantee safe operation. If the required switching status (on or off) is not present – due to a defect or sticking contacts – a fault message is immediately generated and transmitted to the control system. This can then act accordingly to prevent damage. After all, safety also means detecting faults and reacting. Contact opening in the safety chain is ensured by opening two relays connected in series with a short time lag (approx. 20 ms) per switching output. The differentiation between a sensor and actuator in one device, each with separate safety data, enables the user to focus his attention mainly on the rotary encoder, on the switching contacts or on both. He knows which part is integrated with which SIL value in his application. Optionally, the rotary encoder data can also be output using the CANopen Standard profile or SSI. The user has the choice.
All relevant parameters can be set by the customer to set the device up optimally. To prevent values from being changed 'unintentionally', each intervention has to be verified with a checksum that has to be transmitted to the NOCN. Safety has absolute priority.
The switching cam encoders have been used successfully in pitch and yaw control for a long while. They are also available with an SSI (NOCE) and analogue interface (NOCA). Together with the TWK measurement gear ZRS, the position can actually be determined play-free.
If only a rotary encoder is required, TWK is able to offer several SIL2-certified models. The latest is the fail-safe over EtherCAT (FSoE) TRK/S3. Like the NOCN, this also originates from the reliable and robust series of magnetic dual-chamber devices. This design supplies devices with a protection class of up to IP69K with high shock and vibration resistance up to 500 m/s². All Ethernet features that enable user friendly handling are implemented. Corresponding parameter libraries are available.
Other interfaces are also available as part of this series: PROFIsafe via PROFINET (TRT/S3), CANopen (TRN) and CANopen Safety (NOCN58/S3), SSI (TRE) with additional incremental signals as well as the analogue interface (TRA) that is still used.
The latest development is an HBx rotary encoder with a resolution of 4 million steps (> 21-bit) - equally robust and reliable - which is also available as an incremental rotary encoder.
The SIL2 vibration sensor NVA rounds off the product range for the wind power industry. Specifically developed for wind turbines, this sensor measures oscillations and vibrations in a range from 0.1 to 60 Hz in the x and y direction. It outputs the measurement values in analogue form and via CANopen Safety. The sensor is used to measure slow interference vibrations caused e.g. by rotor imbalance. Higher-frequency transmission vibrations can also be registered. The frequency ranges can be optionally separated using digital filters. If specific limit values are exceeded due to defects on the turbine, two independent switching outputs interrupt the safety chain or carry out other switching processes. This device can be extensively parametrised. This includes limit values, amplification, averaging, etc. Finally, an integrator function is implemented; this totals limit value overshoots over a longer period of time and only reacts after a delay. If, for instance, the overshoots decline, it may be that no damage occurs to the turbine and that the system does not have to be stopped. The NVA does not then trigger in this case. In the event of severe shock, however, the NVA always interrupts the safety chain independently of the integrator (shock detection).
The wind turbine is therefore always in safe sensor hands.
