Innovative clutches and brakes for wind power plants

Germany is the third-largest wind power producer worldwide after China and the USA and had the greatest wind power output in Europe in 2016 with more than 50,000 MW installed capacity. In 2016, more than 28,200 wind power plants on land and at sea supplied in total around 80 billion kWh of electricity. This equates to approximately 12 per cent of the electricity generated in Germany. There is a significant trend towards larger and higher performance wind turbines in these plants.

As a result, in 2016, the average output of a land-installed wind power plant was approximately 2.8MW - that is 4 per cent more than in 2015 and 155 per cent more than in 2000. In contrast, with components such as motors, the trend is tending towards smaller, more compact components with higher performance density, because the less weight the engine pod ultimately has, the more costs can be saved in tower construction. As a manufacturer of safety brakes, torque limiters and shaft couplings, mayr power transmission is also promoting this development. Therefore, the company has now developed an innovative, high-performance torque limiter from the ROBA-slip hub series which can be directly installed into the generator of a wind power plant.

The torque limiter connects the generator rotor with the generator shaft, simultaneously supports the generator rotor and reliably protects the transmission against damage caused by overload. Regarding the advantages of the new torque limiter, Andreas Merz, Product Manager at mayr power transmission explains: "With this integrated solution, users save not only installation space, but also on weight, material and costs for additional construction elements, for example a shaft misalignment compensation coupling or bearing."

Equipped for difficult operating conditions

In wind power plants, the ROBA-slip hub protects the transmission against generator-side peak loads, for example against impact during network synchronisation or a generator short-circuit. This process concerns load-holding overload clutches, which operate using frictional locking. They transmit the torque via friction linings, which are pre-tensioned using cup springs. In case of overload, the flange with the drive element slips through against the resistance of the friction linings. In the process, the transmitted torque reacts proportionally to the cup spring pre-tension: the higher the cup spring pre-tension, the higher the transmitted torque.

Andreas Merz explains: "The clutches which we have produced for wind power plants with an output of 2MW, for example, have a torque range of 50 to 80kNm. The clutches are adjusted and the slippage set to the required torque of 65kNm on a test stand specially developed for this purpose. As a result, we ensure that the clutches display homogeneous characteristics and operate reliably and precisely". The robust ROBA-slip hubs by mayr power transmission are tailored to the high demands and difficult environmental conditions and are designed with Corrosion Protection C3. Andreas Merz adds: "In general, we currently also have projects with clutches up to 200kNm - for plants up to 5MW."

Besides innovative torque limiters, mayr power transmission is also setting new standards with intelligent monitoring modules for their yaw and pitch brakes, because in wind power, too, the monitoring of electromagnetic brakes is increasing in importance. The new, intelligent ROBA-brake-checker module operates without sensors; instead it recognises the movement of the armature disk through the analysis of current and voltage, and knows the condition of the brake at any given time. As well as the switching condition, it monitors temperature and wear on the tension path or the tensile force reserve, i.e. whether the magnet still has sufficient power to attract the armature disk.

As a result, significantly more processes are now depicted with this new module than with conventional microswitches and sensors. On reaching the tensile force reserve, the ROBA-brake-checker emits a warning signal early enough so that the brake can still operate for a defined time. During this time, the wind power plant operator or manufacturer can undertake targeted maintenance coordinated with their work process. In addition, the module simultaneously assumes control of the brake and as a result replaces a rectifier. The switching condition monitoring and brake control unit are therefore combined in one device.

Condition monitoring without switches

As a result of the ROBA-brake-checker operating without sensors, no microswitches or proximity sensors have to be attached to the exterior of the brake in order to monitor the switching condition, and safety brakes can be used in the basic constructional design. Furthermore, additional wiring becomes obsolete, and so does the sealing of switches and sensors, depending on the protection type. In contrast to a system with switches and sensors, which are exposed to impacts and vibrations due to their installation position on the brake, monitoring with the ROBA-brake-checker occurs from the control cabinet, i.e. from a protected environment. Failures due to icing and false signals due to contamination with substances such as brake dust are therefore excluded. Thanks to the electrical switching of the ROBA-brake-checker, the system availability can be increased, because critical spark formation no longer occurs on the switching contactor which, on conventional switching mechanisms, frequently leads to adhesion of the contacts.

mayr power transmission provides safety brakes especially developed and tested for yaw and pitch drives with their ROBA-stop-M brakes. Andreas Merz explains: "All brake components are safely dimensioned and are manufactured only from high-quality, tested and proven materials. Our brakes are designed so that they reliably achieve their specified braking torque under all occurring operating conditions, irrespective of air humidity or the ambient temperature within the respective region". And this is also confirmed by Germanic Lloyd (GL), who have certified the Cold Climate Version of the ROBA-stop-M brake for cold temperature operations of -40degC. The company always ensures careful quality control: This includes quality assurance measures during the design process and a comprehensive final inspection. Prior to delivery, all brakes are extensively tested on test stands, and the function-relevant values are documented. An electronic database in which measurement values are archived with the corresponding serial numbers of a product ensures 100-percent traceability.

Besides brakes for yaw and pitch drives, mayr power transmission provides further safety brakes for diverse operating areas in the field of wind power. Andreas Merz summarises: "As a power transmission specialist, we have a wide spectrum of solutions: this spectrum extends, for example, from calliper brakes for the main drives of small plants, via the safety brakes for passenger service lifts, right up to robust, corrosion-protected outdoor safety brakes. The latter are found in the drives of supports for installation ships, for example, or in the lifting drives of cranes on offshore platforms. And our range of torque limiters is also extensive: We have various torque limiters for access equipment drives in the towers of wind power plants, switchable clutches for the drives of maintenance and installation platforms, as well as high-performance large-scale clutches for transmission test stands".

For more information about the company's products for wind power plants please visit www.mayr.com.