Ice detection system for wind turbines
Ice detection on wind turbines – a difficult balancing act between safety and yield maximization. With the rotor blade based ice detection system, Polytech offers an ice detection system for wind turbines that detects precisely the smallest ice masses and thus switches off the wind turbines as late as possible without compromising safety and enables automatic restarting even at night and fog without visual inspection on site.
- Precise ice detection from 10 kg onwards thanks to sensor technology in the rotor blade
- This minimizes the standstill
- Automatic restart possible DNV GL certified
- Retrofit available for all types of turbines
Heavy rotor blades swing more slowly than light rotor blades. On this simple idea, the operation of Polytech ice detection is based. With fiber-optic acceleration sensors in the rotor blade, the changed oscillation behavior is detected and the ice mass is calculated therefrom.
Fiber-optic sensors are passive sensors and can therefore be installed deep in the rotor blade. Due to the exposed position in the blade, even the smallest changes in the oscillation behavior are detected and ice masses distributed along the blade are detected reliably from approx. 10 kg.
As soon as meteorologically induced icing conditions prevail, the parallel installed, gondola-based ice detection system for wind turbines of a market leader switches off (rotor speed drops to zero).
Since ice on the rotor blade does not form a point-shaped but a two-dimensional shape, a certain ice formation is classified as harmless. The thin layer of ice breaks when broken into small pieces. In this case, Rotor Ice Control measured an ice formation of approx. 10 mm or an ice mass which corresponds to 0.4% of the total mass of the rotor blade.
Rotor Ice Control later gave the ice signal (upper graphic, red) on this reference system and released the WKA again earlier (red line in the upper graphic falls back to zero: „No ice“).
The precise measuring of the actual ice masses on the rotor blade allows maximum wind times (red line in the lower graph, wind speed is plotted on the right y-axis) to be taken advantage of when all safety aspects are observed.
Furthermore, the lower graph shows the temperature profile in green. The shutdown of the turbine by the alternative ice detection system, the calculation of which is based on meterological data, took place at the time when the outside temperature fluctuated around the critical zero line and the conditions for ice were given.
With the aim of optimizing the yield of the wind turbine, a later switch-off would have been possible and would have been reasonable with the full guarantee of the required safety, as described as „other hazards“. Of § 5 BImSchG.
Integration into wind turbines
Rotor Ice Control offers various interfaces to the plant control system to stop the wind energy system automatically and without human intervention. The system can be self-sufficient, i. Without data connection. However, a data connection is recommended, among other things to make the system easier to maintain.
Installation and commissioning
The installation and commissioning of the ice detection system takes about 1 day. For sufficient calibration, approx. 2 weeks of ice-free time are required. If the system is to be put into operation immediately, sufficient precision can be achieved with existing calibration data of a system of the same type. However, it is advisable to individually calibrate each ice detection system for wind turbines, since the behavior of each wind turbine varies slightly, even if it is of the same type. The calibration works automatically and refreshes every year in the summer months to take into account changed behavior.
The ice detection system works flawlessly under all conditions above a wind speed of approx. 3 m / s, even when the system is switched off. From this wind speed, the rotor blades are sufficiently excited to vibrate, so that ice can also be detected in the case of a twisting or stationary system.
Advantages of a rotor blade ice detection system
The installation of the sensors in the rotor blade is measured directly and directly at the site of the incident. While gondola-based systems can only check whether the gondola at other flow conditions and at a different level are above ground icing conditions, sensors in the rotor blade measure directly and without negatively influencing factors such as, for example, The waste heat of the machine house.
Thus, the start and end of a critical icing event can be precisely determined and need not be derived from the result of other sensors. Downtimes are shortened with the help of this precise switch-off and the detection of ice-freeness. Furthermore, the visual control of ice-freeness on site can be eliminated by means of a modified operating permit and an automatic return of the system can be realized.
Specific advantages of the Polytech rotor blade detection system
The fiber-optic sensors installed by Polytech work purely with light signals and are therefore passive. A light pulse is sent from the hub via a fiber optic cable to the sensor and reflected there. No electrical cables are installed. As a result, the sensors can be installed in the vicinity of the rotor blade tip and work very precisely due to the large deflection of the rotor blade tip.
Compared to electrical strain gauges, sensors based on glass fiber technology convince by a significantly longer service life. Polytech had a life expectancy of at least 20 years in several accelerated aging tests.
The measuring technology used for the ice detection system for wind turbines forms the basis for a future rotor blade monitoring system.
Rotor Ice Control can be combined with all common rotor blade heating systems, optimizes their operating times and provides reliable information on the deicing performance.
The Rotor Ice Control System requires minimal maintenance. All Polytech’s own components do not require any maintenance, only the built-in heating / cooling unit has to be replaced regularly.
In an extensive field test, an increase of 120 MWh in a 3 MW plant could be demonstrated within a winter period. The Polytech system has been compared to a manufacturer’s serie system.
Authorization / approval
A certification by the DNV GL was carried out in September 2014. Furthermore, there is an expert opinion which describes Rotor Ice Control as a „state-of-the-art“, which makes it also suitable for the most demanding regulatory requirements.
Detailed technical data
- Interfaces: IEC 61400-25, CAN, Modbus TCP, analog, digital, others on request
- Dimensions of control cabinet: 48 x 35 x 21 cm
- Power Consumption: <150 W
- Delivery time: 6 – 8 weeks
For further technical data please contact us.