Load measurement in rotor blades Robust sensor design
Rotor blades are subjected to extreme environmental conditions and strain. Due to the ever-increasing length of rotor blades, growing demands are placed on monitoring. The solution from Phoenix Contact continuously monitors the stresses and loads placed on the rotor blades. When the set limit values are exceeded, alarms are sent, and operators are always kept informed of the condition of the rotor blades.
The rotor blades are critical components of a wind turbine generator (WTG). With the trend towards ever-longer blades, a monitoring system is becoming increasingly important. The rotor blades are subject to very large dynamic forces which can lead to structural damage to the blades over the service life. Damage can be detected early by continuously monitoring loads and vibrations. This data enables optimized load-based control of wind turbine generators, which means that the stress on the blades is reduced to a minimum. Damage is detected at an early stage and eliminated with little effort. By recording the load spectrum, changes in the structure of the rotor blade are monitored throughout the entire service life.
Rotor monitoring system (RM-S) The solution for load monitoring
The rotor monitoring system (RM-S) measures the behavior under load as well as bending moments in the rotor blades of wind turbine generators. To do so, strain gauges are attached to the inner side of the rotor blades of a wind turbine generator near the base of the blade. The core element of the solution is a Phoenix Contact PLCnext Control device. The controller is connected to the sensors in the rotor blades via directly connected Axioline modules. To protect the system against surge voltages and lightning strikes, protective devices are installed for the sensor cables, the antenna input of the router, and the power supply. Optionally, a modem can be used to upgrade the system for direct communication. In addition to the controller interfaces, a PROFIBUS or CAN interface can be integrated to establish an internal bus connection.
Phoenix Contact has developed special sensors that are suitable for the special conditions inside a wind turbine generator rotor blade. These sensors are built so robustly that they can be installed reliably even under adverse conditions and at the same time are well protected against external influences.
The controller acquires the signals from the connected sensors. During this quick signal processing, the measured values are filtered and checked for plausibility. Additionally, the measured values are used to determine the minimum, medium, and maximum bending moment, as well as the speed the rotor rotates at. If the set limit values are exceeded, an alarm can be set using freely programmable digital outputs. The processed data is made available simultaneously to the higher-level controller for signal scanning. Through the network, all raw data can be saved in a Microsoft SQL database or in CSV format to an SD card or an FTP server, and can be evaluated using an independent system. The RM-S also records the present load spectrum. Load spectrum mapping is used for acquiring vibration amplitudes that cause structural damage to the rotor blades over the entire service life. These values make it possible to estimate the remaining service life.
As a retrofit or for new installations:
The RM-S can be integrated directly into the electrical design of the system or retrofitted into existing systems. The retrofit version consists of a fully configured control cabinet, which is built into the hub and is integrated into the controller via the existing interfaces.
Optionally, the data can be transmitted directly to the operator via the modem. In the case of new installations, the required hardware, such as the controller and I/O modules, is integrated directly into the wind turbine generator’s pitch control cabinet. In this case, the software is transferred to the controller using an SD card.
- Condition-based maintenance of rotor blades with early detection of damage
- Reduced strain on the blades with load-optimized closed-loop control of the wind turbine generator
- Reliable operation with robust components suitable for the conditions encountered in wind turbine generators
- Open system for optimum integration into existing systems