Long in disrepair, the French Grand Moulin des Places windmill recently took on a new role – converting wind energy into electricity. According to ABB, a Swiss manufacturer of automation systems, this could lead to other windmill to generator projects. The windmill is can produce electricity from wind speeds between 2 and 25 m/s.

Once grain, now power

The windmill has four blades, or sails, each fitted with variable section. These slide from a closed position for minimal wind capture, to an open one, with sail sections nearly side-by-side, for maximum wind capture. A PLC regulates sail deployment according to wind speed with a hydraulic cylinder. The PLC program uses a cross-reference table between wind speed and sail position, constantly adjusting for best power production.
An orientation vane at the back of the roof points into the wind and signals the roof drive to position the sails into the wind. In high winds, however, the rotor disc turns 90° to the wind. In this position, the rotor remains stationary.
All machinery is under the windmill’s roof. The main shaft now drives a belt that transmits torque to a speed increaser, so rotor speed is compatible with a 37-kW generator.
If the generator were directly connected to the grid, it would have to reach more than 1,500 rpm before synchronizing its current flow. To avoid the requirement of precise speed, engineers inserted a 4 quadrant, 37-kW inverter between the generator and grid. Now, even in low wind speeds, the generator produces useful current even though it’s only rotating at a few hundred rpm. Then, an ABB ACS800 drive outputs 400 V at 50 Hz at all times. The setup lets the windmill produce power over a wide range of wind speeds. The electrical cabinet (including the drive) is in the lower section of

the windmill.
Controlling the generator
To control the equipment, an AC500 industrial Programmable Logic Controller coordinates data from sensors, follows operating and safety instructions, and sends commands to the actuators. The controller is in a lower section of the building,  communicating with the input-output modules in the upper section via radio link. Two modems (master and slave) ensure the link, while allowing Modbus communications between controller and input-output module.
The AC500 PLC monitors:
·    Weather data from rooftop sensors (wind speed and direction, outdoor temperature and humidity),
·    Production data and windmill availability
·    Position of the accuators for each blade or sail flap
·    Switch positions
·    Brake position
·    Generator temperature, and, when necessary, the PLC signals an emerging stop

The PLC’s program operates the windmill by sending instructions to the drive at wind speed from 2 to 25 m/s. For wind speeds more than 25 m/s, a safety application “feathers” the blades and activates hydraulic brakes.
A man-machine interface in the controller cabinet lets the operators monitor the installation’s condition, electricity production parameters (voltage, power), weather conditions, state of the hydraulic equipment (controlling the brake and blades), and operating time of the equipment.

Alarms and faults are also shown and stored. Software engineers designed ten screens using software called CP400, which works with the ABB software for programming the controller.

Finally, lights that convey the turbine’s general condition are mounted outside the windmill and visible from the operator's home. The lights let that person check the windmill status: active (green), waiting for good operating conditions (yellow), or in fault condition (red). An uninterruptible power supply ensures power for the PLC, the control interface, and automation components.

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