How does a wind turbine brake

The braking system of a wind turbine is a complex and precise engineering project, which is not just a simple "brake pad", but a multi-level, collaborative safety system.

The core goal is to safely and controllably stop or reduce the speed of the large impeller when needed.

When needed "usually includes the following situations:

Excessive wind speed (usually exceeding 25 meters per second): To prevent the fan from running too fast and causing structural damage.

Power grid failure or power outage: requires safe shutdown.

Daily maintenance or overhaul: Provide a safe working environment for technicians.

Emergency situation: If the sensor detects a serious malfunction (excessive vibration, gearbox overheating, etc.).

Modern large-scale wind turbines mainly use the following three braking methods to work together:

1. Pneumatic braking - primary and main methods
This is the most commonly used and core braking method, achieved by changing the aerodynamic characteristics of the blades.

Principle: The end of each blade can rotate a certain angle (usually 90 degrees) around its axis. This action is called 'rowing'.

Process:

Under normal circumstances, the blades face the wind at the optimal angle (angle of attack), efficiently capturing wind energy.

When braking is required, the control system commands the blades to rotate, causing the leading edge to turn towards the wind direction or the blade edge to turn towards the wind direction.

In this way, the blades transform from efficient "wings" to high drag "wooden boards", with a sharp decrease in lift and a significant increase in drag, resulting in a rapid decrease in speed until they come to a stop.

Advantages:

No mechanical wear: Because it utilizes air resistance without physical contact friction.

Reliable: Even if power is lost, the battery can provide backup power for the propeller system.

Adjustable: The power can be adjusted by partially feathering, or by fully feathering to achieve emergency braking.

2. Mechanical brakes (disc brakes) - auxiliary and parking brakes
Similar to car disc brakes, but usually not used as the primary means of deceleration.

Location: Installed on the high-speed shaft (after the gearbox output end and before the generator), as this shaft has high speed and low torque, the required brake device size can be made smaller.

Function:

Parking: After the pneumatic brake has basically stopped the impeller (the speed has dropped to an extremely low level), the mechanical brake caliper clamps the brake disc, firmly locking the fan to prevent slow rotation caused by gentle breeze or inertia. This is crucial for maintaining personnel safety.

Emergency backup: In extreme cases where the pneumatic brake fails completely, it serves as the last safety barrier.

Characteristics: To avoid excessive wear and heat generation, modern fan designs minimize the frequency of mechanical braking and typically only use it after complete shutdown.

3. Electric brake (power generation brake) - auxiliary adjustment mode
Braking is achieved through the generator itself.

Principle: When the generator is disconnected from the power grid, the energy of the rotating system can be consumed by consuming electrical energy on the braking resistor (converting kinetic energy into thermal energy and dissipating it), or by controlling the reverse torque of the generator through power electronic devices to assist in deceleration.

Function: It is mainly used for adjusting and assisting deceleration, especially during the disconnection process, in conjunction with pneumatic brakes to achieve smooth stopping.

Collaborative workflow of braking system (taking strong wind shutdown as an example):
The wind speed sensor detects that the sustained wind speed exceeds the cut-out wind speed (such as 25m/s).

The control system first issues a command to activate the pneumatic brake: the blades start to pitch and the impeller speed decreases.

At the same time, electric brakes may activate to help consume energy.

When the impeller speed drops to near zero (e.g. a few revolutions per minute), the mechanical brake is activated, clamping the brake disc to completely stop and lock the fan.

The fan enters a safe shutdown state.

Special case: Braking during power loss
Safety is the primary consideration. The fan is equipped with an uninterruptible power supply (UPS) or a backup battery. Even if the external power grid is completely cut off, the backup power supply can still provide power for the control system and the pitch system, ensuring that the blades can successfully pitch and achieve aerodynamic braking. This is the most critical fault safety design.

summary
In short, the braking of a wind turbine is a "combination punch":

Main force: Aerodynamic braking (feathering), responsible for the majority of braking and power control.

Parking: Mechanical brake, responsible for locking after a stable stop to ensure safety.

Assist: Electric brakes to help smooth the braking process.

This multiple and redundant safety system ensures that even in adverse weather or fault conditions, massive wind turbines can be safely and reliably shut down.