What are various ways and mechanisms to regulate and ensure

What are various ways and mechanisms to regulate and ensure safe operation of a wind turbine (HAWT)?

Solution

Answer:

The safety system for a wind turbine is independent of the normal control system. It brings the turbine to a safe condition in case a serious or a potentially serious condition exists. This is usually done by bringing the turbine to standstill with the application of a brake. Under normal operation the normal control system is capable of ensuring the safety whereas the independent safety system acts as back-up in case the normal control system fails to bring the turbine to safety. Safety can also be ensured by operator controlled emergency stop push button.

For reliability the safety system is usually redundant and hardwired fail safe without any computer or microprocessor interface and designed to keep the system in operation with the help of several normally open relay contacts which and held closed when the system is healthy. If the contact is lost the system trips. The trip may involve the following actions:

1. Disconnecting all the electrical supply connections.

2. Allowing fail safe pitching to feather position

3. Allowing spring applied shaft brake to engage

The following are the typical tripping conditions which may trigger the system shutdown

1. Rotor overspeed- Emergency overspeed set point is higher than normal overspeed set point. It may be noted that the normal control system is designed to shut down the system in case the normal overspeed set point is reached. Overspeed trip ensures that the material design stresses are not exceeded due to high speed.

2. Vibration high trip to prevent any structural damage.

3. Normal controller faulty trip

4. Emergency push button pressed by operator

The normal regulation and control may consist of the following:

A. Supervisory control:

It brings the turbine from one state to another. This typically include the following:

-Stand-by when the turbine is ready to run, waiting for suitable opportunity to bring to operation

-Start-up

-Power production

-Shut-down

-Stopped with fault

Supervisory control must check that each preceeding step is completed before suceeding step in initiated. If any step is not completed within a predetermined time, the supervisory control system brings the turbine to shut-down mode.

B Closed Loop Control

The closed loop controller is usually a software based system that adjusts the turbine to remain on a predefined operating curve or characteristics. Typical control loops include the following:

-Control blade pitch to regulate power output in case wind speed is more than rated

-Control blade pitch in order to follow a predetermined speed ramp during start-up or shut-down of the unit

-Control generator torque in order to regulate speed in a variable speed turbine.

-Control yaw motors in order to minimise the yaw tracking error.