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Speed control of hydro turbines

This post’s subject is the speed control of turbines in hydro power plants. This control is important to keep stability in the presence of disturbances, providing power according to the demand and keeping constant frequency.

Control System

This is the flowchart of speed control’s turbine.

Inside the speed regulator, has the controller and hydraulic amplifier. Usually is used a digital controller PID to all types of hydro turbines. Can use a genetic algorithm to controller’s adjustments and fuzzy logic to monitor the PID control’s gains. The hydraulic amplifier receives output signal from the controller in a microprocessor to activate valves and servomotors. This is a controller to Pelton turbines in 50 Hz, called governor.

Are used position sensors to valves and servomotors and a speed sensor measures the turbine’s frequency, which must stay in 50 or 60 Hz, to stay in synchrony with the generator. Usually an inductive sensor with a permanent magnet or a iron toothed wheel measures the speed turbine.

Regulating speed of Pelton turbines

The speed regulator depends on the used type of turbine. To control speed of Pelton turbines are used nozzles with valves in shape of needle to control the flow rate.

Some Pelton turbines has 5 nozzles.

Why the Pelton turbine’s buckets have this shape shown below? The water is distributed equally in the two halves, water jet turns almost 180º, maximizing the impulse force. The cut in the bucket is to prevent a bucket interferes in the impulse of another. Are made of one single piece to avoid fatigue.

Speed control of Francis and Kaplan turbines

In the Francis turbine, the flow rate is controlled by the distributor, which is a set of wicket gates in form of airfoil.

The angle of wicket gates is controlled by servomotors, the later receive commands from microprocessor of hydraulic amplifier which determines the position to control speed. The Kaplan turbines also use distributors. The blades of Kaplan turbine itself can have the angle adjusted to control speed.

 

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About Pedro Ney Stroski

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