∼ About HG
∼ Armature Reaction
∼ Excitation Systems
∼ Electrical Braking
Electrical braking... Braking... Stop... Why electrical braking? Why braking? Why stop?
So many questions! Because we want to stop the unit, or we need to!
How it happens? Considering an automatic stop sequence, we just press the STOP button.
In order to minimize the consequences of the heating and the cavitation it is desirable to reduce the time during the stop process of the unit by using the electrical braking. The electromagnetic torque of a hydro generator is a braking one, in opposition with the one of the hydraulic turbine (the prime mover) which is an active torque.
How do we obtain a braking torque after the deexcitation and the disconection from the grid? We'll shortcircuit the stator's terminals and we'll excite the rotor using an ancillary supply (the main supply is the one from the terminals). We'll obtain the rated current in the stator, though the voltage is much much lower (the terminals are short circuited). Now the torque is back! This torque act like a braking one, so we obtained the electrical braking! The hydro generator will not be pushed over its limits because the electrical parameters/ values does not exceed the nominal/ rated ones.
The result of the electrical braking is a reduced time during the stop process of the unit, with two main advantages: