3. Electromagnetic sources of permanent excitation

3.1 Alternator case

During network disturbances, variations in electromagnetic torque occur. This torque is the sum of :

• a constant torque ;

• a damped, virtually sinusoidal periodic torque, corresponding to the oscillations of the unit after the fault has been eliminated, with a frequency of the order of 0.3 to 1.5 Hz ;

• a torque with a frequency of 50 Hz, due to the presence of a DC component in the stator current, which is damped with a time constant...