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If speed of alternator increases
Frequency decreases
Frequency increases
Frequency remain same
None of above
Frequency increases
The frequency of the generated voltage in an alternator is directly proportional to the speed of the rotor. As the rotor speed (synchronous speed) increases, the rate at which magnetic flux lines cut the stator conductors increases, resulting in a higher frequency of induced EMF.
The frequency of the generated voltage in an alternator is directly proportional to the speed of the rotor. As the rotor speed (synchronous speed) increases, the rate at which magnetic flux lines cut the stator conductors increases, resulting in a higher frequency of induced EMF.
f=120PNтАЛ тАФ Relation between frequency, poles, and speed
NsтАЛ=P120fтАЛ тАФ Synchronous speed calculation
An alternator operates based on Faraday's law of electromagnetic induction. The frequency is defined by the relation f=120PNтАЛ, where P is the number of poles and N is the speed in RPM. Since the number of poles P is fixed by the machine design, an increase in N leads to a linear increase in f.
Frequency is directly proportional to rotor speed.
Constant speed is mandatory for maintaining a steady grid frequency (50Hz in India).
Any variation in speed affects the output frequency of the alternator.
Predictable relationship between mechanical speed and electrical output.
Easy frequency control via prime mover speed regulation.
Sensitive to mechanical input fluctuations.
Requires precise governor control to maintain constant frequency.
Synchronous generators in power plants.
Variable speed AC drives.
In India, the standard power system frequency is 50 Hz.
Option A is incorrect because frequency decreases only if speed decreases.
Option C is incorrect because frequency is dependent on speed, not independent.
B is correct тАФ Frequency increases because it is directly proportional to the rotor speed of the alternator.
Always remember that for a synchronous generator connected to an infinite bus, the speed is locked to the grid frequency; therefore, in steady-state grid operation, speed remains constant even if the load changes.