When the speed of an alternator changed from 3600 RPM to 1800 rpm the generated emf/phase becomes
When the speed of an alternator changed from 3600 RPM to 1800 rpm the generated emf/phase becomes One-half.
The generated EMF in an alternator is directly proportional to its speed, and is given by the following formula:
EMF = 2πfNZ
f is the frequency of the generated voltage
N is the number of turns in the armature winding
Z is the number of poles in the alternator, and speed is in RPM.
Since frequency, the number of turns, and the number of poles are constant, the EMF is directly proportional to the speed of the alternator.
Therefore, if the speed is halved from 3600 RPM to 1800 RPM, the generated EMF per phase will also be halved.