Nearly all electrical power in the world is generated by the 3-phase synchronous generator, which is also known as the ac generator or the alternator.
Stator of ship ac generator
It consists of three stationary coils (called the stator, armature, or phase coils), which are physically separated in space by 120° from each other, and a rotor with a dc coil that produces the dc magnetic field. Both the stator and rotor coils are individually embedded in ferromagnetic cores with an air gap that is consistent with the electrical and mechanical design requirements.
f = P/2*n/60 = n*p / 120 cycles/ sec / (Hz)
Simplified cross section of a 3-phase generator with three stator coils and salient poles.
A thermodynamic prime mover drives the rotor, which generates voltage in each phase of the three identical stator coils. The 3-phase voltages are equal in magnitude but 120° out of phase in time (or in ωt to be precise). The stator coils are usually connected in 3-phase Y.
That way, the conductors in the stator slots need to have insulation to the ground for only 1/√3 = 0.577 or 57.7% of the line voltage, and hence, more conductors can be packed in the slots.
In the conventional generator, the dc excitation field current comes from a small separate exciter via slip rings and carbon brushes.
One mechanical revolution of a 2-pole rotor generates one electrical cycle (360 electrical degrees) in the stator coil voltage.
In a 4-pole rotor, one mechanical revolution generates 4/2 = 2 electrical cycles (2 × 360 electrical degrees).
A rotor with P number of poles driven at n rpm generates
P/2 × (n/60) electrical cycles per second
How to calculate ship generator frequency
Therefore, the generator frequency is given by:
f = P/2*n/60 = n*p / 120 cycles/ sec / (Hz)
The prime mover must drive the generator at a constant speed to generate power at a constant frequency (60 Hz or 50 Hz).
One mechanical degree = P/2 electrical degrees
