I am a little confused and am seeking clarification, please, from your good selves….
My ST alternators are rated at 7.5 KVA. The rated output current (at around 230 volts) is about 32 amps (stator). The field winding (rotor) is nameplate rated at 2.7 amps at about 62 volts.
The cross sectional area (diameter) of the winding wire is usually proportional to the current the winding has to carry. So, I would expect the stator windings (required current carrying capacity of 32 amps) would be substantially heavier than those for the stator (required current carrying capacity of 2.7 amps). But it is the other way round!
The 4 rotor windings have substantially larger cross sectional areas than the stator coils. I would have expected commercial sense to limit the rotor windings to the minimum required and also to limit centrifugal forces by keeping the rotating mass down. In my view, the cooling effectiveness of the rotating bobbins on the 4 rotor coils is good, and there is plenty of room left on the winding former so there is unlikely to be a heat build up in the middle of the field windings.
When I refer to the stator windings, I am talking about the main output windings and NOT the harmonic or “tell-tale” bulb windings, which, as one would expect, are of low cross sectional area compared to the main stator windings.
1. Why are the rotor windings larger than the stator windings ?
2. What am I missing ?
Regards,
Ian