Underexcited saturation state in cylindrical rotor synchronous machines

In this paper the recognition of actual saturation levels is evaluated in its influence on the magnetic stability limit, also called underexcitation limit, as well as its thermal influence on the end zone.

It is shown that while the machine during underexcitation operation is less saturated than during overexcited operation it still shows saturation behavior. Using the appropriate saturation state for the evaluation of the underexcitation limit allows an increase in this operation. However, it introduces more complicated boundary conditions for voltage scaling of said limit, as appropriate saturation states for higher and lower operational voltages need to be considered as well.

In thermal investigations it is shown how saturation influences radial flux losses, pressure finger losses, and core and end tooth losses. While saturation appears to have little influence on the pressure finger losses, it increases radial flux loss as well as core and end tooth losses significantly.

As the loss distributions shows: When increasing the underexcited operational range using more appropriate saturation states, a thermal evaluation of the end zone must occur as well to ensure safe operation.