What is typically the limiting factor in the current capacity of rotating armature generators?

The limiting factor in the current capacity of rotating armature generators is primarily the brushes and slip rings. These components are crucial for conducting current from the rotating armature to the external circuit. The performance of the brushes and slip rings can be affected by factors such as their size, material, and the contact pressure between the brushes and the slip rings.

As the current flowing through the generator increases, the heat generated at the contact points of the brushes and slip rings also rises. This can lead to increased wear, potential for electrical arcing, and limitations on the maximum safe operating current. If the brushes and slip rings cannot handle the increased current without overheating or damaging, they become the bottleneck for the generator's overall current capacity.

While other factors such as rotor design, generator size, and external load can impact the generator's performance, it is the brushes and slip rings that play a critical role in determining how much current can safely be transmitted from the rotating armature without detrimental effects.