What type of voltage is produced if an alternating current generator is driven without field excitation?

When an alternating current generator is driven without field excitation, it can still produce a small amount of voltage known as residual voltage. This phenomenon occurs because there is often a small amount of magnetic field left in the generator's core from previous excitation. The residual magnetism can induce a voltage in the generator's winding as it rotates, even without applied field excitation.

This residual voltage is typically much lower than the normal operating voltage that would occur with proper field excitation, but it is significant enough to be measurable. In some cases, this residual voltage can be used to initiate the excitation process when the generator is brought online, allowing for normal operation to resume. The existence of residual voltage reflects the ability of the generator's design to leverage any remaining magnetic properties, which is a fundamental aspect of generator operation.