Q2Electrical Machines and Drives

A separately excited generator has its field winding supplied from an independent external DC source, giving it the advantage of stable output voltage that does not collapse even under heavy or short-circuit load conditions, since the field excitation is unaffected by armature loading, and it can operate over a wider, more linearly controllable output voltage range including intentionally very low voltages. Its main disadvantage is the added cost, complexity, and space requirement of a separate exciter source, unlike a self-excited generator which builds its own field current from its own residual magnetism and armature output, making it simpler and cheaper but more prone to voltage instability and loss of excitation under fault conditions.