Why does an induction generator usually need an electrical supply network or capacitors to operate?

An induction generator requires an external electrical supply network or capacitors because it does not contain its own source of magnetic field.1

In a standard induction machine, the magnetic field is typically established by currents drawn from an electric supply network. When connected to such a network, the machine can operate as a generator if a prime mover drives the rotor faster than its synchronous speed. The network provides the necessary magnetizing current to create the rotating magnetic field required for the machine to function.12

For stand-alone operation, where no external supply network is present, the generator must rely on capacitors. These capacitors provide the reactive power (leading current) needed to excite the stator windings and establish the rotating magnetic field, allowing the machine to generate electrical power independently. Without either the network or capacitors to supply this magnetizing component, the induction machine cannot produce the magnetic field essential for energy conversion.132