Self-excited generators, both DC and AC types, rely on a process where a small initial voltage is generated to kickstart the generation process without requiring an external power source.
A self-excited DC generator typically starts with residual magnetism in its field poles. When the generator is initially brought up to speed by manually rotating its shaft or through another means, the residual magnetic field induces a small voltage in the armature windings. This initial voltage is fed back into the field windings through a voltage regulator or controller. As the voltage builds up in the field windings, it strengthens the magnetic field, causing further voltage generation in the armature windings. This positive feedback loop continues until the generator reaches its operating voltage and frequency.
Self-start generators refer to those that can automatically initiate their startup sequence without human intervention. These systems often integrate sophisticated control circuits or sensors that detect the need for power generation, such as when grid power fails in standby generators. Typically, a self-start generator includes a starter motor powered by an onboard battery or other energy source. When a signal triggers the generator to start, the starter motor initiates rotation of the engine, which in turn drives the generator. Once the generator reaches sufficient speed and voltage output, it switches from using the starter motor to generating power independently.
Self-excited AC generators operate similarly to their DC counterparts but are more complex due to the alternating nature of the current they produce. In an AC generator, initial excitation can occur through residual magnetism or through a separate exciter system. The exciter is a smaller generator or an exciter winding connected to the main generator’s shaft. Initially, residual magnetism or a small voltage from the exciter produces an AC voltage in the stator windings of the main generator. This AC voltage is then rectified and fed back into the field windings through a voltage regulator or controller. As the magnetic field in the field windings strengthens, it induces further voltage in the stator windings, creating a self-sustaining process of voltage generation.
Self-excitation in generators is achieved through various methods depending on the type and design of the generator. For both DC and AC generators, it typically involves the use of residual magnetism or an initial voltage source to kickstart the generation of electrical power. This process requires careful design of the field windings, armature windings, and control circuitry to ensure stable and reliable operation. In modern generators, electronic voltage regulators or control systems play a crucial role in monitoring and adjusting the excitation levels to maintain optimal performance and voltage regulation under varying load conditions.