A self-excited generator is a type of DC generator that initiates its own field excitation to generate electrical power. The process of starting a self-excited generator involves creating an initial magnetic field within the generator’s field winding. Here is a detailed explanation of how a self-excited generator starts:
- Components of a Self-Excited Generator:
- A self-excited generator consists of a rotor (armature), a stator (field winding), brushes, and a commutator. The field winding is a coil of wire wound around the stator, and the rotor consists of a coil of wire connected to a commutator.
- Initial Conditions:
- Initially, the generator is at rest, and there is no magnetic field in the field winding. Therefore, there is no induced electromotive force (EMF) in the armature.
- Manual Rotation or External Voltage:
- To initiate the starting process, the rotor may be manually rotated to create an initial magnetic field. Alternatively, an external voltage source can be applied to the field winding to induce a small initial magnetic field.
- Induced EMF in the Armature:
- As the rotor starts to turn or an external voltage is applied, a small induced EMF is generated in the armature coil due to the changing magnetic field.
- Current Flow in the Field Winding:
- The induced EMF in the armature causes a small current to flow through the field winding. This initial current establishes a weak magnetic field around the field winding.
- Regeneration Process:
- The weak magnetic field induces a slightly larger EMF in the armature. This induced EMF further increases the current flowing through the field winding, thus strengthening the magnetic field.
- Positive Feedback Loop:
- This process continues, creating a positive feedback loop. As the magnetic field strength increases, so does the induced EMF in the armature, leading to a higher current flow in the field winding and a stronger magnetic field.
- Saturation:
- The process continues until the magnetic field saturates, reaching a point where further increases in the field current do not significantly enhance the field strength.
- Steady-State Operation:
- At this point, the generator has reached steady-state operation. The self-excited generator is now capable of generating a stable and continuous electrical output without the need for an external voltage source.
- Voltage Regulation:
- The generated voltage can be regulated by adjusting the resistance in the field circuit. This helps maintain a constant voltage output under varying load conditions.
In summary, a self-excited generator starts by establishing an initial magnetic field within the field winding through manual rotation or an external voltage source. The induced EMF in the armature initiates a positive feedback loop, gradually building up the magnetic field strength until the generator reaches steady-state operation, producing a stable electrical output.
