- Performance Curves Definition: Performance curves show how a DC generator’s output voltage changes with different load currents, indicating voltage regulation efficiency.
- Separately Excited DC Generator: This type of generator, though costly, can maintain constant terminal voltage by increasing field excitation to counteract voltage drops.
- Series Wound DC Generator: The terminal voltage starts at zero with no load and increases with load, but is affected by armature reaction and resistance drops.
- Shunt Wound DC Generator: This generator has a rapid voltage drop as the load increases due to strong armature reactions, leading to poor performance.
- Compound Wound DC Generator: Combines shunt and series field effects, maintaining constant voltage by balancing voltage drops and rises in different windings.
Performance curves of a DC generator are graphs that show how the output voltage changes as the load current varies from no load to full load. These are also known as characteristic curves. These curves help us understand the voltage regulation of different types of DC generators. Better performance is indicated by lower voltage regulation.
Performance Curve of Separately Excited DC Generator
Though this type of DC generators are rarely used due to its cost for the separate excitation but the performance of these DC generators are quite satisfactory. In separately excited DC generators, the terminal voltage as the load increases and the load current started to flow.
There is slight drop in the terminal voltage due to armature reaction and IR drop but these drop can be eliminated by increasing field excitation and then we can get constant terminal voltage. In the diagram below, the curve AB is showing this characteristic.
Performance Curve of Series Wound DC Generator
In series DC generators, the terminal voltage at no load is zero because no current flows through the field winding. As the load increases, the output voltage rises. The terminal voltage varies widely with small changes in load current. Due to armature reaction and ohmic drop in the armature winding, the output voltage is lower than the generated voltage.
Performance Curve of Shunt Wound DC Generator
In shunt wound DC generators, there is always some voltage at no load due to the shunt field winding. As the load increases, the terminal voltage drops quickly because of strong demagnetizing armature reaction and resistance drop. This drastic reduction in terminal voltage leads to a decrease in load current, resulting in poor performance of this type of generators.
Performance Curve of Compound Wound DC Generator
At no load, the performance curve of this type of DC generator is same as that of shunt field generators because at no load, there is no current in the series field winding. When the load increases, then the terminal voltage drops due to the shunt DC generator, but the voltage rise in the series DC generator compensates the voltage drop. For these reason the terminal voltage remains constant. The terminal voltage can also make higher or lower by controlling the amp-turns of the series field winding. In the diagram below, the curve FG is showing this characteristic.
