Short Answer
Self-excited generators use their own generated voltage to supply current to the field winding. In this type, the field winding is connected to the armature, so no external source is required.
Separately excited generators use an external power source to supply current to the field winding. This allows better control of the magnetic field and output voltage, but requires additional equipment.
Detailed Explanation:
Difference between self-excited and separately excited generators
Self-excited generator
A self-excited generator is a type of DC generator in which the field winding gets its current from the generator itself. This means that part of the generated voltage is used to excite the field winding.
In this type, when the generator starts rotating, a small voltage is produced due to residual magnetism present in the poles. This small voltage causes a small current to flow through the field winding. As the field current increases, the magnetic field becomes stronger, which in turn increases the generated voltage. This process continues until the generator reaches its normal operating voltage.
Self-excited generators are simple in construction and do not require any external source for excitation. They are widely used in practical applications because of their convenience and lower cost.
There are three types of self-excited generators: shunt, series, and compound generators. Each type has different characteristics depending on how the field winding is connected.
However, self-excited generators have some limitations. The control of output voltage is not very precise, and the performance depends on residual magnetism. If residual magnetism is lost, the generator may fail to build up voltage.
Separately excited generator
A separately excited generator is a type of DC generator in which the field winding is supplied with current from an external source, such as a battery or another generator.
In this case, the field circuit is completely independent of the armature circuit. This allows better control over the field current and, therefore, better control over the output voltage.
Since the excitation is independent, the generator can produce voltage even without relying on residual magnetism. This makes it more reliable in certain situations.
Separately excited generators are commonly used in laboratories, testing systems, and applications where precise voltage control is required.
However, they require an external power supply, which increases the cost and complexity of the system.
Key differences
The main difference between these two types lies in the source of excitation. In self-excited generators, the generator supplies its own field current, while in separately excited generators, the field current comes from an external source.
Self-excited generators are simpler and more economical, but they offer less control over voltage. Separately excited generators provide better control and stability but are more complex and costly.
Another difference is in starting. Self-excited generators depend on residual magnetism to start generating voltage, while separately excited generators do not have this limitation.
In terms of applications, self-excited generators are commonly used in general-purpose applications, while separately excited generators are used where accuracy and control are important.
Conclusion
Self-excited and separately excited generators differ mainly in how their field windings are powered. Self-excited generators use their own output, while separately excited generators use an external source. Each type has its own advantages and is chosen based on application needs.