Types of DC Generators: Self and Separately Excited

DC generators are classified into different types based on the method of field excitation that produces the magnetic flux necessary for generating electromotive force (EMF). The main types of DC generators are:

Permanent Magnet DC Generator
In this type, the magnetic field is produced by permanent magnets instead of field windings. These generators are usually small and used for low power applications such as dynamos in bicycles or motorcycles. They are simple and compact but the magnetic field strength can deteriorate over time, which affects the generator's performance. They are generally not used in industrial applications due to their limited power output.

Separately Excited DC Generator
This generator has its field windings energized by an independent external DC source. There is no electrical connection between the armature circuit and the field circuit. The field current is controlled independently, which allows the magnetic flux (and therefore the output voltage) to be regulated independently of the armature current.

Self-Excited DC Generator
In these generators, the field winding is energized by the current generated by the generator itself. They rely on residual magnetism to start producing a small voltage when the armature rotates. This voltage builds up the field current, which then increases the output voltage in a cumulative manner until it reaches a steady state. Self-excited DC generators are further classified based on how the field winding is connected:

Shunt Wound Generator: The field winding is connected in parallel (shunt) with the armature winding. It has a constant output voltage over a range of loads.

Series Wound Generator: The field winding is connected in series with the armature winding. The output voltage varies more significantly with load.

Compound Wound Generator: This type combines both series and shunt field windings to provide the benefits of both types. It can be further classified into:

Short Shunt Compound Generator: Shunt field winding is connected across the armature only.

Long Shunt Compound Generator: Shunt field winding is connected across both the armature and the series field winding.

These types allow the DC generator to be used in various applications based on the needed voltage regulation and load characteristics.

1. 24PEE303 – ELECTRICAL MACHINES I UNIT - II DC GENERATOR TYPES OF DC GENERATORS

2. In practical  DC generators , the magnetic field is produced by electromagnets rather than permanent magnets. The DC generators are then classified based on the connection of field winding in the generator circuit. On this basis, DC generators are classified into the following two types: Separately Excited DC Generators Self-Excited DC Generators TYPES OF DC GENERATORS

3. SEPARATELY EXCITED DC GENERATOR A DC generator whose magnetic field winding is excited from an independent source of DC electric supply like battery is called a  separately excited DC generator . Figure-1 shows the connection diagram of a separately excited DC generator.

4. The type of DC generator whose magnetic field winding is excited from the output of the generator itself is known as a  self-excited DC generator . Depending upon the manner in which the field winding is connected to the armature, self-excited DC generators are classified into the following three types Series DC generator Shunt DC generator Compound DC generator SELF-EXCITED DC GENERATORS

5. SERIES DC GENERATOR

6. SHUNT DC GENERATOR

7. COMPOUND DC GENERATOR A  compound dc generator  is one which has two sets of field windings on each magnetic pole one is in series and the other is in parallel with the armature winding. The compound dc generators may further be divided into the following two types − Short-shunt Compound DC Generator Long-shunt Compound DC Generator

8. SHORT-SHUNT COMPOUND DC GENERATOR

9. LONG-SHUNT COMPOUND DC GENERATOR

10. APPLICATIONS OF DC GENERATORS SEPARATELY EXCITED DC GENERATORS A separately excited DC generator requires an independent external DC source for the excitation of field winding. Thus, it is expensive and being rarely used. Following are some application of separately excited DC generators : These are able to produce a wide range of voltage output, they are primarily used in laboratory and commercial testing. These are used in speed regulation tests. These generators operate in a stable condition with any change in field excitation. Therefore, they are also used in supplying power to the DC motors, whose speed being to be controlled.

11. SERIES DC GENERATORS A series DC generator has limited applications. Some of the applications of a series DC generator are as follows: The rising characteristics of a series DC generator makes it suitable for voltage boosting applications in the feeders in the various types of distribution systems. A series DC generator has the tendency to supply constant load current. Hence, several series generators can be connected in series to provide high voltage DC power transmission at constant load current. The series DC generators are also used in supplying field excitation current in DC locomotives for regenerative breaking. The series generators also find applications in series arc lightening.

12. SHUNT DC GENERATORS A shunt DC generator produces constant terminal voltage for small distance operations. Therefore, these are used in following applications: They are used for battery charging applications. Shunt DC generators with field regulators are used for lighting and power supply purposes. Use for giving excitation to the alternators.

13. COMPOUND DC GENERATORS The compound DC generators are used in following applications: The over compounded generators have ability to compensate voltage drop in the transmission lines and tends to maintain constant voltage at the consumer's end. Therefore, the over compounded generators are used in supplying loads through long transmission lines. Cumulative compound generators are used for supplying power to DC motors. Cumulative compound generators are used for lighting, power supply purposes and for heavy power services, etc. The differential compound generators are used for arc welding purposes where a large voltage drop and constant current is required.