Separately excited DC generator is one of the important type of DC generator in electrical field. The Separately Excited DC Generator simply means that the field winding is get excited by another independent power source. In here we are plan to discuss four characteristic of this special type generator such as
- No Load Characteristic of Separately excited DC generator
- Load Characteristic Separately excited DC generator
- External characteristic Separately excited DC generator
- Armature Characteristic and Regulation curve Separately excited DC generator
Normally These type of Separately excited generators are much suitable for applications which need speed variation from low speed to higher speed. Following characteristic shows that how they perform on speed variation characteristic theoretically.
1.No Load Characteristic
The relationship between the generator terminal voltage and the excited current is draw under this conditions.
- Zero current in the armature (Ia=0)
- Prime mover is operating with the rated speed of the generator
Vt = Ea – Ia Ra
Ia Ra = 0
Vt = Ea
Current is flow in the field circuit. The characteristic is almost linear in its initial portion and it is having a change after certain value of field current (If) . This deviation occurs because of the magnetic saturation of the higher materials use for this type of DC Generators.
2. Load Characteristic
In order to get the load characteristic of a separately excited DC generators the armature circuit is closed by connection a load across the terminal . The generator terminal voltage (Vt) and the excitation current (If) are measured by varying the load connected across the terminals under the following conditions.
i) The generator speed, N is fixed by the prime mover in its rated value.
ii) Armature current, Ia is constant by varying the current flow in the field circuit when the load varies.
3. External characteristic
The armature terminal is opened and the field current (If) is increase in already to get the rated voltage in its terminals. When this DC generator is operating what the rated speed.
The increase in field current is stop with V rated and a load is connected across the generator terminals by varying the load connected terminal voltages. Ant this armature current are measured under this conditions.
The internal characteristic is obtained by consideration of the armature reaction in the main flux with the increase of load current .
The reduction of the armature resistance form the internal characteristic is to obtain will give use the external characteristic of this generator.
4. Armature Characteristic and Regulation curve
For a particular field current excitation the armature and terminal voltage drops for it no load value. When the load current increase. The relationship between the excitation current If and the load current (IL) under following conditions.
i). Vt is kept constant in this rated value
ii). n constant prime mover is operated with rated speed is obtained is called armature characteristic.
Hope that you have get some basic understanding on the characteristics of Separately excited DC generators and we are plan t discuss some of several features of this type of special DC generators in our future articles.
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