Types Of Dc Generator

Types of D.C. Generators According to the way in which their fields are excited, generators are classified into: 1. Separately excited D.C. Generator are those whose field magnets are energized from an independent source of D.C. Current. Separately excited generators are often used in feedback control systems when control of the armature voltage over a wide range is required.

If

I

Brush +

L O A D

Eg Field Winding Brush

V

-

R

Ra = Armature Resistance

2. Self excited D.C. Generators are those whose field magnets are energized by the currents produced by the generators themselves.

There are 3 types of self-excited D.C. Generators named according to the manner in which their field coils are connected to the armature. These are : • • •

Shunt wound D.C. Generator Series wound D.C. Generator Compound wound D.C. Generator

3. Shunt wound D.C. Generator have field windings and armature windings connected in parallel (shunt). The output varies inversely with load current. It contains many turns of fine wires. When a generator is in operation, whether or not it is delivering load current, the shunt field is always excited.

I

Ish Ia Shunt Field Rsh

+ Ra

L O A D

Eg

V

-

Rsh – Shunt Field Resistance Ra - Armature Resistance 4. Series wound D.C. Generator have field windings and armature windings connected in series. Outputs vary directly with load currents. Series-wound generators have few practical applications. It has few turns of heavy wires. When a generator is in operation, the series field is excited only when a load current is being supplied. In series generator, therefore, the terminal voltage is very low at light loads because of the excitation or load current is low. Ia=Ise=I + Eg

Rse

Series Field L O A D

V

5. Compound wound D.C. Generator have both series field windings and shunt field windings. These generators combine the characteristics of series and shunt generators. The output voltage remains relatively constant for all values of load current within the design of the generator. Compound generators are used in many applications because of the relatively constant voltage.

a. Short Shunt shunt field winding directly in parallel with the armature brushes and the series field winding connected between the parallel combination of shunt field and armature. I

Series Field Ish Ia Shunt Field

Eg

L O A D

V

b. Long Shunt shunt field is connected in parallel with the series field and armature. Ish

I

Series Field Ia Shunt Field Eg

L O A D

V