The document describes the key characteristics of a DC generator, including: 1) The no-load saturation characteristic (E0/If) which shows the relationship between no-load generated EMF and field current at a fixed speed. 2) The internal or total characteristic (E/Ia) which gives the relationship between induced EMF and armature current, accounting for armature reaction. 3) The external characteristic (V/I) which gives the relationship between terminal voltage and load current, accounting for voltage drops from armature resistance.

1. Email- dilouarbd@gmail.com
By Dilouar Hossain
Topic: DC Generator

2. Generator Characteristics

3. DC Generator Characteristics
1. No-load saturation Characteristic (E0/If)
 It is also known as Magnetic Characteristic or Open-circuit
Characteristic. It shows the relation between the no-load
generated e.m.f. in armature, E0 and the field or exciting
current If at a given fixed speed. It is just the magnetisation
curve for the material of the electromagnets.
 Its shape is practically the same for all generators whether
separately-excited or self-excited.
2. Internal or Total Characteristic (E/Ia)
 It gives the relation between the e.m.f. E actually induces in
the armature (after allowing for the demagnetising effect of
armature reaction) and the armature current Ia.
 This characteristic is of interest mainly to the designer

4. 3. External Characteristic (V/I)
 It is also referred to as performance characteristic or
sometimes voltage-regulating curve.
 It gives relation between that terminal voltage V and
the load current I. This curve lies below the internal
characteristic because it takes into account the voltage
drop over the armature circuit resistance.
 The values of V are obtained by subtracting IaRa from
corresponding values of E. This characteristic is of
great importance in judging the suitability of a
generator for a particular purpose.

5. External Characteristic
These are three main reasons for the drop in terminal voltage of a
shunt generator when under load.
 (i) Armature resistance drop :
As the load current increases, more and more voltage is
consumed in the ohmic resistance of the armature circuit.
Hence, the terminal voltage V = E − Ia Ra is decreased where
E is the induced e.m.f. in the armature under load condition.
 (ii) Armature reaction drop:
Due to the demagnetising effect of armature reaction, pole flux
is weakened and so the induced e.m.f. in the armature is
decreased.
 (iii) The drop in terminal voltage V due to (i) and (ii) results
in a decreased field current .
If which further reduces the induced e.m.f.

6. Shunt-generator characteristics
1.Armature-circuit
resistance,
2. Armature reaction,
3. Reduction in the field
current.

7. Thank you……