The correct answer is: A. Series generator
A series generator is a type of DC generator that has the field winding connected in series with the armature winding. This type of generator is used for feeding long DC transmission lines because it has a high output voltage and a low output current. The high output voltage is necessary to overcome the voltage drop in the transmission line, and the low output current helps to reduce the power losses in the line.
A shunt generator is a type of DC generator that has the field winding connected in parallel with the armature winding. This type of generator is used for applications where a constant voltage is required, such as in battery charging.
An over compound generator is a type of DC generator that has the field winding connected in series with the armature winding, and an additional field winding connected in parallel with the armature winding. This type of generator is used for applications where a high output voltage and a high output current are required, such as in traction motors.
A flat compound generator is a type of DC generator that has the field winding connected in series with the armature winding, and an additional field winding connected in parallel with the armature winding. The additional field winding is connected in such a way that it cancels out the effect of the armature reaction. This type of generator is used for applications where a constant voltage is required, even under varying load conditions.