Page 224 - Electrician - TT (Volume 1)

ELECTRICIAN - CITS

Dc series motor
IN series motor, speed decreases as load increases. At heavy load, torque is high and speed become low. When
load is removed completely / lightly loaded the speed of the motor becomes dangerously high. So DC Series
motor is not used in places where load may be removed. A DC series motor can never be started without load /
light load. It is a variable speed motor;self-adjust as per load.

Characteristics of dc series motor
• In series motor
• T αØI
a
• Ø αI a
• T α Ia .
2
After saturation, flux is constant
so T αIa
T / Ia Characteristics
Here from the equation at first curve is parabolaand then it is straight line.

N / Ia Characteristics
Speed torque characteristics
(N/T) In DC series motor, at constant load, Eb is constant.

Characteristics of dc shunt motor
In DC shunt motor the field is connected in parallel with armature. Field current is almost constant. Sofield flux
almost remains constant.
Torque / armature current characteristics
General Torque equation
Ta α Φ Ia

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CITS : Power - Electrician & Wireman - Lesson 30-37 CITS : Power - Electrician & Wireman - Lesson 30-37