Page 203 - Electrician - TT (Volume 1)

ELECTRICIAN - CITS

Hysteresis loss
• Occurs in the armature of the dc machine
• magnetic field reversals as it passes under successive poles.
• Small amount of power wasted in reversal of magnetism is called hysteresis loss.

• In other words, due to magnetization & de-magnetization of core.
• P = K f V B max Watts
1.6
h
h
V- volume of armature in m³.
Eddy current loss
• emf induces in armature conductors

• in addition, small amount of voltage is also induced in the armature core
• this cause the circulating current in the armature core, called eddy current.
• Power loss due to this current is called eddy current loss.
• Eddy current can be reduced by making the core resistance high.
• Core resistance can be increased by making the core of thin, round iron sheets called laminations.

• Laminations are separated by varnish which has high resistance to avoid the flow of current from one lamination
to the other.
• Pe = B max f t v Watts
2
2 2
Mechanical losses
• Friction loss e.g., bearing friction, brushes friction etc.
• Windage loss e.g., air friction of rotating parts.
Constant losses
• (1) Iron losses

• (2) Mechanical losses
• (3) Shunt field losses.
Variable losses
• Armature copper loss (I a Ra)
2
• Series field copper loss (I se R se).
2
Power stages of a dc generator
Power stages of a dc generator tell us how much mechanical power is converted into electrical power and into
losses.

190

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