Unit II
Electrical Machines
, Contents
• 2.1 Transformer: Working principle, emf equation, Voltage ratio,
current ratio and transformation ratio, losses.
• 2.2 DC motor construction - parts its function and material used.
• 2.3 DC motor -Principle of operation.
• 2.4 Types of DC motors, schematic diagram, applications of dc shunt,
series and compound motors.
• 2.5 Universal motor: principle of operation, reversal of rotation and
applications.
• 2.6 Stepper motor: types, principle of working and applications.
, Introduction
• The transformer is a static device (i.e. the one which does not contain
any rotating and moving parts) which is used to transfer electrical
energy from one AC circuit to another AC circuit, with increase or
decrease in voltage / current but without any change in frequency.
• It is important to remember that input to a transformer and output
from a transformer both are alternating (AC) quantities.
, Function of a Transformer
• The electrical energy is generated and transmitted at extremely high
voltages.
• The voltage is then reduced to a lower value for domestic and
industrial use.
• This is done by using a transformer.
• When the voltage level is reduced, the transformer is called a step-
down transformer.
• When the voltage level is increased, the transformer is called a step-
up transformer.
• When a transformer changes the voltage level, it changes the current
level also.
Electrical Machines
, Contents
• 2.1 Transformer: Working principle, emf equation, Voltage ratio,
current ratio and transformation ratio, losses.
• 2.2 DC motor construction - parts its function and material used.
• 2.3 DC motor -Principle of operation.
• 2.4 Types of DC motors, schematic diagram, applications of dc shunt,
series and compound motors.
• 2.5 Universal motor: principle of operation, reversal of rotation and
applications.
• 2.6 Stepper motor: types, principle of working and applications.
, Introduction
• The transformer is a static device (i.e. the one which does not contain
any rotating and moving parts) which is used to transfer electrical
energy from one AC circuit to another AC circuit, with increase or
decrease in voltage / current but without any change in frequency.
• It is important to remember that input to a transformer and output
from a transformer both are alternating (AC) quantities.
, Function of a Transformer
• The electrical energy is generated and transmitted at extremely high
voltages.
• The voltage is then reduced to a lower value for domestic and
industrial use.
• This is done by using a transformer.
• When the voltage level is reduced, the transformer is called a step-
down transformer.
• When the voltage level is increased, the transformer is called a step-
up transformer.
• When a transformer changes the voltage level, it changes the current
level also.
