# Induction Motors Essay

2648 Words Mar 21st, 2016 11 Pages
Introduction to Machines &
Power Systems
(EPM1076)

Chapter 4c

Synchronous Machines

Objectives:
In this chapter the following topics will be discussed.
 Introduction to synchronous generator
 Construction details

 Principle of operation and emf equation
 Equivalent circuit and voltage regulation
 Short-circuit and open-circuit tests
 Parallel operation
 Synchronizing procedures

Chapter IV

EPM1076

2

Introduction to Synchronous Machines
A synchronous machine is an ac rotating machine whose speed under steady state condition is proportional to the frequency of the current in its armature.
The magnetic field created by the armature currents rotates at the same speed as that created by the field
Convert rad/s to Hz, 2πf = (P/2) 2πfm f = (P/2) fm
Since nm = 60 fm f = (P/2) (nm /60)
Hence, nm = (120 f )/ P
That means the frequency of the induced emf, f is proportional to the rotor speed. nm = mechanical speed of magnetic field (or rotor speed) in r/min. f = electrical frequency, in Hz
Chapter IV

EPM1076

7

Examples of a rotating electric machines:

• DC field winding on the rotor,
May function as a generator (MECHANICAL  ELECTRICAL)

AC armature winding on the stator,
May function as a synchronous motor :

( ELECTRICAL  MECHANICAL )

Chapter IV

EPM1076

8

Introduction to Synchronous Generator
• Usually, AC power is generated by three-phase synchronous generators (Alternators)
• Generate bulk power (1700 MW) at 6.6 - 28 -kV
• Must be driven at a constant speed in synchronism with the frequency of the power generated.
• The position of the armature and the field circuit is interchanged in synchronous generators compared to the dc machines as:

( Armature-winding in Stator, and
Field-winding in Rotor )
Chapter IV

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 The armature winding, being rated for higher power is much larger than the field winding. Therefore, it can be better placed in the stationary member.
 Cooling arrangement is easier if the armature is in the stator.  The field coils carry relatively small current and hence the power can be supplied easily to the field

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