Induction Motors Essay
In this chapter the following topics will be discussed.
Introduction to synchronous generator
Principle of operation and emf equation
Equivalent circuit and voltage regulation
Short-circuit and open-circuit tests
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 …show more content…
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
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 )
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 )
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