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

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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 current on the rotor, which is rotating at the synchronous speed and a steady torque.

Synchronous machines are commonly used as generators especially for large power systems, such as turbine generators and hydroelectric generators in the grid power supply.
Because the rotor speed is proportional to the frequency of excitation, synchronous motors can be used in situations where constant speed drive is required.

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Chapter IV

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Angle in Electrical and Mechanical Unit
-For 2 pole machine, when the rotor rotates for one revolution, the induce emf varies for one cycle. i.e. θ
= θm, (refer to figure 2)
-Where θ is the angle in electrical degrees or radians and θm is the mechanical angle.
- For a 4 pole machine, as the rotor rotates for one revolution (θm = 2π), the induced emf varies for two cycles (θ = 4π) (refer to figure 2)
-Hence, θ = 2θm or in general, θ = (P/2) θm (Eqn 1)
-Where P = number of pole.

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Figure 2

2 pole

4 pole

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By taking derivatives on both side of Eqn 1. ω = (P/2) ωm
Where ω is