10/01/2019
4.Three Phase Circuits - Google Docs
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INTRODUCTION
This chapter has been divided into following topics:
1) 2) 3) 4) 5) 6)
Basic concepts of Poly phase Circuits and its advantages Generation of three phase supply Star – Delta Connections (Balanced load) Relationship between phase and line currents and voltages Phasor diagrams Measurement of power by two wattmeter method
POLYPHASE SYSTEMS 1) Poly phase alternators have two or more windings symmetrically spaced
around the armature. Such alternators produce as many independent alternating voltages as the number of windings (Phase).
2)
These voltages in the individual windings have the same magnitude and frequency but they have definite phase difference. The amount of phase difference depends upon the number of windings.
3)
Thus, by using appropriate poly phase alternator, it is possible to generate two phase and three phase ac and from these to obtain four, six, nine, twelve phase AC depending upon the requirements. These systems are collectively known as poly phase systems.
ADVANTAGES OF 3- Φ SYSTEM OVER 1- Φ SYSTEM 1) The output of a 3- φ machine is greater than that of 1- φ machine of the
same size.
2)
The total power output of a 3- φ machine is not fluctuating as in the case of a 1- φ machine. It has a higher efficiency.
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