The Three Phase Circuits

THE 'Y' CONNECTION

GENERAL DEFINITIONS:

• The conductors connected to the three points of a three-phase source or load are called lines.
• The three components comprising a three-phase source or load are called phases.
• Line voltage is the voltage measured between any two lines in a three-phase circuit.
• Phase voltage is the voltage measured across a single component in a three-phase source or load.
• Line current is the current through any one line between a three-phase source and load.
• Phase current is the current through any one component comprising a three-phase source or load.
• In balanced “Y” circuits, line voltage is equal to phase voltage times the square root of 3, while line current is equal to phase current.

THE DELTA CONNECTION

For Delta Circuits:

Eline = Ephase

Iline = Square root of 3(Iphase)

THE DELTA - DELTA CONNECTION

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• All sources are represented by a set of balanced 3-phase variables
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• Loads are three phase with equal Z's (impedances)
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• Line impedance are equal in all three phases

• All three variables have the same amplitude
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• All three variables are in phase 120^o 

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• All three variables have the same frequency
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