Tuesday, March 17, 2015

Three Phase Circuit



The Y Connections
           -  each phase is connected between a line and the neutral.

Phase Voltage = Line to neutral voltage(Va, etc.).
Phase Currents = Line currents(Ia, etc.).
Neutrals Connect the 3 phases.




The Delta Connections
            - each phase is connected in two lines.


Phase Voltage = Line voltages(Vab, etc.).
Phase Currents = Currents from line to line(Iab, etc.).
Neutral is not present.



Definition of the following:

Phase - it is simply the branch of the circuit.
Line - wires that connect the source to the load.
Neutral - the 4th wire in the three phase system. It's where the phases of a Y connection come together.
Line Currents - the current flowing in each of the lines(Ia, Ib, Ic).
Line Voltage - the voltage between any two of the lines(Vab, Vbc, Vac).
Phase Currents & Voltages - the voltages and currents across and through a single branch (phase) of the circuit. It depends on whether the connection is Wye or Delta!



Y connected  source



Delta connected source



Y connected load




Delta connected load

 
Reminders:

  • All 3 variables have the same amplitude
  • All 3 variables have the same frequency
  • All 3 variables are 120o in phase
  • All 3 sources are represented by a set of balanced 3-phase variables
  • All loads are 3-phase with equal impedance's
  • Line impedance are equal in all 3 phases


Balanced 3-phase circuit:
















































































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