Single Phase System

Single phase is a system which has only one equal phase also the magnitude is equal.
This two figure is considered as a single phase system because it has a single source in figure (a) and for the figure (b) it has two source but it has equal magnitude and phase angle.


Now the topics will move on to another topic and it is the three phase system. First is the balance three phase system or the system which is the magnitude is equal but the phase is different or they have the equal distance angle to each other.

Balanced three phase voltages is usually seen in AC generator. AC generator is a specific example of three phase voltages because it produces three phase voltage. AC generator has a rotating magnet (called the rotor) and a stationary winding surrounded to the magnet (called the stator). Here is the drawing sample of AC generator.

ac generator

The coils that indicated a prime is a three phase voltage output and they are 120 degrees apart around the stator and also the other letter is the neutral of the respective letters that have prime. This is the sinusoid of three phase voltage.

3phase sinusoid

Two types of three phase sources connection. (WYE and DELTA)

wye delta connection

y delta

Phase Sequence is the time order in which the voltages pass through their respective maximum values. There are two types of sequences: Positive sequence or abc and negative sequence or acb.

negative positive


If there is a balance sources also there is a balanced load. Balanced load can be define as the magnitude and phase angle are equal in which one phase.

ydella load

Those equation inside the box helps to transform the load into WYE-DELTA or DELTA-WYE vice versa.


It is the system where the three phase system with a balanced WYE-connected source and a balanced WYE-connected load.

EXAMPLE: solve the current I in each line

yy connection

As we see it is equal load and every line so to make it easier  I will just solve one line only because they have equal magnitude and only I will do is to solve their phase angle by adding the angle of the first current by the angle phase of their respective voltage source.




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