This document discusses balanced and unbalanced loads in three-phase power systems. It defines a balanced three-phase supply as one where the voltages have the same magnitude and differ by 120 degrees. A balanced load is where the impedances of the three phases are exactly the same. It also defines unbalanced loads and supplies. The document provides power equations for both star-connected and delta-connected balanced loads. It concludes by stating that depending on impedance matching, loads can be classified as balanced or unbalanced, and these different load types have their own power equations and three-phase quantities.

1. 1.3 Balanced and unbalanced load
P. Maria Sheeba
AP/ECE, MZCET
1

2. Discussion of last class
• Last class, we discussed about the star and
delta connection and its difference based on
their needs in three phase power supply
system.
• In today’s class, we will see about the
balanced and unbalanced loads of star and
delta connection and also the power equation
with reference to previous class.

3. 1.3.1 Balanced three phase supply:
• A three phase supply is said to be balanced, when all
the three voltages have the same magnitude but differ
in phase by 120° with respect to one another.
• The three phase supply is said to be unbalanced,
even if one of the above conditions is not satisfied.
MZCET 3
Balanced Supply

4. MZCET 4
1.3.2 Balanced Load:
• A three phase load is said to be balanced, when the
impedances of all the three phases are exactly the same. Even
if one of them is different from the other, then the three
phase load is said to be unbalanced

5. • In a three phase balanced load, whether star connected or delta connected,
the magnitudes of the phase currents are the same but differ in phase by
120o with respected to one another
1.3.3 Unbalanced Load
• But in an unbalanced load, when a three phase balanced supply is given, the
magnitudes and phases of all the three phase currents will be different.
MZCET 5

6. 1.4 Power Equation
6

7. 1.4 Power Equation
1.4.1 Star Connection
The total power in the circuit is the sum of the three phase
powers. Hence ,
Total Power =3 x phase power=
7

8. 1.4.2 Power for delta connection
MZCET 8
cos3 phph IEP 
Lph VEbut 
3
L
ph
II 
cos
3
3  L
L
I
VP
cos3 LL IVP 

9. Summary
• Depending upon the impedance matching the
loads are being classifies as balanced and
unbalanced loads.
• These loads have their own power equation
and other three phase quantities.
• In the next class, we will see how the power is
generated in the three phase circuit.