In this topic, you study the meaning of balanced load in 3 phase system and three Phase balanced system.
The load on a three-phase system may be either star or delta connected irrespective of the type of connection for armature windings of the alternator. If all phase impedances of the three-phase load are exactly identical in respect of magnitude and their nature, it is said to be a balanced, three-phase load.
For example. if each phase of the three-phase load has a resistance of 10 Ω and inductive reactance of 25 Ω it will form a balanced, three-phase load. However, ¡f one of the phases has a capacitive reactance of 25 Ω in place of inductive reactance. then inspite of equal impedances in all the phases, the load will not be the balanced one. In practice. a three-phase motor connected across the supply forms a balanced load (Fig. 1).
Fig. 1: Loading of a three-phase system
The lighting and heating loads which are resistive in nature are normally connected between one line and neutral. The electricity authorities always try to distribute such single-phase loads on all the three phases as equally as possible. Thus, in such condition, all these single-phase loads also form a balanced. star-connected load.
Three Phase Balanced System
A three-phase system is said to be balanced when it possesses the following characteristics :
(i) The e.m.f.s (voltages) for three phases are equal and phase displaced by 120 electrical degrees.
(ii) The impedance in any one phase is identical to that in either of the other two phases.
(iii) The resulting currents in different phases are equal and have same phase angles. Or, in other words, they are also phase displaced from each other by 120 electrical degrees.
(iv) Equal power and equal reactive power flow in each phase.
Definite efforts are made to keep the three-phase system in balanced condition by using balanced loading. It is important to note that all the relations which are developed or conclusions which are reached in respect of three-phase systems are entirely based on the assumption that these systems are balanced.
