Electrical Engineering ⇒ Topic : Unbalanced 3-Phase Loads
Unbalanced 3-Phase Loads
We know that there are two types of 3-phase loads viz Y-connected load and A-connected load.So far we have considered balanced 3-phase loads i.e. the loads that have the same impedance and power factor in each phase. In case of balanced 3-phase loads, the three load phase voltages are equal in magnitude displaced 120° from each other. The same is true with regard to the three load phase currents and the three line currents. Also power delivered to each of the three load impedances is the same. Therefore, the problems on balanced 3-phase loads can be solved by considering one phase only ; the conditions in the other two phases being similar.
In practice, we come across situations where 3-phase loads are unbalanced i.e. loads in one or more phases have different impedances and/or power factor. In such a case, the three load phase voltages are unequal in magnitude and displaced by unequal angles from each other. The same is true with regard to the three load phase currents and the three line currents. Also power delivered to each of the three load impedances is different. The problems on unbalanced 3-phase loads are more difficult to deal with. It is because the conditions in the three phases are different and we have to determine the circuit values (i. e. phase current, line current, load phase voltage, power etc.) for each phase separately. In practice, we may come across the following unbalanced 3-phase loads :
(i) Four-wire star-connected unbalanced load
(ii) Unbalanced A-connected load
(iii) Unbalanced 3-wire, Y-connected load.
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