Text from page-1
BALANCED THREE-PHASE CIRCUITS The voltages in the three-phase power system are produced by a synchronous generator (Chapter 4). In a balanced system, each of the three instantaneous voltages have equal amplitudes but are separated from the other voltages by a phase angle of 120o. The three voltages (or phases) are typically labeled a, b and c. The common reference point for the three phase voltages is designated as the neutral connection and is labeled as n. We may define either a positive phase sequence (abc) or a negative phase sequence (acb) as shown below. The three sources Van, Vbn and Vcn are designated as the line-to-neutral voltages in the three-phase system.