Introduction to Three-phase Circuits

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1Introduction to Three-phase CircuitsBalanced 3-phase systemsUnbalanced 3-phase systems2Introduction to 3-phase systemsSingle-phase two-wire system: Single source connected to a load using two-wire systemSingle-phase three-wire system: Two sources connected to two loads using three-wire system Sources have EQUAL magnitude and are IN PHASE3Balanced Two-phase three-wire system: Two sources connected to two loads using three-wire system Sources have EQUAL frequency but DIFFFERENT phasesCircuit or system in which AC sources operate at the same frequency but different phases are known as Phase System: A generator consists of two coilsplaced perpendicular to each other The voltage generated by one lags the other by 90 .4Balanced Three-phase four-wire system: Three sources connected to 3 loads using four-wire system Sources have EQUAL frequency but DIFFFERENT phasesThree Phase System: A generator consists of three coilsplaced 120 apart. The voltage generated are equal in magnitude but, out of phase by 120.

The phase sequenceis the time order in which the voltages pass through their respective maximum values. 25 o V an V p 0 o bn V p 120 o cn V p 120 120o 120o 120o Phase sequence : V an leads V bn by 120o and V bn leads V cn by 120o This is a known as abc sequence or positive sequence + ...

  Phases, Sequence, Phase sequence