8.1 Introduction8.2 Polyphase system8.3 Advantages of three-phase system over single-phase system8.4 Generation of three-phase emfs8.4.1 Phasor diagram8.5 Naming the phases8.6 Phase sequence8.7 Double-subscript notation8.8 Interconnection of three phases8.9 Star or wye (Y) connection8.9.1 Relation between phase voltage and line voltage8.9.2 Relation between phase current and line current8.10 Mesh or delta (∆) connection8.10.1 Relation between phase voltage and line voltage8.10.2 Relation between phase current and line current8.11 Connections of three-phase loads8.12 Power in three-phase circuits8.13 Power measurement in three-phase circuits8.14 Three-wattmeter method8.15 Two-wattmeter method8.16 Two-wattmeter method (balanced load)8.16.1 Determination of power factor from wattmeter readings8.16.2 Determination of reactive power from two wattmeter eadings8.17 Effect of power factor on the two wattmeter readings8.17.1 Power factor is unity (cos ɸ = 1) or ɸ = 0°8.17.2 Power factor is 0.5 (cos ɸ = 0.5) or ɸ = 60°8.17.3 Power factor is more than 0.5 But less than one (i.e., 1 > cos ɸ > 0.5) or 60° > ɸ > 0°8.17.4 Power factor is less than 0.5 But more than 0 (i.e., 0.5 > cos ɸ > 0) or 90° > ɸ >60°8.17.5 Power factor is 0 (cos ɸ = 0) or ɸ = 90°