1. Chapter 12Three Phase Circuits Chapter Objectives: • Be familiar with different three-phase configurations and how to analyze them. • Know the difference between balanced and unbalanced circuits • Learn about power in a balanced three-phase system • Know how to analyze unbalanced three-phase systems • Be able to use PSpice to analyze three-phase circuits • Apply what is learnt to three-phase measurement and residential wiring Huseyin Bilgekul Eeng224 Circuit Theory II Department of Electrical and Electronic Engineering Eastern Mediterranean University

2. Power in a Balanced System • The total instantaneous power in a balanced three phase system is constant.

3. Power in a Balanced System • The complex power per phase is Sp. The total complex power for all phases is S.

4. Power in a Balanced System Ip Vp Vp Ip Vp VL VL VL VL Ip Vp Vp Ip Ip Ip VL Vp VL • Notice the values of Vp, VL, Ip, IL for different load connections. Y connected load. Δ connected load.

5. Power in a Balanced System

6. Single versus Three phase systems • Three phase systems uses lesser amount of wire than single phase systems for the same line voltage VL and same power delivered. a) Single phase system b) Three phase system • If same power loss is tolerated in both system, three-phase system use only 75% of materials of a single-phase system

8. VL=840 V (Rms) IL Capacitors for pf Correction

10. Unbalanced Three Phase Systems • An unbalanced system is due to unbalanced voltage sources or unbalanced load.In a unbalanced system the neutral current is NOT zero. Unbalanced three phase Y connected load. Line currents DO NOT add up to zero. In= -(Ia+ Ib+ Ic) ≠ 0

12. Three Phase Power Measurement Two-meter method for measuring three-phase power

13. Residential Wiring Single phase three-wire residential wiring