1. 1 Eeng 224 Chapter 12 Three Phase Circuits Huseyin Bilgekul Eeng224 Circuit Theory II Department of Electrical and Electronic Engineering Eastern Mediterranean University 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

2. 2 Eeng 224 Power in a Balanced System  The total instantaneous power in a balanced three phase system is constant.

3. 3 Eeng 224 Power in a Balanced System  The important consequences of the instantenous power equation of a balanced three phase system are:

4. 4 Eeng 224 Power in a Balanced System  The complex power per phase is S p. The total complex power for all phases is S.

5. 5 Eeng 224 Power in a Balanced System  The complex power per phase is S p. The total complex power for all phases is S.

6. 6 Eeng 224 Power in a Balanced System  Notice the values of V p, V L, I p, I L for different load connections. VLVL VLVL VLVL VpVp VpVp VpVp IpIp IpIp IpIp VLVL VpVp IpIp VLVL VLVL VpVp VpVp IpIp IpIp Y connected load.Δ connected load.

7. 7 Eeng 224 Power in a Balanced System

8. 8 Eeng 224 Single versus Three phase systems  Three phase systems uses lesser amount of wire than single phase systems for the same line voltage V L 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

9. 9 Eeng 224

10. 10 Eeng 224 V L =840 V (Rms) Capacitors for pf Correction ILIL

11. 11 Eeng 224

12. 12 Eeng 224 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. I n = -(I a + I b + I c ) ≠ 0

13. 13 Eeng 224

14. 14 Eeng 224 Three Phase Power Measurement  Two-meter method for measuring three-phase power

15. 15 Eeng 224 Residential Wiring Single phase three-wire residential wiring