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 Eeng 224 Power in a Balanced System The total instantaneous power in a balanced three phase system is constant.
3 Eeng 224 Power in a Balanced System The important consequences of the instantenous power equation of a balanced three phase system are:
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 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 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 Eeng 224 Power in a Balanced System
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
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10 Eeng 224 V L =840 V (Rms) Capacitors for pf Correction ILIL
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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
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14 Eeng 224 Three Phase Power Measurement Two-meter method for measuring three-phase power
15 Eeng 224 Residential Wiring Single phase three-wire residential wiring