Introduction to Electrical Systems Course Code: EE 111 Course Code: - PowerPoint PPT Presentation

Introduction to Electrical Systems Course Code: EE 111 Course Code: EE 111 Department: Electrical Engineering Department: Electrical Engineering Instructor Name: B G Fernandes Instructor Name: B.G. Fernandes E ‐ mail id: bgf @ee iitb ac in E ‐ mail id: bgf @ee.iitb.ac.in EE 111: Introduction to Electrical Systems Tue, Sep 1/15 Prof. B.G.Fernandes Lecture 18 08, 2009

Sub ‐ Topics: • Hysteresis & Eddy current loss • Hysteresis & Eddy current loss • Loss representation in equivalent circuit Loss representation in equivalent circuit EE 111: Introduction to Electrical Systems Tue, Sep 2/15 Prof. B.G.Fernandes Lecture 18 08, 2009

Review NI φ = ℜ 1 If μ r → ∞ (core is highly permeable) AT required to establish φ in the core = 0 ℜ → 0, ⇒ If core gets saturated ( φ does not change with ‘i') d φ φ d ⇒ → di 0 0 1 ⇒ ⇒ → → l l 0 0 EE 111: Introduction to Electrical Systems Tue, Sep 3/15 Prof. B.G.Fernandes Lecture 18 08, 2009

‘v’ is input voltage ⇒ ‘i' is limited by ‘r’ (winding resistance) ⇒ should not allow the core to saturate ⇒ should not allow the core to saturate ⇒ provide an air gap ⇒ all the AT is used to establish φ in the air gap φ ⇒ Inductance reduces and leakage flux would increase EE 111: Introduction to Electrical Systems Tue, Sep 4/15 Prof. B.G.Fernandes Lecture 18 08, 2009

Leakage flux is negligible Fringing is negligible g g g g EE 111: Introduction to Electrical Systems Tue, Sep 5/15 Prof. B.G.Fernandes Lecture 18 08, 2009

Air gap = 4mm Leakage flux is more EE 111: Introduction to Electrical Systems Tue, Sep 6/15 Prof. B.G.Fernandes Lecture 18 08, 2009

EE 111: Introduction to Electrical Systems Tue, Sep 7/15 Prof. B.G.Fernandes Lecture 18 08, 2009

Air gap 4mm EE 111: Introduction to Electrical Systems Tue, Sep 8/15 Prof. B.G.Fernandes Lecture 18 08, 2009

Air gap 4mm EE 111: Introduction to Electrical Systems Tue, Sep 9/15 Prof. B.G.Fernandes Lecture 18 08, 2009

e.g. l ℜ = ℜ 1 μ 1 1 A 1 1 l l 2 ℜ = μ 2 A 1 2 l ℜ = μ 0 3 μ 3 A A 0 2 2 EE 111: Introduction to Electrical Systems Tue, Sep 10/15 Prof. B.G.Fernandes Lecture 18 08, 2009

Magnetization Curve: Consider a ‘brand new’ core (not magnetized) ‘I’ Consider a ‘brand new’ core (not magnetized) ‘I’ = 0 0 ∴ H = 0 & ⇒ φ = 0 ( B = 0 ) ‘I’ ( H ) ⇒ φ also ( B ) ⇒ φ also ( B ) For low values of ‘I’ (& ∴ H) B linearly till point ‘C’ Increase ‘H‘ further Increase H further ⇒ corresponding increase in ‘B’ is non linear . B is non linear . ⇒ ‘B’ remains ≅ constant ⇒ Core is saturated ⇒ Core is saturated EE 111: Introduction to Electrical Systems EE 111: Introduction to Electrical Systems Tue, Sep 11/15 Prof. B.G.Fernandes B.G.Fernandes Lecture 18 08, 2009

⇒ B ‐ H curve (OD) is the magnetization curve ⇒ from OC circuit is assumed(?) to be linear ⇒ f OC i it i d(?) t b li NI l φ = ℜ = , ℜ ℜ μ μ μ μ r A A 0 ⇒ In this region is assumed to remain ℜ constant constant ∴ μ r is constant ⇒ ‘C’ is point where saturation starts ⇒ C is point, where saturation starts ⇒ Knee point CD core is saturated variation of ф (B) with i(H) is non ‐ linear EE 111: Introduction to Electrical Systems Tue, Sep 12/15 Prof. B.G.Fernandes Lecture 18 08, 2009

⇒ ⇒ ℜ ℜ is not constant is not constant ⇒ as the degree of saturation ∴ µ r is not constant. It i t t t It as saturation t ti ∴ℜ depends on the operating flux density ⇒ change in ‘ φ ’ beyond ‘C’ is small ⇒ ‘ φ ’ is produced by ‘I’ flowing in a coil ⇒ φ is produced by I flowing in a coil ⇒ this coil has its own resistance ⇒ I 2 R loss ⇒ I 2 R loss Where do we operate the magnetic circuit ? EE 111: Introduction to Electrical Systems EE 111: Introduction to Electrical Systems Tue, Sep 13/15 Prof. B.G.Fernandes B.G.Fernandes Lecture 18 08, 2009

Generating action: conductor is rotated in the magnetic field conductor is rotated in the magnetic field ∝ e lv B ∴ ‘e’ can be by B ∴ e can be by B ‘F’ limits ‘v’ F limits v Motoring action : ‘I’ carrying conductor placed in a magnetic field ‘I’ carrying conductor placed in a magnetic field experiences force ∝ ∝ F F BIl BIl ∴ If ‘I’ , I 2 R loss , temperature rise, η F F ∴ ∝ B A ⇒ operate the magnetic circuit at C ⇒ operate the magnetic circuit at ‘C’ EE 111: Introduction to Electrical Systems EE 111: Introduction to Electrical Systems Tue, Sep 14/15 Prof. B.G.Fernandes B.G.Fernandes Lecture 18 08, 2009

Hysteresis: Brand new core: As ‘i' (from A ‐ B), H & ∴ φ or B φ A ‘i' (f A B) H & B ‘i' now decreases (B ‐ C) B ‐ H curve will follow a different path (PQ) When i = 0 (H=0), B = B r Residual magnetism Residual magnetism EE 111: Introduction to Electrical Systems Tue, Sep 15/15 Prof. B.G.Fernandes Lecture 18 08, 2009