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Questions and Answers
What is the formula for calculating the air gap reluctance Rg in a magnetic circuit?
What is the formula for calculating the air gap reluctance Rg in a magnetic circuit?
- Rg = $ rac{ u_0 A_g}{l_g}$
- Rg = $ rac{l_g}{ u_0 A_g}$ (correct)
- Rg = $ rac{A_g}{l_g u_0}$
- Rg = $ rac{A_g l_g}{ u_0}$
Which parameter is NOT needed to determine the magnet operating flux density Bm?
Which parameter is NOT needed to determine the magnet operating flux density Bm?
- Applied external demagnetizing magnetic field intensity (Ha)
- Temperature of the magnet (correct)
- Magnet area (Am)
- Magnet length (lm)
Which statement about steel reluctance in magnetic circuits is true?
Which statement about steel reluctance in magnetic circuits is true?
- Steel reluctance can be negligible under certain conditions. (correct)
- Steel reluctance is always significant in calculations.
- Steel reluctance increases the flux density.
- Steel reluctance does not affect magnet behavior.
What does the slope of the air gap line represent in the magnetic circuit analysis?
What does the slope of the air gap line represent in the magnetic circuit analysis?
What does a higher value of the relative magnetic permeability (μr) indicate about a permanent magnet?
What does a higher value of the relative magnetic permeability (μr) indicate about a permanent magnet?
What happens to the magnet operating point when an external demagnetizing field is applied?
What happens to the magnet operating point when an external demagnetizing field is applied?
In the context of magnetic circuits, what is typically considered negligible for simplifying the circuit analysis?
In the context of magnetic circuits, what is typically considered negligible for simplifying the circuit analysis?
During no-load conditions, where does the magnet operating point occur?
During no-load conditions, where does the magnet operating point occur?
What is the effect of the air gap line on the magnet's flux density when an external field is applied?
What is the effect of the air gap line on the magnet's flux density when an external field is applied?
Which aspect must be analyzed to determine the effects of reluctance in a magnetic circuit?
Which aspect must be analyzed to determine the effects of reluctance in a magnetic circuit?
What does a non-straight demagnetization curve in the second quadrant indicate about a magnet?
What does a non-straight demagnetization curve in the second quadrant indicate about a magnet?
In the equivalent circuit of permanent magnets, what does the Norton equivalent circuit represent?
In the equivalent circuit of permanent magnets, what does the Norton equivalent circuit represent?
Which components make up the external reluctance of the magnet flux path?
Which components make up the external reluctance of the magnet flux path?
What is represented by the voltage source of the external mmf in the magnetic circuit?
What is represented by the voltage source of the external mmf in the magnetic circuit?
What does the leakage reluctance branch represent in the magnet's equivalent circuit?
What does the leakage reluctance branch represent in the magnet's equivalent circuit?
How is the intrinsic coercive force (Hci) characterized in relation to the magnet?
How is the intrinsic coercive force (Hci) characterized in relation to the magnet?
In the context of magnetic circuits, what is the primary use of electric circuit analysis?
In the context of magnetic circuits, what is the primary use of electric circuit analysis?
Which of the following is NOT a source of reluctance in magnetic circuits?
Which of the following is NOT a source of reluctance in magnetic circuits?
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Study Notes
Demagnetization in Permanent Magnets
- A non-linear demagnetization curve indicates easier magnet demagnetization, classifying it as low-grade permanent magnet (PM).
- Coercive force necessary to reduce a magnet’s intrinsic flux density to zero is termed intrinsic coercive force (Hci).
- Coercivity (Hc) pertains to the normal flux density.
Equivalent Circuit of Permanent Magnets
- Electric circuit analysis is utilized to determine the operating point in magnetic circuits, treating the magnet as a flux source.
- Norton equivalent circuit represents the magnet as a current source for remnant flux (Φr) parallel to internal reluctance (Rm).
- External reluctance includes air gap reluctance (Rg) in series with steel reluctance (Rs).
- Leakage reluctance indicates leakage flux (Φl) not crossing the air gap.
- Magnets can also be influenced by an external magnetic field represented as a voltage source of external magnetomotive force (Fa).
Calculating Reluctances and Flux Density
- Air gap reluctance (Rg) and magnet reluctance (Rm) are calculated using:
- Rg = lg / (μ0 * Ag)
- Rm = lm / (μ0 * μr * Am)
- For analytical simplification, leakage flux and steel reluctance are often considered negligible.
- Operating flux density (Bm) can be represented as:
- Bm = (1 / (lg * Am * μr)) * (B − μ0 * μr * Ha) + (Φl / Φg)
Key Variables in the Equation
- Am: Area of the magnet
- lm: Length of the magnet
- Br: Remnant flux density of the magnet
- Ag: Area of the air gap
- lg: Length of the air gap
- μr: Relative magnetic permeability of the magnet
- Ha: Applied external demagnetizing magnetic field intensity
Graphical Representation of Magnet Operating Point
- The magnetic circuit can be analyzed graphically using the demagnetization curve and air gap line.
- At no-load conditions, the operating point is found at the intersection of the demagnetization curve and air gap line, defining it as no-load operating point.
- The slope of the air gap line is known as the permeance coefficient (PC).
- Application of an external demagnetizing field shifts the air gap line horizontally, reducing the operating flux density (Bm).
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