Topic 1 : Magnetic Concept and Transformer Magnetism Magnetic Circuit Transformer Construction Transformer equivalent circuit Transformer test, efficiency and regulation.

MAGNETISM

Magnetic field A magnet has two poles – N and S Shape of steel fillings on a sheet over a magnet are shown below.

Magnetic field The shape and density of the chains formed enable us to form a mental picture of a magnetic field and lead to the idea of magnetic flux lines. The density of the lines depends on the strength of the magnet. The area in which the steel filling are affected by the magnet is become thinner further away from the magnet.

Characteristic of magnetic flux The direction of flux is from North to South. Each line of magnetic flux forms a closed loop. Lines of electric flux never intersect. Lines of magnetic flux are like stretched elastic cords, always trying to shorten themselves. Lines of magnetic flux which are parallel and in the same direction repel one another.

Magnetic field of a current carrying conductor Current going in (left) Current coming out (right). Solenoid.

Force on current carrying conductor Flux of magnet and conductor Interaction of flux produces force   S N Force   S N

Force on current carrying conductor Left-hand rule Index finger FLUX Thumb FORCE Middle finger CURRENT

Electromagnetic induction Two experiments performed by Michael Faraday. Electric current could be produced by the movement of magnetic flux relative to the coil.

Electromagnetic induction Direction of induced emf. Fleming’s right-hand rule. Lenz’s law - The direction of an induced emf is always such that it tends to set up a current opposing the motion or the change of flux responsible for inducing that emf. Thumb FORCE Middle finger CURRENT Index finger FLUKS

MAGNETIC CIRCUIT

Basic Definitions  

Basic Definitions  

Basic Definitions  

Basic Definitions  

Basic Definitions Permeability of different materials Notice the nonlinearity

Basic Definitions  

Basic Definitions  

Comparison of electric and magnetic circuit Electric circuit Magnetic circuit EMF, v MMF, NI Electric field strength, v/m Magnetic field strength, H Current, I Flux, Φ Current density, I/A Flux density, B

Comparison of electric and magnetic circuit Since the magnetic circuit behaves in similar ways as an electric circuit, the laws of electric circuit are applicable to the magnetic circuit. Ohm’s law equivalent : F = ΦS. Kirchoff law equivalent: Φin = Φout Total NI = Total Hl A magnetic circuit can be redrawn as electric circuit equivalent to facilitate the analysis.

Comparison of electric and magnetic circuit