Unit 51: Electrical Technology The Characteristics and Principles of AC and DC Generators and the features of a Range of difference Power Station

Course Aims At the end of this course the learner will be able to… 1.Know the methods used to produce electrical energy 2.Know the properties and applications of conductors, insulators and magnetic materials 3.Know the physical arrangements of supply, transmission and distribution equipment 4.Know how electrical energy is used to support applications of electrical technology

Agenda At the end of the session the learner will be able to… –Describe the principle of operation of alternating current (AC) generators

Electromagnetic Induction Electromagnetic induction describes the phenomenon in which electricity is produced in a conductor by a changing magnetic field. It’s the relative movement of the magnetic flux and the coil that causes an e.m.f. and thus current to be induced in the coil. This is electromagnetic induction

Electromagnetic Induction

(a) When the magnet is moved at constant speed towards the coil, a deflection is noted on the galvanometer showing that a current has been produced in the coil (b) When the magnet is moved at the same speed as in (a) but away from the coil, the same deflection is noted but is in the opposite direction (c) When the magnet is held stationary, even within the coil, no deflection is recorded

Electromagnetic Induction (d) When the coil is moved at the same speed as in (a) and the magnet held stationary the same galvanometer deflection is noted. (e) When the relative speed is, say, doubled the galvanometer deflection is doubled. (f) When a stronger magnet is used, a greater galvanometer deflection is noted (g) When the number of turns of wire of the coil is increased, a greater galvanometer deflection is noted.

The Laws of Electromagnetic Induction Faraday’s Laws of electromagnetic induction state… –An induced e.m.f. is set up whenever the magnetic field linking that circuit changes –The magnitude of the induced e.m.f. in any circuit is proportional to the rate of change of magnetic flux linking the circuit.

The Laws of Electromagnetic Induction Lenz’s Law of electromagnetic induction state… –The direction of an induced e.m.f. is always such that it tends to set up a current opposing the motion or the change of flux responsible for inducing that e.m.f.. (An alternative method to Lenz’s Law of determining relative directions is given by Fleming’s Right-hand Rule – often called the geneRator rule)

Fleming’s Right-Hand Rule Let the thumb, first finger and second finger of the right hand be extended such that they are all at right angles to each other. If the first finger points in the direction of the magnetic field and the thumb points in the direction of motion of the conductor relative to the magnetic field, then the second finger will point in the direction of the induced e.m.f.

Electrical Generators Generators used to produce electrical power require some form of mechanical energy. The mechanical energy is used to move electrical conductors through the magnetic field of the generator

Electrical Generators

The turning of a coil in a magnetic field produces motional emfs in both sides of the coil which add. Since the component of the velocity perpendicular to the magnetic field changes sinusoidally with the rotation, the generated voltage is sinusoidal or AC. This process can be described in terms of Faraday's law when you see that the rotation of the coil continually changes the magnetic flux through the coil and therefore generates a voltage. motional emfsFaraday's lawmagnetic flux

A.C. Generation Ac Generator – YouTubeAc Generator – YouTube The Three-Phase AC GeneratorThe Three-Phase AC Generator