THE GENERATOR 3. Generators are used to provide large scale power production.

Describe the main components of a generator A generator transforms MECHANICAL KINETIC ENERGY ELECTRICAL ENERGY It consists of NS A COILOF WIRE (on an armature) FORCED TO ROTATE ABOUT AN AXLE IN A MAGNETIC FIELD The magnetic field can be from PERMANENT MAGNETS OR AN ELECTROMAGNET These rotating parts make up the ROTOR These stationary parts make up the STATOR

Each slip ring makes contact with a stationary brush that connects to the terminals of the generator. In both cases, the terminals of the generator can be connected to an external load which requires power, such as a light globe, a pump, a town or a vast grid. NS Describe the differences between AC and DC generators Describe the main components of a generator There are some other important components of a generator that connect the coils to the generator terminals. These are the rings (part of the rotor) and the brushes (part of the stator). The split ring commutator makes contact with a brush on either side which connects to the generator terminals. M.Edwards 25/4/02 brush Split-ring commutator In an AC generator, there is a slip ring attached to each end of the coil wire that rotates with the coil and the axle. Since the slip ring is always attached to the same side of the coil, as the coil turns, the current reverses. It is alternating current (AC). In an DC generator, the assembly is the same as a DC motor, comprising of a split ring commutator attached to the coil ends and the axle. The split ring means the current does not reverse direction as the coil turns. It is direct current (DC).

Gather secondary information to discuss advantages/disadvantages of AC and DC generators and relate these to their use Advantages of AC - more efficient in transmitting - easy to change voltage with a transformer - field structure of an AC generator reduces sparking Disadvantages of DC - change in voltage is more complex - line loss is greater - commutator places a limit on the voltages due to sparking -transmission of electricity is not as efficient - DC current unable to operate some appliances - brushes needs to be constantly repaired Advantages of DC - less likely hood of insulation breakdown -it uses the entire conductor in transmission - only requires two conductors - synchronization not required - in underground DC is more efficient than AC Disadvantages of AC -harmful to health -higher voltage means more insulation -travel on the outer section of the conductor which reduces the effective cross-sectional area and increases resistance -requires at least 3 lines -need to by synchronized to keep the frequency same -induces EMF need to be converted into DC so it can be used with some appliances

Compare the structure and function of a generator to an electric motor NS M.Edwar ds 25/4/02 brush Split-ring commutator A simple DC generator has the same parts (structure) as a DC motor. In the generator some force (e.g. falling water, rising steam or a petrol-driven motor) cause the axle to rotate which turns the coil in the magnetic field. This induces an emf (and hence a current) in the coil which is transferred to an external circuit via the brushes and can then do work. In the motor, the emf (and hence current) is supplied, which causes the coil and axle to turn in the magnetic field. The axle can be connected to a load such as model car wheels or a winch. MECHANICAL KINETIC ENERGY ELECTRICAL ENERGY ELECTRICAL ENERGY MECHANICAL KINETIC ENERGY

The diagram below shows a generator. (a)Describe how the generator works (b)Describe how this generator could be transformed into a DC generator.

(a)3 marks Steam or some other moving fluid would turn the turbine. This would induce a current in the coil of wire due to the magnetic field. The current would change direction every half cycle of rotation of the coil of wire producing an AC current, the frequency of which would be equal to the revolutions per second. The AC current flows through wires to slip rings which are attached to the carbon brushes. This allows the current to be accessed through the terminals. (b)2 marks The generator could be transformed into a DC generator by replacing the slip rings with a split ring commutator. This consists of two half cylinders connected to the wires from either end of the coil. These split rings are also connected to carbon brushes. They work by switching contact with each brush as the shaft rotates every half cycle. This ensures that the current flows in one direction only.

Plan, choose equipment or resources for, and perform a first-hand investigation to demonstrate the production of an alternating current Jacaranda Experiment 8.2