Generation Of Electricity PDF

UNCONTROLLED COPY - FOR TRAINING PURPOSE ONLY Revision Service Will Not Be Provided To The Holder TRAINING MAN UAL For Traini ng Purpose Only GENERATION OF ELECTRICITY INTRODUCTION Energy cannot be created or destroyed, but it can be converted from...

UNCONTROLLED COPY - FOR TRAINING PURPOSE ONLY Revision Service Will Not Be Provided To The Holder TRAINING MAN UAL For Traini ng Purpose Only GENERATION OF ELECTRICITY INTRODUCTION Energy cannot be created or destroyed, but it can be converted from one form to another. Some sources of electricity are listed below: Light - solar energy Heat Friction Pressure Chemical Action Magnetism Motion B-M3 ELECTRICAL FUNDAMENTALS Generation of Electricity 1 TRAINING MAN UAL For Traini ng Purpose Only LIGHT When certain photoemissive materials such as selenium are struck by light, light energy is absorbed and electrons are discharged. The electrons are then channelled through a conductor to an electrical circuit. A photoemissive material emits electrons when struck by light One of the applications is in solar powered calculators where the electrical current is produced by light. Although photoelectric devices are limited in use in the modern aircraft, spacecraft and satellites rely heavily on photocells and the sun as a source of electric power. Solar Powered Calculators B-M3 ELECTRICAL FUNDAMENTALS Generation of Electricity 2 TRAINING MAN UAL For Traini ng Purpose Only HEAT Heat can also be used to produce electricity by subjecting two junctions of dissimilar metals to different temperatures. This is called the thermoelectric effect. A thermocouple is a loop of two wires made of dissimilar metals that are joined in two places. Electrical current flows as there is a temperature difference between the two junctions. Examples of thermocouple are iron/constantan, chromel/alumel and copper/zinc. Electrons flow in a thermocouple Thermocouples are used in many electronic temperature sensors in the aircraft. Some examples are the exhaust gas and cylinder head temperature sensors, electronic equipment temperature monitors and some fire detectors. In a cylinder head temperature measuring sensor, one of its junctions is held tightly against a hot engine cylinder head by a spark plug while the other junction is mounted in an area where the temperature is kept relatively constant. Cylinder Head Temperature (CHT) Thermocouple B-M3 ELECTRICAL FUNDAMENTALS Generation of Electricity 3 TRAINING MAN UAL For Traini ng Purpose Only FRICTION Friction can produce static electricity by simply rubbing two dissimilar substances together. Static electricity is however, not a typically useful form of power. In fact, most static electricity found on the aircraft creates problems for both communication and navigation systems as well as advanced electronic devices. When an airplane flies through the air it accumulates a static charge, especially on the aircraft control surfaces. This is even more apparent when flying through any kind of precipitation or even worse, volcanic ash. Static wicks attached to the trailing edges of control surfaces are designed to help dissipate the static charge to the surrounding air. They act as a protection to the flight instruments, radio equipment as well as the flight surfaces. Without the static wicks attached, the static charge on the surface would try to “jump” along the un-conductive control hinges to the rest of the aircraft. This “jump” or arc could cause permanent damage to the surface itself if the static charge had the opportunity to build sufficiently. To further protect against this damaging “jump”, manufacturers also attach conductive bonding strips to keep the static build-up to a minimum. Bonding Strap on an aircraft B-M3 ELECTRICAL FUNDAMENTALS Generation of Electricity 4 TRAINING MAN UAL For Traini ng Purpose Only PRESSURE Pressure is another electricity source. Piezoelectricity means electricity created by applying pressure to certain types of crystals. Since only small amounts of electricity are produced, applications are limited. The piezoelectric effect is used in radio communication microphones to convert sound waves into electrical power. Most piezoelectric devices use crystalline materials such as quartz to produce charge. When a force is applied to certain axis, their molecular structure distorts and electrons are emitted into a conductor. Quartz subjected to pressure An electrical charge builds across the faces of these crystals when they are bent or otherwise subjected to mechanical pressure. The crystal vibrates at its natural frequency and produces alternating voltage with specific frequency when excited by pulses of electric energy. B-M3 ELECTRICAL FUNDAMENTALS Generation of Electricity 5 TRAINING MAN UAL For Traini ng Purpose Only CHEMICAL ACTION Chemical action is often used to produce electricity for aircraft systems. When materials of opposite charges are connected, immersed in an electrolyte and connected through external load, an electron flow is created. A carbon rod immersed in a paste-like electrolyte enclosed in a zinc container can form an alkaline battery. Chemical reaction occurs between the electrolyte and zinc, which changes the zinc into zinc chloride. During this process, electrons are released by zinc and current flows through a wire connecting a light bulb into the carbon rod. Most aircraft contain a battery used for emergency procedures and other functions like engine starting. Electrons flow between two dissimilar materials when they are connected by a conductor and immersed in an electrolyte Batteries on board the aircraft produced electricity through chemical action for the purposes of engine starting and emergency procedures. B-M3 ELECTRICAL FUNDAMENTALS Generation of Electricity 6 TRAINING MAN UAL For Traini ng Purpose Only MAGNETISM Magnetism is one of the most effective ways of producing electricity and is used to produce most electrical power. Electromagnetic induction produces voltage when a conductor is moved through a magnetic field. Most aircraft use generators or alternators to produce electricity by this method. Electricity generated by Electromagnetic Induction The amount of electricity induced is dependent on the rate at which the lines of flux are cut. Thus, the rate can be increased through the increase of the number of flux lines with a stronger magnet or by moving the conductor through the lines faster. B-M3 ELECTRICAL FUNDAMENTALS Generation of Electricity 7 TRAINING MAN UAL For Traini ng Purpose Only MOTION Motion can also be used to generate electricity. By using fossil fuels such as oil, coal and natural gas, mechanical motion is produced to drive generators, which in turn produce electricity. For example, in a gas turbine power plant, fuels are burned to create hot gases that go through a turbine, spinning and turning the copper armature inside the generator and generating an electric current. Gas Turbine Power Plant In the case of a nuclear power plant, nuclear reactions create heat to turn water into steam. The steam goes through a similar turbine, which spins and turns the copper armature inside the generator and generating an electric current. Nuclear Power Plant B-M3 ELECTRICAL FUNDAMENTALS Generation of Electricity 8 TRAINING MAN UAL For Traini ng Purpose Only In a wind turbine, the wind pushes against the turbine blades, causing the rotor to spin and turn the copper armature inside the generator and generating an electric current. Wind Turbine In a hydroelectric turbine, flowing (or falling) water pushes against the turbine blades, causing the rotor to spin and turn the copper armature inside the generator and generating an electric current. Hydroelectric Turbine B-M3 ELECTRICAL FUNDAMENTALS Generation of Electricity 9