Engineering electricity/electronics

Students Learn About:

- power generation/distribution

– electrical energy and power

– simple circuits

- electric motors used in transport systems

– principles
– applications

- control technology
- electrical safety

Students Learn To:

identify the electrical systems used in the transport industry
describe current transmission and simple circuit diagrams
investigate the principles and application of electric motors used in the transport industry, including motor speed control
analyse the basic principles of control technology as applied to the transport industry
appreciate the safe use of electricity and electrical equipment

- power generation/distribution

electrical energy and power

Coal

Coal is used to produce steam that drives a steam turbine. The turbine connects to a generator that is spun, producing electricity. Because coal is a readily available resource this method is very popular in Australia. Unfortunately, this produces huge volumes of carbon dioxide, which contributes to the greenhouse effect.

Hydroelectric

Hydroelectric systems offer electricity without atmospheric pollution. They utilise

water held in dams above the power station. The water's potential energy is converted

to kinetic energy as it travels through pipes to the power station. At the power station,

the water drives a turbine connected to a generator. This produces electricity, and the

water is fed back into water systems for irrigation. While this system sounds totally

"clean", it has large impacts on the surrounding environment because of the damming

and diverting of rivers. It is also only possible in mountainous regions. One

unforeseen side-effect of the Snowy Mountains hydroelectric scheme has been rising

salinity levels because of irrigation and farming in formerly dry regions.

Wind

Wind power is often touted as a solution to power demands. The wind drives a large turbine with blades far more efficient than the ancient windmills. The turbine drives a generator and produces electricity. While it is truly clean, to power larger towns and cities, a very large number of turbines are needed, so large tracts of land must be devoted to it. Wind, in many places, is intermittent and unreliable, which also limits this method.

Solar

Solar power is now used extensively, with large-scale solar photo-voltaic (PV) systems being trialled in large areas in rural Australia. Rooftop solar PVs have been adopted by many households, with the solar panels producing DC electricity that is converted to AC using an inverter. With rooftop PVs coupled to a battery it is possible for households to store electricity generated in the day when nobody is home and use it at night during "peak" time.

Nuclear

One very contentious issue in Australia is nuclear power. In the recent Kyoto summit on global warning, nuclear fission power emerged as a method that does not contribute to global warming. The benefits of nuclear power are great. They operate like coal power stations, but instead of the water being turned to steam by coal powered boilers, the heat from the nuclear reaction is used. Only a small amount of nuclear fuel is required to produce large amounts of heat. It is non-polluting to the atmosphere but it presents other problems. The by-products of nuclear power generation are often contaminated for thousands of years, and there have been two accidents (Three Mile Island and Chernobyl), that occurred because of human error, proving that all the failsafe systems are still vulnerable.

simple circuits

AC vs DC

Transformer

Diodes

Half wave rectifier

Full wave rectifier

- electric motors used in transport systems

principles

Many years ago only DC motors were used in trains, partially because it was difficult to control AC motors when the generator driven by the diesel engine produced DE. Nowadays, however, there are AC induction motors used in diesel electric trains. in NSW older electric trains still run using DC power, while newer electric trains now use AC motors. See Volume 1, pp 77-79 to review how electric motors work.

Shunt wound

Shunt wound motors are rarely used in locomotives. They have constant speed but low starting torque and therefore not suitable if there is a lot of stopping and starting.

Series wound

Series wound motors offer excellent torque at slow speeds and will operate at high speed under light load. This makes them excellent for use in trains, and is a reason why they are widely used.

Compound motors

Compound motors combine the best features of the other two. Good starting torque and will not run away under no-load conditions.

applications

Brushless DC Motor

Regenerative Breaking

- control technology

Positive control technology

Control technology is the use of some type of mechanism or circuit to control the operation of an item. The simple float arm in a toilet controls the water delivery; this is an example of control technology.

In transport, one of the earliest control devices was the governor on steam engines. Centrifugal force caused arms to rise. This controlled a throttle system, which more. or-less maintained the engine at a constant speed under varying loads.

Cars often have electronic cut-outs that sense the speed of the crankshaft and cut the ignition to the car if the engine revs too fast. Control technology has been trilled for years on car suspension, trying to reduce the compromise by engineers between ride and handling, which exists with conventional suspension systems.

Control technology can be a simple mechanical linkage, a simple digital yes/no circuit, or a more complex circuit that reads various inputs to produce a variety of outputs. Control technology is used to trigger safety devices like ABS brakes and airbags. In ABS a wheel begins to lock, the computer reduces the brake pressure, preventing the wheel from locking and the car from skidding out of control. ABS now forms part of Dynamic Stability Control (DSC) on cars, where the DSC can operate individual brakes to improve the cars response to the driver's inputs.

- electrical safety

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