Application of scientific theory to design, develop or maintain structures, machines, systems, and processes: Engineering Science Coursework, UO, UK

Assignment Title: Application of scientific theory to design, develop or maintain structures, machines, systems, and processes

Scenario

You work as a materials engineer and have been tasked with investigating issues with substandard cables manufactured by your company. These cables are made from copper with varying cross sectional areas depending upon their current carrying capacities. Cables are not meeting the required voltage drop characteristics compared to theoretical values, but your manager is not sure of the reason for this and has hypothesised that this could be due to impurities within the copper itself. It has been suggested that the resistivity of the copper used should be investigated.

Task 1

You have been given samples of conductors and you have access to both physical and electrical measurement equipment.

You are required to carry out tests on these conductor samples and present a formal laboratory report.

By comparing and contrasting results obtained in your testing with theoretical material properties you should be able to draw appropriate conclusions. To do this, the laboratory report must be structured to follow a formal scientific method thus ensuring your analysis can be relied upon to be scientifically sound.

You should ensure that your report includes the following elements:

• Qualitative and quantitative representations of the data gathered, using appropriate software
• A description of SI units and unit prefix notation. All formulae must be shown, along with calculations, and answers must be displayed using the appropriate unit prefix form.
• An analysis of results, stating whether or not the original hypothesis is correct.
• Possibilities for improving the experiment to achieve more accurate results with reference to the Scientific Method.
• Full citation/references using an acceptable referencing system.

Task 2

You have been asked to investigate the loading effects on an alternator supplying a load and also charging a car battery at the same time. The output of the alternator has been rectified to smooth dc, and the circuit is shown below.

Using Kirchhoff analysis, determine the initial current in each section along with its direction and the potential difference across the load.

Task 3

1. With the battery in Task 2 fully charged and disconnected, the circuit is re-connected as shown above (the battery now supplying the 19Ω load with other loads and cable resistance included). Determine using Thevenin analysis, the current through the load, the potential difference across the load and the power dissipated by the load.

Task 4

You have been asked to produce waveforms A and B shown to enable laboratory experiments to be carried out. Unfortunately, you only have dc supplies and three ac sinusoidal voltage supplies available. Describe how these supplies can be utilised to produce an approximation to the waveforms A and B showing formulae and calculations used (assuming 100V and 50Hz for the fundamental waveform). Using your calculations, construct the circuit below in Multisim (or something similar) and connect a virtual oscilloscope across the resistor. You must include a clear screen print of the two circuits along with the simulated waveforms. Discuss your findings and suggestions for improvements.

Task 5

Scenario

A company manufacturing extra low voltage fluorescent fittings is looking at improving the adaptability and efficiency of their product.

(i) The circuit shown below is for a typical ELV fluorescent lamp fitting, which operates at 24V 50Hz. Assuming the fluorescent tube has an operating resistance of 30Ω and an ideal transformer, determine:

a. the current supplied by the source

b. the impedance seen at the supply (HV side)

c. the power dissipated by the tube

d. the operating power factor of the fitting

(ii) If the capacitor is now removed from the above circuit and is placed in parallel with the secondary of the transformer, recalculate a to d in question (i).

Using a scale phasor diagram prove your answer to part (ii) d. and evaluate each technique for determining circuit power factor.

(iii) Write a brief report of your findings in parts (i) to (ii) which will be submitted to the company director.

(iv) After reading the report in part (iv) the director asks why the fitting cannot simply be connected to a dc supply and the choke replaced by a resistor. In a written reply to this, explain the operating principle of the transformer in the above circuit and the operating principle and purpose of the choke when used in conjunction with a starter switch in a fluorescent switch start circuit, with particular reference to electromagnetic induction and induced EMFs.

Answer

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