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Magnetic materials properties: e.g. permeability, retentivity, coercivity, B-H curve, hysteresis and iron losses.
Soft magnetic materials: soft iron, silicon steel, mu-metal.
Hard magnetic materials: ferrites.
A. From the list of magnetic materials above select one soft magnetic material and one hard magnetic material. Sketch the B-H curves (hysteresis loops) of both selected materials.
B. Give an example of where each one is used and state which of its properties makes it useful for the purpose.
Insulators properties: e.g. resistivity, breakdown voltage, operating temperatures, mechanical strength.
Solid insulating materials: plastics (e.g. PVC), butyl-rubber, glass, varnishes, paper.
Liquid and gas insulating materials: oil, air, sulphur hexafluoride gas.
A. From the list of insulators above select one solid and one liquid or gas. Describe it in terms of resistivity, maximum voltage capacity, operating temperature and mechanical strength.
B. Give an example of where each one is used and state which of its properties makes it useful for the purpose
Conductor’s properties: e.g. conductivity, resistivity, corrosion resistance, tensile strength and rigidity (hardness and toughness).
Solid conducting materials: e.g. copper, aluminium, steel, brass, carbon, soil (for earth continuity).
Liquid and gas conductors: e.g. electrolytes, conductive gases in fluorescent and discharge lighting.
A. Select one solid and one liquid or gas conductor from the list above. For each of them describe their properties in terms of: conductivity, resistivity, tensile strength and rigidity (where applicable). Then give an example of an electrical use for each of them.
B. State which of its properties makes them suitable for its electrical use.
With the aid of a suitable diagram describe the characteristics and principles of operation of a DC electromagnetic generator, give a real life example.
Note: You should include with your description a labelled diagram of the DC generator and describe the action of each major part.
• With the aid of a suitable diagram describe the characteristics and principles of operation of an AC electromagnetic generator, give a real life example.
Note: You should include with your description a labelled diagram of both the AC generator and its generated waveform and describe the action of each major part.
Task 4
A: Describe four renewable and four non-renewable energy sources, stating advantages and disadvantages of each system
B: Using the information from Task 4A above, justify the use of different energy sources, include a non-renewable source and renewable source, to provide a nation’s electricity supply. Use your own reasoning and/or other resources like, parliamentary reports, Greenpeace opinions, local opposition groups, national and global economics to support your justification.
The future of different methods and fuels, life span of equipment and actual fuels, cost of fuel production, hazards and environmental impact should be included.
For the circuit shown in Fig.6, Impedance A receives 2kW at 0.8 power factor impedance receives 3kVA at 0.4 power factorleading, while impedance C is inductive and consumes 1kW and receives 500VAR. (i) Find the power factor of the entire system, (ii) Find the current I, if VVs=120/_45`v..
The circuit shown in Fig.5 is applied with a 240 V, 50 Hz supply. Find thevalues of R and C so thatVb=3Va and Vb and Va are in phase quadrature
i. Two or more resistors in a circuit are said to be in parallel when all the resistors are connected to the same nodes and the same voltage is appearing across all these elements. Two or more resistors in a circuit are also said to be in series when the current flowing through all the resistors is the same. With the aid of three resistors, Ohm’s law and diagrams derive the two important total resistance formulas for the two connections to verify these two postulates
As a student of Electrical Circuit Analysis at Accra Institute of Technology (AIT), you have been tasked to analyze a linear active, bilateral two terminal network to be implemented at SEAVIEW campus containing impedance and voltage source using Thevenin’s theorem. Demonstrate with diagrams and derived formulas including that for the load current to analyze the circuit.
i. In your own words explain why current is transmitted over long distance as alternating current (ac) and not as direct current (dc)
ii. Compare and contrast a direct current circuit and an alternating current circuit using graphs.
iii. Using your knowledge of the concept of expressing sinusoids in terms of phasors in alternating current (ac) demonstrate how you will obtain the voltages v and V, the phasor current I and sketch phasor diagram if a circuit has a series combination of R=40Ω and L=80 mH and has a current
i=2.0 Cos(500t+10o) (A)
