UNIVERSITY OF ABUJA, FACULTY OF ENGINEERING DEPARTMENT OF ELECTRICAL/ELECTRONIC ENGINEERING 300 LEVEL SECOND SEMESTER EXAMINATIONS, EEE316: ELECTROMECHANICAL DEVICES & MACHINES I 23rd April, 2024. INSTRUCTIONS: Answer FIVE (5) QUESTIONS, QUESTION ONE: DURATION: 2:30 HOURS 1a) What is electromechanical energy conversion. (3 Marks) 1b) With the help of sketches, circuits diagrams, equations and examples, compare generator and motor action. (11 Marks) QUESTION TWO: 2a) List any six essential parts of a practical generator. (4 Marks) 2b) A direct current motor rated 240A, 480V has armature circuit resistance is 0.20. The machine has 6 poles and the armature is lap connected with 864 conductors. The flux per pole is 0.05Wb. Calculate i) The speed and. ii) the gross torque developed by the armature. (10 Marks) QUESTION THREE: 3a) Why is the air-gap very important in electromechanical systems. (6 Marks) 3b) An 8-pole DC generator has 500 armature conductors and a useful flux of 0.1Wb per pole. What will be the EMF generated if it is lap-connected and runs at 2400 rpm? What must be the speed at which it is to be driven produce the same EMF if it is wave-wound? (8 marks) QUESTION FOUR: 4a) Compare and contrast electric circuits and magnetic circuits. (5 Marks) 4b) A 220 V D.C machine has an armature resistance of 0.5 Q. If the full-load armature current is 20 A, find the induced E.M.F. when the machine acts as: i) ii) Generator Motor (9 Marks) QUESTION FIVE: 5a) Derive the equation of induced emf in a generator. (6.5 marks) 5b) A long-shunt compound generator rated 300 kW, 800 V has a shunt resistance of 75 Q, armature resistance 0.03 2, winding resistance 0.011 0, series resistance 0.012 02, divertor resistance 0.036 Q. Calculate the voltage and power generated by the armature when the machine delivers power at full load. (7.5 marks) QUESTION SIX: 6a) What is the advantage of wave windings over lap windings and vice versa? (4 Marks) 6b) A 30kW, 250V, DC shunt generator has armature and field resistances of 0.060 and 1000 respectively. Determine the total armature power developed when working i) As a generator delivering 30kW output and. ii) As a motor taking 30kW input. (10 Marks) QUESTION SEVEN: Real transformer cores are covered with primary windings while the larger secondary winding surrounds the primary windings. Why? (4.5 Marks) A fire alarm system is powered by a small transformer that steps down 240 V ac to 12 V ac. If such a transformer has a primary winding with 2000 turns and the current in the bell is 500 mA, 7a) 7b) i) How many turns are there on the secondary winding? ii) What is the current in the primary windings? iii) What is the power output iv) Sketch the transformer circuit (9.5 Marks)

Write a technical manual/ documentation, that will inform others of the efficiency and inefficiency of all types of motor and generator (ac and dc). Explore how any apparent inefficiencies could be improved. Show examples of these machines and using suitable examples, point out the areas of inefficiency (if applicable) and where and how things can be improved.   Then provide the solution to the following as an example in your report. A 2-pole, single-phase alternator driven at 3000rpm require a mechanical input to its rotor of 30kW when it is delivering its full-load output of 30kW. Under this condition the fixed and variable losses are1100W and 2.8kW respectively, and the rotor field winding is supplied from a 110V dc source. Given that the full-load efficiency is 87%, determine. the frequency generated, the input driving torque on full-load and the rotor field current

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ELECTRIC MACHINERY  do the (iii, iv v)

Write a technical manual of that will inform others of the efficiency and inefficiency of all types of motor and generator (ac and dc). Explore how any apparent inefficiencies could be improved. Show examples of these machines and using suitable examples, point out the areas of inefficiency (if applicable) and where and how things can be improved. Then provide the solution to the following as an example in your report. A 2-pole, single-phase alternator driven at 3000rpm require a mechanical input to its rotor of 30kW when it is delivering its full-load output of 30kW. Under this condition the fixed and variable losses are1100W and 2.8kW respectively, and the rotor field winding is supplied from a 110V dc source. Given that the full-load efficiency is 87%, determine. i) the frequency generated, ii) the input driving torque on full-load and iii) the rotor field current

Q2: Correct the wrong statement if any: 1-The series filed of a series de generator is excited by armature current. 2- The developed power in DC generator armature is function to load current. 3-The commercial efficiency of DC generators is relationship between output mechanical power and developed power in armature winding. 4- If the source frequeney subjected to primary windings increased, the iron losses also decreased. 5-In transformers short circuit test primary voltage will be greater than secondary voltage. GOOD LUCK

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Electric machines / I need a complete expert solution in handwriting for the question. Please provide a correct solution.

Suppose that you were an engineer planning a new electric co-generation facility for a plant with excess process steam. You have a choice of either two 10 MW turbine-generators or a single 20 MW turbine generator. What would be the advantages and disadvantages of each choice?   (Note: Ans with detail hand writing.) step by step and headings

(c) Electric machines can be classified into two categories, state both categories. (d) Describe THREE (3) methods to control the speed of the DC motor. (e) State why induction (asynchronous) machines are not suitable to be used as a generators, (f) An induction machine is the most rugged machine and is widely used in domestic and industry. State its application in single phase and three phase systems.