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Volt Drop - Electrotechnology and Control - Exam, Exams of Electrical Engineering

University of AllahabadElectrical Engineering

Main points of this past exam are: Volt Drop, Inductive Reactance, Current, Resistor, Inductor, Total Current, Circuit Power Factor

Typology: Exams

2012/2013

Uploaded on 03/29/2013

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Cork Institute of Technology
Higher Certificate in Engineering in Mechanical Engineering – Award
(NFQ – Level 6)
Autumn 2007
Electrotechnology & Control
(Time: 3 Hours)
Instructions
Answer Five questions,at least Two from each
section
Use separate answer books for each Section.
All questions carry equal marks.
Examiners: Mr. J. Connolly
Dr. P. Delassus
Mr.S.Cotter.
Mr.T. O’Callaghan.
Q1. A pure inductor of 100mH is connected in parallel with a 20Ω resistor
across a 230 volt 50 Hertz supply.
(i) Draw a neat labelled diagram of the circuit. ( 3 Marks)
Calculate:
(ii) the inductive reactance of the inductor. ( 3 Marks)
(iii) the current in the inductor. ( 2 Marks)
(iv) the current in the resistor ( 2 Marks)
(v) the total current ( 4 Marks)
(vi) the circuit power factor ( 3 Marks)
(vii) the total power consumed by the circuit. ( 3 Marks)
Q2.
(a) Define (i) energy and (ii) power and the units used to represent each.
(5 Marks)
(b) The water in a 160 litres cylinder is heated from 140 C to 600C by means
of a 230 volt, 3kW immersion heater element. Calculate the time taken
to heat the water if the heat transfer efficiency is 90%.
S.H. of water is 4190J/kg0C
1 litre of water = 1kg (10 Marks)
(c) Calculate the cost of heating the water if the cost per unit of electrical
energy is €0.15c (5 Marks)
pf3

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Cork Institute of Technology

Higher Certificate in Engineering in Mechanical Engineering – Award

(NFQ – Level 6)

Autumn 2007

Electrotechnology & Control

(Time: 3 Hours)

Instructions Answer Five questions,at least Two from each section Use separate answer books for each Section. All questions carry equal marks.

Examiners: Mr. J. Connolly Dr. P. Delassus Mr.S.Cotter. Mr.T. O’Callaghan.

Q1. A pure inductor of 100mH is connected in parallel with a 20Ω resistor across a 230 volt 50 Hertz supply. (i) Draw a neat labelled diagram of the circuit. ( 3 Marks) Calculate: (ii) the inductive reactance of the inductor. ( 3 Marks) (iii) the current in the inductor. ( 2 Marks) (iv) the current in the resistor ( 2 Marks) (v) the total current ( 4 Marks) (vi) the circuit power factor ( 3 Marks) (vii) the total power consumed by the circuit. ( 3 Marks)

Q2.

(a) Define (i) energy and (ii) power and the units used to represent each. (5 Marks)

(b) The water in a 160 litres cylinder is heated from 14^0 C to 60^0 C by means of a 230 volt, 3kW immersion heater element. Calculate the time taken to heat the water if the heat transfer efficiency is 90%. S.H. of water is 4190J/kg^0 C 1 litre of water = 1kg (10 Marks)

(c) Calculate the cost of heating the water if the cost per unit of electrical energy is €0.15c (5 Marks)

Q3. (a) List two factors which cause volt drop in a cable. (3 Marks)

(b) A load of 30 Amperes is supplied from a 230 volt distribution board by means of a two core cable. Each cable core has a resistance of 0.13Ω. (i) Draw a labelled circuit diagram. ( 2 marks) Calculate: (ii) the volt drop in the cable ( 3 Marks) (iii) the voltage across the load. ( 3 Marks) (iv) the power loss in the cable. ( 3 Marks) (v) the total power consumed by the circuit. (3 Marks) (c) Is the volt drop in the cable within that allowed by the E.T.C.I. Rules ( 3 Marks)

Q4. (a) An electric kettle element has a resistance of 24Ω and is connected to a 230 volt supply. For the element calculate: (i) the current ( 3 Marks) (ii) the power consumed ( 4 Marks) (b) Calculate the cost of operating the kettle for 10 minutes if electrical energy costs 15 cents per kWh. (5 Marks) (c) If the supply voltage is reduced to 200 volts calculate the power now consumed by the kettle element assuming that the element resistance does not change. ( 8 marks)

Section B ( Control )

Please Use Answer Book B!

Q 5 (a) Describe the construction and operation on an electronic PI controller. ( 10 Marks ) (b) An electronic proportional controller has an input resistor of value 250 Ω, and a feedback resistor of value 1.5 kΩ. Calculate its proportional gain and proportional band %. ( 10 Marks)

Q 6 (a) Explain, with the aid of diagrams, the construction and operation of a double- seated pneumatic control valve and actuator. Why is a double-seated valve used in control rather than a single-seated valve? (10 Marks)

(b) Explain, with the aid of diagrams, the meaning of flow characteristics of control valves. Describe, with the aid of diagrams, the type of valve plug that is required for each characteristic? (10 Marks)