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CORK INSTITUTE OF TECHNOLOGY
INSTITIÚID TEICNEOLAÍOCHTA CHORCAÍ
Semester 2 Examinations 2011/
Module Title: Building Services Electrotechnology 2
Module Code: MANU
School: School of Mechanical, Electrical and Process Engineering
Programme Title: Bachelor of Engineering in Building Services Engineering – Year 1
Programme Code: EBSEN_7_Y
External Examiner(s): Dr Ben Costello, Mr Con Leddy Internal Examiner(s): Mr Sean McShera
Instructions: Answer FIVE Questions
Duration: 2 hours
Sitting: Summer 2012
Requirements for this examination: Use of a Scientific Calculator is permitted
Note to Candidates: Please check the Programme Title and the Module Title to ensure that you have received the correct examination paper. If in doubt please contact an Invigilator.
Q1. (a) A 50 Watt heater is connected to a 230 Volt supply. Calculate the current taken by the appliance. (3 Marks) (b) Calculate the resistance of a 2kW, 230 Volt heating appliance. (4 Marks) (c) A coil of resistance 5Ω takes a current of 10 Amps. Calculate the power dissipated by the coil. (4 Marks) (d) A 230 Volt electric kettle has a heating element of resistance 15Ω, and a 200 volt kettle has an element of resistance 25Ω. Show by calculation which kettle has the greater power rating. (5 Marks) (e) A 200W, 230 Volt motor is in continuous use for 15 hours. Calculate the cost of electrical energy at 14 cents per kWh. (4 Marks)
Q2 An inductance of 250mH is connected in series with a 50Ω resistor across a 100V 50Hz supply. (i) Draw a labelled circuit diagram (3 Marks) Calculate: (ii) the reactance of the coil (3 Marks) (iii) the impedance of the circuit (3 Marks) (iv) the circuit current (2 Marks) (v) the power factor (3 Marks) (vi) for the circuit draw the impedance triangle to scale (6 Marks)
Q3 A 200μF capacitor is connected in series with a 32 Ω resistor across a 230V 50Hz supply. (i) Draw and label the circuit diagram (3 Marks) Calculate: (ii) the reactance of the capacitor (3 Marks) (iii) the impedance of the circuit (3 Marks) (iv) the circuit current (2 Marks) (v) the power factor (2 Marks) (vi) the phase angle (1 Marks) (vii) the voltage across the resistor (2 Marks) (viii) the voltage across the capacitor (2 Marks) (xi) the circuit power (2 Marks)
Some Useful Formula
Capacitive Reactance XC 2... ^1 f C []
Inductive Reactance X (^) L 2... f L []
Impedance Z R^2 X L^2 []
Impedance Z R^2 X C^2 []
Power Factor
Z
p. f . Cos R
Current IT ^ VZT [A]
Current I = V [A] XL
Current I = V [A] Xc
Power P I. V. Cos [W]
