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CORK INSTITUTE OF TECHNOLOGY
INSTITIÚID TEICNEOLAÍOCHTA CHORCAÍ
Semester 1 Examinations 2012/
Module Title: Planning
Module Code: ELEC
School: Electrical & Electronic Engineering
Programme Title: Bachelor of Engineering in Electrical Engineering – Year 2 Bachelor of Engineering (Hons) in Electrical Power Systems – Year 2
Programme Code: EELEC_7_Y EEPSY_8_Y
External Examiner(s): Ms M. Desmond, Mr C. Murray Internal Examiner(s): Mr J. Buckley
Instructions: Answer THREE questions. All questions carry equal marks. In marking scripts the examiner will take account of clarity of expression and communication skills.
Duration: 2 Hours
Sitting: Winter 2012
Requirements for this examination:
Note to Candidates: Please check the Programme Title and the Module Title to ensure that you have received the correct examination. If in doubt please contact an Invigilator.
Q1.
As consultant electrical engineering technician, your job is to plan the layout of a main distribution and metering system for a new shopping centre. The board incorporates both the ESB metering and the main distribution switchgear for the complex. The complex houses: 2 shops each with a load of 50A, 400V, 3-phase, 50 Hz. 1 Shop with a load of 100A, 400V, 3-phase, 50Hz. 1 Main tenant with a load of 250A, 400V, 3-phase, 50Hz.
The board is located within the complex and there is one ESB incoming supply. Each of the shops is individually metered using centralised metering. The distribution board is fed from a 630kVA transformer with 4.75% impedance. A sub distribution board located in each tenant’s premises is fed from the main distribution board.
(a) Draw a line diagram of the main distribution/metering board showing (i) The current ratings and short circuit ratings for all protection devices (ii) The location of all meters. State whether whole current or current transformer metering (C/T metering) will be used. (17 marks)
(b) Indicate the IP rating of the switchboard. (3 Marks)
Q2.
Your employer, a plastic pipe manufacturer, plans to install an additional extruder to extrude PVC pipes. The extruder is driven by an a.c. motor whose shaft power is 110kW.
(i) Calculate the cable size required to supply electricity to this this machine. (5 Marks) (ii) Calculate the kWHrs used by this machine while running for 40 hours. (5 Marks) (iii)Calculate the kVArHrs used by the machine during the same period. (5 Marks) (iv) Calculate the additional power factor correction required (in kVAr) to avoid a P.F. surcharge from E.S.B. (5 Marks) You may assume that:
(a) The machine is 100m from the distribution board supplying it and that the supply cable is fixed to the wall (method C). (b) The efficiency of the motor is 90%. (c) The power factor of the motor is 0.8 lagging (d) The system voltage is 400V, 3 phase 50Hz (e) The motor runs on full load (f) M.D. Tariff Structure applies.
