Cork Institute of Tech Electrotechnology Exams - Sustainable Energy Tech, Semester 1, 2012, Exams of Electrical Engineering

Download Cork Institute of Tech Electrotechnology Exams - Sustainable Energy Tech, Semester 1, 2012 and more Exams Electrical Engineering in PDF only on Docsity! CORK INSTITUTE OF TECHNOLOGY INSTITIÚID TEICNEOLAÍOCHTA CHORCAÍ Semester 1 Examinations 2012/2013 Module Title: Electrotechnology for Mech L7 Module Code: ELEC7007 School: Mechanical & Process Engineering Programme Title: Bachelor of Engineering (Honours) in Sustainable Energy Technology – Year 3 Bachelor of Engineering in Mechanical Engineering – Year 3 Bachelor of Engineering in Manufacturing Engineering – Year 3 Programme Code: ESENT_8_Y3 EMECH_7_Y3 EMANF_7_Y3 External Examiner(s): Mr. Paul Kenny, Mr. Conor Buckley, Mr. Mike McKeon, Dr. Gerry Woods Internal Examiner(s): Mr. Sean McShera Instructions: Attempt Four Questions Duration: 2 Hours Sitting: Semester 1 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 paper. If in doubt please contact an Invigilator. Q1. a) You are designing the electrical distribution cabling in a building, explain using a diagram how you might limit the voltage drop from the transformer source to the final circuit. (4 marks) b) A three phase 15kW induction motor is being installed for the yaw control of a wind turbine. Determine the cable size required supplying the electrical power to the motor, using the tables provided and assuming a multi-core XLPE cable is used. Additional application information: • The motor is located at the turbine hub (40m high) and is supplied from a substation located 60m from the turbine • The motor efficiency is 0.82 (82%) • The motor power factor is 0.85 lagging • The system voltage is 400V, 3-phase 50Hz • 15kW refers to the shaft power of the motor. • Overload protection of the motor is set to 1.5 times the full load current. • Installation Method E from the ETCI Regulation Tables. (13 marks) c) Describe a method that provides „overload protection’ to a motor. (4 marks) d) Explain the reasons why a building energy manager might consider ‘load shedding’ for a factory production line. (4 marks) Q2. A 3-phase load is supplied from the secondary of a star connected transformer with a line voltage of 440V. Each phase of the load has an inductive reactance of 14Ω and a resistance of 18Ω. If the load is connected in; a) Star b) Delta Determine, for each of the connections i) The potential difference (p.d.) across each phase of the load. ii) The current in each phase of the load. iii) The power taken from the supply. iv) The power factor. (20 marks) c) With the aid of a circuit diagram, explain how single phase wattmeters may be used to determine the total power in an unbalanced, 3phase, 4wire, star connected load. (5 marks) ETCI — National Rules for Electrical Installations ERG ‘TALE AS2-F4: XLPE/EPR INSULATED CABLES WITH COPPER CONDUCTORS Continuous current-carrying capacities in amperes Conductor temperature 90°C Reference ambient temperature 30°C Installation methods E, F, G of Table AS2-D | Installation method | Malti-core cables Single-core cables | os | eas at | GS ‘Three loaded conductors, at | conductors | conductors | conductors | conductors Spaced ei iat touching Touching [Fiorizontal | Vertical area of ' | 1 leoo ( ome | To le | |e LF | [rer [de [ | ! | Pe Method E | Method E | Method F | Method F | Method F | Method G | Method G 1 2 3 4 s 6 7 8 1s 26 B - - " “ . 2s 4% n - - - - a” a2 = - - - - 6 63 4 - - - - - 0 % s - - - - 16 Ws 100, = = = = = 3 149 137 16 135 it 1s2 161 3s 18s 188 200 169 176 26 201 ” ns 12 m2 207 26 = ae 7 29 6 310 268 29 333 3B 9S 352 298 7 328 M2 4 39 1m 400 346 437 33 400, 0 ass 10 473 399 504 ooo 464 7” i 185 542 456 575 310 533 661 605 240 ol 336 679 oor 634 73 19 300 741 62) 783 703 736 m2 su 400 - = 940 628 808 (065 1.008 300 - - 1083 946 8 1253 1169 630 = - 1254 1086 vist bass 1362 Note: D, bs the external diameter of the cable ETCI — National Rules for Electrical Installations Tabte AS2-J3 Voltage drop mV / ampere / metre for XLPE insulated multi core cables with copper conductors : Conductor operating temperature 90°C Installation methods A BC E Condactor Methods A & B Methods C & E size mm? I phase I phase 3 phase is u u 7 25 19 19 16 4 2 2 10 6 79 19 68 10 ar 47 40 16 29 29 25 : 23 19 185 160 35 135 Ms 138 1s 30 1.05 0.90 10 087 70 07s 0.65 o7 062 98 058 oso 052 046 120 O48 oar O43 038 150 043 037 036 ox 185 039 032 030 028 240 033 029 02s 024 300 031 | 027 022 020 ‘TamLe AS2-J4 Voltage drop mV / ampere / metre for XLPE ~ insulated single core cables with copper conductors Conductor operating temperature 90°C Installation reference methods F and G 3 phase 1 phase Method F 3 phase Method F Tretia Fiat Method G 30 1.00 O87 oss 0.90 7 071 062 0.65 0.70 95 oss oa? 032 os3 120 oas 039 oae ost 180 038 033 039 045 188 033 028 om 041 240 028 024 030 037 300 025 ort 020 ox