Electrical Machines Exam - Bachelor of Engineering in Electrical Engineering - Summer 2010, Exams of Electric Machines

Download Electrical Machines Exam - Bachelor of Engineering in Electrical Engineering - Summer 2010 and more Exams Electric Machines in PDF only on Docsity! Page 1 of 5 CORK INSTITUTE OF TECHNOLOGY INSTITIÚID TEICNEOLAÍOCHTA CHORCAÍ Semester 2 Examinations 2010 Electrical Machines Module Code: ELEC6016 School: Electrical and Electronic Engineering Programme Title: Bachelor of Engineering in Electrical Engineering Programme Code: EELEC_7_Y2 External Examiner(s): Dr Maeve Duffy Mr Gerard Beecher Internal Examiner(s): Noel Mulcahy Instructions: Answer All Questions Duration: 2 hours Sitting: Summer 2010 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. Page 2 of 5 Q1. a. A 10kV/230V single phase transformer, on no load, takes 2.5A at from the supply. The no load losses are 1470W. Determine i. the power factor of the transformer on no-load (2 marks) ii. the magnetising current Im (2 marks) iii. the core loss current Ic (2 marks) iv. the primary current and overall power factor of the transformer when supplying a load of 160A at 0.9 power factor lagging. You may ignore internal voltage drops (6 marks) b. A transformer has 1200 primary turns and 200 secondary turns. The primary and secondary resistances are 0.2Ω and 0.02Ω respectively and the corresponding leakage reactances are 1.2Ω and 0.05Ω respectively. Calculate i. the equivalent resistance referred to the primary side (4 marks) ii. the equivalent reactance referred to the primary side (4 marks) iii. the equivalent impedance referred to the primary side (2 marks) iv. the phase angle of the impedance (2 marks) Q2. a. The power supplied to a three phase induction motor is 35kW and the stator losses are 1500W. If the slip is 6% determine: i. The rotor copper loss (4 marks) ii. The total mechanical power developed by the rotor (2 marks) iii. The output power of the motor if friction and windage losses are 1kW (2 marks) iv. The Torque developed if the rotor speed is 1425 rpm. (4 marks) v. The efficiency of the motor neglecting rotor iron loss (2 marks) b. A 3 phase 400V star connected 50Hz induction motor has 6 poles and a stator to rotor ratio of 3:1. At a certain load the slip is 3%, determine: i. the synchronous speed (2 marks) ii. the speed of the rotor (2 marks) iii. the slip speed (2 marks) iv. the frequency of the induced emf in the motor (2 marks) v. the voltage of the induced emf in the motor (2 marks)