Download Taking the Voltage - Electrical Power And Machines I - Past Exam Paper and more Exams Electrical Engineering in PDF only on Docsity! Spring Examinations 2010-2011 Exam Code(s) 3BN1, 3BM1 Exam(s) 3rd Year Electronic Engineering 3rd Year Mechanical Engineering Module Code(s) EE302.ii, EE302 Module(s) Electrical Power & Machines II, Electrical Power & Machines Paper No. 1 Repeat Paper No External Examiner(s) Prof. G. W. Irwin Internal Examiner(s) Prof. G. Ó Laighin Dr. M. Duffy Instructions: Answer any three questions. All questions carry equal marks (20 marks). Duration 2 hours No. of Pages 4 including cover Department(s) Electrical & Electronic Engineering Course Co-ordinator(s) Requirements: MCQ Handout Statistical Tables Graph Paper Log Graph Paper Other Material 1. An induction motor is supplied from a balanced 3-phase 440 V supply as shown in Fig. 1. At full load, it draws 41 kW at 0.78 power factor lagging. Fig. 1 (a) Taking the voltage abV = 4400 o, determine the phase currents and the line currents for the given conditions. [9 marks] (b) Determine the wattmeter readings, W1 and W2 for the conditions of part (a) [5 marks] (c) Power factor correction is applied so that the effective impedance per phase becomes Z = (14.2 + j0) . Calculate the corresponding phase currents and the total power. [6 marks] 2. The equivalent circuit model per phase of a 3-phase, 440 V, 1460 rpm, 4-pole, 50 Hz induction motor includes the following values: Stator winding resistance: 0.42 Referred rotor winding resistance: 0.35 Total leakage reactance referred to the stator: 1.68 (a) Neglecting magnetising current, calculate the full load current drawn by the motor. [6 marks] (b) Given that core losses are 2.6 kW and mechanical losses are 3.75 kW at full load, determine (i) the rated output mechanical power, (ii) the full load efficiency and (iii) the output mechanical torque. [8 marks] (c) What values of voltage, current and torque would you expect to measure for a blocked rotor test on this motor? [6 marks] a b c P1 P2 Z Ia Iab Ib Ic Ica Ibc Z Z
