Download Wattmeter Connections - Electrical Power And Machines I - Past Exam Paper and more Exams Electrical Engineering in PDF only on Docsity! EE302.II Electrical Power & Machines II Page 1 of 3 Spring Examinations 2011/2012 Exam Code(s) 3BEI, 3BN, 3BM, 3BSE (Electrical) Exam(s) Third Year Engineering Innovation – Electronic Third Year Electronic Engineering Third Year Mechanical Engineering Third Year Energy Systems Engineering (Electrical) Module Code(s) EE302.II Module(s) Electrical Power & Machines II 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 from four. All questions carry equal marks (20 marks). Duration 2 hrs No. of Pages 3 Discipline Electrical & Electronic Engineering Course Co-ordinator(s) Dr. M. Duffy Requirements: MCQ Handout Statistical Tables Graph Paper Log Graph Paper Other Material EE302.II Electrical Power & Machines II Page 2 of 3 Question 1 A 3-phase induction motor is supplied with a balanced 440 V supply. Power consumption is monitored using the wattmeter connections shown in Fig. 1. For a load of 76.4 Nm at 1463 rpm, P1 = 4.8 kW, P2 = 10.2 kW, and the line current is measured as 23.2 A. Fig. 1 (a) For the given load, calculate: [6 marks] (i) the total power consumption of the motor (ii) the load power factor (iii) the motor efficiency (b) Calculate the motor phase voltages and phase currents and show them on a phasor diagram. [6 marks] (c) Due to a wiring fault, an open-circuit develops in phase A of the motor. Calculate the resulting voltage established at the neutral point of the motor. [8 marks] Question 2 Locked rotor test results for a 3-phase, 420 V, 50 Hz, 2900 rpm, cage-rotor induction motor are given as: V = 119.6 V I = 30.8 A P = 1.71 kW T = 2.17 Nm Magnetising losses are determined separately as 0.9 kW and rotational losses as 2.3 kW. (a) Assuming a star-connected stator, determine the approximate equivalent circuit model per phase of the given induction motor. [10 marks] (b) Determine the output mechanical power and motor efficiency under rated conditions. [10 marks] a b c ~ Z ~ Z ~ Z Ia Ib Ic P1 P2
