Answer Happy

Q2. (a) For the three phase distribution system and loads shown in Figure Q2a: (1) Determine suitable sizes for the two cables such that the load voltages remain within statutory limits. Show all your working, and use the table of cable sizes and parameters provided in Table Q2a. 5 marks Suppose the network designer was aware that an additional load may be connected beside Load 2. Without calculation, describe how the selected cable sizes might be affected. 2 marks 160 m 22 kW, unity power factor 10 kVA, 0.82 lag 55 m Figure Q2a Conductor Resistance Reactance Maximum Cross-section (S2/km) (52/km) Current (mm²) Rating (A) 2.5 8.71 0.11 25 10 2.16 0.094 60 25 0.863 0.086 106 35 0.627 0.083 131 50 0.375 0.082 159 Table Q2a The tests shown in Table Q2b have been carried out on the 400V (line-line) 50Hz star-connected three-phase induction motor shown in Figure Q2b. Calculate the parameters of the IEEE machine model and draw the equivalent circuit (labelled with parameter values). 5 marks M Figure Q2b (b) (ii) 415V, 50Hz
(c) 20 DC resistance (between terminals) No load test P = 192 W 1 = 5.66 A Locked rotor test P = 480 W I= 10 A V = 35 V Table Q2b: Induction motor test results A 690V star-connected three-phase 4-pole induction motor rated at 100 kW mechanical output has the following parameters: R1 = 0.25 0 X, = 0.7 Ω X₂' = 0.7 Q R2' = 0.30 Mechanical losses = 6 kW Xm = 500 (i) When driving a mechanical load while connected to a 690V line-line supply, the motor is found to run at 1363 rpm. Calculate the input current, power factor, and mechanical output power of the motor in these conditions. 6 marks (ii) Explain which circuit element should be connected in parallel with the motor to improve its power factor. 2 marks