Give all your answers correct to 4 d.p. A 400 V, 50 Hz, 6-pole, 950 rpm, star connected induction motor has the following parameters: stator and rotor resistances are 1.35 N each, and stator and rotor leakage reactance are 1.5 N each (magnetising reactance can be neglected). The motor is controlled by simultaneous stator voltage and frequency variation. Voltage boost is not used and the motor is controlled using V/f = constant law. The motor is supplied from a three-phase voltage source inverter. a) The motor operates at 25 Hz. Calculate the ratio of the maximum torque at this frequency with respect to the one at rated frequency, for both motoring and generation. [5 marks] For the motoring case the ratio is: Number For the generation case the ratio is: Number b) For the same 25 Hz operating frequency, calculate ratio of the starting current at this frequency with respect to the starting current at rated frequency. [5 marks] Starting current ratio is: Number
c) Assume that the voltage boost of 50 V (phase voltage) is used. Calculate new value of the phase voltage that would be applied in this case for the operating frequency of 25 Hz. Repeat part b) with this new voltage applied. [6 marks] Phase voltage: Number V Starting current ratio: Number d) A variable-speed electric drive can operate in two distinct speed control regions. Name these regions, explain the principal difference between them and specify which quantity is kept constant in each of the two. [4 marks] 1= 2= 三三三三 Ω Σ Εαποτ Equation A. A IX BIUS X2 x Styles Font Size
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