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A separately excited DC motor has the following data P=20.5kW (rated power); Va=440V (rated voltage); Ia=55A (rated current); n=1000 rpm (rated speed), the load torque is 90% rated torquea.Determine the original responses? Determine the artifical responses when the armature voltage is reduced to 90% rated voltage? b.The armature voltage is reduced to 270V. Draw the artifical responses and determine the rotor speed at that time. Explain the process of braking in this case. c.To stop the DC motor, the armature voltage is reversed and the resistance of 1.75Ω is added to armature circuit. Calculate the rotor speed and the torque at the first time of braking?
HCMC UNIVERSITY OF TECHNOLOGY AND EDUCATION Faculty for High Quality Training Program name: Mechatronics FINAL EXAMINATION SEMESTER – ACADEMIC YEAR 2018-2019 Course name: Electric drives Course ID: ETDR336429E Exam code: 01 Number of pages: 01 Duration: 60 minutes Open-book Question 1: (6/10) A separately excited DC motor has the following data P=20.5kW (rated power); Va=440V (rated voltage); Ia=55A (rated current); n=1000 rpm (rated speed), the load torque is 90% rated torque a Determine the original responses? Determine the artifical responses when the armature voltage is reduced to 90% rated voltage? b The armature voltage is reduced to 270V Draw the artifical responses and determine the rotor speed at that time Explain the process of braking in this case c To stop the DC motor, the armature voltage is reversed and the resistance of 1.75Ω is added to armature circuit Calculate the rotor speed and the torque at the first time of braking? a) The original responses 0d The artifical responses when the armature voltage is reduced to 90% rated voltage 0d b) 0d Document ID: BM1/QT-PĐBCL-RĐTV-E Page: 1/1 the artifical responses Regenerative Braking AB D A’ Regenerative Braking: BD 0d c) the torque at the first time of braking (Nm) 0d 0d Question 2: (4/10) A 208-V, six pole, 60 Hz, Y-connected induction motor, R1=0.6Ω; R2’=0.4; Xeq=5Ω a Calculate the motor speed if the load torque is 30 Nm? b Calculate the smallest voltage source so that the motor could handle the load torque 25 Nm? c Calculate the starting current, starting torque, maximum torque, d Calculate the resistance should be added to rotor circuit to reduce starting current a half e Calculate the resistance should be added to rotor circuit to keep the starting torque equal to the maximum torque a) the motor speed when the load torque is 30 Nm 0d b Document ID: BM1/QT-PĐBCL-RĐTV-E Page: 1/1 c the starting current, starting torque, maximum torque Ist=23.551A0.5d Tst=5.297Nm0.5d Tmax=30.546Nm0.5d d Ist’=11.776A Radd=7.888�0.5d e smax=1 Radd=4.636�0.5d Note: Proctors are not allowed to give any unauthorised explaination Learning outcome mapping [LO 1.1]: Describe structure of electric motors; symbols and roles of electric motors in mechatronic systems [LO 2.1]: Create mathematic models of electricalmechanical responses of typical electric motors [LO 2.2]: Describe structure and working principles of typical electric motors Assessed in Question Question 20/05/2019 Approved by program chair Document ID: BM1/QT-PĐBCL-RĐTV-E Page: 1/1