Important RGPV Question
EC-501,Microprocessor and its Applications
V Sem, EC
UNIT 1 D.C. Machine-I
Q.1 Explain the term armature reaction and commutation and their effects and remedies related to the DC machine in brief. (RGPV Dec 2020)
Q.2 What are brushless DC motors? Explain three phase three pulse (half wave) brushless DC motor with diagram and basic operations principle. Also draw torque-angle characteristics of it and write their applications. (RGPV Dec 2020)
Q.3 Explain the phenomenon of commutation in dc machine. State the methods adopted for minimizing the sparking at the brushes. Explain the cross magnetization and demagnetization effects of armature reaction in a de machine. (RGPV May 2023)
Q.4 Explain the operation of a three point starter with the help of a neat diagram. (RGPV May 2023)
Q.5 What are the advantages of Swinburne method used to determine the efficiency of a DC machine? (RGPV Nov 2023)
Q.6 What is armature reaction in a DC machine how does it affect commutation what steps are taken to have effective commutation? (RGPV Nov 2023)
Q.7 A 4-pole DC series wound fan motor runs normally at 600 r.p.m., a 250V supply taking 20A. The field coils are connected all in series. Estimate the speed if the coils are reconnected in two parallel groups of two in series. Assumed that the flux is directly proportional to the current and ignore losses. The load torque increases as square of the speed. (RGPV Nov 2023)
Q.8 Why is the starting current very high in a DC motor? How does the starter reduce the starting current to a safe value? (RGPV Nov 2023)
UNIT 2 D.C. Machine-II
Q.1 Describe the Swinburne’s test to determine the DC machine efficiency with lab circuit diagram. (RGPV Dec 2020)
Q.2 A 4-pole DC motor runs at 600 rpm on full load and takes 25 A at 450 V. The armature is lap wound with 500 conductors and flux/pole is 0.085 wb. If the supply voltage and torque both are halved, calculate the speed at which the motor will run, neglect stray losses. (RGPV Dec 2020)
Q.3 Classify and explain DC motors with speed-torque curve. (RGPV Dec 2020)
Q.4 Explain how the efficiency of a dc machine is calculated from Swinburne’s test. (RGPV May 2023)
Q.5 What are the methods of speed control of a dc motor? (RGPV May 2023)
Q.6 Why is DC excitation used in a synchronous alternator instead of AC excitation? Explain it. (RGPV Nov 2023)
Q.7 Explain, why does the voltage regulator of alternator go high for the EMF method? (RGPV Nov 2023)
Q.8 How can you determine the synchronous impedance and armature resistance of an alternator? Explain them. (RGPV Nov 2023)
Q.9 The speed regulation of two 1000 kW alternators x and y running in parallel is 100 to 104% and 100 to 105% from full load to no load respectively. How will this machine share a total load of 1600 kW? (RGPV Nov 2023)
UNIT 3 Synchronous Machine-I
Q.1 Determine the voltage regulation of a alternator by synchronous impedance method. Give the lab diagram with brief explanation. (RGPV Dec 2020)
Q.2 The speed regulations of two 800 kW alternators A and B running in parallel are 100% to 104% and 100% to 105% from full load to no load respectively. How will the two alternators share a load of 1000 kW? (RGPV Dec 2020)
Q.3 Explain the different types of braking of dc machines. (RGPV May 2023)
Q.4 What do you mean by voltage regulation of an alternator? Describe some method for determining voltage regulation of an alternator. (RGPV May 2023)
Q.5 What is Armature reaction? Explain the effect of armature reaction on the terminal voltage of an alternator at ZPF lag and ZPF lead with the help of necessary phasor diagram. (RGPV Nov 2023)
Q.6 Sketch the Power-Angle characteristics of a salient-pole Synchronous Machine, including both the generation and motoring modes. Hence, explain why the salient-pole synchronous generator is preferred to the cylindrical synchronous generator in terms of stability. (RGPV Nov 2023)
UNIT 4 Synchronous Machine-II
Q.1 Draw and explain power angle characteristics for salient pole machines. (RGPV Dec 2020)
Q.2 Derive the emf equation of polyphase synchronous machine. Also explain the methods of harmonic elimination from emf waveform of alternator. (RGPV Dec 2020)
Q.3 Explain with lab diagram the parallel operation of two alternator with bright lamp method. Also list the conditions for paralleling. (RGPV Dec 2020)
Q.4 What is negative sequence reactance? Explain experimental methods find negative sequence reactance with laboratory diagram. (RGPV Dec 2020)
Q.5 Explain in brief how slip test is performed to determine X_d and X_q of a salient synchronous machine. (RGPV May 2023)
Q.6 A 3-phase, 4-pole, star-connected turbo-alternator has a smooth cylindrical type rotor. The effective resistance and synchronous reactance per phase are 0.152 and 2.52. Calculate the voltage regulation when delivering 250 A at 6.6 kV and at 0.6 p.f lagging. (RGPV May 2023)
Q.7 Describe the various excitation systems arrangements of synchronous alternators. (RGPV May 2023)
Q.8 Draw the phasor diagrams of salient-pole synchronous generator supplying lagging, leading and unity power factor loads. (RGPV May 2023)
Q.9 Explain the working principle of reluctance motor. Draw and explain the torque-speed characteristics of reluctance motor. (RGPV May 2023)
Q.10 Why is synchronous motor non-self starting? Discuss the various starting methods of synchronous motors. (RGPV May 2023)
Q.11 What is negative sequence reactance? How negative and zero sequence reactances are measured in the laboratory? (RGPV Nov 2023)
Q.12 The results of a ‘Slip-Test’ for determining direct-axis (X) and quadrature-axis (X) reactances of a star-connected, salient-pole alternator are given below: Phase values: V max = 108V; V min =96V, I max 12A, Imin 10A. Hence the two reactances will be. (RGPV Nov 2023)
UNIT 5 Synchronous Machine-III
Q.1 Write short notes on: (RGPV Dec 2020)
- a) Hunting and damper winding
- b) ‘V’ curves and inverted ‘V’ curves
- c) Repulsion motor
Q.2 Describe the construction, working principle and derive the expression of torque of switched reluctance motor. Also draw the characteristics of SRM. (RGPV Dec 2020)
Q.3 Explain the effect of damper winding in an alternators. (RGPV May 2023)
Q.4 A three-phase 6.6 KV, 50 Hz, 500 KVA, star connected alternator has an effective resistance of 50/phase and synchronous reactance of 50/phase. Determine the voltage regulator at full load at unity power factor. (RGPV May 2023)
Q.5 Explain the following any two: (RGPV May 2023)
- a) Stepper motor
- b) Hysteresis motor
- c) Repulsion motor
Q.6 Describe the three-lamp synchronisation method is used to synchronise an alternator with an infinite bus. (RGPV Nov 2023)
Q.7 Describe the construction, working principle and derive the expression of torque of switched reluctance motor. Also draw the characteristics of SRM. (RGPV Nov 2023)
— Best of Luck for Exam —
