Why DC series is suited for traction applications? U CO5 May 2015 Define Torque. R CO1 May 2010 What is the precaution to be taken during starting of a DC series motor? Why? U CO1 Nov 2010 What is back emf in DC motor? What is its significance? R CO1 Nov 2011 Explain why Swinburne’s test cannot be performed on DC series motor. U CO1 Nov 2011 List various method of starting DC motor. R CO1 Nov 2016 What is meant by dynamic breaking in DC motor? R CO1 Nov 2016 State the advantages of Swinburne's test. R CO1 In every DC motor, a generator action occurs. Justify Ev CO3 How to reverse the direction of rotation of a DC motor? U CO1 the applications of various DC motors R CO5 At what load does the efficiency is maximum in DC shunt machines? U CO3 How does 4-point starter differ from 3-point starter? U CO1 List the different methods of speed control employed for DC series motors. R CO1 Part B Sl. No. Question M BT CO Month / Year Give the reasons for using “starters” to start D.C. motors. Draw the circuit of anyone type of starter and explain its operation. A series of resistance 1Ω between terminals runs at 800 rpm at 200 V with a current of 15 A. Find the speed at which it will run when connected in series with a 5Ω resistance and taking the same current at the same supply voltage. 3 5 8 R R Ap CO1 CO1 CO3 Nov 2010 May 2015 Explain the different methods of excitation and characteristics of DC motors with suitable diagrams. 16 U CO1 CO4 Nov 2011 Explain the Ward – Leonard system of controlling the speed of a DC shunt motor with the help of a neat diagram. 16 U CO1 Nov 2011 With a neat sketch, explain the working of 4 point starter. 16 U CO1 Nov 2012 Nov 2015 Draw a neat sketch of 3 point starter and explain its working. 8 U CO1 Nov 2013 May 2011 Derive from the fundamental, emf and torque equations and explain the characteristics of DC motor. What are the merits and demerits of Hopkinson’s test? 12 4 Ap R CO1 CO1 Nov 2013
Discuss in detail about armature speed control of DC shunt motor. A 500 V DC shunt motor running at 700 rpm takes an armature current of 50 A. its effective armature resistance is 0.4 Ω. What resistance must be connected in series with the armature to reduce the speed to 600 rpm, the torque remaining constant? 8 8 U Ap CO1 CO3 May 2014 May 2012 Explain in detail the construction and working operation of Retardation test on DC motor. Derive in detail the condition for maximum efficiency of DC machine. 10 6 U Ap CO1 CO3 Nov 2015 Explain the method to obtain efficiency at full load by conducting Hopkinson’s test. 16 U CO1 May 2016 The no-load test of a 44.76 kW, 220 V, DC shunt motor gave the following figures: Input current = 13.25 A; field current = 2.55 A; resistance of armature at 750C = 0.032 Ω and brush drop = 2 V. Estimate the full load current and efficiency. 16 Ap CO3 May 2016 With a circuit, explain how to obtain efficiency of D.C. generator by conducting Swinburne’s test. 16 U CO1 Nov 2016 In a Hopkinson’s test on a pair of 500 V, 1000 kW shunt generators, the following data was obtained: Auxiliary supply, 30 V at 500 V: Generator output current, 200A. Field currents, 3.5 A 1.8 A. Armature circuit resistances, 0.075Ω each machine. Voltage drop at brushes, 2V (each machine). Calculate the efficiency of the machine acting as a generator. 16 Ap CO3 Nov 2016 The speed of a 500 V DC shunt motor is raised from 700 rpm to 1000 rpm by field weakening, the total torque remaining constant. Ra and Rsh are 0.8 and 750 ohms respectively and the current lower speed is 12 A. calculate the additional shunt field resistance required assuming the magnetic circuit to be unsaturated. 6 An CO3 May 2011 A 230 V motor has an armature resistance of 0.3 ohms and takes an armature current of 40 A on a certain load. By how much must the main flux be reduced to raise speed by 50% and 25% if the developed speed is constant? Neglect saturation and armature reaction. 8 An CO3 May 2010