SIDDHARTH GROUP OF INSTITUTIONS :: PUTTUR Siddharth Nagar, Narayanavanam Road QUESTION BANK (DESCRIPTIVE)

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SIDDHARTH GROUP OF INSTITUTIONS :: PUTTUR Siddharth Nagar, Narayanavanam Road 517583 QUESTION BANK (DESCRIPTIVE) Subject with Code : PSD (16EE223) Year & Sem: III-B.Tech & II-Sem Course & Branch: B.

1 SIDDHARTH GROUP OF INSTITUTIONS :: PUTTUR Siddharth Nagar, Narayanavanam Road QUESTION BANK (DESCRIPTIVE) Subject with Code : PSD (16EE223) Year & Sem: III-B.Tech & II-Sem Course & Branch: B.Tech - EEE Regulation: R16 UNIT I CONVERTER FED DC MOTORS 1. Draw and explain operation of 3 phase full converter fed by SEDC motor? 2. Draw and explain operation of 3phase full converter fed by dc shunt motor? 3. Draw and explain operation of 3 phase semi converter fed by dc series motor? 4. With neat circuit diagram explain the dynamic braking and plugging of SEDC motor. 5. Draw and explain the block diagram of closed loop speed control of DC motor for Below and above base speed. 6. Explain the operation of DC motor for Closed Loop Speed control with block diagram? 7. A 200 volts, 875rpm, 150 amperes SEDC motor has an armature resistance of 0.06ohm. It is fed from a single phase fully controlled converter with an AC source voltage of 220volts, 50Hz.Assumingcontinuous conduction, calculate the firing angle for rated Motor torque and speed of 750rpm? 8. Explain the operation of3-ɸ full converter fed by DC series motor with necessary waveforms? 9. A 150hp, 500volts SEDC motor is operating at 1050rpm is controlled by 3-ɸ semi converter Which is operating from 3-ɸ, 450volts, 50Hzsupply. The rated armature current of the motor is 150A.The motor parameters are R a =0.099Ω,L a =0.63mH,K aɸ =0.33V/rpm.Find the no load Speed at α=0 0,α=45 0.Assuming no load current is 10% of rated current. Calculate the firing Angle at 1650rpm at rated torque?. 10. Explain the operation of single phase fully controlled converter fed DC separately excited Motor with neat Waveforms and derive the expressions for speed and torque? POWER SEMICONDUCTOR DRIVES Page 1

2 UNIT II FOUR QUADRANT OPERATION OF DC DRIVES 1. Write short notes on a) Plugging b) Dynamic braking c) Regenerative braking? 2. Explain the speed torque characteristics of a SEDC motor connected to a 3-ɸ full converter With relevant equations? 3. With a neat diagram, explain the four quadrant operation of a DC drive in all four quadrants When fed by a Three phase dual converter? 4. A 220V, 970rpm, 100A dc separately excited motor has an armature resistance of 0.05Ω.It is Braked by plugging from an initial speed of 1000rpm.Calculate a) Resistance to be placed in armature circuit to limit braking current to twice the full load value, b) Braking torque c) Torque when the speed has fallen to zero. 5. With a neat diagram, explain the operation of a DC drive in all four quadrants when fed by a Single phase dual converter with necessary circuit diagrams? 6. a) Draw and explain operation of single phase full converter fed by SEDC motor? 6 M b) Derive the speed and torque equations of a fully controlled converter connected to SEDC motor with continuous current operation? 7. Two independent 1-ɸ semi-converters are supplying the armature and field circuits of the SEDC motor for controlling its speed. The firing angle of the converter supplying the Field, adjusted such that maximum field current flows. The machine parameters are: R a =0.25Ω, R f =147Ω, motor voltage constant K v = V/A-rad/s. The load torque is T = 45 N-m at 1000 rpm. The converter is fed from a 208 V, 50 Hz AC supply. The friction and windage losses are neglected. Find a) the field current, b) The delay angle of the armature converter c)the input power factor of the armature circuit converter. 6 M 8.Explain how four quadrant operations is achieved by dual converters for SEDC motor? 9. Explain in detail the working of a multi quadrant control of chopper fed DC series motor? 10. Explain the operation of the two quadrant chopper fed DC drive system? POWER SEMICONDUCTOR DRIVES Page 2

3 UNIT III CHOPPER FED DC MOTORS 1. What are the methods of control strategies of chopper control? Which is best suited for DC motor control? 2. A dc shunt motor fed from 400 V dc source through a chopper has the following parameters -3 2 R a =0.02 Ω, R f =0.04 Ω, k 5 x 10 Nm / Amp. The average armature current of 300 Amps is ripple free of a chopper duty cycle of 50% determine i. Input power from the source ii. Motor speed and iii. Motor torque 3. A 230 V, 1100 rpm, 220 Amps separately excited DC motor has an armature resistance of 0.02 Ω. The motor is fed from a chopper, which provides both motoring and braking operations. Calculate i. The duty ratio of chopper for motoring operation at rated torque and 400 rpm ii. The maximum permissible motor speed obtainable without field weakening, if the maximum duty ratio of the chopper is limited to 0.9 and the maximum permissible motor current is twice the rated current. 4. What are the advantages of operating choppers at high frequency? 6 M 5. Mention the applications of chopper fed DC drives? 6 M 6. Why thyristors are not preferred now days for chopper fed DC drives? 7. State the conditions for a continuous current conduction mode for DC motor? 8. Explain whether discontinuous conduction mode will occur in the operation of chopper fed DC drives? 9. Draw the diagram of a regenerative chopper fed separately excited DC motor drive? 10. How critical is the current loop design in a four quadrant DC motor drive? POWER SEMICONDUCTOR DRIVES Page 3

4 UNIT IV CONTROL OF INDUCTION MOTOR V 1. Why low frequency operation control is not preferred? f 2. When is an induction motor said to be working in a field weakening mode? 3. List the demerits of the rotor resistance control using SCR switching with external resistance? 4. Give the expression for torque of a static rotor resistance controlled three phase induction motor? 5. What are the disadvantages of static rotor resistance control? 6 M 6. What is meant by slip power and Explain using a power circuit the working of a static Kramer drive system? 7. Name the different types of slip power recovery schemes and Bring out the advantages of CSI over VSI fed induction motor drives? 8. A three phase 400 V, 15 KW, 1440 RPM, 50 Hz star connected induction motor has rotor leakage impedance of (0.4 +j1.6)ω. The stator leakage impedance and rotational losses are assumed negligible. If the motor is energized from a 120 Hz, 400 V, 3 phase source, the calculate i. Motor speed at rated load ii. The slip at maximum torque occurs iii. The maximum torque 9. A three phase star connected 60 Hz, 4 pole induction motor has following parameters for equivalent circuit R s =R r =0.024Ω and X s =X r =0.12Ω. The motor is controlled by variable frequency control with constant (V/F) ratio for operating frequency of 12 Hz calculate i. The breakdown torque as a ratio of its value at the rated freq for both motoring and braking ii. The starting torque and rotor current in terms of their values at the rated frequency POWER SEMICONDUCTOR DRIVES Page 4

5 UNIT V CONTROL OF SYNCHRONOUS MOTORS 1. What is meant by self controlled synchronous motor drive and Write any four Special features of self controlled synchronous machine? 2. Give some applications of self controlled synchronous motors and What is meant by margin angle control of synchronous motor drive? 3. What is meant by power factor control of synchronous motor drive and Give two salient features of cycloconverter used to control synchronous motor speed? 4. What are the applications of cycloconverter fed synchronous motor drive and What happens to the stator current of a synchronous motor when f V is kept constant? 5. Discuss using a block diagram the operation of a voltage source inverter fed synchronous motor in the true synchronous mode? 6. Explain the closed loop control scheme of adjustable speed synchronous motor drive and mention its need and advantages and what is PMSM and mention its types? 7. What are Describe using a schematic how the speed of an inverter fed brushless DC motor can be controlled? 8. A 7 MW 3 phase 12 KV star connected 6 pole 50 Hz 0.9 leading power factor synchronous motor has X s =10Ω,R s =0Ω. The rated field current is 40 A. The machine is controlled by variable frequency control at constant V/F ratio up to the base speed and at constant voltage above base speed. Determine i. Torque ii. The field current for the rated armature current at 750 rpm and 0.8 leading power factor 9. A 6MW 3 Phase 11 KV, star connected 6 pole 50 Hz 0.9 lagging power factor synchronous motor has synchronous reactance equal to 9Ω and armature resistance equal to 0Ω. The rated field current is 50 A. The machine is controlled by variable frequency control at constant V/F ratio up to the base speed and at constant voltage above base speed. Determine i. Torque and field current for the rated armature current, 750 RPM and 0.8 leading power factor ii. Armature current and power factor for half the rated motor torque, 1500 rpm and rated field current. 10. A 3 phase 400 volt 50 Hz 6 pole star connected wound rotor synchronous motor has Z s =0+j2 Ω. Load torque proportional to speed 2, is 340 NM at rated synchronous speed. The speed of the motor is lowered by keeping V/F constant maintain unity power factor by field control of the motor. For the motor operation at 600 rpm, calculate i. Supply voltage ii. Armature current iii. Excitation angle iv. Load angle POWER SEMICONDUCTOR DRIVES Page 5

R13 SET - 1. b) Describe different braking methods employed for electrical motors. [8M]

R13 SET - 1. b) Describe different braking methods employed for electrical motors. [8M] Code No:RT32026 R13 SET - 1 III B. Tech II Semester Regular Examinations, April - 2016 POWER SEMICONDUCTOR DRIVES (Electrical and Electronics Engineering) Time: 3 hours Maximum Marks: 70 Note: 1. Question