Monday, December 24, 2012
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Sunday, December 23, 2012
Fluid Mechanics and Machinery
QUESTION BANK
Sub Code/Name: Fluid Mechanics & Machineries
UNIT- I PART-A
1. Define viscosity?2. What is compressibility?
3. Define dynamic viscosity?
4. What is cause for viscosity?
5. Give some example of surface tension ?
6. Define vapour pressure?
7. Define vapour pressure?
8. Give the Euler’s equation of motion?
9. What is bernouillie’s equation for real fluid?
10. State momentum equation and Impulse momentum equation?
11. State moment of momentukm equation?
12. State Bernouillie’s theorem?
13. Differentiate steady and unsteady flow?
14. State the assumptions in Bernoulli’s equation.
UNIT- I PART-B
1. a) Derives Euler’s Equation of Motion and proves the Bernoulli’s equation. (12 Marks)
b) Define the terms: i) Steady and unsteady flows ii) Specific weight (4 Marks)
2. a) Define the terms: i) Kinematics of flow ii) Uniform and non-uniform flows iii) Rotational and irrotational flows (6 Marks)
b) The Velocity Distribution for flow over a flat plate is given by u=(2/3)y-y2, Where u is the point velocity in metre per second at a distance y metre above the plate. Determine the shear stress aty=0 and y=15 cm. Assume dynamic viscosity as 8.63 poises (10Marks)
3. a) A pipe 200mm long has a slope of 1in100 and tapers from 1.2m diameter at the high end to 0.6m diameter at the low end and carries 100litres/sec of oil (Sp. Gr.=0.8). If the pressure gauge at the high end reads 60kN/m², determine i) Velocities at the two ends and ii) pressure at the lower end. (12 Marks)
b) One litre of crude oil weighs 9.6 N. Calculate its Specific weight and density (4 Marks)
4. Two large plane surfaces are 150mm apart. The space between the surfaces is filled with oil of viscosity 0.972Ns/m². A flat thin plate of o.5m² area moves through the oil at velocity of 0.3m/sec. Calculate the drgg force
i) When the plate is in the middle of the two plane surfaces and
ii)When the thinplate is at a distance of 30mm from one of the planes.(16 Marks)
5. a) Derive the three dimensional Continuity equation. (10 Marks)
b)Define the following i) Compressibility ii) Vapour pressure iii) Capillarity (6Marks)
6. a) Two plates are placed at a distance of 0.15mm apart. The lower plate is fixed while the upper plate having surface area 1.0 m2 is pulled at 0.3nm/s. Find the force and power required to maintain this speed, if the fluid separating them is having viscosity 1.5 poise. (8 Marks)
b) An oil film of thickness 1.5 mm is used for lubrication between a square plate of size 0.9m *0.9m and an inclined plane having an angle of inclination 200 . . The weight of square plate is 392.4 N and its slides down the plane with a uniform velocity of 0.2 m/s. find the dynamic viscosity of the oil. (8 Marks)
7. A pipe 300m long has a slope of 1 in100 and tapers from 1m diameter at the high end to 0.5m at the low end . The quantity of water flowing is 5400 m3/min. If the pressure at the high end is 49033 N/m², find the pressure at the low end. What is the change in pressure if the head loss between the two sections is 0.45m of water? (16 Marks)
8. 250 liters/sec of water is flowing in a pipe having a diameter of 300mm. If the pipe is bent by 135° (that is change from initial to final direction is 135°), find the magnitude and direction of the resultant force on the bend. The pressure of water flowing is 39.24N/cm². (16 Marks)
9. The diameter of a pipe gradually reduces from 1m to 0.7m. The pressure intensity at centerline of 1m section 7.848kN/m² and the rate of flow of water through the pipe is 600liters/sec. Find the intensity of pressure at the centerline of 0.7m section. Also determine the force exerted by flowing water on transition of the pipe. (16 Marks)
10.a) State the momentum equation. How will you apply momentum equation for determining the force exerted by a flowing fluid on a pipe bend? (12 Marks)
b) Define Moment of Momentum equation. Where this equation is used? (4 Marks)
UNIT- II PART-A
1. What do you mean by the term ‘Boundary Layer’?2. What is Laminar sub-layer?
3. Define Momentum thickness in Boundary Layer concept.
4. Sketch the development of Boundary layer over a flat plate.
5. Define the term ‘Turbulence’
6. Define: ‘Hydraulic Gradient Line’
7. Define: ‘Total gradient Line’
8. What is the expression for head loss due to friction in Darcy formula ?
9. What are the factors to the determined when viscous fluid flows through the circular pipe ?
10. What do you understand by the terms a) major energy losses , b) minor energy losses?
11. Give an expression for loss of head due to sudden enlargement of the pipe :-
12. Give an expression for loss of head due to an obstruction in pipe
13. What are the basic educations to solve the problems in flow through branched pipes?
UNIT- II PART-B
1. a) Define Displacement thickness. Derive an expression for the Displacement thickness. (10 Marks)b) Define: i) Laminar Boundary layer ii) Laminar Sub-layer (6 Marks)
2. a) A thin plate is moving in still atmospheric air at a velocity of 5m/sec. The length of the plate is 0.6m and width 0.5m. Calculate i) the thickness of the boundary layer at the end of the plate and ii) Drag force on one side of the plate. Take density of air as 1.24 kg/m3 and kinematic viscosity 0.15 strokes. (10 Marks)
b) What do you understand by the term Boundary layer and Boundary Layer theory? (6 Marks)
3. a) A plate of 600mm length and 400mm wide is immersed in a fluid of specific gravity 0.9
and kinematic viscosity 10-4 m²/sec. The fluid is moving with a velocity of 6 m/sec. Determine i) boundary layer thickness ii) shear stress at the end of the plate, and iii) drag force on one side of the plate. (12 Marks)
b) Differentiate Laminar & Turbulent Flow. (4 Marks)
4. a) What do you understand by the terms: Major energy losses and Minor energy losses (8 Marks)
b) Obtain expression for head loss in a sudden expansion in the pipe. List all the assumptions
made in the derivation. (8 Marks)
5. a) Derive the darcy-Weishach equation. (10 Marks)
b) Water is flowing through a pipe of diameter 250mm with a velocity of 3m/sec. Find the head loss due to friction for a length of 5.5m, if the coefficient of friction f is given by f = [0.03 (0.08/Re0.3)] where kinematic viscosity = 0.01strokes. (6 Marks)
6. The difference in water level between two tanks which are connected by three pipes in series is 15m. Lengths and diameters of these pipe are 300m, 150m, 200m and 30cm, 20cm, and 30cm respectively. Find the discharge through the pipe line and tabulate all losses if friction factor for three pipes are taken as 0.02, 0.025 and 0.03 (16 Marks)
7. a) A sudden enlargement of a water main from 230mm to 460mm diameter, the hydraulic gradient rises by 10mm. Estimate the discharge. (10 Marks)
b) Obtain expression for head loss in a sudden contraction in the pipe. (6 Marks)
8. Determine the length of an equivalent pipe of diameter 20cm and friction factor is 0.02 for a given pipe system discharging 0.1 m3/sec. The pipe system consists of the following. i) 10m line of 20cm diameter with friction factor 0.03, ii) three 90° bend with k=0.5 for each, iii) two sudden expansion of diameter 20cm to 30cm , iv) a 15cm line of 30cm diameter with friction factor is 0.025 and v) a global valve fully open with k=10. (16 Marks)
9. Two reservoirs whose water surface elevations differ by 40m are connected by a pipe line 30cm in diameter and 3km long. In order to increase the discharge, an additional pipe line 20cm in diameter and 1.5km long is laid parallel from the mid point of the first one upto the lower reservoir. What is the increase in discharge due to newly laid pipe? Assume friction factor f = 0.02 (16 Marks).
UNIT- III PART-A
1. Define Dimensional Analysis2. Define dimensionally homogeneous equation.
3. What are the methods of dimensional analysis?
4. State Buckingham’s Π theorem
5. What is dimensionless number?
6. What are the condition for hydraulic similitude?
7. Explain the significance of Froude Model law
8. Explain the terms: Model and Prototype
9. List advantages of Dimensional Analysis.
10. Explain Model analysis.
UNIT- III PART-B
1. a) Explain with example, dimensional homogeneity of a physical equatyion. (6 Marks)b) Describe in detail the method of dimensional analysis using Buckingham’s π theorem. (10 Marks)
2. a) Define i) Geometric similarity ii) Dynamic similarity iii) Kinematic similarity. (6 Marks)
b) The efficiency of a fan η depends upon following factors : 1) Density ρ 2) Dynamic viscosity μ 3) Diameter D 4) Discharge Q and 5) Angular velocity ω, Show that η = Φ [μ/D²ωρ , Q/D3ω ]. (10 Marks)
3. The pressure difference ΔP in a pipe of diameter D and length L due to turbulence flow depends on the velocity V, viscosity μ, density ρ and roughness K. Using Buckingham’s π theorem, obtain an expression for ΔP. (16 Marks)
4. The discharge Q through an oil ring depends on the diameter D of oil ring, speed Nrpm, mass density ρ of oil, absolute viscosity μ of oil, surface tension σ and specific weight ע of oil. Show that Q = ND3 f [ μ / ρND² , σ / ρN²D3 , ע / ρN²D ] (16 Marks)
5. Power P developed by a water turbine depends upon rotational speed N, operational head H, diameter D, breath B of runner, density ρ, viscosity μ and gravity g show that P = ρD5N5 Φ[H/D, B/D, ρD²N/μ, ND/(gH)1/2 ] (16 Marks)
6. Torque T of a propeller depends upon density of liquid ρ, viscosity μ, speed N, linear velocity V, diameter of the propeller shaft D. Using Buckingham’s π theorem show that T= ρN²D5 f[ ND/V, ρND²/μ ] (16 Marks)
7. a) A pipe of diameter 1.5m is required to transport an oil of specific gravity 0.9 and viscosity 3X10-2poise at the rate of 3000lit/sec. Tests were conducted on a 15cm diameter pipe using water at 20°C. Find the velocity and rate of flow in the model. Viscosity of water at 20°C is 0.01poise. (8 Marks)
b) The ratio of length of a sub-marine and its model is 30:1. The speed of the sub-marine (prototype) is 10m/sec. The model is to be tested in a wind tunnel. Find the speed of air in wind tunnel. Also determine the ratio of drag (resistance) between the model and prototype. Take the value of kinematic viscosity for sea water and air as 0.012strokes and 0.016strokes respectively. The density for sea water and air is given as 1030kg/m3 and 1.24kg/m3 respectively. (8 Marks)
8. a) The pressure drop in an aero-plane model of size 1:40 of its prototype is 80N/cm². The model is tested in water. Find the corresponding pressure drop in the prototype. Take density of air 1.24 kg.m3. The viscosity of water is 0.01poise while the viscosity of air is 0.00018poise. (10 Marks)
b) Derive Euler, Froude and Weber numbers. (6 Marks)
UNIT- IV PART-A
1. What is a hydraulic turbine?2. How will you classify the turbine?
3. Differentiate between the reaction and impulse turbine
4. Define specific speed of turbine
5. Give example for a low head, medium head and high head turbine.
6. What is Draft tube?
7. What is cavitation? How can it be avoided in reaction turbine?
8. Define the term ‘Governing of a turbine’
9. What are the functions of Surge tank?
10. Differentiate between an inward and an outward flow reaction turbines.
11. List out advantages of Francis turbine
12. Mention main components of Centrifugal pump
UNIT- IV PART-B
1. A jet of water having velocity of 20m/sec strikes a curved vane, whish is moving with a velocity of 10m/sec. The jet makes an angle of 20° with the direction of motion of vane at inlet and leaves an angle of 130° to the direction of motion of vane at outlet. Calculate i) Vane angles, so that the water enters and leaves the vane without shock. ii) work done per second per unit weight of water striking the vane per second. (16 Marks)2. A jet of water having velocity of 15m/sec strikes a curved vane which is moving with a velocity of 5m/sec. The vane is symmetrical and it so shaped that the jet is deflected through 120°. Find the angle of the jet at inlet of vane so that there is no shock. What is the absolute velocity of jet at outlet in magnitude and direction and the work done per unit weight of water. Assume the vane to be smooth. (16 Marks)
3. A jet of water having velocity of 30m/sec strikes a series of radial curved vanes mounted on a wheel which is rotating at 200rpm. The jet makes an angle of 20° with the tangent to the wheel at inlet and leaves the wheel with a velocity of 5m/sec at an angle of 130° to the tangent to the wheel at outlet. Water is flowing from outward in a radial direction. The outer and inner radii of the wheel are 0.5m and 0.25m respectively. Determine i) Vane angles at inlet and outlet ii) work done per unit weight of water iii)efficiency of wheel. (16 Marks)
4. The penstock supplies water from a reservoir to the pelton wheel with a gross head of 500m. One third of the gross head is lost in friction in the penstock. The rate of flow of water through the nozzle fitted at the end of the penstock is 2m3/sec. The angle of deflection of the jet is 165°. Determine the power given by the water to the runner and hydraulic efficiency of the pelton wheel. Take speed ratio=0.45 and Cv=1 (16 Marks)
5. A pelton wheel having a mean bucket diameter of 1m and is running at 1000rpm. The net head on the pelton wheel is 700m. If the side clearance angle is 15° and discharge through nozzle is 0.1m3/sec. Find i) Power available at the nozzle ii) Hydraulic efficiency of the turbine. (16 Marks)
6. A reaction turbine works at 450rpm under a head of 120m. Its diameter at inlet is 120cm and the flow area is 0.4m². The angle made by absolute and relative velocities at inlet are 20° and 60° respectively with the tangential velocity. Determine i) The volume flow rate ii) The power developed iii) Hydraulic efficiency (16 Marks)
7. As inward flow reaction turbine has external and internal diameters as 1m and 0.6m respectively. The hydraulic efficiency of the turbine is 90% when the head on the turbine is 36m. The velocity of flow at outlet is 2.5m/s and discharge at outlet is radial. If the vane angle at outlet is 15° and width of the wheel is 100mm at inlet and outlet, Determine i) the guide blade angle ii) speed of the turbine iii) vane angle of the runner at inlet iv) volume flow rate of turbine v) power developed. (16 Marks)
8. A Pelton turbine is required to develop 9000kW when working under a head of 300m the impeller may rotate at 500rpm. Assuming a jet ratio of 10 and an overall efficiency of 85%. Calculate i) quantity of water required ii) diameter of wheel iii) Number of jets iv) Number and size. of bucket on the runner. (16 Marks)
9. The following data is given for a Francis turbine. Net head = 80m, Speed = 700rpm, Shaft power = 300kW, Overall efficiency = 80%, Hydraulic efficiency = 90%, flow ratio =0.2, and breadth ratio = 1. The thickness of vane occupies 4% of circumferential area of the runner, velocity of flow is constant at inlet and outlet and discharge is radial at outlet. Determine i) Diameters of runner at inlet and outlet, assume D2=D1/2. ii) Width of wheel at inlet iii) Guide blade angles iv) runner vane angles at inlet and outlet. (16 Marks)
10. i) Draw a neat sketch of Kaplan turbine, name the parts and briefly explain the working. (8 Marks)
ii) Define specific speed of the turbine? Derive an expression for the specific speed. (8 Marks)
UNIT- V PART-A
1. What is meant by Pump?2. What is meant by Priming?
3. Differentiate between the single acting pump and double acting pump
4. What are the functions of air vessels?
5. Define slip, percentage slip and negative slip of a reciprocating pump
6. Define Manometric efficiency
7. Define Mechanical efficiency.
8. Define overall efficiency.
9. Define speed ratio, flow ratio.
10. Mention main components of Reciprocating pump.
11. What is indicator diagram?
12. What is meant by Cavitations?
UNIT- V PART-B
1. A radial flow impeller has a diameter 25cm and width 7.5cm at exit. It delivers 120litres of water per second against a head of 24m at 1440rpm. Assuming the vanes block the flow area by 5% and hydraulic efficiency of 80%. Estimate the vane angle at exit. Also calculate the torque exerted on the driving shaft if the mechanical efficiency is 95%. (16 Marks)2. Find the power required to drive a centrifugal pump which delivers 0.04m3/sec of water to a height of 20m through a 15cm diameter pipe and 100m long. The overall efficiency of the pump is 70% and coefficient of friction is 0.15 in the formula Hf= 4flv2 / 2gd. (16 Marks)
3. A centrifugal pump having outer diameter equal to 2 times the inner diameter and running at 1200rpm works against a total head of 75m. The velocity of the flow through the impeller is constant and equal to 3m/sec. the vanes are set back at an angle of 30° at outlet. If the outer diameter of the impeller is 600mm and width at outlet is 50mm. Determine i) Vane angle at inlet ii) Work done per sec by the impeller iii) Manometric efficiency. (16 Marks)
4. The impeller of a centrifugal pump has an external diameter of 450mm and internal diameter of 200mm and it runs at 1440rpm. Assuming a constant radial flow through the impeller at 2.5m/sec. and that the vanes at exit are set back at an angle of 25°. Determine i)Inlet vane angle ii) The angle, absolute velocity of water at exit makes with the tangent and iii) The work done
per N of water. (16 Marks)
5. The diameter and stroke of a single acting reciprocating pump are 200mm and 400mm respectively, the pump runs at 60rpm and lifts 12litres of water per second through a height of 25m. The delivery pipe is 20m long and 150mm in diameter. Find i) Theoretical power required to run the pump ii) Percentage of slip iii) Acceleration head at the beginning and middle of the delivery stroke. (16 Marks)
6. The length and diameter of a suction pipe of a single acting reciprocating pump are 5m and 10cm respectively. The pump has a plunger of diameter 150mm and stroke of length of 300mm. The centre of the pump is 4m above water surface in the pump. The atmospheric pressure head is 10.3m of water and pump is running at 40rpm. (16 Marks)
7. Two geometrical similar pumps are running at the speed of 750rpm. One pump has an impeller diameter of 0.25m and lifts the water at the rate of 30 lit/sec against a head of 20m. Determine the head and impeller diameter of the other pump to deliver half the discharge. (16 Marks)
8. i) What is reciprocating pump? Describe the principle and working of a double acting reciprocating pump with a neat sketch. (12 Marks)
ii) Define slip, percentage slip and negative slip of a reciprocating pump. (4 Marks)
9. A double acting reciprocating pump running at 60rpm is discharging 1.5m3 of water per minute. The pump has a stroke length of 400mm. The diameter of the piston is 250mm. The delivery and suction heads are 20m and 5m respectively. Find the power required to drive the pump and the slip of the pump. (16 Marks)
10. A double acting reciprocating pump has a bore of 15cm diameter and stroke 30cm long. The piston rod diameter is 25mm. The crank rotation speed is 60rpm. The water is lifted to a height
of 20m and the percentage of slip is -2 (negative value). Find the actual discharge of the pump
and the power required to lift the water. (16 Marks)
ELECTRICAL DRIVES AND CONTROL
ME 2205 Electrical Drives and Control:
QUESTION BANK
SUBJECT CODE & NAME : ELECTRICAL DRIVES AND CONTROL
YEAR / SEM : II / III
UNIT IINTRODUCTION
PART-A ( 2 MARKS)
1. Define Drives
2. Define Electric Drives.
3. What are the basic elements of Electric Drives?
4. Write the classification of Electric Drives.
5. Draw the block diagram of Electric Drive.
6. What is meant by Group drive? Give an example.
7. What is meant by Individual drive? Give an example.
8. What is meant by Multimotor drive? Give an example.
9. What are the advantages and disadvantages of Individual drive system?
10. What are the advantages and disadvantages of Group drive system?
11. What are the advantages of electric drive over mechanical drive?
12. Mention the drawbacks of electric drives.
13. What are the factors influencing the choice of electric drives?
14. Mention the functions of Power modulators.
15. Compare Individual, Group and Multimotor drives.
16. What are the motors used in Electric drives?
17. Mention the necessity of power rating?
18. Write down the dissipation equation due to convection process.
19. Draw the heating and cooling curve for a particular electric drive.
20. What are the classes of duty for an electric motor?
21. What is meant by continuous duty?
22. What is meant by continuous duty variable load?
23. What happens if the motor is selected at highest load handling capacity at continuous duty variable?
24. What is meant by time intermittent duty?
25. What is meant by periodic intermittent duty?
26. What is duty factor?
27. Give the assumptions for heating and cooling calculation.
28. What is heating curve?
29. Define Heating time constant (ξ1).
30. What is cooling curve?
31. Compare A.C drives and D.C drives.
32. What is meant by short time rating of motor?
33. What are the factors that affect the power rating and size of electric drives?
PART-B
1. Explain the factors governing the selection of motors. (16)
2. Discuss in detail the determination of power rating of motors. (16)
3. (i) Explain the different types of loading of drives. (8)
(ii) Explain the choice of selection of the motor for different loads. (8)
4. (i) Describe the simplifications based on which the heating and cooling calculations of an electric motor are made. (3)
(ii) Establish the heating time constant and the heating curves. (13)
5. (i) Compare the D.C and A.C drives. (6)
(ii) Write a brief note on classes of duty for an electric motor. (10)
6. Draw the typical temperature rise-time curve and derive the equation for temperature rise in an electric drive. (16)
7. Explain the loading of an electric motor and its duty cycle with a simple diagram. (16)
8. Explain in detail about the various types of electric drives. (16)
9. A 100 kW motor, having rated temperature rise of 60°C, has full-load efficiency of 80% and the maximum efficiency occurs at 85% full load. It has thermal time constants of 80 minutes and 65 minutes. It is cyclically loaded, 120% of full load for one hour and 50% of full load for the next hour. Find the temperature rise after 3 hours. (16)
10. The thermal time constant and final steady temperature of a motor on continuous running is 30 minutes and 60°C. Find out the temperature.
i) After 15 minutes at this load.
ii) After 1 hour at this load.
iii) If temperature rise at 1 hour rating is 60°C, find the maximum steady temperature.
iv) What will be the time required to increase the temperature from 40°C to 60°C at 1 hour rating. (16)
UNIT II
DRIVE MOTOR CHARACTERISTICS
PART-A ( 2 MARKS)
1. Why motor characteristics are important?
2. Why DC series motor should never be started on no-load?
3. Why a fly-wheel setup is used in DC series motor?
4. Why differential compound motors are not used in practical?
5. What is the main reason of fitting fly-wheel along with the motor?
6. Draw the mechanical (or) speed –torque characteristics of all types of DC Motors.
7. State the condition at which the starting toque developed in a slip-ring induction motor is maximum.
8. State the different modes of operation of three phase induction machines.
9. What is mechanical characteristics of a motor?
10. Give the application where DC Shunt, DC Series and DC Compound motors are used.
11. Draw the torque-slip characteristics of a three phase squirrel cage induction motor.
12. What is meant by braking?
13. Mention the Classifications of Braking.
14. What are the advantages and disadvantages of Electrical Braking?
15. Explain the plugging method of braking.
16. Why regenerative braking is not possible ion DC Series motor without modification?
17. Give the types of braking used for DC Motors.
18. What is meant by Regenerative braking in DC Motor?
19. Mention the demerits of mechanical braking.
20. Give the advantage of dynamic braking.
21. What is meant by rheostat (or) dynamic braking?
22. What is meant by Plugging in DC Motor?
23. Draw the speed-torque characteristics of various type of loads.
24. What are the conditions for the stable operations of the motors?
25. List the electrical braking for DC Compound Motor.
26. Differentiate Mechanical and Electrical Braking.
27. Draw the speed-torque characteristics of three phase induction motor.
28. Write short notes about the different types of loads
PART-B
1. (i) List out the advantages and disadvantages of electrical braking over mechanical braking. (8)
(ii) Discuss any one method of electrical braking of DC Machines. (8)
2. Explain the Speed-Torque characteristics of three phase induction motor with neat diagrams. (16)
3. Explain about the speed-torque characteristics of a DC Shunt Motor with suitable graph and equations (16)
4. Explain about the quadrantal diagram of speed-torque characteristics for a motor driving hoist load. (16)
5. Explain how an induction motor is brought to stop by (i) Plugging and (ii) dynamic braking. (16)
6. Explain the various methods of braking of induction motors. (16)
7. Draw and explain various load characteristics of DC Shunt Motor. (16)
8. Explain Rheostat braking in DC Series Motor and Plugging in DC Shunt Motor. (16)
9. Explain various methods of braking of DC Shunt Motors with neat diagrams. (16)
10. Explain Various methods of braking of DC Series Motors with neat diagrams. (16)
11. (i) Explain the speed – torque curve of single phase induction motors in detail. (8)
(ii) Explain the method of regenerative braking employed in DC Motors.(8)
12. Explain about the speed-torque characteristics of a DC Compound Motor with suitable graph and equations. (16)
13. A 220V shunt Motor has an armature resistance of 0.062 Ω and with full field has an emf of 215V at a speed of 960 rpm, the motor is driving an overhauling load with a torque of 172 Nm. Calculate the minimum speed at which the motor can hold the load by means of regenerative braking. (16).
UNIT III
STARTING METHODS
PART-A ( 2 MARKS)
1. What are the functions of starters?
2. What are the factors influencing the selection of starters?
3. Why starter is necessary for starting a DC Motor?
4. What are the starters used for starting DC Motors?
5. Why is starting current high in a DC Motor?
6. What are the protective devices used in DC Motor Starters?
7. How does the four point starter differ from three point starter?
8. Explain the function of NVR coil in DC Motor Starters?
9. Explain the function of OLR coil in DC Motor Starters?
10. What are the different methods of starting three phase induction motors?
11. How many terminals are provided on the terminal box of a squirrel cage induction motor to be started by a star-delta starter?
12. Mention the reasons for most of the three phase induction motors provided with delta connected stator winding?
13. Write the applications of three phase induction motors?
14. Mention the merits of DOL starter.
15. Mention the demerits of DOL starter.
16. Why stator resistance starter is rarely used?
17. What are the effects of increasing rotor resistance on starting current and starting torque?
18. How reduced voltage starting of induction motor is achieved?
19. How automatic starters are working in DC Motors?
20. How we start the wound-rotor (slip-ring) motors?
21. Why single phase induction motor is not self-starting?
PART-B
1. Draw a neat schematic diagram of a three point starter and explain its working. (16)
2. Draw a neat schematic diagram of a four point starter and explain its working. (16)
3. Explain with neat circuit diagram, the star-delta starter method of starting squirrel cage induction motor. (16)
4. Explain the typical control circuits for DC Series and Shunt motors (16)
5. Explain the different starting methods of three phase squirrel cage induction motors with neat sketches. (16)
6. Explain different methods of starting of DC Motors. (16)
7. Explain with neat diagram the starting of three phase slip ring induction motor. (16)
8. Draw and explain the push-button operated direct-on line starter for three phase induction motor. (16)
9. Draw and explain the manual auto-transformer starter for three phase induction motor. (16)
UNIT IV
CONVENTIONAL AND SOLID STATE SPEED CONTROL OF D.C DRIVES
PART-A ( 2 MARKS)
1. Enumerate the factors on which the speed of a DC Motor depends.
2. By what methods can the speed of a DC Shunt Motor be controlled?
3. Why the field control is considered superior to armature resistance control for DC Shunt Motors?
4. What is the effect of inserting resistance in the field circuit of a DC Shunt Motor on its speed and torque?
5. What is meant by speed control?
6. Mention the different methods of speed control employed for DC Series Motor.
7. What is meant by armature control?
8. What will be the effect of change in supply voltage on the speed of DC Shunt Motor?
9. What are the advantages and disadvantages of armature resistance control of DC Shunt Motor?
10. What are the advantages and disadvantages of Field control (or) Flux control method?
11. What is meant by flux control (or) field control method?
12. In which type of control the field current and armature current kept constant?
13. How we select the shunt and series motor based on the torque and speed in particular application?
14. Write down the applications of Ward-Leonard system of speed control.
15. What are the advantages and disadvantages of Ward-Leonard method of speed control?
16. Write down the disadvantages and applications of armature diverted method of speed control of DC Series Motor?
17. What is meant by solid state speed control?
18. What are the advantages and disadvantage of solid state drive methods?
19. What is meant by DC Chopper?
20. What is meant by duty cycle?
21. What are the different types of Chopper?
22. What is the function of freewheeling diode?
23. Write the output equation for single phase half and full converters.
24. What are the arrangements are available using Power semiconducting materials?
25. What are the two main methods for speed control of DC Shunt Motor?
26. What are the advantages of thyristor control on speed control of DC Motor?
27. Why Chopper based D.C drives give better performance than rectifier controlled drives?
28. Name the solid state controllers used for the speed control of D.C Shunt motor and Series Motor.
29. What is free-wheeling?
PART-B
1. Explain with neat sketch the chopper control method of speed control of DC Motors. (16)
2. Explain with neat sketches about the DC Shunt Motor speed control by using single phase fully controlled bridge converter. (16)
3. Discuss the Ward-Leonard speed control system with a neat circuit diagram. Also mention its advantages and disadvantages. (16)
4. Explain how the speed of a DC Shunt Motor can be varied both above and below the speed at which it runs with full field current. (16)
5. (i) Explain with neat sketch the operation of chopper fed DC Series Motor drive. Also, derive the expression for average motor current. (10)
(ii) Explain Time ratio control and Current limit control. (6)
6. Explain the speed control schemes of DC Series Motor. (16)
7. Explain the different methods of speed control employed in DC Shunt Motor. (16)
8. Explain the control of DC drives using rectifiers and choppers. (16)
9. Explain the single phase half wave converter drive speed control for DC drive with waveforms. (16)
10. Explain in detail the single phase semi-converter speed control for DC drive for separately excited motor. (16)
11. A 500V series motor having armature resistance and field resistance of 0.2 Ω and 0.3 Ω respectively runs at 500 rpm when taking 70A. Assuming unsaturated field, find out its speed when field diverter of 0.684 Ω is used constant load torque. (16)
12. A 250V DC Series Motor takes 40A of current when developing a full load torque at 1500 rpm. Its resistance is 0.5 Ω. If the load torque varies as the square of the speed determine the resistance to be connected in series with the armature to reduce the speed to 122 rpm. Assume the flux is proportional to the field current. (16)
UNIT V
CONVENTIONAL AND SOLID STATE SPEED CONTROL OF A.C DRIVES
PART-A ( 2 MARKS)
1. List the different methods of speed control of three phase induction motor.
2. Write short notes about cascaded method of speed control?
3. Define Slip.
4. What is slip-power recovery system?
5. What are the advantages of Slip-power recovery system?
6. What is meant by Voltage control in induction motor? and where it is applicable?
7. What is meant by Voltage / Frequency control?
8. What are the main features of V/f control?
9. What is meant by Stator frequency control?
10. What is meant by AC Voltage controller?
11. Mention the advantages and disadvantages of Stator voltage control.
12. What are the possible methods of speed control available by using inverter?
13. Why we go for PWM inverter control?
14. Write the classifications of PWM techniques.
15. What is meant by Cyclo converter?
16. Write the types of cyclo converter.
17. Write the applications of Cyclo converter.
18. Write down the limitation of cyclo converter method of speed control.
19. Compare the Static Kramer and Scherbius System.
20. What are the advantages and disadvantages of Static Scherbius scheme of speed control?
21. Write the speed equation of an induction motor.
22. What is VVVF control?
PART-B
1. Draw the power circuit arrangement of three phase variable frequency inverter for the speed control of three phase induction motor and explain its working. (16)
2. Explain the V/f control method of AC drive with neat sketches. (16)
3. Discuss the speed control of AC motors by using three phase AC Voltage regulators. (16)
4. Explain the speed control schemes of phase wound induction motors. (16)
5. Explain the concatenation operation of three phase induction motors. Hence derive the speed experienced for the cascaded set. (16)
6. Explain in detail about Slip power recovery scheme. (16)
7. Explain the different methods of speed control used in three phase induction motors. (16)
8. Explain the working of following methods with neat circuit diagram. i) Kramer system ii) Scherbius system (16)
9. Explain in detail rotor resistance method of speed control of a slip ring induction motor. (16)
10. (i) Explain the operation of Pole changing method of speed control. (8)
(ii) Explain the pole amplitude modulation method. (8)
11. Explain the static Kramer method and static scherbius method of speed control of three phase induction motor. (16)
12. Explain in detail about the various methods of solid state speed control techniques by using inverters.(16)
13. Explain the solid state stator voltage control technique for the speed control of three phase induction motor. (16)
14. Explain the various methods of speed control of a three phase induction motor when fed through semiconductor devices. (16)
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