SIDDHARTH GROUP OF INSTITUTIONS :: PUTTUR

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SIDDHARTH GROUP OF INSTITUTIONS :: PUTTUR Siddharth Nagar, Narayanavanam Road 517583 QUESTION BANK (DESCRIPTIVE) Subject with Code : ET(16EE212) Year & Sem: II-B.

1 SIDDHARTH GROUP OF INSTITUTIONS :: PUTTUR Siddharth Nagar, Narayanavanam Road QUESTION BANK (DESCRIPTIVE) Subject with Code : ET(16EE212) Year & Sem: II-B.Tech & II-Sem UNIT I DC GENERATORS Course & Branch: B.Tech - ECE Regulation: AUTONOMOUS 1. Explain the constructional details of a D.C generator? [L2][CO1][10M] 2. Explain principle of operation of D.C generator? [L2][CO1][10M] 3. The resistance of the field circuit of a shunt wound D.C generator is 200 ohms. When the output of the generator is 100 KW. The terminal voltage is 500V and the generated E.M.f is 525V.Caluculate 1)Armature resistance 2)The value of generated E.M.f when the output is 60KW with a terminal voltage of 520V. [L4] [CO1][10M] 4. Short shunt compound generator delivers a load current of 30 A at 220 V and has armature, series field and shunt field resistances of 0.05 Ω, Ω and 200 Ω respectively. Calculate the induced e.m.f and the armature current. Allow 1.0 V per brush for contact drop. [L4][CO1][10M] 5. a) Describe the different types of generator. [L1][CO1][5M] b) Explain how voltage builds up in D.C shunt generator. [L2][CO1][5M] 6. Explain the characteristics of D.C generator? [L2][CO1][10M] 7. An 8-pole, lap-connected dc generator has 12 coils with 8 turns per coil. It is driven at 1500 rpm. If the flux per pole is 30 mwb, calculate the emf generated. If the machine is waveconnected, find the speed at which it is to be driven to generate the same emf as calculated with lap connection. [L4][CO1][10M] 8. The armature of a 4 pole, lap-wound D.c shunt generator has 120 slots with 4 conductors per slot.the flux per pole is 0.05 wb. the armature resistance is 0.05ohm.and shunt field resistance is 50 ohm. Find the speed of the machine when supplying 100Kw at a terminal voltage of 250V. [L4][CO1][10M] 9. a) Derive expression for generated E.M.f of a D.C generator? [L4][CO1][5M] b) Explain about applications of D.C generators. [L2][CO1][5M] 10. a) How will you find the direction of emf using Fleming s Right hand rule [L1][CO1][2M]

2 b) Define critical resistance of a D.C shunt generator? [L1][CO1][2M] c) Why does saturation curve starts from some value higher than zero? [L1][CO1][2M] d) Define armature reaction in D.C machines [L1][CO1][2M] e) Write down the E.M.F equation of D.C generator? [L1][CO1][2M] UNIT II DC MOTORS 1. a) Explain the working principle of D.C motor. [L2][CO2][5M] b) State the voltage and power equation of D.C motor explaining each term. [L1, L2][5M] 2. a) Derive the expression for electro magnetic torque. [L4][CO2][5M] b) Why a series motor cannot be started on no load? [L1][CO2][5M] 3. Explain the characteristics of D.C motor. [L2][CO2][10M] 4. a) A 250 VD.C series motor has armature and series field resistance of 0.25and 0.15 ohms respectively. a) caluculate the current for developing a torque of 80Nm at 1200 r.p.m b) Caluculate the percentage reduction in flux when the motor runs at 1800 r.p.m at half the current obtained in part (a). [L4][CO2][10M] 5. a) Explain types of D.C motor. [L2][CO2][5M] b) A 250V,4 pole D.C shunt motor has two circuit armature winding with 500 conductors. The armature circuit resistance is 0.25 ohms, field resistance is 125 ohm and the flux per pole is 0.02Wb.Find the speed and torque developed if the motor draws 14A from the mains. [L1, L4][CO2][5M] 6. Explain the operation of starter with neat sketch. [L2][CO2][10M] 7. Explain any two methods of speed control of D.C shunt motor. [L2][CO2][10M] 8. Explain swinburne s test for finding the efficiency of D.C machine. [L2][CO2][10M] 9. Explain various losses in D.c machine. [L2][CO2][10M] 10.a) Why swinburne s test is also called no load test? [L1][CO2][2M] b) Write the condition for maximum efficiency. [L1][CO2][2M] c) Which method is preferred when speed of D.C shunt motor is to be controlled above rated value. [L1][CO2][2M] d) What is back E.M.F?Explain the significance of back E.M.F? [L1][CO2][2M] e) State and explain Flemings left hand rule. [L1,L2][CO2][2M]

3 UNIT III SINGLE PHASE TRANSFORMERS 1. a) Explain the working principle of operation of single-phase transformer. [L2][CO3][5M] b) Explain why transformer rating will be given in KVA but not in KW. [L2][CO3][5M] 2. a) Derive the emf equation of a single-phase transformer. [L4][CO3][5M] b) A transformer with an output voltage of 4000V is supplied at 220V. If the secondary has 2000 turns, calculate the no. of primary turns. [L4][CO3][5M] 3. Explain the constructional details and types of single-phase transformers. [L2][CO3][10M] 4. Draw the equivalent circuit parameters of a single-phase transformer. [L1][CO3][10M] 5. a) Define efficiency and voltage regulation of a transformer. Show how the power factor affects both of them. [L1, L2][CO3][5M] b) Draw the phasor diagram for R and L load. [L1][CO3][5M] 6. a) Explain the various losses and derive the condition for maximum efficiency of a transformer. [L2][CO3][5M] b)a 10KVA,2000/400V single phase transformer has the following data R 1 =5 Ω, X 1 =12 Ω, R 2 =0.2 Ω, X 2 =0.48 Ω. Determine the secondary terminal voltage at full load,0.8 p.f lagging when the primary supply voltage is 2000V. [L4][CO3][5M] 7. a) Define regulation of transformer and also derive the condition for zero voltage regulation. [L1][CO3][5M] b) At 400V and 50 Hz the core loss of a transformer was found to be 2400W when the transformer is supplied at 200V, and 25 Hz, core loss is 800W. Calculate the hysteresis and eddy current losses at 400V 50Hz. [L4][CO3][5M] 8. Explain the O.C & S.C tests on single-phase transformer? Explain with neat circuit diagrams. [L2][CO3][10M] 9. A 20 KVA 2000/200V single phase transformer has primary resistance and Inductive reactance are 2Ω and 5Ω respectively the secondary resistance and inductive reactance are 0.04Ω and 0.2Ω respectively.calculate the voltage regulation i).at full-load 0.9 p.f lagging ii). at half load 0.8 p.f leading. [L4][CO3][10M] 10. a)why transformer rating is kva? [L1][CO3][2M] b) Define regulation of transformer? [L1][CO3][2M] c) What are properties of an ideal transformer? [L1][CO3][2M]

4 d) By which test iron loss and copper loss are measured? [L1][CO3][2M] e) Why DC-supply is not given to transformer? [L1][CO3][2M]. UNIT IV 3-PHASE INDUCTION MOTORS 1. Explain how rotating magnetic field produced in 3-phase induction motor. [L2][CO4][10M] 2. a) Derive torque equation of 3-phase induction motor under running condition. [L4][CO4][5M] b) Derive condition for maximum torque under running condition [L4][CO4][5M] 3. a)the stator of a 3-phase,4 pole induction motor is connected to a 50 HZ supply.the rotor runs 5M at 1455 r.p.m at full load. Determine i)synchronous speed ii) slip at full Load speed b) Derive condition for maximum torque under running condition. [L4][CO4][5M] 4. a) Explain the constructional details of 3phase induction motor. [L2][CO4][5M] b) If three phase induction motor with 6-poles runs at 970 r.p.m when connected to a 50HZ supply calculate i)percentage slip ii)frequency of rotor currents [L4][CO4][5M] 5. a) Explain the torque slip characteristics of 3-phase induction motor. [L2][CO4][5M] b) A 3-phase induction motor is wound for 4 poles and is supplied from 50 Hz system. Calculate: (i) the synchronous speed. (ii) the speed of the motor when slip is 4% and (iii) The rotor current frequency when the motor runs at 600 r.p.m. [L4][CO4][5M] 6. Explain the difference between slip ring and squirrel cage induction motor. [L2][CO4][10M] 7. a) Explain the principle of operation of 3-phase induction motor [L2][CO4][5M] b) A 3-phase 50HZ, 4 pole induction motor has a slip of 4% calculate a) Speed of the motor b) Frequency of rotor emf [L4][CO4][5M] 8. a) Derive the expression for the rotor e.m.f and rotor current of an induction motor [L4][CO4][5M] b) An 8 pole,3-phase,50 Hz induction motor has a rotor resistance of 0.025Ω/phase and a rotor stand still reactance of 0.1 Ω/phase. At what speed is the torque maximum? What proportional of maximum torque is the starting torque? [L4][CO4][5M] 9. a) Explain why the rotor of 3-phase induction motor can never attain synchronous speed [L2][CO4][5M] b) Explain the terms slip, slip speed, rotor frequency, rotor emf [L2][CO4][5M] 10. a)define slip and write its formula [L1][CO4][2M] b) Write the expression for maximum torque and starting torque [L1][CO4][2M] c) Define synchronous speed. [L1][CO4][2M]

5 d) List the advantages of wound rotor induction motor. [L1][CO4][2M] e) Why rotor bars are kept skewed. [L1][CO4][2M] UNIT V SYNCHRONOUS MACHINES 1. (a) Explain the constructional features of 3-Ø alternators with the help of neat diagrams. [L2][CO5] (b) Find the distribution factor for a 36 slot, 6 pole, single layer 3- phase winding. 2. (a) Explain the working principle of a three-phase alternator. [L2][CO5] (b) Calculate the EMF of a 4 pole, 3-Φ, star connected alternator running at 1500 rpm from the following data: flux per pole = 0.1 wb, total number of slots =48, conductors per slot (in two layers) = 4, coil span = Explain the Synchronous impedance method for calculating the regulation of a three phase alternator. [L2][CO5][10M] 4. Explain the theory of operation of a synchronous motor. [L2][CO5][10M] 5. Obtain the expression of EMF induced in an alternator. 6.(a) Explain the difference between salient pole and round rotor machines. [L2][CO5][5M] (b) A 3- phase 6-pole, 1000 rpm star connected alternator has 90 slots on the armature. Each slot has 8 conductors and the winding is short pitched by 3 slots. Find the induced EMF between lines, if the flux per pole is 75 mwb. 7. (a) Write the difference between salient and non- salient pole type of rotors [L2][CO5][5M]. (b) The coil span for the stotor winding of an alternator is (electrical). Find the pitch factor of the winding. 8. The stator of a three phase 16 pole alternator has 214 slots and there are 4 conductors per slot connected in 2 layers and the conductors of each phase are connected in series. If the speed of the alternator is375 rpm, calculate induced Emf per phase. Resultant flux in the air gap is 5 mwb per pole sinusoidally distributed. Assume the coil span as electrical 9. (a) A 4pole alternator has an armature with 25 slots and 8 conductors per slot and rotates at 1500 rpm and the flux per pole is 0.05 wb. Calculate the EMF generated, if winding factor is

6 0.96 and all the conductors in a phase are in series. [L4][CO5] (b) Sketch and explain the open circuit and short circuit characteristics of a synchronous machine. How voltage regulation can be calculated by the use of their results. 10. (a) Define voltage regulation of a alternator. (b) Define winding factor. (c) Write down the formula for distribution factor and pitch factor. (d) Define synchronous reactance. (e) Define leakage reactance in an alternator. Prepared by: Dr.B.Rajani / P.Chandra Sekhar.

2014 ELECTRICAL TECHNOLOGY

SET - 1 II B. Tech I Semester Regular Examinations, March 2014 ELECTRICAL TECHNOLOGY (Com. to ECE, EIE, BME) Time: 3 hours Max. Marks: 75 Answer any FIVE Questions All Questions carry Equal Marks ~~~~~~~~~~~~~~~~~~~~~~~~~~