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QUESTION BANK 2016 SIDDHARTH GROUP OF INSTITUTIONS :: PUTTUR Siddharth Nagar, Narayanavanam Road – 517583 QUESTION BANK (DESCRIPTIVE) Subject with Code : ET(15A02306) Course & Branch: B.Tech - ECE Year & Sem: II-B.Tech & I-Sem Regulation: R15 UNIT –I DC GENERATORS 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, 0.030 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. b) Explain how voltage builds up in D.C shunt generator. 6. Explain the characteristics of D.C generator? [L1][CO1][5M] [L2][CO1][5M] [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 45A at a terminal voltage of 250V. [L4][CO1][10M] 9. a) Derive expression for generated E.M.f of a D.C generator? b) Explain about applications of D.C generators. 10. a) How will you find the direction of emf using Fleming’s Right hand rule b) Define critical resistance of a D.C shunt generator? ELECTRICAL TECHNOLOGY [L4][CO1][5M] [L2][CO1][5M] [L1][CO1][2M] [L1][CO1][2M] Page 1 QUESTION BANK 2016 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] Prepared by: J.YUGANDHAR / V.VAISHNAVI. 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). 5. a) Explain types of D.C motor. [L4][CO2][10M] [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? e) State and explain Flemings left hand rule. [L1][CO2][2M] [L1,L2][CO2][2M] Prepared by: J.YUGANDHAR / V.VAISHNAVI. ELECTRICAL TECHNOLOGY Page 1 QUESTION BANK 2016 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. 2. a) Derive the emf equation of a single-phase transformer. [L2][CO3][5M] [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. b) Draw the phasor diagram for R and L load. [L1, L2][CO3][5M] [L1][CO3][5M] 6. a) Explain the various losses and derive the condition for maximum efficiency of a transformer. [L2][CO3][5M] b) The efficiency at unity power factor of 6600/384 V, 100 KVA, 50 Hz single-phase transformer is 98% both at full-load and at half full-load. The power factor on no load is 0.2 and the full-load regulation at a lagging power factor of 0.8 is 4%. Draw the equivalent circuit referred to LV side and insert all the values. [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. The maximum efficiency of 50 KVA transformer is 97.4% and occurs at 90% of the full-load. Calculate the efficiency of transformer at (i). Full-load 0.8 power factor lagging (ii). Half full-load 0.9 power factor. 10. a)Why transformer rating is kva? [L4][CO3][10M] [L1][CO3][2M] b) Define regulation of transformer? [L1][CO3][2M] c) What are properties of an ideal transformer? [L1][CO3][2M] d) By which test iron loss and copper loss are measured? [L1][CO3][2M] ELECTRICAL TECHNOLOGY Page 1 QUESTION BANK 2016 e) Why Dc-supply is not given to transformer? [L1][CO3][2M] Prepared by: J.YUGANDHAR / V.VAISHNAVI. 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. 4. a) Explain the constructional details of 3phase induction motor. [L4][CO4][5M] [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 5. a) Explain the torque slip characteristics of 3-phase induction motor. [L4][CO4][5M] [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. 6. Explain the difference between slip ring and squirrel cage induction motor. 7. a) Explain the principle of operation of 3-phase induction motor [L4][CO4][5M] [L2][CO4][10M] [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) A 5 h.p,230V,50 HZ induction motor has a rated full load speed of 950 r.p.m.The induced voltage per phase of rotor at stand still is 100V.calculate,i)number of poles and % full load speed ii)rotor induced voltage and its frequency at full load. [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 10. a)Define slip and write its formula [L2][CO4][5M] [L1][CO4][2M] b) Write the expression for maximum torque and starting torque [L1][CO4][2M] c) Define synchronous speed. [L1][CO4][2M] d) List the advantages of wound rotor induction motor. ELECTRICAL TECHNOLOGY [L1][CO4][2M] Page 1 QUESTION BANK 2016 e) Why rotor bars are kept skewed. [L1][CO4][2M] Prepared by: J.YUGANDHAR / V.VAISHNAVI. UNIT –V SYNCHRONOUS MACHINES 1. (a) Explain the constructional features of 3-Ø alternators with the help of neat diagrams. [L2][CO5] (b) A 16 pole, 3-Φ, alternator is coupled to a engine running at 375 rpm. It supplies an IM that has a full load speed of 1450 rpm. Find the slip & number of poles of the alternator. 2. (a) Explain the working principle of a three-phase alternator. [L4][CO5][10M] [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 = 1500. [L4][CO5][10M] 3. 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. [L4][CO5][10M] Obtain the expression of EMF induced in an alternator. 4. (a) Explain the difference between salient pole and round rotor machines. [L2][CO5] (b) An alternator is operating at no load has an induced EMF of 346.4 V/ph and a frequency of 60Hz. If the pole flux is decreased by 15% & the speed is increased by 6.8%; determine i. the induced EMF ii. frequency. [L4][CO5][10M] 7. (a) A 550 V, 55 KVA single phase alternator has an effective resistance of 0.2Ω. A field current of 10A produces an armature current of short circuit and an emf of 450 V of open circuit. calculate i)synchronous impedance and reactance ii) full load regulation when the power factor is 0.8 lagging. (b) A three phase star connected alternator driven at 900 rpm is required to generate a line voltage of 460V at 60 Hz on open circuit. The slots has 2 slots/pole/phase and 4 conductors/slot. Calculate i) no. of poles ii) the useful flux per pole. [L4][CO5][10M] 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 ELECTRICAL TECHNOLOGY Page 1 QUESTION BANK 2016 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 1500 electrical [L4][CO5][10M] 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 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. [L4][CO5][10M] [L1][CO5][2M] (b) Define winding factor. [L1][CO5][2M] (c) Write down the formula for distribution factor and pitch factor. [L1][CO5][2M] (d) Define synchronous reactance. [L1][CO5][2M] (e) Define leakage reactance in an alternator. [L1][CO5][2M] Prepared by: J.YUGANDHAR / V.VAISHNAVI. ELECTRICAL TECHNOLOGY Page 1 QUESTION BANK 2016 SIDDHARTH GROUP OF INSTITUTIONS :: PUTTUR Siddharth Nagar, Narayanavanam Road – 517583 QUESTION BANK (OBJECTIVE) Subject with Code : ET(15A02306) Course & Branch: B.Tech -ECE Year & Sem: II-B.Tech & I-Sem Regulation: R15 UNIT – I DC GENERATORS 1. The D.C. Generator works on the principle of [ ] A) Flemings left hand rule B) Ampere’s law C) Lenz’s law D)Faradays laws of Electromagnetic induction 2. Laminated yoke in a dc generator reduces [ ] A) Iron losses B) Temperature rise C) Speed regulation D) Sparking on load 3. The EMF generated in a D.C. Generator depends on [ ] A) No. of turns in the armature B) Flux / pole C) Speed D) All 4. The load current and field current of a DC shunt generator are 50A and5A respectively. Its armature current is________ [ ] A) 50A B) 55A C) 45A D) 40A 5. In a d.c shunt generator the field winding is connected in................. to the armature. [ ] A) parallel B)series C) both A & B D) none of the above 6. The current relation in dc separately excited generator is A) If= Ia B) IL=Ia C) Ia=-IL D) Ia=0 7. A D.C. Generator is a machine that converts [ ] [ ] A) Electrical energy into Mechanical energy B) Electrical energy into Electrical energy C) Mechanical energy into Mechanical energy D)Mechanical energy into Electrical energy 8. The brush voltage drop in d.c machine is about ……. A) 0.1V B) 2V C) 10V D) 20V 9. The purpose of commutator in a d.c. generator is to_______ A) reduce sparking at brushes ELECTRICAL TECHNOLOGY [ ] [ ] B) convert the induced a.c. into d.c. Page 1 QUESTION BANK 2016 C) increase output voltage D) provide smoother output 10. Which of the following DC Generators is suitable for charging Batteries? A) Shunt generator B) Series Generator C) Differentially compounded Generator D) None 11. The current relation in dc compound generator is A) Ia=Ish+IL B) Ia=Ish C) Ia=IL D) Ia=0 [ ] [ ] [ ] [ ] [ ] [ ] 12. Residual magnetism is essential in the field electromagnets for building up of voltage of all types of d.c generators except................. A) shunt B) compound C) separately excited D) series 13. The critical resistance of the D.C. generator is the resistance of A) armature B) field C) load D) brushes 14. The armature of a d.c. machine is made of________ A) wrought iron B) silicon steel C) cast steel D) soft iron 15. A separately excited d.c generator is normally not used because A) It is costly B) Separate d.c source is required for field circuit C) Terminal voltage rises with increase in load D) None of these 16. The purpose of brush in a d.c. machine is to________ A) prevent sparking B) clean the commutator C) collect current from the commutator D) none of these 17. For short shunt compound generator, which of the following equation is correct? A) IA=ISH+IL B) IL=IA+ISH C) IA=ISE D) All 18. The induced emf in the armature of d.c generator is ……… A) Statically induced emf B) Dynamically induced emf C) Self induced emf` D) None 19. If residual magnetism is present in a dc generator ,the induced emf at zero will be A) zero B)small C)the same as rated voltage D)high 20. Function of yoke is A) To provide mechanical support to the poles B) Reduce losses C) carry current D) All ELECTRICAL TECHNOLOGY [ ] [ ] [ ] [ ] [ ] Page 1 QUESTION BANK 2016 21. For a given d.c generator, the magnitude of generated voltage depends on ______ [ ] 22. A 200V DC Generator has a shunt field resistance of 200ohms. Its field current is___ [ ] A) Flux only B) Speed only C) No. of poles only D) All A) 1A B) 2A C) 3A D) 4A 23. Which of the following machine converts mechanical energy into electrical energy A)Motor B)Generator C)Both D)None 24. Classification of D.C. Generators are depending on the method in which [ ] [ ] [ ] A) field windings are connected to the armature circuit B) the armature circuit is connected to the load C) the field windings are connected to the load D) none of the above 25. The current relation in dc series generator is A) Ise= Ia +IL B) Il=Ise- Ia C) Ia=IL D) All 26. The Commutator segments of a D.C. Machine are insulated from each other by a thin layer 0f _________ A) Bakelite B) PVC C) Hard rubber D) Mica 27. Copper brushes in D.C. machine are used [ ] [ ] [ ] [ ] [ ] A) where low voltage and high currents are involved B) where high voltage and low currents are involved C) in both of the above cases D) none of the above cases 28. Brushes in D.C machines are made of A) Carbon B) Soft Copper C) Hard Copper D) all the above 29. Magnetic field in a D.C generator is produced by A) Electro magnets B) Permanent magnets C) both (a) and (b) D) None 30. In D.C. generator Lap winding is used for A) high voltage , high current ELECTRICAL TECHNOLOGY B) low voltage , high current Page 1 QUESTION BANK 2016 C) high voltage , low current D) low voltage , low current 31. Which of the following D.C. generator cannot build up on open-circuit? A) Shunt B) Series C) Short Shunt D) Long Shunt 32. The External Characteristics of a D.C. generator gives the relation between A) V and IL B) E and Ia C) Eo and If D) V and If 33. The Internal Characteristics of a D.C. generator gives the relation between A) V and IL B) E and Ia C) Eo and If D) V and If 34. The O.C. Characteristics of a D.C. generator gives the relation between A) V and IL B) E and Ia C) Eo and If D) V and If 35. Which of the following D.C. generator is used for arc welding A) Shunt B) Series C) cumulative compound D) Differential compound 36. Which of the following D.C. generator is used as Boosters A) Shunt B) Series C) cumulative compound D) Differential compound 37. In D.C. generator Wave winding is used for A) high voltage , high current B) low voltage , high current C) high voltage , low current D) low voltage , low current 38. Bearings in a D.C. machine is used to A) reduce the friction B) carry current C) reduce the losses D) none 39. In cumulative compound D.C. generator the total flux ØT= A) ØSh+ ØSe B) ØSh- ØSe C) ØSh= ØSe D) none 40. In Differential compound D.C. generator the total flux ØT= A) ØSh+ ØSe B) ØSh- ØSe C) ØSh= ØSe D) none [ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ] Prepared by: J.YUGANDHAR / V.VAISHNAVI. ELECTRICAL TECHNOLOGY Page 1 QUESTION BANK 2016 UNIT –II DC MOTORS 1.The purpose of commutator in a d.c.Motor is to________ A) convert the induced d.c. into a.c B) reduce sparking at brushes C) increase output voltage D) provide smoother output 2. Which dc motor is generally preferred for cranes A) differentially compound motor B)shunt motor C) cumulatively compound motor D) series motor 3. For short shunt compound motor, which of the following equation is correct? A) IA=ISH -IL B) IL=IA+ISH C) IA=ISE D) All 4. Which motor should not be started on no-load A) differentially compound motor B)shunt motor C)cumulatively compound motor D) series motor 5. A D.C.Motor is a machine that converts [ ] [ ] [ ] [ ] [ ] [ ] [ ] A) Electrical energy into Mechanical energy B) Electrical energy into Electrical energy C) Mechanical energy into Mechanical energy D) Mechanicalenergy into Electrical energy 6. The load current and field current of a DC shunt motor are 40A and 4A respectively. Its armature current is________ A) 44A B)36A C) 1A D) 40A 7. In a d.c series motor the field winding is connected in................. to the armature. A) series B) parallel C) both A & B D) none of the above ELECTRICAL TECHNOLOGY Page 1 QUESTION BANK 2016 8. The EMF generated in a D.C. Motor is called as A)Back emf B) Generated emf C) Both(A)&(B) D) None 9. Which of the following DC Motor is used in traction A) Shunt Motor B) Series Motor C) Differentially compounded Motor D) None 10.The current relation in dc Series Motor is [ ] [ ] [ A) Ise= Ia +IL B) Il=Ise- Ia C) Ia=IL= Ise D) All 11. The condition for maximum power in case of dc motor is A)backemf=2*supply voltage B)back emf=1/2* supply voltage C)Both D)None [ ] ] 12. Which of the following rule/law can be used to determine the direction of rotation of dc motor [ ] A) Lenz’s law B) Faraday’s law C) Coulomb’s law D) Fleming’s left hand rule 13.Which of the following is a electrical machine A)Motor B)Generator C)Both D)None 14.The D.C.Motor works on the principle of [ ] [ ] A) Flemings left hand rule B) Ampere’s law C) Lenz’s law D) Faradays laws of Electromagnetic induction 15. A 100V DC Motor has a shunt field resistance of 100ohms. Its field current is_____ [ A) 1A B) 2A C) 3A D) 4A 16.The current relation in dc compound Motor is [ A) Ish= Ia +IL B) Ish=IL- Ia C) Ia=IL D) Ia=0 ELECTRICAL TECHNOLOGY ] ] Page 1 QUESTION BANK 2016 17.The speed of a dc motor can be controlled by varying A) Its flux per pole B) resistance of the armature circuit C) applied voltage D) all of the above 18. The direction of D.C.series motor can be changed by A) interchanging the Supply terminals B) interchanging the Field terminals C) Either (a) & (b) D) None [ ] [ ] 19. The current drawn by a 120V D.C. motor of armature resistance 0.5Ω and back emf 110V is ______ ampere [ ] A) 20 B)240 C)220 D)5 20. The shaft torque of a D.C. motor is less than the armature torque because of __losses [ A) copper B) mechanical C) iron D) rotational 21. Which of the following motor is used in centrifugal pumps, Blowers and fans ] [ ] [ ] [ ] 24. In D.C. series motor the electromagnetic torque developed is directly proportional to [ ] A) differentially compound motor B)shunt motor C)cumulatively compound motor D) series motor 22. Which of the following motor is used in Traction, Trolley and cars A) differentially compound motor B)shunt motor C)cumulatively compound motor D) series motor 23. Which of the following motor is used in Elevators, Shears and Punches A) differentially compound motor B)shunt motor C)cumulatively compound motor D) series motor A) Ia B) Ia2 C) 1/Ia D) 1/Ia2 25. In D.C. shunt motor the electromagnetic torque developed is directly proportional to [ A) Ia B) Ia2 C) 1/Ia D) 1/Ia2 ELECTRICAL TECHNOLOGY ] Page 1 QUESTION BANK 2016 26. The Ta/Ia graph of a D.C. series motor is [ ] A) parabola from no-load to over load B) straight line throughout C) parabola throughout D) parabola upto full-load and a straight line at over loads 27. Starters in D.C. motor is used to [ A) to limit starting current to a safe value B) to limit voltage C) to limit speed D) none ] 28. The most economical method of finding no-load losses of a large D.C.shunt motor is ---Test A) Hopkinson’s test B) Swinburne’s test C) retardation D) Field’s 29. Ward-Leonard system of speed control is not recommended for A) wide speed range B) constant speed operation C) frequent motor reversals D) very low speeds 30. In case of D.C. motor connected across A.C. mains A) the motor will burn [ ] [ ] [ ] B) the motor will run at rated speed C) the motor will run at corresponding synchronous speed D) the motor will run at low speed 31. A three point starter is considered as suitable for [ ] A) Shunt motors B) Shunt as well as compound motors C) Shunt, compound and series motors D) all D.C. motors 32. A 220V shunt motor develops a torque of 54 N-m at armature current of 10A. The torque produced when armature current is 20A,is [ ] A) 54 N-m B) 81 N-m C) 108 N-m D) None of the above 33. A D.C. motor develops a torque of 200 N-m at 25 rps. At 20 rps it will develop a torque of ----N-m [ A) 200 B) 160 C) 250 D) 128 ELECTRICAL TECHNOLOGY ] Page 1 QUESTION BANK 2016 34. The speed of a D.C motor is directly proportional to A) Eb/Ø B) Eb* Ø C) Eb2 D) none 35. Which one is the Direct test of D.C motor A) Brake test B) Swinburne’s test C) Hopkinson’s test D) none 36. At noload condition of D.C motor the armature torque Ta = A) TL B) Tsh + TL C) Tsh D) none 37. Which one is the In - Direct test of D.C motor A) Brake test B) Swinburne’s test C) Both a & b D) none 38. The _____ torque which is used to do the useful work A) shaft torque B) Loss torque C) armature torque D) none 39. The _____ torque which is used to overcome the losses A) shaft torque B) Loss torque C) armature torque D) none 40. Turning or Twisting force about an axis is known as A) shaft torque B) Loss torque C) torque D) none [ ] [ ] [ ] [ ] [ ] [ ] [ ] Prepared by: J.YUGANDHAR / V.VAISHNAVI ELECTRICAL TECHNOLOGY Page 1 QUESTION BANK 2016 UNIT –III SINGLE PHASE TRANSFORMERS 1. The two windings of a transformer is A) conductively linked B) inductively linked C) not linked at all D) electrically linked. 2. The efficiency of a transformer is mainly dependent on A) core losses. B) copper losses. C) stray losses. D) dielectric losses. 3. In a transformer the voltage regulation will be zero when it operates at A) unity p.f. B) leading p.f. C) lagging p.f. D) Zero p.f. leading 4. An ideal transformer is one which A) has more losses C) has no losses and leakage reactance B) 750 C) 7.5 D) 0.13 7. The main purpose of performing open-circuit test on a transformer is to measure its A) Copper loss B) total loss C) core loss D) heat loss 8. Transfer of electrical power from primary to secondary in a transformer takes place A) Electrically B) Electromagnetically [ ] [ ] [ ] [ ] [ ] [ ] D) none of the above 9. The path of a magnetic flux in a transformer should have A) high resistance B) high reluctance ELECTRICAL TECHNOLOGY ] D) copper loss A) 75 C) low resistance [ D) All the above 6. To step 120 V ac up to 900 V ac, the turn’s ratio must be C) magnetically ] B) does not work 5. Which of the following is minimized by laminating the core of a transformer? A) Eddy current loss B) Hysteresis loss C) Heat loss [ [ ] D) low reluctance Page 1 QUESTION BANK 2016 10. The efficiency of a transformer will be maximum when [ A) copper losses = hysteresis losses B) hysteresis losses = eddy current losses C) eddy current losses = copper losses D) copper losses = iron losses ] 11. Which of the following is not a part of transformer installation? [ ] [ ] A) Conservator B) Breather C) Buchholz relay D) Exciter 12. A transformer cannot raise or lower the voltage of a D.C. supply because A) there is no need to change the D.C. voltage B) a D.C. circuit has more losses C) Faraday's laws of electromagnetic induction are not valid since the rate of change of flux is zero D) none of the above 13. A transformer is so designed that primary and secondary have……………… A) high leakage reactance B) tight magnetic coupling C) large resistance [ ] [ ] B) amperes D) kVA 17. When load on a transformer is decreased ___________ loss is decreased A) Eddy current B) hysteresis C) friction D)Copper 18. Which of the following does not change in transformer A) Voltage B) Current C) Power D) Frequency 19. Silicon steel used for laminating the core to reduce A) Hysteresis loss B) Eddy current loss C) Copper loss D) All ELECTRICAL TECHNOLOGY ] D) 25 percent 16. The transformer ratings are usually expressed in terms of A) volts C) kW [ D) Secondary winding 15. Efficiency of a power transformer is of the order of A) 100 percent B) 98 percent C) 50 percent ] D)good electric coupling 14. Which winding in a transformer has more number of turns? A) Low voltage winding B) High voltage winding C) Primary winding [ [ ] [ ] [ ] Page 1 QUESTION BANK 2016 20. Eddy current loss will depend on A) Frequency B) flux density C) thickness D) All 21. Short circuit test on transformer is conducted to determine A) Current loss B) Copper loss C) Voltage loss D) Iron loss 22. Which of the following type transformer is wide in use A) Shell type transformer C) Both A) Eddy current loss B) Hysteresis loss C) Windage loss D) Copper loss 25. Sumpner’s test is conducted on transformers to determine A) Temperature B) Stray losses C) All day efficiency D) None 26. The highest level voltage of generation in india is A) 33KV B) 11KV C) 132KV D) All 27. Which of the following is step up transformer A) If K<1 B) If K>1 C) If K=1 D) All 28. Which of the following is step down transformer A) If K<1 B) If K>1 C) If K=1 D) All 29.Transformation ratio is denoted by a letter of A) V B) I C) K D) P 30. Hysteresis loss will depends on ELECTRICAL TECHNOLOGY ] [ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ] B) Core type transformer D)None 24. Which loss is not common between a transformer and rotating machine A) f2 [ B) f3 Page 1 QUESTION BANK 2016 C) f D) f1.6 31. Total core loss is also called as -------------? A) Eddy current loss B) Hysteresis loss C) Magnetic loss D) Copper loss 32. Which of the following are variable losses? A) Eddy current loss B) Hysteresis loss C) shunt field loss D) armature copper loss 33. The basic function of a transformer is to change A) the power level B) the power factor C) the level of the voltage D) the frequency [ ] [ ] [ ] 34. R1 is the resistance of the primary winding of the transformer. The turn ratio in terms of primary to secondary is K. Then the equivalent resistance of the primary referred to secondary is [ A) R1/K B) K²R1 C) R1/K² D) K*R1 35. Voltage regulation of transformer is given by A) (E2 - V2) / V2 B) (E2 - V2) / E2 C) (V2 - E2) / V2 D) (V2 - E2) / E2 36. Transformer oil is used as A) an insulator B) a coolant C) both 1 and 2 D) inert medium 37. Conservator tank is used A) to take up the expansion of oil due to temperature rise B) to act as an oil storage C) for better cooling of transformer D) none of the above 38. In a transformer which of the following losses are zero ? A) iron loss B) copper loss C) mechanical loss D) all of the above 39. Breather is provided in a transformer to A) absorb moisture of air during breathing ] [ ] [ ] [ ] [ ] [ ] B) provide cold air in transformer C) absorb moisture from air entering in transformer D) filter the transformer oil ELECTRICAL TECHNOLOGY Page 1 QUESTION BANK 2016 40. The leakage flux in a transformer depends upon [ A) the applied voltage B) the load current C) the frequency D) the mutual flux ] Prepared by: J.YUGANDHAR / V.VAISHNAVI. UNIT –IV 3-PHASE INDUCTION MOTORS 1. The frequency of the rotor current in a 3 phase 50 Hz, 4 pole induction motor at full load [ speed is about A) 50 Hz. B) 20 Hz. C) 2 Hz. D) Zero. ] 2. In a 3 – phase induction motor running at slip ‘s’ the mechanical power developed in terms of air gap power Pg is [ ] A) (s -1)Pg . B) Pg/ (s -1). C) (1-S) Pg. D) s Pg . 3. The rotor frequency for a 3 phase 1000 RPM 6 pole induction motor with a slip of 0.04 is________Hz [ ] A) 8 B) 4 C) 6 D) 2 4. The frame of an induction motor is usually made of A) Silicon steel B) cast iron C) aluminum D) bronze 5. The efficiency of an induction motor can be expected to be nearly A) 60 to 90% B) 80 to 90% C) 95 to 98% [ ] [ ] [ ] D) none 7. If any two phases for an induction motor are interchanged ELECTRICAL TECHNOLOGY ] D) 99% 6. The number of slip rings on a squirrel cage induction motor is usually A) two B) three C) four [ Page 1 QUESTION BANK 2016 A) The motor will run in reverse direction B) the motor will run at reduced speed C) the motor will not run D) the motor will burn 8. An induction motor is [ ] [ ] 10. In three-phase induction motors sometimes copper bars are placed deep in the rotor to [ ] A) Self-starting with zero torque B) self-starting with high torque C) Self-starting with low torque D) non self-starting 9. A 3-phase slip ring motor has A) double cage rotor B) wound rotor C) short-circuited rotor D) any of the above A)Improve starting torque B)reduce copper losses C)improve efficiency D)improve power factor 11. The rotor of an induction motor runs at A) Synchronous speed B) below synchronous speed C) above synchronous speed D) any of the above 12. The shaft of an induction motor is made of A) Stiff B) flexible C) hollow D) any of the above [ ] [ ] 13. A 3-phase 440 V, 50 Hz induction motor has 4% slip. The frequency of rotor e.m.f will be A) 200 Hz B) 50 Hz C) 2 Hz D) 0.2 Hz 14. The starting torque of a squirrel-cage induction motor is [ ] [ ] A) Low B) negligible C) same as full-load torque D) slightly more than full-load torque 15. For which motor the speed can be controlled from rotor side? A)Squirrel-cage induction motor B) Slip-ring induction motor C) Both A and B D) None 16. The maximum torque in an induction motor depends on ELECTRICAL TECHNOLOGY [ ] [ ] Page 1 QUESTION BANK 2016 A) Frequency B) rotor inductive reactance C) square of supply voltage D) all of the above 17. Which type of bearing is provided in small induction motors to support the rotor shaft[ A) Ball bearings B) Cast iron bearings C) Bush bearings D) None of the above ] 18. The shape of the torque/slip curve of induction motor is A) parabola B) hyperbola C) rectangular parabola D) straight line [ ] 19. In an induction motor, no-load the slip is generally A) less than 1% B) 1.5% [ ] C) 2% D) 4% 20. In Ns is the synchronous speed and s the slip, then actual running speed of an induction motor will be [ ] A) Ns B) S*Ns C) (l-S)Ns 21. In case of the induction motors the torque is A) inversely proportional to (slip) 2 C) Inversely proportional to slip D) (Ns-l)S B) directly proportional to (slip) [ ] [ ] [ ] [ ] 2 D) directly proportional to slip 22. Rotor rheostat control method of speed control is used for A) squirrel-cage induction motors only B) slip ring induction motors only C) both A & B D) none 23. In three-phase squirrel-cage induction motors A) Rotor conductor ends are short-circuited through slip rings B) rotor conductors are short-circuited through end rings C) rotor conductors are kept open D) rotor conductors are connected to insulation 24. If a 3-phase supply is given to the stator and rotor is short circuited rotor will move A) In the opposite direction as the direction of the rotating field B) in the same direction as the direction of the field C) in any direction depending upon phase sequence of supply D) none ELECTRICAL TECHNOLOGY Page 1 QUESTION BANK 2016 25. The stating torque of the slip ring induction motor can be increased by adding _____ to the rotor [ ] A) external inductance B) external resistance C)external capacitance D)both resistance and inductance 26. Slip ring motor is preferred over squirrel cage induction motor where A) high starting torque is required C) heavy pull out torque is required [ ] B) load torque is heavy D) all of the above 27. In squirrel cage induction motors, the rotor slots are usually given slight skew in order to [ ] [ ] [ ] [ ] 31. In a three-phase induction motor, the number of poles in the rotor winding is always [ ] A) Reduce windage losses C) reduce accumulation of dirt and dust 28. Slip rings are usually made of A) copper C) phospor bronze B) reduce eddy currents D) reduce magnetic hum B) carbon D) aluminium 29. An induction motor with 1000 r.p.m. speed will have A) 8 poles B) 6 poles C) 4 poles D) 2 poles 30. An induction motor is identical to A) D.C. compound motor B) D.C. series motor C) synchronous motor D) asynchronous motor A) zero B) more than the number of poles in stator C) less than number of poles in stator D) equal to number of poles in stator 32. The speed of a squirrel-cage induction motor can be controlled by all of the following except A) changing supply frequency B) changing number of poles C) changing winding resistance D) reducing supply voltage 33. The low power factor of induction motor is due to A) rotor leakage reactance B) stator reactance ELECTRICAL TECHNOLOGY [ ] [ ] Page 1 QUESTION BANK 2016 C) the reactive lagging magnetizing current necessary to generate the magnetic flux D) all of the above 34. A squirrel cage induction motor is not selected when [ ] [ ] [ ] A) initial cost is the main consideration B) maintenance cost is to be kept low C) higher starting torque is the main consideration D) all above considerations are involved 35. The power factor of a squirrel cage induction motor is A) Low at light load only B) Low at heavy load only C) Low at light and heavy load both D) Low at rated load only 36. The slip of an induction motor normally does not depend on A) rotor speed B) synchronous speed C) shaft torque D) core-loss component 37. Find the number of poles required, when the frequency is 50Hz and speed of the motor is 500 rpm? [ ] A) 5 B) 10 C) 12 D) 24 38. Which of the following induction motor has the highest starting torque? A) Squirrel cage induction motor B) slip ring induction motor C) same in both induction motors D) none of the above 39. A 4 pole 50 Hz induction motor is running at 1470 rpm. What is the slip value? A) 0.2 B) 0.02 C) 0.04 [ ] [ ] [ ] D) 0.4 40. Which of the following motors is /are widely used? A) Squirrel cage induction motor B) slip ring induction motor C) either of these D) none of the above Prepared by: J.YUGANDHAR / V.VAISHNAVI. UNIT –V SYNCHRONOUS MACHINES ELECTRICAL TECHNOLOGY Page 1 QUESTION BANK 2016 1. The magnitude of the three voltage drops in an alternator due to armature resistance, leakage reactance and armature reaction is solely determined by [ A) load current, Ia B) p.f of the load C) Whether it is a lagging or leading p.f load D) field construction of the alternator 2. The effect of armature reaction for an alternator for zero power factor lagging [ A) cross magnetizing B) wholly demagnetizing C) non- effective D) magnetizing 3. At leading p.f the armature flux in an alternator ____________ the rotor flux. [ A) opposes B) aids C) distorts D) does not affect 4. The power factor of an alternator is determined by its [ A) speed B) load C) excitation D) prime mover 5. What parameter of load influences the armature reaction of an alternator? [ A) power B) Voltage 6. 7. 8. 9. C) power factor of load D)none The effect of armature reaction for an alternator for power factor leading ____ A) magnetizing B) wholly demagnetizing C) non-effective D) distorting When the load on an alternator is varied, its terminal voltage is also vary due to A) armature resistance B) armature leakage reactance C) on account of armature reaction vary D) all of the above Zero power factor method of an alternator is used to find its A) efficiency B) voltage regulation C) armature resistance D) synchronous impedance Under no-load condition, power drawn by the prime mover of an alternator goes to A) produce induced emf in armature winding B) meet no- load losses C) produce power in the armature D) meet cu losses both in armature and rotor windings ] ] ] ] ] [ ] [ ] [ ] [ ] 10. As load p.f of an alternator becomes more leading, the value of generated voltage required to give rated terminal voltage [ ] A) increases B) remains unchanged C) decreases D) varies with rotor speed 11. The voltage regulation of an alternator having 0.75 leading p.f load, no-load induced emf of 2400V and rated terminal voltage of 3000V is __________ percent [ ] A) 20 B) -20 C) 150 D) -26.7 ELECTRICAL TECHNOLOGY Page 1 QUESTION BANK 2016 12. Synchronous impedance method is known as A) MMF method C) ASA method [ ] [ ] [ ] B) EMF method D) none 13. Zero power factor method another name is _____________ A) Potier method B) MMF method C) EMF method D) ASA method 14. Ampere Turn method is also named as _____________ A) Potier method B) MMF method C) EMF method D) ASA method 15. What are the characteristics required for potier method of computing voltage regulation [ A) Open circuit characteristic ] B) Short circuit characteristic C) Zero power factor full load voltage characteristic D) all of the above 16. Which quantities are usually determined using the zero-power factor characteristics of a synchronous machine? [ ] A) leakage reactance drop B) voltage drop due to armature reaction C) armature reaction ampere turns D) all of the above 17. Which method of regulation is called pessimistic method? A) EMF method B) MMF method C) Potier method [ ] D) none 18. When a synchronous motor is running at synchronous speed, the damper winding produces [ ] A)damping torque B) eddy current torque C) torque aiding the developed torque D) no torque 19. Which of the following relation is correct? [ A) Xd = Xq B) Xd < Xq C) Xd > Xq D) None ELECTRICAL TECHNOLOGY ] Page 1 QUESTION BANK 2016 20. If the excitation is increased, the power factor is A) unity power factor B) leading power factor C) lagging power factor D) none of the above 21. If the excitation is reduced, the power factor is A) unity power factor B) leading power factor C) lagging power factor D) none of the above 22. Maximum power developed is depends on A) voltage B) reactance C) both 1and 2 D) load angle 23. Field winding of an alternator is A) DC excited B) AC excited C) both(A) & (B) D) none 24. Regulation of an alternator supplying resistive or inductive load is: A) always positive B) always negative C) either of the above or zero [ ] [ ] [ ] [ ] [ ] [ ] D) none 25. Regulation of an alternator supplying capacitive load is: A) always positive B) always negative C) either of the above or zero D) none 26. Which kind of rotor is most suitable for turbo alternators which are designed to run at high speed [ ] A) Salient pole type B) Non-salient pole type C) Both (A) and (B) above D) None of the above 27. The frequency of voltage generated by an alternator having 4 poles and rotating at 1800 rpm is [ ] A) 60 Hz B) 7200 Hz C) 120 Hz D) 450 Hz 28. The number of electrical degrees passed through in one revolution of a four pole alternator is [ ] A) 360: B) 720 C) 1080 ELECTRICAL TECHNOLOGY D) 2160 Page 1 QUESTION BANK 2016 29. A 10 pole AC generator rotates at 1200 rpm. The frequency of AC voltage in cycles per second will be [ ] A)120 B)110 C) 100 D) 50 30. The rating of an alternator is usually expressed in terms of A) full load current B) rated voltage C) KVA D) KW 31. If an alternator is operating at leading P.F A) alternator is over excited B) alternator is under exciter C) torque angle is negative D) none 32. The salient pole type rotors have A) larger diameter B) smaller axial length C) larger axial length D) both A & B [ ] [ ] [ ] 33. The synchronous speed of an alternator having 2 poles and operating on a 50Hz supply is[ A) 1500rpm B) 1800rpm C) 3000rpm D) 6000rpm 34. The power factor of an alternator depends on [ A) Load B) Speed of rotor C) Core losses D) Armature losses ] ] 35. The number of electrical degrees passed through in one revolution of a two pole alternator is [ A)3600 B)7200 C) 10800 D)21600 ] 36. An electric motor in which the both the rotor and stator fields rotates with the same speed is called a _____ motor [ ] A) D.C B) charge C) synchronous D) universal 37. The direction of rotation of a synchronous motor can be reversed by reversing A) current to the field winding B) supply phase sequence C) polarity of rotor poles D) none of the above ELECTRICAL TECHNOLOGY [ ] Page 1 QUESTION BANK 2016 38. In a synchronous motor,the magnitude of stator back e.m.f Eg depends on A) speed of the motor B) load on the motor C) both the speed and rotor flux D) D.C. excitation only 39. In a synchronous motor, the rotor Cu losses are met by A) motor input B) armature input C) supply lines D) D.C source [ ] [ ] 40. A synchronous motor running with normal excitation adjusts to load increases essentially by increase in its [ ] A) power factor B) torque angle C) back e.m.f D) armature current Prepared by: J.YUGANDHAR / V.VAISHNAVI. ELECTRICAL TECHNOLOGY Page 1