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Set No. 1 II B.Tech I Semester Regular Examinations, November 2007 ELECTRICAL ENGINEERING ( Common to Mechanical Engineering, Chemical Engineering, Mechatronics, Metallurgy & Material Technology, Production Engineering and Automobile Engineering) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks ⋆⋆⋆⋆⋆ 1. Derive the formulas used for star to delta and Delta to star. [16] 2. 2. (a) Explain the principle behind the generation of 3-φ e.m.f and phase sequence (b) Three inductive coils, each with a resistance of 15 ohms and an inductance of 0.03 H are connected i. in star and ii. in delta, to 3-φ 400 V, 50 Hz supply. Calculate for each of the above case i. phase current and line current and ii. total power absorbed. [8+8] 3. (a) A 4 pole d.c. generator has a wave wound armature with 792 conductors. The flux/pole is 0.0121Wb. Determine the speed at which it should be run to generate 240V on no load. (b) A d.c. generator generates an emf of 520V. It has 2000 armature conductors, flux/pole of 0.013Wb, speed of 1200rpm and the armature winding has 4 parallel paths. Find the number of poles. (c) When driven at 1000rpm with a flux/pole of 0.02Wb, a d.c. generator has an emf of 200V. If the speed is increased to 1100rpm and at the same time the flux/pole is reduced to 0.019Wb/pole, what is the induced emf? [5+5+6] 4. (a) Why is the speed of a shunt motor practically constant? (b) Draw the characteristics of shunt and series motors. [4+12] 5. (a) A 1-phase transformer working at 0.8 power factor has an efficiency of 94% at both three forth full load and at full load of 600 KW. Determine the efficiency at half full load. (b) 10 KVA transformer has a turns ratio of 500/250V. The primary winding is connected to 1500V, 50Hz, supply. Calculate i. The secondary voltage on open circuit.

ii. Primary and secondary full load currents iii. The maximum flux in the core. [8+8]

6. (a) How do you classify the induction motors. Give the constructional details of them. (b) Define slip and give an account of the quantities which vary with slip. [8+8] 7. (a) Explain the construction of salient pole Alternator? (b) A 3-phase star connected alternator has an open circuit line voltage of 6599 volts. The armature resistance and synchronous reactance are 0.6 ohms and 6 ohms per phase, respectively. Find terminal voltage and voltage regulation if load current 180A at power factor of i. 0.9 lagging ii. 0.8 leading. [8+8] 8. (a) Sketch and describe the construction of a moving coil ammeter and give the principle of operation. (b) A moving coil instrument gives full scale deflection with 15mA and has a resistance of 5. Calculate the resistance of the necessary components in order that the instrument may be used as i. a 2A - Ammeter ii. a 100V voltmeter. [8+8] ⋆⋆⋆⋆⋆ 2 of 2

Set No. 2

II B.Tech I Semester Regular Examinations, November 2007 ELECTRICAL ENGINEERING ( Common to Mechanical Engineering, Chemical Engineering, Mechatronics, Metallurgy & Material Technology, Production Engineering and Automobile Engineering) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks ⋆⋆⋆⋆⋆ 1. (a) Explain about “Dot convention” in the case of mutually coupled circuits. (b) Explain briefly “How you can use mutual inductance principle to the trans-

former”. [8+8] 2. (a) Derive an expression for the instantaneous value of alternating current in terms of its max.value, angular velocity, and time. (b) An alternating current is represented by the following equation i = 100 Sin (100 π t) How long will it take for the current to attain values of 20,30, 50, 80 and 100A? (c) Explain the terms: frequency, cycle, and period time in connection with a.c. Circuits. [6+5+5] 3. (a) A four pole dc generator runs at 900rpm and is lap wound and has a useful flux per pole of 0.07wb. The armature windings consists of 220turns each of 0.004 ohms resistance. Calculate the terminal voltage when running at 900rpm if the armature current is 50A. (b) A four pole lap wound generator has 56 coils with 6 turns per coil. The speed is 1150 rpm. What must be the flux per pole in order to generate 265V ? How many commutator bars are required for this generator? [10+6] 4. (a) Explain DC motor principle and its working (b) A 250v shunt motor on no-load runs at 1000rpm and takes 5A the total armatureand shunt field resistances are 0.2 and 250 respectively calculate the speed when loaded and taking current of 50A if armature reaction weakens the filed by 3%. [6+10] 5. (a) Derive the EMF equation of a transformer. (b) In no load test on a 1-phase transformer the following test data were obtained. i. Primary voltage 220V ii. Secondary voltage 110 V iii. Primary current 0.5A iv. Power input 30Watts v. Resistance of primary winding = 0.6 Calculate i. turns ratio ii. magnetizing component of no load current. iii. working component of no load current. iv. iron loss. [8+8]

6. Explain about Delta/Delta connection of Transformers in detail A500 -KVA, 3phase 50 Hgs Transformer has a voltage Ratio (line voltages) of 33/11 KV and is Delta/Star connected. The resistances per phase are : High voltage 35, low voltage876 and the Iron loss is 3050 W. Calculate the efficiency at full load and one-half of full load respectively (a) at unity PF (b) 0.8 PF. [16] 7. (a) What are the three voltage drops occurring in an alternator on-load? (b) A 550 V, 55 KV A, single phase alternator has an effective resistance of 0.2 ohm. A field current of lOA produces an armature current of 200 A on short circuit, and an emf of 450 V on open circuit. Calculate i. The synchronous reactance; ii. The full- load regulation with power factor 0.8 lagging. [8+8]

8. (a) Sketch and describe the construction of a moving coil ammeter and give the principle of operation. (b) A moving coil instrument gives full scale deflection with 15mA and has a resistance of 5. Calculate the resistance of the necessary components in order that the instrument may be used as i. a 2A - Ammeter ii. a 100V voltmeter. [8+8] ⋆⋆⋆⋆⋆ 2 of 2

Set No. 3

II B.Tech I Semester Regular Examinations, November 2007 ELECTRICAL ENGINEERING ( Common to Mechanical Engineering, Chemical Engineering, Mechatronics, Metallurgy & Material Technology, Production Engineering and Automobile Engineering) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks ⋆⋆⋆⋆⋆ 1. (a) Derive an expression for co-efficient of coupling. (b) Two coils having the inductances of 0.12 milli heneries and 0.072 milli heneries

and their mutual inductance is 1.15H. Find coupling co-efficient. [10+6] 2. (a) Define peak factor, form factor. (b) Calculate form factor for the sinusoidal wave form. [8+8] 3. (a) With neat sketches, explain the construction and functions of the various parts of a d.c. machine. (b) Calculate the emf generated by a 6 pole lap wound armature with 65 slots and 12 conductors per slot, when driven at 1000 rpm. The flux/pole is 0.02 Wb. [10+6] 4. (a) Explain DC motor principle and its working (b) A 250v shunt motor on no-load runs at 1000rpm and takes 5A the total armatureand shunt field resistances are 0.2 and 250 respectively calculate the speed when loaded and taking current of 50A if armature reaction weakens the filed by 3%. [6+10] 5. (a) On what factors the induced EMF in the transformer windings depends. Justify the answer with appropriate derivation. (b) A double wound 1- phase transformer is required to step down from 1900V to 240V, 50Hz . It is to have 1.5V per turn . Calculate the required number of turns on the primary and secondary windings respectively. The peak value of flux density is required to be not more than 1.5 wb/m2 . Calculate the required cross sectional area of the steel core. If the output is 10KVA . Calculate the secondary current. [8+8] 6. (a) “An induction motor cannot run at synchronous speed”. Give reason. (b) A 4-pole, 50Hz, 3-phase induction motor runs at 1440 rpm with a load torque of 200 N-M. If the stator loses are 2,200W, and the friction torque is 5 N-M. Calculate its efficiency, and the rotor copper loss. [8+8] 7. (a) Discuss the construction, and principle of operation of a 3-phase synchronous generator. (b) A 3-phase, star-connected, round-motor synchronous generator, rated at 10 KV A, and 230 V has synchronous reactance of 1.2 ohms per phase, and an armature resistance of 0.5 ohms per phase. Calculate the percentage voltage regulation at full load with i. 0.8 lagging p.f.

ii. 0.8 leading p.f. [8+8] 8. (a) Sketch and describe the construction of a moving coil ammeter and give the principle of operation. (b) A moving coil instrument gives full scale deflection with 15mA and has a resistance of 5. Calculate the resistance of the necessary components in order that the instrument may be used as i. a 2A - Ammeter ii. a 100V voltmeter. [8+8] ⋆⋆⋆⋆⋆ 2 of 2

Set No. 4

II B.Tech I Semester Regular Examinations, November 2007 ELECTRICAL ENGINEERING ( Common to Mechanical Engineering, Chemical Engineering, Mechatronics, Metallurgy & Material Technology, Production Engineering and Automobile Engineering) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks ⋆⋆⋆⋆⋆ 1. Two coils having self inductances are 0.9H and 0.4H.their mutual Inductance is 0.3H. Find the Equivalent Inductance when both are magnetized in (a) same direction (b) opposite direction. Derive the formula used. [6+10] 2. (a) Deduce an expression for the total power input for a balanced 3-φ load in terms of line voltage, line current and p.f. (b) A balanced mesh-connected load of (8 +j6) ohms per phase is connected to a 3-φ, 50 Hz, 230V supply system. Calculate i. line current ii. power factor iii. power iv. reactive volt ampere and v. total volt ? ampere. [8+8] 3. (a) With neat sketches, explain the construction and functions of the various parts of a d.c. machine. (b) Calculate the emf generated by a 6 pole lap wound armature with 65 slots and

12 conductors per slot, when driven at 1000 rpm. The flux/pole is 0.02 Wb. [10+6] 4. (a) Derive an expression for the torque developed in N-m and in Kf-m in a dc motor. (b) Determine the value of torque in Kg-m developed by the armature of a 6pole wave-wound motor having 492 conductors, 30mwb per pole when the total armature current is 40A. [8+8] 5. (a) In a test for the determination of the losses of a 440V, 50Hz transformer, the total iron losses were found to be 2500W at normal voltage and frequency. When the applied voltage and frequency were 220V, 25Hz, the iron loss were found to be 850W. Calculate the hysterisis and eddy current losses at normal voltage and frequency. (b) The following readings were obtained from OC and SC tests on 8KVA, 400/120V, 50Hz , transformer. OC Test on LV side 120V 4A 75W SC Test on HV side 9.5V 20A 110W Calculate the voltage regulation and efficiency at full load 0.8 P.F lagging. [8+8] 6. Explain about Delta/Delta connection of Transformers in detail A500 -KVA, 3phase 50 Hgs Transformer has a voltage Ratio (line voltages) of 33/11 KV and is Delta/Star connected. The resistances per phase are : High voltage 35, low voltage876 and the Iron loss is 3050 W. Calculate the efficiency at full load and one-half of full load respectively (a) at unity PF (b) 0.8 PF. [16] 7. (a) Why do we prefer field winding of an alternator as a rotating element and armature as a stationary element, give reasons. (b) A 3- phase star connected alternator is rated at 1500KVA, 12KV. The armature effective resistance and synchronous reactance are 2 Ohms and Ohms per phase respectively. Calculate % regulation for a load of 1200KW at 0.8 PF lag and 0.707 PF lead. [6+10]

8. (a) Describe with the diagram the construction of a repulsion type moving iron instrument with particular reference to the means used for i. deflection ii. control iii. damping. (b) A moving iron voltmeter in which full scale deflection is given by 100V, has a coil of 10000 turns and a resistance 2000. Calculate the number of turns required on the coil of the instrument is converted for use as an ammeter reading 20A full scale deflection. [8+8] ⋆⋆⋆⋆⋆ 2 of 2