SET - 1
Code No: X0424
II B.Tech I Semester (R07) Regular Examinations, Nov- 2010
ELECTRICAL TECHNOLOGY
(Com. to ECE.EIE, BME, ECC)
Time: 3 hours
1.
Max Marks: 80
Answer any FIVE Questions
All Questions carry equal marks
a) With a neat Sketch, explain the functions of various parts of a D.C. Machine
(8M)
b) An 8 pole lap wound generator armature has 960 conductors, a flux of 40mwb and a
speed of 400 rpm. Calculate the emf generated on open circuit. If the same armature is
wave wound, at what speed it be driven to generate 400 volts?
(8M)
2.
a) Describe with neat sketch, the working of a three point starter used for D.C shunt motor.
(8M)
b) A series motor of resistance 1Ω is connected between terminals of 200V runs at 800
rpm with a current of 15A. Find the speed at which it will run when the motor is connected
in series with a 5Ω resistance and taking the same current from the same supply voltage.
(8M)
3.
a) Explain the operating principle of a single phase transformer? Derive its EMF equation.
(8M)
b) A single phase 50Hz transformer has a core cross – sectional area of 100 cm2, and the
maximum flux density of 1.25Wb/m2. There are 1200 turns in primary and 100 turns in the
secondary windings. Calculate the induced e.m.fs on both sides.
(8M)
4.
a) Define voltage regulation of a transformer. Deduce the expression for the voltage
regulation.
(8M)
b) A 200/1000V, 50Hz single phase transformer give the following test results:
O.C. Test (LV Side): 200V, 0.7A, 70W
S.C. Test (HV Side): 15V, 10A, 85W
Calculate the parameters of the equivalent circuit referred to the LV Side.
(8M)
5.
a) Derive an expression for the torque developed in an induction motor.
(8M)
b) A 4 pole, 50 Hz, 3 phase induction motor has a rotor resistance of 0.21 ohm per phase
and standstill reactance of 0.7ohm per phase. Calculate the speed at which maximum
torque is developed.
(8M)
6.
a) Explain the constructional features of an alternator.
(8M)
b) A500V, 50 kVA single phase alternator has an effective armature resistance of 0.2 ohm.
An excitation current of 10A produces 200A armature current on short circuit and an emf
of 450 V on open circuit. Calculate the synchronous reactance.
(8M)
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SET - 1
Code No: X0424
7.
8.
Explain with neat diagrams the principle of operation of a
a) AC Servo Motor
b) Stepper Motor
(8M)
(8M)
a) Compare the Moving Iron and Moving Coil instruments.
(8M)
b) Explain the essential forces required for effective functioning of a measuring
instrument.
(8M)
2 of 2
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SET - 2
Code No: X0424
II B.Tech I Semester (R07) Regular Examinations, Nov- 2010
ELECTRICAL TECHNOLOGY
(Com. to ECE.EIE, BME, ECC)
Time: 3 hours
Max Marks: 80
Answer any FIVE Questions
All Questions carry equal marks
1.
a) Explain the operating principle of a D.C. Generator? Derive its EMF equation.
(8M)
b) A 4 pole generator with wave wound armature has 51 slots each having 24 conductors.
The flux per pole is 0.01Weber. At what speed must the armature rotate to give an induced
emf of 220V. What will be the voltage developed if the winding is lap connected and the
armature rotates at the same speed.
(8M)
2.
a) Explain the various losses that occur in a D.C Machine.
(8M)
b) An 8 kW, 250V, 1200 rpm dc shunt motor has Ra = 0.7ohm. The field current is
adjusted until on no load with a supply of 250V, the motor runs at 1250 rpm and draws
armature current of 1.6A. A load torque is then applied to the motor which causes
armature current rise to 40A and the speed falls to 1150 rpm. Determine the reduction in
the flux per pole due to the armature reaction.
(8M)
3.
a) Explain the constructional details of single phase transformers
(8M)
b) A single phase transformer is connected to a 230V, 50Hz supply. The net cross
sectional area of the core is 60cm2. The number of turns in primary is 500 and in the
secondary 100. Determine
i) Transformation ratio
ii) EMF induced in the secondary winding
iii) Maximum flux density in the core
(8M)
4.
a) Explain the method of conducting open circuit and short circuit tests on single phase
transformer?
(8M)
b) The percentage resistance and reactance of a transformer are 2% and 4% respectively.
Find the approximate regulation on full load at:
i) Unity power factor
ii) 0.8 power factor lagging and
iii) 0.8 power factor leading.
(8M)
a) Explain the working principle of a three phase induction motor.
(8M)
b) A 3- phase, 50Hz induction Motor is wound for 4 poles. Calculate
i) The synchronous speed
ii) The rotor speed when slip is 4% and
iii) Rotor frequency when rotor runs at 600 rpm
(8M)
5.
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SET - 2
Code No: X0424
6.
7.
8.
a) How EMF is induced in a 3 phase alternator? Derive the expression for EMF induced in
an alternator in terms of pitch and distribution factors.
(8M)
b) A 3-phase, 6 pole, star connected alternator revolves at 1000 rpm. The stator has 90
slots and 8 conductors per slot. The flux per pole is 0.05Wb. Calculate the voltage
generated by the machine if the winding factor is 0.96.
(8M)
a) Describe the construction and working of a shaded pole motor
(8M)
b) What is a stepper motor? Enumerate its advantages and applications.
(8M)
a) Briefly explain the principle of Measuring Instruments.
(6M)
b) With a neat sketch, explain in detailed principle and operation of Moving Iron
Ammeter.
(10M)
2 of 2
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SET - 3
Code No: X0424
II B.Tech I Semester (R07) Regular Examinations, Nov- 2010
ELECTRICAL TECHNOLOGY
(Com. to ECE.EIE, BME, ECC)
Time: 3 hours
Max Marks: 80
Answer any FIVE Questions
All Questions carry equal marks
1.
2.
3.
a) Explain the classification of D.C. Generators.
(8M)
b) The armature of a 12 pole d.c. shunt generator has 50 slots and is wave wound with 12
conductors per slot, the generator is running at a speed of 625 rpm and supplies a resistive
load of 15 ohm at a terminal voltage of 300V. The armature resistance is 0.5 ohm and field
resistance is 60 ohms. Find the armature current, the generated emf and the flux per pole.
(8M)
a) Explain the different characteristics of D.C. Shunt and Series Motor.
(8M)
b) A 250V DC Shunt motor has an armature resistance of 0.5Ω and a field resistance of
250Ω. When driving a constant torque load at 600 rpm, the motor draws 21A. What will
be the new speed of the motor if an additional 250Ω resistance is inserted in the field
circuit?
(8M)
a) Draw and explain phasor diagram of single phase transformer operating on no load.
(8M)
b) A transformer has a primary winding of 800 turns and a secondary turns of 200. The
load current on the secondary is 80A at 0.8p.f lagging. The primary current is 25A at
0.707p.f lagging. Determine the no load current of the transformer and the phase with
respect to the voltage.
(8M)
4.
a) Derive the condition for maximum efficiency of a single phase transformer?
(8M)
b) A 600 kVA, single phase transformer has an efficiency of 92% both at full load and half
load at unity power factor. Determine its efficiency at 60% of full load at 0.8 p.f lag. (8M)
5.
a) Explain the differences between squirrel cage and slip ring induction motors.
6.
(8M)
b) A 3-phase induction Motor of 50 Hz has a full load speed of 960 rpm. Calculate
i) number of poles
ii) slip frequency
(8M)
a) Explain the synchronous impedance method of computing the voltage regulation of
alternator.
(8M)
b) The stator of a 3-Phase, 50Hz, 8 pole alternator driven at 750 rpm has 72 slots. The
winding has been made with 36 coils having 10 turns per coil. Calculate the rms value of
induced emf per phase if the flux per pole is 0.15 mwb and is sinusoidally distributed.
Assume full pitch coils have been used on the stator.
(8M)
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SET - 3
Code No: X0424
7.
a) Discuss the function of an A.C. Tachometer. Explain its Construction and working.
(8M)
b) What are the applications of stepper motor and synchros?
(8M)
8.
a) Explain with neat sketch the principle of operation of permanent magnet type moving
coil voltmeter.
(10M)
b) Compare the merits and demerits Moving coil and Moving iron instruments.
(6M)
2 of 2
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SET - 4
Code No: X0424
II B.Tech I Semester (R07) Regular Examinations, Nov- 2010
ELECTRICAL TECHNOLOGY
(Com. to ECE.EIE, BME, ECC)
Time: 3 hours
Max Marks: 80
Answer any FIVE Questions
All Questions carry equal marks
1.
a) Define O.C.C of a D.C generator. Explain how it is obtained for a given generator.(8M)
b) A 30 kW, 250V, d.c shunt generator has a full load voltage regulation of 6%. If the field
current when supplying rated load is 1.47A. Find
i) Field circuit resistance
ii) Armature resistance
(8M)
2.
a) Derive an expression for torque of a D.C. Motor
(8M)
b) A 250V shunt motor on no load runs at 1000 rpm and takes 5A. The total armature and
shunt field resistances are 0.2 ohm and 250 ohm respectively. Calculate the speed when
loaded and taking a current of 50A, if the armature reaction weakens the field by 3%.
(8M)
3.
a) What is meant by the equivalent resistance of a transformer? How is it calculated in
primary terms and secondary terms?
(8M)
b) A 3300/220V, 30 kVA single phase transformer takes a no load current of 1.5 A when
the low voltage winding is kept open. The iron loss component is equal to 0.4A, find
i) no load input power
ii) Magnetizing component and power factor of no load current.
(8M)
4.
a) Define efficiency and regulation of a transformer. Show how the power factor affects
both of them.
(8M)
b) A 220kVA transformer has an efficiency of 98% at full load. If the maximum efficiency
occurs at three quarters of full load, calculate efficiency at half load. Assume negligible
magnetizing current and p.f of 0.8 at all loads.
(8M)
5.
a) Explain various power stages of a 3- phase Induction motor
(8M)
b) A 3-phase induction motor has 4 poles and is connected to 400V, 50Hz supply.
Calculate the actual rotor speed and rotor frequency when the slip is 6%
(8M)
6.
a) Derive the expressions for distribution factor and pitch factor of alternator.
(8M)
b) A 3-Phase, 50Hz, 20 pole alternator with star connected stator winding has 180 slots on
the stator. Each slot consists of 8 conductors. The flux per pole is 25mwb and is
sinusoidally distributed. The coils are full pitch. Calculate the speed and generated EMF.
(8M)
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SET - 4
Code No: X0424
7.
a) Explain the principle of operation of single phase Induction Motor.
b) Explain with neat sketches the principle of operation of Stepper Motor.
8.
a) Explain the terms Deflecting torque and Controlling torque with reference to the
indicating instruments
(10M)
b) List out the applications of Moving Coil and Moving Iron Instruments.
(6M)
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(8M)
(8M)