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iv) the armature, field and load currents when the terminal voltage is found to be
150 V. Neglect the effect of armature reaction and brush drop and assume
armature resistance to be 0.8
4. a) what are Interpoles ? Why are Interpoles designed to provide mmf more than
the armature mmf in the commutating zone. Draw the resultant resultant flux
density wave form.
b) Derive the formula for demagnetizing and cross magnetizing AT/pole.
(or)
c) Describe the cause of sparking between brushes and commutator by
commutation process
d) The following information is given for a 300 kW, 600 V, long-shunt
compound generator: Shunt field resistance=75, armature resistance including
brush resistance=0.03, commutating field winding resistance=0.011, series
field resistance=0.012, divertor resistance =0.036. When the machine is
delivering full load, calculate the voltage and power generated by the armature.
5. a) State the principle by which generators convert mechanical energy to electrical
energy.
b) A 4 pole, lap wound, 246 armature conductors DC generator delivers a full
load current 400A. It has shunt field current of 12A and 123 commutator
segments in the commutator ring of the machine. If the brushes are advanced by 3
commutator segments on full load. Find (a) demagnetizing AT/pole and (b) cross
magnetizing AT/pole
(or)
c) A four-pole 220 V dc shunt generator supplies a load of 3 kW at 220 V. The
resistance of the armature winding is 0.1ohms and that of the field winding is
110 Ohms. Calculate the total armature current, the current flowing through
armature conductors, and the EMF induced. Assume that the armature winding is
wave wound.
d) Explain the Armature Reaction with neat diagrams and graphical
representation.
6. a) Explain with neat diagram the 3-point starter.
b)Explain the necessity of starter. Explain the speed control techniques of a dc
series motor.
(or)
c)Draw and explain different characteristics D.C. shunt motor.
d)A 230V DC shunt motor having an armature resistance of 0.3 takes 3A
excluding a field current of 1A when running on no-load. Determine its efficiency
taking currents as a) 30A; b) 50A and c) 70A
7. a)Draw and explain are the different speed control methods of DC shunt motor.
b)A 220 V shunt motor takes 60 A when running at 800 RPM. It has an armature
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resistance of 0.1 ohm if the magnetic flux is weakened by 20 % and contact drop
per brush is 1V and total torque remains constant.
(or)
c) Explain the following speed control technique for series motor.
(i) Diverter control
(ii) tapped field control
d) Derive the condition for maximum efficiency of DC generator
e) List out the losses of DC machine
8. a) Explain the significance of back E.M.F. derive the condition for maximum
power in DC Motor.
b) Derive the torque equation of DC motor.
(or)
c) Explain with a neat circuit diagram Swinburnes test on DC shunt motor to
find the efficiency of DC machine when if runs as motor and generator? Mention
the advantages and disadvantages of this method?
d) A 400 V DC shunt motor takes 5 A at no-load. Its armature resistance
(including brushes) is 0.5 ohm and shunt field resistance is 200 ohm. Estimate the
KW output and efficiency when the motor takes 50 A on full load
9. a) Explain the brake test on DC shunt motor
b) The following reading are obtained when doing a load test on DC shunt motor
using a brake drum. Spring balance reading: 10Kg and 35 Kg. Diameter of drum
is 40 cm. Speed of the motor is 950 RPM and applied voltage is 200V; line
current is 30A. Calculate the output power and efficiency.
(or)
c) Draw and explain characteristics D.C. series motor.
d) A 600V dc shunt motor drives a 60kw load at 1000rpm . the field resistance is
100ohms and armature resistance is 0.15ohms. stray load loss is negligible. In
case of motor efficiency is 85%, determine
i) the rotational losses
ii) the speed at no load
10. a)With neat circuit diagram explain the Hopkinsons test and list out Mention
the advantages and disadvantages
b)The Hopkinsons test on two shunt machines gave the following results for full
load. The supply current was 15 A at 200 V. The generator output current was
85A. The field currents for motor and generator were 2.5 A and 3 A respectively.
The armature resistance of each machine was 0.05. Find the efficiency of each
of the machines under the above loading conditions.
(or)
c) Enumerate the various losses in a dc machine. Which of the losses are
constant? derive the expression for the efficiency of a dc generator and a dc
motor.
d) Draw the power stages of DC Generator and DC motor.
e) A 220 V shunt motor has armature and field resistance of 0.2 and 220
respectively. The motor is driving a constant load torque and running at 1000 rpm
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drawing 10 A current from the supply. Calculate the new speed and armature
current if an external armature resistance of value 5 is inserted in the armature
circuit. Neglect armature reaction and saturation.
11. a) Explain the construction of the transformer
b) Draw and explain phasor diagram of transformer on all types of load.
(or)
c) Explain various losses and derive the condition for minimum efficiency of a
transformer.
b) A 600 KVA single phase transformer when working at upf has an efficiency of
92% at full- load and also at half load. Determine its efficiency when it operates
at upf and 60% full-load.
12. a) With neat diagram, explain the equivalent circuit of 1 phase transformer.
b) In a 25 KVA 2000/200 volts transformer iron and copper losses are 350 and
400
watts respectively. Calculate the efficiency on UPF at (i) Full load (ii)
Half full load. Determine the load for maximum efficiency and iron and copper
losses in this case.
(or)
c) Explain the working principle of transformer and derive the emf equation
d) A transformer on load takes 1.5 amps at a power factor of 0.2 lagging when
connected across 50 Hz 230 V supply. The ratio between primary and secondary
number of turns is 3. Calculate the value of primary current when secondary is
supplying a current of 40 amps at a power factor of 0.8 lagging. Neglect the
voltage drop in the windings. Draw the relevant phasor diagram.
13. 3) a) Determine the load for maximum efficiency and iron and copper losses in
this case of transformer and find maximum KVA Efficiency
b) Prove that the secondary resistance R 2 and reactance X2 of the transformer
referred to primary side are R2/K2 and X2/K2 respectively, where K is
transformation ratio.
(or)
c) Explain why hysterisis and eddy current losses occur in a transformer.
d)When a transformer is supplied at 400 V 50 Hz the hysterisis loss is found to be
310 watts and eddy current loss is found to be 260 watts. Determine the
hysterisis
and eddy current loss when the transformer is supplied at 800 V
100 Hz.
14. a) Discuss the effects of variation of frequency and supply voltage on iron losses
of transformer.
b) Derive the expression for voltage regulation of a transformer from the
simplified approximate equivalent circuit and obtain condition for zero
regulation.
c) A 20 KVA 2000/200 V single phase transformer has the following parameters.
H. V. Winding: R1 = 3 ohm, X1 = 5.3 ohm,
L. V. Winding: R2 = 0.05 ohm, X2 = 0.1 ohm
Find the voltage regulation at
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Draw the equivalent circuit of the transformer (i) referred to LV side and (ii)
referred to HV side inserting all the parameter values.
21. a) Explain with neat diagram the operation of on and off load tap changing
(or)
b) Draw the phasor diagrams and winding connection of a three-phase
transformer for (i) Group 1: phase displacement of zero degrees, (ii) Group 2:
phase displacement of 180 degrees.
22. a) Derive the equation for saving in copper in using Auto transformer when
compared to two winding transformer.
b) What are the applications of auto transformers?
(or)
c) Explain with neat diagram the operation of Differnet types
d) what is called open delta? Campare open delta with delta-delta
23. a) Explain open delta of 3-phase transformers with diagram? And campare open
delta with scott connection
b) Explain the three phase transformer to two phase transformer conversion and
vice versa?
(or)
c) A 20 KVA, 2400/240V two winding step down transformer is connected as an
auto transformer with additive polarity. Compute: (i) Original current capacity of
HV winding (ii) Original current capacity of LV winding (iii) KVA rating of auto
transformer using current capacity of LV winding as calculated in (iv) per cent
increase in KVA capacity of auto transformer as compared to original two
winding transformer (v) percent overload of 2400V winding when used as an
auto transformer.
24. a) Derive the equation for saving of copper in using Auto transformer when
compared to two winding transformer.
b) What are the applications of auto transformers? and campare auto trnafromer
with two winding transformer
(or)
c) Describe the principle of regulating the voltage with the help of tap changers.
d) Three single phase ideal transformers, each of rating 5kVA, 200V/400V, 50 Hz
are available. i)The LV sides are connected in star and HV sides are connected in
delta. What line to line 3-phase voltage should be applied and what will be the
corresponding HV side line to line voltage will be? Also calculate and show the
line and phase current magnitudes in both LV & HV sides corresponding to rated
condition. ii)The LV sides are connected in delta and HV sides are connected in
delta. What line to line 3-phase voltage should be applied and what will be the
corresponding HV side line to line voltage will be? Also calculate and show the
line and phase current magnitudes in both LV & HV sides corresponding to rated
condition.
25. a) describe four possible ways of connections of 3-phase transformers with
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relevant relations amongst voltages, currents on both h.v and l.v sides
(or)
b) Explain the T-T Connections?
c) Explain the conversion process of three phase to two phase in T-T connection
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