Important RGPV Question
EX-402 (Electrical Machine 1)
IV Sem, EX
UNIT-1 Transformer I
Q.1 Discuss about the open-circuit test and short circuit test on single phase transformer.
(RGPV Nov 2023)
Q.2 A 6300/210 V, 50 Hz, single phase transformer has per turn c.m.f of about 9 volts and maximum flux density of 1.2 T. Find the number of high voltage and low voltage turns and the net cross sectional area of the core.
(RGPV Nov 2023)
Q.3 If part of a primary winding of a transformer were accidentally short circuited what would be the immediate effect? Discuss in detail.
(RGPV Nov 2023)
Q.4 A 20 kVA, 2000/200 V single phase transformer has the following parameters. H.V. Winding: R₁ = 3 Ω, Χ₁ = 5.3 Ω L.V. winding: R₂= 0.05Ω, Χ, = 0.1 Ω. Find the voltage regulation at
i) Power factor of 0.8 lagging i
ii) UPF
iii) 0.707 power factor leading
(RGPV Nov 2023)
Q.5 Discuss about the Excitation Phenomenon in Transformer.
(RGPV Nov 2023)
Q.6 Explain the construction and working principle of a single phase transformer and derive its EMF equations.
(RGPV June 2023)
Q.7 A single phase 50 Hz transformer has 100 turns on the primary and 400 turns on the secondary winding. The net cross-sectional area of core is 250 cm². If the primary winding is connected to a 230 V, 50 Hz supply, determine,
i) The e.m.f. induced in the secondary winding
ii) The maximum value of flux density in the core.
(RGPV June 2023)
Q.8 Explain the process of finding efficiency of transformer by Sumpner’s test.
(RGPV June 2023)
Q.9 A 40 kVA transformer has iron loss of 450 W and full- load copper loss of 850 W. If the power factor of the load is 0.8 lagging. Calculate
i) Full-load efficiency
ii) The kVA load at which maximum efficiency occurs and
iii) The maximum efficiency.
(RGPV June 2023)
Q.10 Why single phase induction motor is not self starting? Explain the double revolving field theory.
(RGPV June 2022)
Q.11 Calculate the efficiency for half, full load of a 100 kVA transformer for the P.F. of unity and 0.8 the copper loss at full load is 1000 W and iron loss is 1000 W.
(RGPV June 2022)
Q.12 Describe the construction and working principle of single phase transformer.
(RGPV Dec 2020)
Q.13 What is an auto transformer? Derive an expression for saving of copper when auto transformer is used.
(RGPV Dec 2020)
Q.14 Derive the expression for saving of copper in auto transformer.
(RGPV June 2022)
Q.15 A single phase transformer 20kVA, 2200V/220V gives the test data.
O.C test: 148W 220V 4.2A L.V. side
S.C. test: 360W 86V 10.5A H.V side
Obtain the approximate equivalent circuit referred to LV side.
(RGPV Dec 2020)
Q.16 Explain the Sumpners test of a single phase transformer.
(RGPV Dec 2020)
Q.17 Explain about hysteresis and eddy current losses in transformer.
(RGPV June 2020)
Q.18 Explain about open circuit and short circuit tests in single phase transformer.
(RGPV June 2020)
Q.19 Write short notes on Sumpner’s test.
(RGPV June 2020)
Q.20 Write short notes on Power and distribution transformer.
(RGPV June 2023)
Q.21 The total core loss of a specimen of silicon steel is found to be 1500 W at 50 Hz keeping the flux density constant the loss become 3000 W when the frequency is raised to 75 Hz. Calculate separately the hysteresis and eddy current losses of each of these frequencies.
(RGPV June 2022)
Q.22 Explain construction, working and advantages of a single phase auto transformer.
(RGPV June 2020)
Q.23 Explain about pulse and high frequency transformers.
(RGPV June 2020)
Q.24 The power supplied to a 3-phase 4 pole, 50 Hz induction motor is 50 kW and the corresponding stator losses are 2.5 kW. While motor is operating with 4% slip, the mechanical losses are 1.2 kW. Calculate the efficiency of the motor and shaft torque.
(RGPV June 2020)
Q.25 Give impact of unbalanced supply and harmonies on performance of three phase induction motor.
(RGPV June 2020)
UNIT – 2 Transformer II
Q.1 Explain the need of parallel operation of single phase transformers. Give the condition to be satisfied for their successful parallel operation.
(RGPV Nov 2023)
Q.2 Two transformers A and B of ratings 500 kVA and 250 kVA are supplying a load of 750 kVA at 0.8 pf lagging. Their open-circuit voltages are 405V and 415V respectively. Transformer A has 0.01 p.u. resistance and 0.05 p.u. reactance and transformer B has 0.015 p.u. resistance and 0.04 p.u. reactance. Find
i) Circulating current at no-load
ii) The load current shared by each transformer
iii) kVA and power factor of each transformer.
(RGPV Nov 2023)
Q.3 Why breather is connected with the conservator and not with the main tank of the transformer?
(RGPV Nov 2023)
Q.4 Explain Scott connection for 3 phase to 2 phase conversion and show that the primary neutral divides the teaser primary winding in the ratio 2:1.
(RGPV June 2023)
Q.5 Two single-phase transformers A and B rated at 600 kVA and 500 kVA respectively are operated in parallel to supply a load of 1000 kVA at 0.8 lagging power factor. The resistance and reactance of transformer A are 3% and 6.5% while that of transformer Bare 1.5% and 8%. Calculate the kVA loading and the power factor at which each transformer operates.
(RGPV June 2023)
Q.6 Write short notes on Pulse and high frequency transformers.
(RGPV June 2023)
Q.7 Explain the operation of Scott connections for balanced and unbalanced load with the help of phasor diagram.
(RGPV June 2022)
Q.8 What is meant by inrush currents in transformer? Specify the nature of inrush current and it’s problem during transformer charging.
(RGPV June 2022)
Q.9 Draw the physical connection and phase diagram of the following transformer connection:
i) DO
ii) Td11
(RGPV Dec 2020)
Q.10 Explain the parallel operation of transformers with essential conditions. Also write its advantages.
(RGPV Dec 2020)
Q.11 Write short notes on
(a) All day efficiency
(b) Cooling of transformer
(RGPV Dec 2020)
Q.12 Explain about parallel operation of transformers and its application.
(RGPV June 2020)
Q.13 Explain about conservator and breather in transformers.
(RGPV June 2020)
UNIT – 3 Three phase Induction Motor-I
Q.1 Explain the construction and working principle of a three phase induction motor.
(RGPV Nov 2023)
Q.2 A 4-pole, 3-phase 50 Hz induction motor has a star-connected rotor. The rotor has a resistance of 0.1 Ω per phase and standstill reactance of 2 Ω /phase. The induced emf between the slip rings is 100 V. If the full-load speed is 1460 rpm. Calculate:
i) The slip
ii) The emf induced in the rotor in each phase
iii) The rotor reactance per phase
iv) The rotor current
v) Rotor power factor
Assume slip rings are short-circuited.
(RGPV Nov 2023)
Q.3 Explain the Torque-Slip and Torque Speed characteristics of an 3-phase Induction motor.
(RGPV Nov 2023)
Q.4 Explain the different speed control methods of squirrel cage induction motor.
(RGPV Nov 2023)
Q.5 Explain the procedure of drawing the circle diagram of an induction motor. How is the performance characteristics obtained from it?
(RGPV Nov 2023)
Q.6 What is a main differences between Squirrel Cage and Slip Ring Induction Motors?
(RGPV June 2023)
Q.7 A 150 kW 3000 V, 50 Hz, 6-pole star-connected induction motor has a star- connected slip ring rotor with a transformation ratio of 3:6 (stator/rotor). The rotor resistance is 0.12 per phase and its per phase leakage inductance is 3.61 mH. The stator impedance may be neglected. Find the starting current on rated voltage with short-circuited slip rings.
(RGPV June 2023)
Q.8 Draw the torque speed characteristics of double cage rotor motor. How these characteristics are different from squirrel cage induction motor?
(RGPV June 2022)
Q.9 How do changes in supply voltage and frequency affect the performance of an induction motor?
(RGPV June 2023)
Q.10 Losses and efficiency of three phase induction motor.
(RGPV June 2023)
Q.11 Bring out clearly, with the help of neat sketches the difference between the 3 phase slip ring induction motor and three phase squirrel cage induction motor.
(RGPV June 2022)
Q.12 Explain how the performance of three phase induction motor is predetermined using the circle diagram by conducting the necessary test?
(RGPV June 2022)
Q.13 Explain these terms in short:
i) Cogging and crawling
ii) Double cage and deep cage
(RGPV June 2022)
Q.14 Explain the construction and working principle of three phase induction motor.
(RGPV Dec 2020)
Q.15 Describe the power flow diagram of three phase induction motor.
(RGPV Dec 2020)
Q.16 Write short notes on Cogging and crawling
(RGPV Dec 2020)
Q.17 Write short notes on Circle diagram.
(RGPV Dec 2020)
UNIT – 4 Three Phase Induction Motor-II
Q.1 Discuss about the three phase induction motor breaking methods.
(RGPV Nov 2023)
Q.2 Explain the No load tests and blocked rotor tests for an 3-phase induction motor.
(RGPV June 2023)
Q.3 Explain the phenomenon of cogging and crawling. Also discuss double cage and deep bar induction motor.
(RGPV June 2023)
Q.4 Describe the working of self excited and externally excited induction generator.
(RGPV June 2022)
Q.5 Explain these terms:
i) Braking
ii) Induction motor
(RGPV June 2022)
Q.6 Explain the torque-speed characteristic of three phase induction motor in detail.
(RGPV Dec 2020)
Q.7 With the help of neat sketch, explain star-delta starting for three phase induction motor.
(RGPV Dec 2020)
Q.8 Explain braking and its types for a three phase induction motor.
(RGPV Dec 2020)
Q.9 Describe the principle of induction generator.
(RGPV Dec 2020)
Q.10 Explain about power-speed characteristic of three phase induction motion. Also tell its losses and efficiency.
(RGPV June 2020)
Q.11 Give comparison between Slip ring and squirrel cage motors.
(RGPV June 2020)
Q.12 Give speed control and braking mechanism in three phase induction motor.
(RGPV June 2020)
Q.13 Explain about cogging and crawling mechanism in three phase induction motor.
(RGPV June 2020)
UNIT – 5 Single Phase Motors
Q.1 How does using double revolving field theory? Also explain the principle of operation of single phase induction motor.
(RGPV Nov 2023)
Q.2 Explain the construction and working principle of a single phase A.C. series motor.
(RGPV Nov 2023)
Q.3 Explain the types, construction and working principle of a servomotor.
(RGPV Nov 2023)
Q.4 Discuss about the induction motor steady-state performance under varying quality of supply and stator winding short circuit location using negative sequence current.
(RGPV Nov 2023)
Q.5 Draw and explain the equivalent circuit of a three-phase induction motor.
(RGPV June 2023)
Q.6 Explain the double revolving field theory, equivalent circuit and its determination of single phase induction motor.
(RGPV June 2023)
Q.7 Explain the construction and working principle of a single phase linear induction motor.
(RGPV June 2023)
Q.8 A 4-pole, 250 W, 115 V, 60 Hz capacitor-start induction motor takes a full-load line current of 5.3 A while running at 1760 r.p.m. If the full load efficiency of the motor is 64%, find
i) Motor slip
ii) Power factor and
iii) Full-load torque.
(RGPV June 2023)
Q.9 Write short notes on:
i) Linear induction motor ii) Servo motor
(RGPV June 2022)
Q.10 Write short notes on:
i) DC shunt motor
ii) AC Series motor
(RGPV June 2022)
Q.11 What do you mean by SPP related to electrical machine? What is it significance
(RGPV June 2022)
Q.12 Explain the method of speed control of three phase induction motor by:
i) Varying the supply frequency
ii) By varying rotor resistance
(RGPV June 2022)
Q.13 Explain double revolving field theory in single phase induction motor.
(RGPV Dec 2020)
Q.14 Describe capacitor start capacitor run method for starting single phase induction motor.
(RGPV Dec 2020)
Q.15 Write short notes on the Linear induction motor
(RGPV Dec 2020)
Q.16 Discuss in detail about Servo motors.
(RGPV June 2020)
Q.17 Write about types of single phase induction motor with their working principle.
(RGPV June 2020)
Q.18 Write short notes on the following:
a) Linear Induction Motor
b) Single phase A.C. series motor
(RGPV June 2020)
— Best of Luck for Exam —
