DAM

Important Question for GTU Exam 

1.      Explain the factors that affect the choice of specific magnetic loading in case of a induction machine.

2.      Derive an output equation for 3-ф induction motor with usual notation.

3.      Explain the factors that affect the choice of specific electric loading in case of a induction machine.

4.      Write a note on choice of average flux density in air gap in connection with 3-phase IM.

5.      Explain the effect of Harmonic induction torque and Harmonic synchronous torque on the performance of 3 phase induction motor.

6.      State the rules for the selection of rotor slots in 3-phase squirrel cage induction motor.

7.      Describe the methods for reducing the effect of harmonics torque in 3-phase squirrel cage induction motor.

8.      Explain main differences between design of 1-phase and 3-phase induction motor.

9.      Compare the output equation of both 1-phase and 3-phase IM.

10.  Compare different 1-phase induction motor in a point of view of design.

11.  Discuss the effect of variation of main dimension (D&L) on performance (Rating, losses & efficiency) of 3-ф induction motor.

12.  Define ‘electric loading’ and ‘magnetic loading’ in connection with 3- phase induction motor.

13.  Prove that torque produce by 5TH harmonics is in backward direction & 7TH harmonics is in forward direction.

14.  What is dispersion coefficient? What is its effect on max. power factor.

15.  Calculate the value of capacitance for maximum starting torque in 1- phase induction motor.

16.  Explain design procedure for stator of single phase induction motor.

17.  Explain methods of improving starting torque of induction motor.

18.  Discuss the effects for rotor design of a single phase induction motor.

19.  Develop a flow chart and discuss algorithm for main dimension for 3-Phase induction motor.

20.  Draw and explain briefly the current distribution wave form spread over one pole pitch in bars and end rings of squirrel cage induction motor.

21.  Prove that the out put of single phase machine is two third of that of a three phase machine.

22.  Explain the effect of skewing the rotor slots in a squirrel cage induction motor.

23.  Derive the equation of capacitance to give maximum starting torque of capacitor start single phase induction motor.

24.  Derive the relation for total leakage reactance in a single phase induction motor.

25.  Derive the equation of rotor resistance referred to stator side, for a squirrel cage induction motor.

PROBLEMS:-

1.      Find the main dimensions, number of stator turns per phase & number of stator slots for a 25KW, 415V, 50Hz, 2880rpm,3-ф delta connected induction motor. Assume that: specific magnetic loading=0.48wb/m2, specific electric loading=21000ac/m, Efficiency=88%, power factor=0.87, stator winding factor=0.9451. Take ratio (L/τ) = 0.7.

2.      Determine the D and L of a 70 Hp, 415V, 3-phase, 50-Hz, star connected, 6 pole induction motor for which ac = 30000 amp.cond/m and Bav = 0.51 wb/m2. Take Efficiency = 90 % and pf = 0.91. Assume Pole pitch τ = L. Estimate the number of stator conductors required for a winding in which the conductors are connected in 2-parallel paths. Choose a suitable number of conductors/ slots, so that the slot loading does not exceed 750 amp. cond.

3.      A 22kW,3 phase,4 pole 50 Hz,415V star connected induction motor has 48 slots each containing 20 conductors. Calculate the values of bar and end ring currents. The number of rotor bars is 55. The machine efficiency of 0.88 and a power factor of 0.89. The rotor mmf may be assumed of 85 percent of stator mmf. If current density is 6 A/mm2 find area of rotor bar and area of end ring.

4.      Design a 10HP, 440V, 3-Phase, 4-pole, 50Hz squirrel cage induction motor which is to be started using a star-delta starter. Find the main dimensions, number of turns per phase & number of stator slots. Assume:-Average flux density in the gap=0.45wb/m2 , Ampere conductors per meter=23000, efficiency=0.85, Power factor=0.84, stator winding factor=0.955. Choose the main dimension to give an overall good design.

5.      Design a cage rotor for a 40 HP, 3-phase, 400V,50 Hz, 6 pole, delta connected induction motor having a full load efficiency of 87% and a full load pf of 0.85. Take D = 33 cm and L = 17 cm. Stator slots – 54, conductors/slot = 14. Assume suitable missing data if any.

6.      Determine the main dimensions, no of radial ventilating ducts, no of stator slots and no of turns per phase of a 3.7 kW, 400 volts, 3 phase, 4 pole, 50 Hz Squirrel cage induction motor to be started by a star delta starter. Assume: Average flux density in air gap = 0.45 wb/m2 , ampere conductors per meter=23000, efficiency=0.85 and power factor=0.84.

7.      Find the main dimensions of a 15kW, 3 phase, 400V, 50Hz, 2810 r.p.m. squirrel cage induction motor having efficiency of 0.88 and a full load power factor of 0.9 Assume: Specific magnetic loading=0.5 Wb/𝑚2 ; Specific electric loading=25000 A/m. Take rotor peripheral speed as approximately 20m/s at synchronous speed.

8.      Determine the main dimension, turns/phase, conductors, cross sectional area and slot area of a 250 HP, 3- phase. 50 Hz, 400 Volt 1410 rpm Slip ring induction motor. Assume average flux density = 0.5T, AC/m = 30000 efficiency =0.9, PF = 0.9 winding factor 0.955 and current density = 3.5 A/mm2 . The slot space factor is 0.4 and the ratio of core length to pole pitch is 1.2. The machine is delta connected.

9.  A 15 KW , 400 Volt 3-phase , 50 Hz , 6 pole induction motor has a diameter 0f 0.3 metre and core length 0.12 metre .the no of stator slots = 72 with 20 conductors per slot. The stator is delta connected. Calculate the value of magnetizing current per phase if the length of the air-gap is 0.55 mm. The gap contraction factor is 1.2. Assume the MMF required for the iron parts to be 30% of the air-gap MMF. Coil span = 11 slots.

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Derive output equation of synchronous machine.

Explain factors affecting specific electric loading and specific magnetic loading.

Define SCR of a synchronous machine. Discuss the importance of SCR in the design of synchronous

machine.

What is the role of damper winding in 1) synchronous generator and 2) synchronous motor? Derive the

equation of MMF of damper winding.

Explain how you will estimate MMF required for various parts of magnetic circuit of Synchronous

Machine.

Explain steps for design of field winding of alternator.

Explain evaluation of direct and quadrature axis reactance of alternator.

Explain the effect of air gap length on performance of synchronous of synchronous machine.

Explain flowchart for low speed vertically operated alternator.

Explain terms: 1) Run away speed, 2) peripheral speed.

Explain the factors to be considered while selecting number of armature slots in the design of

synchronous machine.

Explain the design of salient pole rotor in a synchronous machine.

EXAMPLE 11.1, 11.2, 11.3, 11.4, 11.6, 11.7, 11.11, 11.12, 11.13, 11.14, 11.16