ELECTRICAL DEPARTMENT NOTICE BOARD

	Question bank  (8Th semester)
	Electrical Machine Design - II  [ subject code : 180904]
1	Derive an output equation for 3-ф induction motor with usual notation.
2	Write a short note on Harmonic induction torque and Harmonic synchronous torque of squirrel cage induction motor Also give its effect on the selection rotor slots.
3	Explain the points to be considered for the selection of number of stator slots of an 3-phase induction motor.
4	Explain the factors affecting the choice of specific magnetic & electric  loading in case of a induction machine.
5	State the rules for selecting rotor slots of an 3-phase induction motor. Also explain the methods for the reduction of harmonic torque.
6	Explain the current distribution in the bars and the end rings of a squirrel cage induction motor. Also derive the relation for the current in the end ring.
7	Discuss the Methods to reduce the harmonic torque in induction motor
8	Discuss the effect of air gap length on the performance of a 3-phase induction motor.
9	What is dispersion coefficient? What is its effect on (i)max.  power factor (ii) over load capacity of induction motor?
10	Derive the equation of rotor resistance referred to stator side, for a squirrel cage induction motor.
11	Discuss the advantages achieved on selecting larger air gap in a three phase induction motor.
12	Discuss how the magnetizing current can be estimated from the design data in a three phase induction motor.
13	Discuss the effect of variation of main dimension(D&L) on performance (Rating, losses & efficiency) of  3-ф induction motor
14	What are the factors affecting the length of air gap in 3-ф induction motor.
15	Discuss the different types of stator slots used in 3-ф induction motor
19	Prove that torque produce by 5TH harmonics is in backward direction & 7TH harmonics is in forward direction.
20	State the rules for the selection of rotor slots. Describe the methods for reducing the effect of harmonics torque.
21	Explain the effect of skewing the rotor slots in a squirrel cage induction motor.
22	Explain the factors affecting the choice of specific magnetic & electric  loading in case of a synchronous machine.
23	Define SCR and its importance in designing of synchronous machine.
24	Explain the terms “critical speed” and “run away speed” with reference to synchronous machine.
25	Define and explain the term “short circuit ratio” of a synchronous generator and discuss its influences on the machine performance.
26	Explain the factors affecting the choice of specific magnetic & electric  loading in case of a synchronous machine.
27	Derive an output equation for 3-ф Synchronous machines with usual notation.
	Numericals ( For Reference)
	Electrical Machine Design - II  [ subject code : 180904]
1	A 15-kW, 440-V, 4-pole, 50-Hz, 3-phase induction motor is built with a stator bore 0.25m and a core length of 0.16. The specific electric loading is 23000 ampere conductors/meter. Using the data of this machine, determine the core dimensions, number of stator slots and number of stator conductors for 11-kW, 460-V, 6 pole, 50-Hz motor. Assume a full-load efficiency of 84% and power factor of 0.82 for each machine. The winding factor is 0.955.
2	A 15 kW, 400V , 3-phase , 50Hz, 6-pole induction motor has a diameter of 0.3m and the length of the core 0.12m. The number of stator slots is 72 with 20 conductors per slot. The stator is delta connected. Calculate the value of magnetizing current per phase if the length of air gap is 0.55m. The gap contraction factor is 1.2. Assume the mmf required for the iron parts to be 35 per cent of the air gap mmf. Coil span =11 slots.
3	Determine the main dimensions, Number of radial ventilating ducts and the turns per phase of a 3.7 KW, 400V, 3-Phase, 4-pole, 50Hz squirrel cage induction motor which is to be started using a star-delta starter. Assume:-Average flux density in the gap=0.45wb/m2, Ampere conductors per meter=23000, efficiency=0.85, Power factor=0.84. Choose the main dimension to give an overall good design.
4	Determine main dimensions and turns per phase of a 2 MVA, 11 kV 50 Hz 24 pole three phase star connected alternator. Assume average gap density of 0.55 wb/m2, ac = 30000, winding factor 0.955. Use L/τ ratio of 1.25.
5	The following data refer to a 100 hp , 50 Hz, 8 pole 500 V , slip ring induction motor with 3 phase star connected stator winding: Turns per phase: Stator 64; Rotor 35.  Resistance per phase: Stator 0.062 Ω; Rotor 0.019 Ω. Reactance per phase: Stator 0.21Ω; Rotor 0.019Ω.Magnetizing current 35 A/phase.Iron loss 1495W.Friction and Windage loss 760 W. Draw circle diagram and determine The line current, efficiency, power factor and slip at full load and half load conditions. Also find Maximum output and pull out torque.
6	Determine the main dimensions of 20 kW, 3 phases, 400 V 50 Hz, 1450 rpm squirrel cage induction motor. Assume following: Full load efficiency: 85%. Full load power factor: 0.89 lag. Winding factor: 0.955.Specific magnetic loading: 0.45 wb/m2. Specific electrical loading 28000 A/m. Rotor peripheral speed 20 m/sec at synchronous speed.
7	An 11 kW, 3phase, 6 pole, 50 Hz, 220 V star connected induction motor has 54 stator slots, each containing 9 conductors. Calculate the values of bar and end ring currents. The number of rotor bars is 64. The machine has an efficiency of 0.86 and a power factor of 0.85. The rotor mmf may be assumed as 85 percent of stator mmf. Also find the bar and the end ring sections if the current density is 5 A/mm2.
8	The output coefficient of 968KW, 11KV, 0.9 power factor, 20pole, 50Hz,Delta connected induction motor is 200kva/m3-rps. Find the value of main dimension of the machine if the ratio of length to diameter is 0.2. Also calculate the value of main dimension if the specific loadings are increase by 10% each.  Assume that, Efficiency=86%.
9	The losses of 11kw,3-ф,4kv,50Hz,1000rpm induction motor are as below:Total copper loss=950W, total iron loss=500W, total mech. Loss=110W  Find the output, losses & Efficiency of a similar motor with linear dimensions 1.44 times those of given motor.
10	Find the main dimensions, number of stator turns per phase, size of conductors & number of stator slots for a 5HP, 400v, 50Hz, 1500rpm,3-ф squirrel cage induction motor. Assume that: specific magnetic loading=0.46wb/m2, specific electric loading=22000ac/m, Efficiency=83%, power factor=0.84, stator winding factor=0.955. Suggest for cheap design.
11	Obtain the main dimensions for a peripheral speed of 15m/s for 30HP, 440v, 50Hz, 1000rpm,3-ф squirrel cage induction motor. Assume that: specific magnetic loading=0.46wb/m2, specific electric loading=25000ac/m, Efficiency=86%, power factor=0.87, stator winding factor=0.955.Also calculate number of stator turns per phase &size of conductors
12	Determine the main dimensions and Turns per phase (Tph) of a 3000 KVA, 6.6 KV,50HZ, 187 RPM , 3 phase, star connected alternator. Assume average flux density =0.58 wb/m2 ac=35000.Assume pole arc/pole pitch=0.7
13	Calculate the diameter, core length, no of conductors of the stator , size of conductor,no of stator slots of 30 MVA, 11KV, 3000RPM, 50 HZ, star connected Turbo alternator. Assume Bav= 0.55 Wb/m2, ac=55000 A/m Kw=0.955, peripheral velocity= 160m/s
14	Find the current in the bars and end rings of a cage rotor of a 6 pole 3 phase,induction motor having 72 stator slots with 15 conductors in each slot if the stator current per phase is 20A and rotor slots are 55. Hence find the suitable size of the cage bars and end rings.
15	Find the main dimensions, no of stator turns, and number of stator slots of a 30 H.P., 440 Volt, 3 phase, 50 Hz , 960 rpm, sq. cage Induction motor using following data: Specific magnetic loading=0.45wb/m2,Sp.ele.loading=250amp.condctors/cm full load efficiency= 0.86, full load p.f. =0.87.Assume that stator winding is delta connected, for normal running.
16	Determine the main dimensions, turn per phase, number of slots, conductor section and slot area of a 3-phase, 5 H.P., 400 volts, 50 Hz, 1500 rpm squirrel cage induction motor. The machine is to be started by a star-delta starter.Assume: Average flux density in the air gap = 0.5 Wb/m2, ampere conductors per meter =27000, efficiency = 0.8, power factor = 0.8 lagging at full load, winding factor = 0.955, current density = 3.5 A/mm2. Choose main dimensions to give Good overall design.