AIT/IQAC/Aca/19-20/
Acharya Institute of Technology
Department of Electrical and Electronics Engineering
Bengaluru 560107
Assignment no 4 [Academic Year: 2019-20]
Sub with Code: Electrical Machine Design (15EE64/17EE64) Semester : 6 A& B
Marks: 10/05M Date: 25/05/2020
Submission date: 08/06/2020
Q.No Questions CO
1 Discuss the design of slip ring rotor of a three phase induction motor. CO1
2 Discuss the effect of choice of specific magnetic and electric loadings in synchronous machines CO1
3 Define SCR of a synchronous machine, Derive the equation and discuss its effect on machine CO2
performance.
4 Discuss the factors to be considered for while selecting a suitable number of armature slots in CO1
synchronous machines.
5 Derive the output equation of synchronous machine. CO2
6 CO1
What are the steps involved in the design of field winding of salient pole alternator.
7 What are the steps involved in the design of field winding of non-salient pole alternator. CO1
8 During the stator design of 3-phase, 30kW,400V, 6 pole, 50Hz squirrel cage induction motor, CO3
following information has been obtained. Gross length of stator= 0.17m, Diameter of stator
bore=0.33m, Number of stator slots=45, number of conductors per slot=12. Based on above data
design a suitable cage rotor for the above motor. Assume efficiency 88% and power factor as
0.86.
9 Determine main dimensions, air gap length, stator slots, conductors per slot, stator turns per phase CO3
and cross section area of stator and rotor conductors for a 3 phase 15 HP, 400 V, 6 pole, 50 Hz,
975 rpm induction motor. The rotor is star-delta started. Bav=0.45 T, ac=20000 AC/m, pf=0.85,
efficiency=90%. ratio of pole arc to pole pitch=0.85
10 A 11kW, 3 phase, 6 pole, 50Hz, 220V, star connected induction motor has 54 slots in stator CO3
containing 9 conductors per slot. Calculate the value of bar and end ring current. The number of
rotor bars is 64. The efficiency of the machine is 0.86 and has power factor 0.85. the rotor MMF
is assumed as 85% of stator MMF. Also find current in bar and end ring sections if current
density is 5A/mm2 .
11 A 850kW, 6600V, 50Hz, three phase, 12-pole slip ring induction motor has following data. . CO3
Gross length of stator= 45cm, Diameter of stator bore=122cm, Number of stator slots=144,
number of conductors per slot=10, efficiency is 92% and power factor as 0.85, Voltage between
slip rings =600V. Design a wound rotor by giving a length of airgap, rotor core length, diameter
of rotor, rotor slots, rotor conductors per slot, actual rotor turns per phase, actual slip ring voltage,
rotor current per phase, Assume star connected induction machine.
12 A 15kW, 400V, 3 phase, 50Hz, 6 pole induction motor has Gross length of stator= 0.12m, CO3
Diameter of stator bore=0.3m, Number of stator slots=72, number of conductors per slot=20,
stator is delta connected. Calculate the value of magnetizing current per phase if the length of the
Department of EEE, Acharya Institute of Technology,Bangalore-560107
AIT/IQAC/Aca/19-20/
Acharya Institute of Technology
Department of Electrical and Electronics Engineering
Bengaluru 560107
airgap is 0.55mm. the gap contraction factor is 1.2. assume the mmf required for the iron parts to
be 35% of air gap mmf. Coil span = 11slots. Also calculate No load current, core loss component
and no load power factor if the core loss is 500W and friction & windage loss is 100W.
13 The following is the design data available for a 1250kVA, 3300V, 50 Hz, 300 rpm 3Ф star CO3
connected alternator of salient pole type: stator bore D= 1.9m, stator core length = 0.335m, pole
arc/pole pitch = 0.66, turns per phase = 150, single layer concentric winding with 5 conductors
per slot, SCR= 1.2. Assume that the distribution of gap flux is rectangular under the pole arc with
zero values in the inter polar region. Calculate a) specific magnetic loading b) armature mmf per
pole c) gap density over pole arc d) air gap length
Mmf required for air gap is 0.88 of no load field mmf and gap contraction factor is 1.15
14 Find the dimensions of 100MVA, 11Kv, 50Hz, 150RPM 3-Phase water wheel generator. The CO3
average gap density is 0.65T and ampere conductors is 40000. The peripheral speed must be less
than 65m/s in order to limit the run away speed under normal running condition. Winding factor
is 0.955
15 A 500kVA, 500 rpm, 3Ф, 50 Hz, 6600V, star connected, 12 pole salient pole alternator has CO3
following design data: Stator bore = 1.3m, core length = 0.21m, air gap flux per pole= 0.0404wb,
SCR=1.1, MMF rquired for airgap AS 70% of no load field MMF, gap contraction factor is 1.15,
field form factor is 0.7, leakage factor for flux is 1.15, The flux density in pole body is 1.5
wb/m2, the winding depth is 4cm, the ratio of full load field mmf to armature mmf is 1.8, field
winding space factor is 0.7 and field winding dissipates 700W/m2 of inner and outer surface
without temp rise exceeding this permissible limit. Leave 4cm for insulation, flanges and height
of pole shoe along the height of pole. Find a) Length of air gap b) Diameter of rotor at the airgap
surface c) dimension of pole.
16 A 1000 kVA, 3300V, 50Hz, 300 rpm, 3 phase alternator has 180 slots with 5 conductors/slot, CO3
single layer winding with full pitch coils used. The winding is star connected with one circuit per
phase. Determine the specific electric and magnetic loadings, if the stator bore is 2m and the core
length is 0.4m. using the same loadings, determine corresponding data for a 1250kVA, 3.3kV,
50Hz, 250rpm, 3 phase star connected alternator having 2 circuits per phase. The machines have
60 degree phase spread
17 A 1875kVA, 250 rpm, 3Ф, 50 Hz, 3300V, star connected salient pole alternator has following CO3
design data: output coefficient=208, peripheral speed < 32.6m/s, excitation voltage=100V, air gap
length= 0.6cm, 3 ventilating ducts 1cm width, air gap flux per pole= 0.068wb, SCR=1.1, MMF
rquired for airgap AS 70% of no load field MMF, gap contraction factor is 1.15gross length/ pole
pitch=1.23, winding factor=0.955, iron space factor=0.95, leakage factor for flux is 1.2, The flux
density in pole body is 1.4 wb/m2, the winding depth is 4cm, the ratio of full load field mmf to
armature mmf is 1.8, field winding space factor is 0.7 and field winding dissipates 700W/m2 of
inner and outer surface without temp rise exceeding this permissible limit. Leave 4.5cm for
insulation, flanges and height of pole shoe along the height of pole. Find a) Length of air gap b)
Diameter of rotor at the airgap surface c) dimension of pole.
18 Estimate the stator dimensions, stator size, number of conductors, number of slots of 15MVA, CO3
11kv, 3 phase, 50 Hz, 2 pole turbo alternator with 60 degree phase spread. Assume Specific
electric loading = 36000 AC/m, specific magnetic loading = 0.55 Tesla, Current density = 5
Amp/mm2 , peripheral speed = 160 m/s. The winding must be designed to eliminate 5thharmonic.
Department of EEE, Acharya Institute of Technology,Bangalore-560107
AIT/IQAC/Aca/19-20/
Acharya Institute of Technology
Department of Electrical and Electronics Engineering
Bengaluru 560107
19 A 3000RPM, 3 Phase, 50Hz turbo alternator has core length of 0.94m. The average gap density CO3
is 0.45 Tesla and the ampere conductors per m are 25000. The peripheral speed of the rotor is
100 m/s and the length of the air gap is 20mm. Find the kVA output of the machine when the
coils are (i) full pitched (ii) short chorded by 1/3rd pole pitch. The winding is infinitely
distributed with a phase spread of60 degree.
Department of EEE, Acharya Institute of Technology,Bangalore-560107
