DEDAN KIMATHI UNIVERSITY OF TECHNOLOGY
ELECTRICAL AND ELECTRONICS ENGINEERING DEPARTMENT
EEE 5115: ELECTRICAL MACHINE DESIGN
Assignment 1
DATE: JULY 2020
1.
2.
3.
4.
What is the advantage of large number of poles in electrical machines?
Mention the importance of conductor dimensions.
What is unbalanced magnetic pull?
Determine the main dimensions of the 3 limb core (ie 3 phase, 3 leg core type
transformer), the number of turns and cross-sectional area of the conductors of a 350
kVA, 11000/3300 V, star/delta, 3phase, 50 Hz transformer. Assume: Volt/turn = 11,
maximum flux density = 1.25 T. Net cross-section of core = 0.6 d2, window space factor
= 0.27, window proportion = 3:1, current density = 250 A/cm2, ON cooled ( means oil
immersed, self-cooled or natural cooled) transformer having + 2.5% and +5% tapping
on high voltage winding
5. Determine the diameter and length of armature core of a 55kW, 110V, 1000rpm, 4 pole
shunt generator, assuming specific electric and magnetic loadings of 26000
amp.comd/m and 0.5 Wb/m2 respectively. The pole arc should be about 70% of pole
pitch and length of core about 1.1 times the pole arc. Allow 10A for the field current
and assume a voltage of 4V for the armature circuit. Specify the winding used and also
determine the suitable values for the number of armature conductors and number of
slots.
6. What is the advantage of large number of poles?
weight of iron parts decreases
weight of copper part decreases
length of commutator reduces
overall length of machine reduces
Distortion of field form becomes less at full load condition.
7. Mention the importance of conductor dimensions.
The dimension of the conductors directly affects the following factors in rotating
machines:
Allowable temperature rise
Resistivity
Current density
Specific electric loading
8. What is unbalanced magnetic pull?
The unbalanced magnetic pull is the radial force acting on the rotor due to non-uniform
air-gap around armature periphery.
9. Determine the main dimensions of the 3 limb core (ie 3 phase, 3 leg core type
transformer), the number of turns and cross-sectional area of the conductors of a 350
kVA, 11000/3300 V, star/delta, 3phase, 50 Hz transformer. Assume: Volt/turn = 11,
maximum flux density = 1.25 T. Net cross-section of core = 0.6 d2, window space factor
= 0.27, window proportion = 3:1, current density = 250 A/cm2, ON cooled ( means oil
immersed, self cooled or natural cooled) transformer having +_ 2.5% and +_5%
tapping on high voltage winding
10. Determine the diameter and length of armature core of a 55kW, 110V, 1000rpm, 4 pole
shunt generator, assuming specific electric and magnetic loadings of 26000
amp.comd/m and 0.5 Wb/m2 respectively. The pole arc should be about 70% of pole
pitch and length of core about 1.1 times the pole arc. Allow 10A for the field current
and assume a voltage of 4V for the armature circuit. Specify the winding used and also
determine the suitable values for the number of armature conductors and number of
slots.