The non-uniform distribution of alternating current in a conductor due to the presence off other current carrying conductors in the locality, is called as proximity effect.
Proximity Effect Factor
Two single core cable
Where, xp² = 8 . p .√(10ˆ-7 .kp / Rdct)
f = Frequency
kp = Factor determined by conductor construction
dc = Diameter of conductor
Rdct =DC resistance
S = Spacing between conductor centres
- When two or more AC current carrying conductors are close to each other. Than distribution of current in each conductor is affected due to the varying magnetic field of each other.
- The varying magnetic field produced by alternating current induces eddy currents in the adjacent or nearer conductors.
- Due to this, when the nearby conductors , the current is concentrated at the farthest side of the conductors.
- When the nearby conductors are carrying current in opposite direction to each other, the current is concentrated at the nearest parts of the conductors.
- The proximity effect also increases with increase in the frequency. This circulating current increases the resistance of the conductor and push away the flowing current through the conductor, which causes the crowding effect.
Reducing proximity effect
- these effect can be reduced by selecting the core and number of turns that optimizes the number of layers.
- An increased number of layers decreases the losses after the first selection.
- Foil winding layers reduces the losses more effectively as compared to round wires on a single layer. Interleaving the winding also reduces the this effect.
- Interleaving decreases the effective number of layers in each section of winding. thus, the resulting field build up more uniformly than rising gradually in between.
proximity effect are absent in case of DC currents, as frequency of DC current is zero.
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