Eddy Currents Increase Winding Losses

AC currents in conductors generate ac magnetic fields which in turn generate eddy currents that cause a nonuniform current density in the conductor . Effective resistance of conductor increased over dc value.

Eddy currents

)2 if conductor w,sp dimensions greater than a skin depth.

Eddy currents

• m = magnetic permeability of conductor; m = mo for nonmagnetic conductors.

• s = conductivity of conductor material. Numerical example using copper at 100 °C

Frequency

50

5

20

500

Hz

kHz

kHz

kHz

Skin

10.6

1.06

0.53

0.106

Depth

mm

mm

mm

Mnimize eddy currents using Leitz wire bundle. Each conductor in bundle has a diameter less than a skin depth.

Twisting of paralleled wires causes effects of intercepted flux to be canceled out between adjacent twists of the conductors. Hence little if any eddy currents.

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