At power frequencies, skin and proximity effect are Negligible at small frequency.

Skin effect – Skin effect is a tendency for alternating current (A.C) to flow mostly near the outer surface  of an electrical conductor, such as metal wire.

Proximity effect – Proximity effect is a phenomenon  which is observed in conductors carrying alternating current. When a conductor carries A.C. power, the constantly varying magnetic field  induces eddy currents in the nearby conductors. In conductors  where the current flows in the same direction, this results in increased current density in the nearby conductors due to the changes in the current distribution across the cross – section of the conductor. Thus the resistance of the  conductor increase.