Proximity Effect, Skin Effect, and Eddy Current Losses

Introduction

There is much confusion about calculating the wattage losses within an operating AC facility power distribution system. Despite large bodies of published knowledge to the contrary, many facility and utility engineers persist in performing simple line loss calculations based upon known wire conductor specifications and published DC resistance values. Consequently, when discussions of possible energy usage reduction measures are raised, these same personnel frequently cause substantially beneficial projects to go unimplemented. EASI specializes in identifying and eliminating or reducing AC distribution losses in fully operational, fully loaded commercial and industrial power systems. This paper is our simple statement that all of our work is based upon standard, published calculative methods, and considers long acknowledged and quantified phenomenon contributing wattage losses to operating AC power systems. The particular focus herein is upon proximity effect losses and eddy current losses in magnetics and distribution wiring.

Proximity Effect

The AC current in two round, parallel wires is not distributed uniformly around the conductors. The magnetic fields from each wire affect the current flow in the other, resulting in a non-uniform current distribution, which in turn, increases the apparent resistance of the conductors. In parallel round wires, we call this the proximity effect.

EASI applies proprietary mathematics routines to identify the distribution losses associated with proximity and skin effects. EASI quantifies the AC losses in conductors, switchgear, protective systems, and the windings of any magnetic device within a closed facility electrical distribution system. Without proximity analysis the actual distribution losses can be much higher than the predicted DC losses.

Proximity Losses in AC Conductors and Magnetic Devices

Proximity effect is an AC power system phenomenon that can greatly increase magnetic losses over DC resistance or skin effect values alone. Closed form analysis in the form of a set of hyperbolic equations is possible without resulting to 3-D finite analysis programs. However, a full harmonic analysis must be used on the governing equations or loss estimates may be off by orders of magnitude. As a result, EASI uses a proprietary computer program in order to quickly calculate the results of design changes upon facility distribution system losses.

What is Proximity Effect?

Most power engineers are familiar with the tendency of a current to flow on the outside of a conductor at higher frequencies. With skin effect, the current distribution is affected by the conductor's own magnetic field, increasing the losses. Proximity effect is similar, but is the mutual influence of multiple current carrying conductors. Their interaction causes uneven current distribution in the conductors, again increasing losses.


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