WAZIPOINT Engineering Science & Technology: What Happen If Cables Placed In Magnetic Metal Conduit

Saturday, July 11, 2015

What Happen If Cables Placed In Magnetic Metal Conduit

Single Phase Cable in Non-magnetic Enclosure

What Happen If Cables Placed In Magnetic Metal Conduit 

Do we know what happen if cables in a magnetic metal conduit? Yes, at least we know that in any circumstances it should not be installed individual phase of an ac (alternating current) circuit in separate magnetic metal conduit. 

Most of us we follow these important rules for cable installation, but everyone can’t explain why we should follow this; what happen if individual ac phase placed in a separate metal conduit.

Yes of course, some of us are little advanced; we know we don’t place individual ac phase in metal conduit because of excessive heat may occur in that situation. 

Anyway, separate phases should not pass through magnetic structures because overheating can occur due to excessive hysteresis and eddy current losses.

Already question is arisen, is it acceptable to passes all the phases together through in a magnetic conduit? Yes, it is wise to passes through all the phases in any magnetic enclosure simultaneously so that maximum cancellation occurs of the resultant magnetic field. 

This procedure huge reduces the magnetic field, though increases the skin and proximity effect of cable. Because of proximity of magnetic materials some losses occurs in conductor just placing the cable near the magnetic materials, amount of losses depends on volume of materials.


Skin Effect:

In an ac circuit, current tends to flow through over the outer surface of conductor than the inner side, means that current density is greater near the outer surface of the conductor. This effect is called skin effect. 

Due to skin effect, a long cable center axis is surrounded more magnetic field than surface, as a result inductance increase toward the center. Finally resistance increase and conductance decrease in the center than surface.

 Proximity Effect:

If ac conductors are placed in closely, there is a tendency for the current to shift to the portion of the conductor that is away from the other conductors of that cable. This is called proximity effect. 

So, we can say: Insulated conductors should not be installed in metallic conduits and also not run close to magnetic materials. For example- high voltage underground power cable frequently need to passes along the metallic materials like gas pipe line, water pipe line, etc. which may dangerously electrified by induced voltage if not properly grounded both of metallic pipe and cables metallic sheath.

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