ആര്മറുകള് കേബിളുകളെ മെക്കാനിക്കലായി പ്രൊടെക്റ്റ് ചെയ്യാനാണെന്ന് എല്ലാവര്ക്കും അറിയാമല്ലോ. ഈ വിഷയം മലയാളത്തിനേക്കാള് ഇംഗ്ലീഷ് ആയിരിക്കും നല്ലത് എന്നതിനാല് ബാക്കി ആ ഭാഷയില് കിടക്കട്ടെ.
As all know, when current passes through a conductor, magnetic field will be created around it and the direction of the magnetic field depends upon the direction of the electrical current. Armours are mainly for the mechanical protection of cables (conductors).
Consider a steel wire armoured cable with two conductors that used to connect a single phase load.
As the direction of the current in one conductor is opposite to that of the other, magnetic fields produced in these conductors will have opposite directions and hence will cancel.
That is, no effective magnetism will be present in the case of two core steel armoured cables and is same in the case with 3core /4core cables that are connected to three phase balanced loads.
Now consider a single conductor having steel wire armour.
If we study this cable it can be considered as a transformer, the current carrying conductor being the primary and the steel wire armour the secondary.
When current start flowing through the conductor, magnetism will be produced around the conductor. As the cable is surrounded by steel armour, magnetism will also link to it.Outcome of this will induce e.m.f in the armours and will definitely circulate current in the ‘secondary’, (eddy current) and of course heat!.
Therefore, if single core cables are to be used for higher power transmission, Non ferrous/ Magnetic materials must be used as armours. That is why, single core cables used from the transformers to the LV panels are of AWA, Aluminium Wire Armoured cables.