hdpe for ehv cable

Hello,
I want to know that why in ehv cables above 66 kV HDPE is prefered for outer jacketing than PVC .

Regards
Kumar M

Hello

PVC is a mixture of a number of chemicals and clay. Sheaths of PVC are generally for inside use but I am aware in Japan of XLPE, EHV cables up to 225 kV.back in the 1970s and they had PVC sheaths.

In contrast, polyethylene is a polymer to which a number of chemicals have been added. (UV resistant chemicals, color pigment, anti-oxidants and so on.) High density polyethylene is also tougher than low or medium density polyethylene. Polyethylene in general well matches the thermal properties of the HV and EHV, XLPE cable cores and is excellent in providing damage and corrosion protection to the heavy cables over the long haul. That is why it is specified .

Thank you.

Thanks sir,
But I also want to know why we use a layer of graphite over sheath in ehv cables

Regards
Mandeep

Hello again,

In India, a dual sheath is used. The first layer is the standard polyethylene material and the outer layer is semi-conducting, non cross-linked polyethylene. The reason for this is to electrically check at the factory if there are any holes or discontinuities in the first layer.

Perhaps, in your country or area, they are checking the continuity of the sheath at the factory by using a graphite coating.