Size of copper tape for High voltage cables
Size of copper tape for High voltage cables
(OP)
Can anybody tell me how to calculate the size of the copper tape in case of high voltage cables?
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Size of copper tape for High voltage cables
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RE: Size of copper tape for High voltage cables
Scott Peterson
Training Manager
Power Plus Engineering
www.epowerplus.com
RE: Size of copper tape for High voltage cables
RE: Size of copper tape for High voltage cables
RE: Size of copper tape for High voltage cables
RE: Size of copper tape for High voltage cables
The copper tape have two functions.
(a) The copper tape will be a low impedance return path for the fault current (because of the close proximity with the conductor). The copper must be able to withstand the prospective fault current for the fault duration. The cable manufacturer will specify the cable rating for earth fault currents. I will leave the calculations to the cable manufacturer and specify the prospective earth fault current. Cables making use of copper tape have a low earth fault current rating (Typical 4kA but depends on Cable manufacrurer). In other parts of the world, individually screened conductor using wire are used instead of tape with earth fault current ratings of up to 10kA. Some users opt to earth only one side of the screen.
(b) The second function of the tape is to help conduct heat generated by the three conductors. Heat will be conducted radially outwards away from the conductor. Heat will accumulate in the centre of the cable between the three conductors and the copper tape will help in conducting this heat to the oposite side of the conductors, closer to the jacket/armouring/sheath. The thicker your tape are, the better heat transfer and the higher cable rating you will have. Only if you are designing the actual cable will it be required to calculate the actual copper tape size.
You can refer to IEC60287 for the actual calculations. The earth fault current capability calculations will be particularly difficult as you have to use a dynamic model. The steady state thermal calc's can easilly be done by hand.
RE: Size of copper tape for High voltage cables
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RE: Size of copper tape for High voltage cables
"Short Circuit Performance of Metallic shields and Sheaths of Insulated Cable (Second Edition)", ICEA Publication P-45-482, 1979
Siemens Power Cables and their Application, 1990
"Rating of Conductors For Short Duration Currents", V.T. Morgan, Proc. IEE, Vol. 118, No. 314, March/April 1971.
"The Short-Circuit Rating of Thin Metal Tape Cable Shields", R.C. Mildner and others, IEEE Transactions on Power Apparatus and Systems, Vol. PAS-87, No. 3, March 1968, pp. 749-759.
I'll have to disagree with KJvR about the second function. For single core cables, with shields grounded at both ends, increasing the thickness of the tape will decrease the resistance and increase induced shield currents and losses, causing more heating and lower current carrying capacity.
RE: Size of copper tape for High voltage cables
RE: Size of copper tape for High voltage cables
When you move into MV and higher voltage applications for cables, you have to use semiconductor around the cable. Semiconductor does have a relative high resistance, and due to capacitive coupling there are always small currents in the screen.
P = I²R ===> High power, even if the currents are relative small, and this burns the semiconductor. To minimize the resistance, a screen is added with the semiconductor.
The thickness of the tape is thus dependant on a function of the total resistance (semiconductor + metallic screen) and the possible induced shield current.
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