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SPEC F150January, 2008
FormulaShort Circuit Current for Copper Shields
In the three conductorcables, a copper tape is applied over each extruded semi-conducting insulation shield with
a helical gap. Because the three copper tape shields are cabled in intimate contact with the bonding (grounding)
conductor, their combined total cross-sectional areas may be considered an integral shielding system for the pur-
pose of calculating short circuit capacity. It is not possible however, to determine the contact resistance between
the components, due to possible oxides or film which may form on the components or movement of the cable
core during handling. It may be advisable to consider the short circuit capacity of the individual shields indepen-
dently. Because the insulation shields are in thermal contact with the inner PVC jacket, the maximum short circuit
temperature T2 is 200C. Refer to ICEA P-45-482, Short Circuit Performance of Metallic Shields and Sheaths on
Insulated Cable, for calculations involving cables that have other operating parameters.
Under these temperature conditions the short circuit current formula is: I = amperesM . A_________
t
Meaning of Symbols: A = Effective cross-sectional area, shield or sheath
B = Tape overlap (mils) (usually 375)b = Thickness of tape (mils)dis = Diameter over semiconducting insulation shields (mils)d
m= Mean diameter of shield or sheath (mils)
ds = Diameter of wires (mils)I = Short circuit current (amperes)w = Width of tape (mils)n = Number of serving or braid wires or tapesL = Overlap of tape (percent)t = Short circuit duration (seconds)
M = 0.058 for 5-15kV cables0.060 for 25-46kV cables
FORMULA FOR
TYPE OF SHIELD OR SHEATH CALCULATING A
1. Wires applied either helically, as a braid or serving;
or longitudinally with corrugationsnds
2. Helically applied tape, not overlapped 1.27 nwb
3. Helically applied flat tape, overlapped 4 bdm x 100
2(100-L)
4. Corrugated tape, longitudinally applied 1.27[(dis+50)+B]b
5. Tubular sheath 4 bdm
2
Short Circuit Current for Copper Shields
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SPEC F150January, 2008
FormulaShort Circuit Currents for Copper Shields
Effective Cross-Sectional Area in kcmil
ShortC
ircuitCurrentKiloAmperes
1 Cycles
16 Cycles
2 Cycles
30 Cycles
4 Cycles
60 Cycles
8 Cycles
100 Cycles
Allowable Copper Shield Short Circuit Currents for 515 kV
1 10 100
0.01
0.1
100
10
1
0.058 .AI = _______ t
A= Effective cross-sectional area (circular mils)
t= Short circuit duration (seconds)
I= Short circuit current (amperes)
Temperature excursion range 100C200C
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Phone: 888-593-3355
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SPEC F150January, 2008
FormulaShort Circuit Currents for Copper Shields
ShortCircuitCurrentKiloAmperes
1 10 100
1 Cycles
16 Cycles
2 Cycles
30 Cycles
4 Cycles
60 Cycles
8 Cycles
100 Cycles
0.01
0.1
100
10
1
Allowable Copper Shield Short Circuit Currents for 2546 kV
Effective Cross-Sectional Area in kcmil
A= Effective cross-sectional area (circular mils)
t= Short circuit duration (seconds)
I= Short circuit current (amperes)
Temperature excursion range 95C200C
0.060 .AI = _______
t