ELECTRICAL FORMULAS FOR POWER CABLE

Power Cable Capacitance (C) Formula

Single Conductor Shielded Cable

C = 0.024113 x e/ [log (d2/d1)] microfarad/ kilometer

where:

e = dielectric constant for XLPE = 2.3, PVC = 5.0-7.0

d2 = diameter under insulation

d1 = diameter over the insulation

Power Cable Insulation Resistance (IR) Formula

According to ICEA Specification

IR @ 15.6 degrees C = K log (d2/d1) Megaohm - 1000ft

According to JIS Specification

IR @ 20.0 degrees C = 3.665 x 10^-12 x p x log (d2/d1) Megaohm - km

where:

d2 = diameter under insulation

d1 = diameter over the insulation

K = constant (XLPE = 20,000; PVC = 500)

p = volume density (ohm-cm) ; XLPE = 2.5 x 10^15, PVC = 1 x 10^13

Power Cable Inductance (L) Formula

Multiple conductor cable or single conductor cable arranged in parallel and three single conductor arranged in triangular

L = 0.46 log (S/d) + 0.19 mH/km

where:

d = diameter of conductor

S = distance between conductor

Power Cable Charging Current (Ic) Formula

Ic = 2 x pi x fC x v/ 1.73 Amp/km

where:

C = capacitance (F/km)

V = rated line to line voltage (Volt)

f = frequency (Hz)

Power Cable Potential Gradient Formula

E = (v/1.73)/ X ln (d2/d1) kV/mm

where:

X = distance from center of the conductor (mm)

V = rated line to line voltage

d2 = diameter under insulation

d1 = diameter over the insulation