## Monday, November 7, 2011

### 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)