Medium voltage switchgear application guide

Medium voltage switchgear application guide
Appendix 5: cables
(cont’d)
MV cables capacitance
single-pole cable
individually screened three-pole cable
K
C
C
C
belted three-pole cable
4 - TYPE OF CONDUCTOR
A and cable mechanically is comprised united of either conductors. one conductor, or several electrically distinct
The ■single-pole different types individually of cables screened insulated cables, by extruded solid dielectrics are:
■individually ■belted three-pole screened cables. three-pole cables,
■the The metal type part of metal: of the annealed conductor electrolytic is defined copper by:
annealed aluminium, or 3/4 hard or sometimes
■electric ■self-induction resistance coefficient per unit (L of in length H/km) (R which in ohm/km),
geometrical size and the relative disposition of depends the conductors. essentially on the
■the rated cables section capacitance. (mm2),
5 - MV CABLES CAPACITANCE
The capacitance of a cable depends on the construction type:
■ single-pole
cable capacitance
cables:the
C is that conductor measured is between surrounded the conductor by a screen and and the the
which is earthed.
screen
■ individually screened three-pole
by a screen and the cable capacitance
cables:each
is that measured conductor between is surrounded
conductor and its individual screen which is earthed. each
■ belted three-pole
there is a capacitance
cables:a
K between screen conductors surrounds and a capacitance three conductors C between and
a conductor and the screen which is earthed.
Ic= The 3 capacitive C ωV which current causes Icof capacitance a network in C the only event to intervene of an earth whatever fault is:
cable type.
the
In practice, C for for a star-connected individually screened capacitance, cables. the cable makers indicate:
Upon ■the value request, 3 K the + C cable for belted maker cables.
measured between the three inter-connected will tell you the conductors capacitance and the C2(C2= metal sleeve. 3 C)
date
11/94
- B•3•2 -
revised
05/2004
page 10