Cable voltage grade selection

[Girish Pillai]

Hi,

I want to select the voltage grade for my 22 kV incoming cable.

I understand for a cable denoted with U0/Un (Um, is

U0 is the rated power frequency voltage between conductor and earth or metallic screen for which the cable is designed.
U is the rated power frequency voltage between conductors for which the cable is designed.
Um is the maximum value of the "highest system voltage'' for which the equipment may be

So based on this i am not able to decide whether i have to go for cable with a voltage grade of 12/20 (24) or 18/24 (36).

as 12/20 (24) can be used for a maximum of 24 kV.

Can anyone provide an explanation to selected which??

 

[7anoter4]

In IEC 60502-2 CH. 4.1 Rated voltages it is stating :
“The rated voltage of the cable for a given application shall be suitable for the operating conditions in the system in which the cable is used. To facilitate the selection of the cable, systems are divided into three categories: A,B and C.
A if the supply source is disconnected within 1 min maximum.
B if the supply source is disconnected within 60 min maximum.
C-indefinite time.
From Table 1 – Recommended rated voltages U0:
if you intend to use the cable indefinite time in one phase_to_ground fault[ C condition] then for up to 24 kV maximum line_to_line voltage recommended Uo=18 kV -then 18/24 kV].
In A or B condition may be employed 12/20 cable.