Power Cable Calculation MV/HV
Power Cable Calculation MV/HV
(OP)
Hi every one,
In our substation, the route of the HV power cable is through trench and pipe ducts. Pipe ducts consititute 25% of the route.
For Cable calculations, how should we consider the laying method of the cable. Trench, Pipe duct or the worst of both.
Or we do the calculation separately for Trench part and separately for pipe duct route and take into consideration the worst case.
What IEC recommends in such scenario.
Thanks for you time,
Ohms
In our substation, the route of the HV power cable is through trench and pipe ducts. Pipe ducts consititute 25% of the route.
For Cable calculations, how should we consider the laying method of the cable. Trench, Pipe duct or the worst of both.
Or we do the calculation separately for Trench part and separately for pipe duct route and take into consideration the worst case.
What IEC recommends in such scenario.
Thanks for you time,
Ohms






RE: Power Cable Calculation MV/HV
Unless you consider using different cable sizes for the trench and duct sections and joining them(In my opinion not a good solution), you should consider the worst case which is pipe duct.
Hope this helps
HBarton
RE: Power Cable Calculation MV/HV
RE: Power Cable Calculation MV/HV
The IEC STD 287 may be useful:
IEC 287-1-1: 1994, Electric cables - Calculation of the current rating - Part 1: Current rating equations (100 % load factor) and calculation of losses - Section 1: General
IEC 287-2-1: 1994, Electric cables - Calculation of the current rating - Part 2: Thermal resistance - Section 1: Calculation of thermal resistance
IEC 853, Calculation of the cyclic and emergency current rating of cables
regards
RE: Power Cable Calculation MV/HV
what if installation in pipe ducts constitutes 5% (or 1%) of the route? should we still consider this as the worst case for IEC287 cable derating calculations? is there a related clause in IEC or other standard that binds route length to what is considered "worst case".
example given: 100m in a trench and 5m in a pipe duct to enter a building. Could those 5m be safely "ignored"? How can you prove this?
thanks...
RE: Power Cable Calculation MV/HV
Regards
Marmite
RE: Power Cable Calculation MV/HV
Definition of "short" is left to engineering judgement.
RE: Power Cable Calculation MV/HV
My feeling is that IEC287 derating formulas are obtained for lim d->inf, where d is the length of cable. Thus, they are valid to apply for long runs but lead to overdimensioning when applied for 'short' runs.