medium voltage conductor

[mara24]

Hi, what guidelines should I follow to select cable type for MV feeders (motors and transformers). I'm trying to obtain information about best practices to use either one cable with 3 conductors or 3 separate cable (single conductor). Any help will be apreciated, I'm new in the EE field.

 

[rbulsara]

Single conductors in raceway are more common in the USA.

3-conductor cables, not necessarily in raceways, are more common in Asia (Indian subcontinent). Mainly due to cost factor.

Talk to a good sales engineer of leading MV cable manufacturers in your area or speak to a good electrical contractor, specializing in MV cable installations.

 

[RalphChristie]

mara24:

You have just mentioned one choice, that between single core and 3 core conductors. The company I am working with, use single core where the conductor size has to be big, and 3-core for the smaller distribution networks. But there can be more:

Choice between aluminium and copper conductors:
Aluminium conductors are larger than copper conductors for the same current-carrying capacity, which may add to installation costs. The choice will mainly be an economic one, influenced by availability and the relative prices of the two metals at that stage.

Aluminium may be considered in high corrosive areas.

The choice of cable insulation type:

For normal distribution purposes, the choice is between PILC and XLPE.
XLPE have a higher current rating for the same conductor size
PILC tends to be more expensive than XLPE for the same conductor size
XLPE has a larger overall diameter for the same conductor size
PILC cables provide better corrosion resistance than XLPE
PILC has a higher average life span.
XLPE cables are better suited to be moved frequently after installation.

Single core cables may offer an economical choice, especially in high current applications.
Single core cables are easier to repair after a cable fault
On smaller applications, 3-core cables are easier and quicker to install.

Normally, once a choice is made, companies tend to stick to a specific type of cable, in order to prevent confusion, eliminate need for re-training, and reduce stock levels.

Hope this helps

Regards
Ralph



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[benlanz]

For MV class applications you should always use a shielded power cable. If the cable is shielded the bundling configuration has little to do with the reliability. EPR insulation is a favorite of the industrials for its robust dielectric properties. However, we do not recommend a tape shield because it severely limits any kind of IEEE standardized preventive diagnostics/ non destructive fault location techniques after about 10 years. We recommend a concentric or LC shield. I hope this helps.

Benjamin Lanz
Vice Chair of IEEE 400
Sr. Application Engineer
IMCORP- Power Cable Reliability Consultants

 

[peebee]

EPR - cheaper (I think) and easier to bend than XLPE but higher leakage current (and therefore higher operating cost) than XLPE and therefore better suited to shorter runs than XLPE -- typical choice for campus distribution systems but not used for long utility runs.

XLPE -- less leakage & therefore lower operating costs on long runs -- better choice for utilities with long runs than EPR would be.

Re benlanz statement: "For MV class applications you should always use a shielded power cable" -- I think there's a bit of leeway there at the low end of MV applications, I would have recommended shielded for all MV over 2kV or over 5kV, I'd need to check IEEE for the exact number, maybe someone else is more familiar with that cutoff..... But I'm nearly certain that shielding is rather optional in the 600 to 2000v range.