Underground cable trenches within a Wind Farm 1

[koutsias]

Underground medium voltage (33 kV) cables are to be laid in trenches to connect the 50 individual wind generators of 2 MW each to be erected in a wind farm / park.

The wind farm covers a hilly area of approximately 3 km x 3 km and the trenches are to be excavated along one side of the earthen roads that will be prepared/constucted for erecting the wind generators.

Given that the wind farm area consists of leased land, is not fenced and is accessible to everybody including the individuals owning the nearby fields, what kind of mechanical protection is recommended for the underground cables so as to exclude the possibility of electrocution of a person who may mechanically or manually dig over the cables?

Any recommendations / suggestions / standards are appreciated in advance.

 

[Marmite]

It depends on the regulations in force in the location as to what you would require. I work in the UK where we have regulations (ESQC Regs) with state that the cables have to be marked and protected. For 33kV we use either interlocking plastic tiles, concrete cable tiles, or tile tape if the cable is laid by cable plough. The protection is usually installed 150mm above the top of the cable to give adequate warning. All of these have lettering warning of the presence of HV cables below. If the land is arable (ie likely to be ploughed) we would aim for 1150mm cover to the top of the cable, or duct. Other Companies here have slightly different measurements, but in the same ballpark. The normal laying depth in the UK for 33kV cables is 800-1000mm.
Regards
Marmite

 

[itsmoked]

A meter even seems shallow for arable land.

I suspect a concrete culvert would be the safest bet.

Pipelines have similar issues and a meter, often, isn't enough.
Note the sod rippers.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[controlsdude]

I know the NEC if in USA goes into specifics on underground spaces that anyone has access to all the time

article 300.50 covers it

table 300.50

30k puts it at 600 mm for direct burial.

I would crack that nec book open and read it.

 

[controlsdude]

sorry thats 900 mm for 30k

 

[dpc]

For what it's worth here are the US National Electrical Code MINIMUM requirements for a 33 kV circuit:

Direct-Buried Cable 900 mm
Rigid PVC Conduit 600 mm
Rigid Steel Conduit 150 mm
Concrete encased 100 mm

Warning tape is required unless encased in concrete

 

[7anoter4]

Hi koutsias
I agree with all above .I think -it is very expensive, indeed- a cable duct bank [6*6"plastic conduits embedded in 2-3 inches- exterior steel reinforced concrete-it is the maximum protection and it facilitates further development also. This duct bank has to be buried too 2.5-3 ft under the soil.
But for cable run all 150 -200 ft a manhole should be provided- including some cable trays.
Best Regards