Loss calculation in undergound Transmission Cables

I have no experience in wind power farm projects which I am very interested to learn more.I believe it still follow many coventional electrical engineering practices in transmission and distribution.

You can use the data or specifications provided by some respectable cable manufacturers to know the impedence or internal resistance per km of each type/size of cable for your losses calculations.This loss differ slightly between different manufacturers and different types of insulation materials and armouring.For AC 3-core or 4-core cables,the main losses are contributed by copper resistance.Capacitive and inductive losses are comparatively very small.LV DC cables should have higher losses.

Cable loss is directly proportional to the linear lengths,crossection area of conductor,and current (ampere to be conducted or current desity,A/sqmm) and temperature of conductors.Depending on the KVA/KW capacity of each wind turbine/alternator (power generation point) and the distance to the next generation point to be parallel with,the right size and type of cable shall be selected.

My logical thinking is that for economical sizing,each turbine capacity should be more than 500KVA (480A per Phase at 600V,3 phase) on 20 metre pole which is depending mainly on wind velocity and diameter of wind turbine.To avoid air turbulance,may be they should be placed 50 metres apart.With these assumtions,you need at least 300sqmm cu cables to carry the power generated at each point to 0.6/22kv step-up transformer.My point is that one has to step-up the generated voltage say 415 or 600V to 11kv (for e.g.) at the base of each turbine then only transmit the synchronised power to the common busbars near the grid line or intermitant point,may be 5 or 10km away.This way you will save a lot of copper and cable losses,that will pay for the 0.6/11kv step-up TX.From 11kv you can economically step-up to the grid voltage with 5,10,15 or 20 MVA transformers.11kv switchgears and cables are much more economical than 22kv with little cable losses as well.

I may be wrong in my approach to this "design" of the scheme that I can only imagine.It all depends on the KVA size of each turbine.

Best regards,

Khor.