Analyzing Cable Costs

Hi,

Please follow the steps:

• First decide the voltage .
• Then decide about the load. (4000 kW)
• Consider the Short Circuit Rating
• Decide about the type of cable laying
• Finalise the cross section based on the above factors.

It is quite obivious that the cross section of 11 kV will be higher and therby cost for cable, support structure will be more.

N.Suresh

Hi,

Please follow the steps:

• First decide the voltage .
• Then decide about the load. (4000 kW)
• Consider the Short Circuit Rating
• Decide about the type of cable laying
• Finalise the cross section based on the above factors.

It is quite obivious that the cross section of 11 kV will be higher and therby cost for cable, support structure will be more.

N.Suresh

doubt:

actually the cross section of the cable depends upon the current rating.so higher voltage means it takes lesser current .Then why you said that cross section of 11 kV will be higher .current higher -cross section high-cost is high.(this is my opinion)

my question is can i take two different cable size for comparision

Hi ,

What i understand from Mr. Nagarajan answer is , cross section of 11 KV cable is always higher than 6.6 KV cable considering cable size is same .i.e a 300 sqmm ,11KV cable have higher cross section than 300 sqmm , 6.6KV .As higher rated voltage cable require more insulation material (XLPE .. etc) so more cross section area.

Hi,

Well, there are some items I assumed, but the calculation is not so difficult.

Example 1:

4000kW; approx. 430A; 6.6kV; Ik= 31.5kA; cable length= 100m; CB switch off time=0.15s;
IEC/VDE regulation; ambient temperature = 45°C; cable laid on cable tray; XLPE cable multi.

Cable according to short circuit:

According to data above, the cross section of each cable must be (worst case) mind. 85mm2 resp. 95mm2 (cable type)

Cable according to load:

Reduction factor:

Laying on tray: 0.91

Temperature: 0.87

Total= 0.91x0.87=0.7917

430A/ 0.7917 = 543A è for this value you have to find a cable which is bigger than 95mm2 (short circuit)

Cable load according IEC= 3x95è 304A

Max. cable load: 2x304A = 608A

Check: 543<608

You should use two cable 3x95/16 parallel for this Motor.

Example 2:

4000kW; approx. 250A; 11kV; Ik= 31.5kA; cable length= 100m; CB switch off time=0.15s;
IEC/VDE regulation; ambient temperature = 45°C; cable laid on cable tray; XLPE cable multi.

Cable according to short circuit:

According to data above, the cross section of each cable must be mind. 85mm2 resp. 95mm2

Cable according to load:

Reduction factor:

Laying on tray: 0.91

Temperature: 0.87

Total= 0.91x0.87=0.7917

250A/ 0.7917 = 316A è for this value you have to find a cable which is bigger than 95mm2 (short circuit)

Cable load according IEC= 3x95è 304A

Check: 250<304

You should use one cable 3x95/16 for this Motor.

Last comment:

You can optimize the cable cross section if you change laying factor, temperature, etc.

Hope that the calculation is helpful.

BR

Wormnhaque

download from dutch side

vision

http://www.phasetophase.nl/en_index.html

configure all your cases voltage and load patterns in the demo mode

calculate loadflow an go to results (it wil do for max 20 nodes)

but your case will fit