Cable sizing

Hello Bens

For a proper answer to be given, there are some factors which need to be known:

A) Type of soil:

1. Sand
2. Silt
3. Loam
4. Clay
5. Shingle
6. Other - Please specify
   

B) Ground water Level, on monthly basis (Full year required)

C) Thermal Conductivity of "Soil"

D) Type/s of Cable = Conductor:

1. Copper SWA
2. Copper Lead Clad SWA
3. Copper Lead Sheath
   
4. Aluminium
   
5. Aluminium Tape Armoured
   
6. Other - Specify

E) Type of Cable = Insulation

1. XLPE
2. Polyethelene
3. PVC
4. Oil Filled Paper
5. Other - Please specify

F) Distance of Cable Route Primary 11kV

G) Distance of Cable Route Secondary 11kV

H) Connection Method Primary:

1. Overhead Bushing
2. Termination box - Dry
3. Termination box - Oil Filled
4. Other - Please Specify

J) Connection Method Secondary:

1. Overhead Bushing
2. Termination box - Dry
3. Termination box - Oil Filled
4. Other - Please Specify

K) Transformers:

1. Single Phase (# separate per bank, plus a spare on-site)
   
2. Three phase
   

There are other factors, but the above are the main ones.

Please reply with thank you.

Kind Regards....

Thanks Sparky,

Please find hereafter some details:

A) Type of soil:

1. Sand
   

B) Ground water Level, on monthly basis :not sure: Hot climate (little rain/yearly)

C) Thermal Conductivity of "Soil" : Let say 1.2

D) Type/s of Cable = Conductor:

1. Copper SWA

E) Type of Cable = Insulation

1. XLPE

F) Distance of Cable Route Primary 11kV : 4.5 km (between S/S & Xformer)

G) Distance of Cable Route Secondary 11kV: Same as primary

H) Connection Method Primary:

1. Termination box - Dry

J) Connection Method Secondary:

1. Termination box - Dry

K) Transformers:

1. Three phase
   

Could you please give a methodology for calculation

I get a little disturbed when I see comments like this which do not appear to be homework problems, but rather questions from electrical engineers (or similar) that should know these answers.

Cable derating information is obtainable in either your local electrical standard or from the cable manufacturer's website (or one of the other cable manufacture's websites).

Thank you anyway

ye i agree with you it apperars that some of our friends are trying to save the cost of consultency or a PEs services!

crm

Hello again Bens

Because your proposed route is in sand, and an arid region, the sand acts as a thermal insulator, and can cause early overheating with cable failure.

That happened in New Zealand's largest City, around 10 years ago, and the Central Business District had to run on trailer-mounted emergency diesel plants for some eight weeks, until a temporary 3 phase pole line at 110kV was run across the city from the supply to bypass the failed cables.

The heating of cables is well-known, as 40+ years ago in Christchurch, we located the failure spots on a frosty morning, by driving along the cable route, and where the frost was not showing, that's where the diggers went in.

The problem in Christchurch was overcome, by overdigging the cable route, and adding a pierced water line along above the cable.

The water constantly feeds into the sand, keeping it moist, and the heat is carried away quite OK. That "watering" system has been in service now for over 40 years, and no further cable failures.

It is essential you consult the cable makers re your intended installation.

The number of variables mean that they know their own cables best, and there is no "General Calculation" which covers all possibilities.

If you use the Cable Maker's Engineering advice, (Important to get it in writing), if a failure later occurs they also "become involved with the replacement".

In earlier years (50+ years ago) Cable Makers in the UK did not realise the thermal insulation qualities of dry sand, once the ground-water level dropped in a dry year, and on several occasions had to contribute to the replacement costs of cables, because Supply Authorities in NZ used the UK Cable Maker's Engineering advice for Cable Installations (And got that advice in writing).

Kind Regards....

Thank you very much for your valauble advices.

Best regards

Hello

I have answered your Post/comments,

Generally best to use the Cable Maker of your particular cable, but try:

http://relemaccables.com/

If you are still needing help, reply with

Kind Regards....

Normally cable manufacturer publishes de rating factors in side ground,in a cable duct and exposed in air and de rating factors for other cable laying activities if not you can ask the cable manufacturers for this data and calculate the de rating factors and voltage drops and select the cable that would be much better.

crm

Hi Bens,

I think www.aberdare.co.za will answer your question satisfatorily. Check it out - they also publish a free cable sizing booklet.

All the best!

top dog

Good Site , thank you