Electrical Requirements for an Industrial Park

With all assumption that a 23 year kid is designing a total electrical circuit for an Industrial park and that too a quite large one (hopefully not his project work) We have to keep all the factor of safety in picture.

So assuming that needs a couple of MVA load - let us put in a 200MVA transformer with switched capacitor bank for pf correction.

As mentioned in prev post - the cables (assuming underground) should be SS sheathed (wo do not know the location) with say 2 gauge (comes out to be about 7mm diameter wires) that must be protection if some body wants to trample over it.

These cables can be additionaly routed using schedule 120 pipes (comes out to be about 0.56" wall thickness at 6" or 0.44" in 4")

So the trucks now can not flatten it.

With this amount of protection it may be difficult to replace the cables, so we should go for best conductor- let us go for Ag with lowest resistivity - thus it will have less chances of getting burnt in the pipe or Au since before it gets burnt or the electrical system is messed up due to the design, it will be replaced (because of getting stolen)

Hi sb,

You are absolutely right . Such a large electrical project is to be designed by qualified ,experienced and licenced electrical person and is not a child's play. My comment was only a joke and ment nothing serious.

Don't worry, my answer was so too.

Too many students want their project completed at net or project identified at net but why at CR4 ?

You open a link and you don't know the problem is a real one or a paper one.

after reading all your comments I'm surely reluctant to ask. I am electrical eng student whose doing my final year project. This is actually my project I am doing at a company..Its a live project which they have given to us. We are thrown out into the ocean with no guidance. That is why i asked this doubts. Can you please tell me when calculating voltage drop for the cables. the formula used is VD=mV/A/m * Ib*L/1000.

the mV/A/m value is taken from a table.where can i get this value?Where can I obtain this table?

Your origioal post said "We designed the street lights using a HPS 250W with mounting height of 10m and space betwn of 35m.we need design da distribtion to da industries and and provide supply 4 STP and WTP. Also planin on givin 240V supply 2 da street lights. I knw how 2 calculate the voltage drop...but how do u choose the circular mil and K value? also wen calculatin VD for street lamp do u take each lamp and calculate VD or the furtherest 1 frm source. also how do u calculate the current carrying capacity of Aluminium.?how do u select number of feeders?also can u can we get site where we can download NEC 2008."

1. Where are your located?

2. You can not download the 2008 NEC. You have to buy it.

Voltage drop = amps x resistance of the conductor. Resistance usually is based on a 1000 ft basis. So you will need to calculate R for each span. Remember use conductor distance.

Example: assume that the amperage for 1 light is A and you have 4 poles with lights on one street lighting circuit. The amperage thru the 1st span is 4A, 3A thru the 2nd span, 2A thru the 3rd span and 1A thru the last span. Using the formula the VD thru the first span is 4A x R, 3AxR for the second span etc. To get the total VD add the individual voltage drops together and you have the VD at the last light.

Likely you will be using #4 triplex cable or something similar. Check the following site for cable information. It gives the characteristics for different size cables. You can locate other sites for street lighting.

Hi Roger,

Good that you have reacted at least now. My assumption is correct. You need not be reluctant to ask your doubts. You should have made this statement in the beginning itself.

No body become an expert after passing out of engineering college. It takes years of experience to carry out design work of a project. It is good that you are thrown out with out guidance. Now you have to do your own research . It is hard job which you have to do it yourself so that you learn.

To start with I shall give you some guidance .

1. Make a drawing of the area locating the power source location of the light points with dimension, cable route , method of cable laying ( under ground / overhead) and the electricity rules and regulation of the electricity supplier/ board/ government /municipal authority have to be considered.The budgetary sanction of the project.

2 . Calculate the total load and its distribution ,available power supply( 3 phase/ single phase , voltage) weather conditions and ambient temperature of location

3. Cable size , voltage drop and length calculation will depend on 1 & 2

4. If the cable distribution is under ground the terminal looping and connector boxes have to be designed accordingly. The individual cable from the connector box to the light point will be different.

5. Earthing provision and protective system has to be designed

5. Estimate of materials required and labour cost.

6. Finally estimate the time required for completing the project with available resources

Thank You Sir for your assistance.it does help with a bit of direction. Sorry for my ignorance.Everything we are doing according to IS norms. We have at the moment designed the scheme of street lights with what distance we will place the street lights and what type of fittings have been chosen. Next we have to calculate the voltage drop to see what conductor size we are using. We using aluminium conductors since it is cheaper for cabling. We are doing underground cabling for providing 3 phase supply to the street lights. We are ignoring the weather conditions and taking in to account the rest. I just want to know the mV/A/m drop for a 4 core Al cable.it is obtained from a table value. Where can i obtain this table?aslo when calculatating the size we have to take into account the short circuit current. is it alrite multiplying the rated current by the factor 3?

check here for cable information

http://www.cable.alcan.com/NR/rdonlyres/7997EC4B-21C6-4542-B892-77A7056DA8DE/0/UT0001.pdf

Hi Roger,

Since you are following IS code it is much easy. For Aluminium conductor heavy duty 1.1 kV rating PVC insulated armoured and un armored cables please refer IS 1554 Part I and Part Part II- 1964 ( Rating as per IS 3961 part II 1967). You can design your cable system based on that, it is authentic no body can challenge it. Similar charts with voltage drop is provided by the reputed Indian cable manufacturers also.Their charts are also based on IS .

The ratings are based on following assumptions

a) Maximum conductor temperature 70 ° C

b) Ambient temperature 40 ° C

c) Ground temperature 30°C

d) Thermal resistivity of soil 150°C cm/watts

e) Depth of laying 750 mm

f) Thermal resistivity of PVC 650° C cm/watt

Further rating factor is given for variation of ambient temperature, variation of ground temperature, thermal resistivity etc. for a.b,c,d , e and f

Normally accepted standard and followed (Estimated) Voltage drop for PVC cable 1.1 kV Aluminium conductor is given below.

Sq mm Voltage Drop V/KM/ A

1.5 41.60

2.5 25.00

4.0 15.70

6.0 10.40

10 .0 6.20

16.0 4.00

25 .0 2.50

35.0 1.80

50..0 1.30

The maximum permissible voltage drop is 3%

The National Electrical Code (NEC) has a very boring seminar class to meet the National Fire Protection Association 70 code. It only took me 16 hours (two full work days) to able to interpret the enormous amount of information in this code. This code incorporates many critical characteristics not normally considered by an electrical engineer, and certainly not an engineering student. For an example, what type of insulation material should be used on the conductor, neoprene rubber, teflon, PVC? Does the cable have to be run inside a conduit and what type of material for the conduit? And for a final example, how many power handling conductors will safely fit in a conduit. (Remember these wires will get hot as the draw increases, so filling the conduit with copper will surely eventually cause a fire.) So for an informative exercise continue with your calculations, but you don't have an engineering or electrician's license or insurance to cover yourself. Be careful. As far as your project analysis if you assume that a copper alloy will retain 95% of the conductivity of pure copper, then using the value you have for cable lengths you can calculate the wire resistance. But without knowing the size of your theoretical power distribution grid, you should remember that this may become a transmission line problem.