Selecting Cable Size for 2MVA Transformer

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Dear Mr.chandimas,

Is it Generator Transformer or Distribution Transformer.? This point has a definite impact.

Regarding cable selection, you should not use single core cable, sincne it will get heated due to inductance. Therefore you have to use Three and Half core cable.

The LV sisde current for a PF of 0.8 lag and 415 Volts is 3478.01 Amps, where as you have referred the LV side current is 2800 Amps which indicates the P.F is higher than 0.8. and work out to 0.993, which is higher for design aspect. You have to design the cable sizing for a PF of 0.8 lag.

Take a value for current density as 0..625 Amps (for Elec.Grade Aluminium) as absolute value and multiply this 0.625 by the De-Rating factor for the cable which depends upon 5 parameters, like above the ground, under ground, Temp.Rise with in the conductor etc., etc. Devide the LV current by the corrected current density and adopt the nearest higher size. This may work out to 0.5 Amps per Sq.MM.

Hence Cable Area Required = (3478.01)/(0.5) = 6956.02 Sq.MM rounded to 7000 Sq.MM.

Considring 150 MM width and 10 MM thick Aluminium Bus Bar, youthe required Bus Bar will be (7000)/ (!50 x10) = 4.666 Bars, and the nearest higher quantity is 5 nos. and for Neutral it will be 150 x 10 3 nos. of Bus Bar to be used.

Hence you have to use 150 x 10 x 5 nos. Bus bar for each phase and 150 x 10 x 3 nos for neutral (or ) 7 nos. of 1000 Sq. MM Three and Half Core cable which ever way you want you can select.

DHAYANANDHAN.S

What does your local codes say about below ground cabling installed next to an active volcano?

I don't like to repeat myself, but in this case I propose to open the post of 09/10/2015 Cable Problem and read my notes about how to chose a correct cable.

About if to chose three_core or single_core cable it will be another problem.

In Europe for instance three_core cables are usually employed.

In spite of the currents unbalance in parallel cables is higher, the voltage building-up and the circulating shield current-if the shield is grounded both ends I'd prefer single_core cables instead of three-core cables.

The cable will be light weight and more flexible, the heat evacuation is better then the current density is higher [less number of cables per phase].It is my opinion.

However, since you don't need parallel cables a 3 phases of 33/19 kV - if under fault conditions, the system would operated for a short time [1 hour or less] with one phase earthed- will be o.k. I think.

You've got to be kidding (Joking)!!! Hopefully only you will be introduced to Dr. Darwin and win the top 5 Star Award and not kill anyone else or take down the National Grid!!

If I am right in my suspicions, and there is any justice, chandimas10 is still a struggling student.↓

Transformer Data Sheet for Design of an Auxiliary System for a Coal Power Plant

Cheaters get more rewards today than they ever did. Why fight it. They will have a better chance building a toaster from scratch than they ever will understanding why the answer is 42.

I am rapidly losing all hope for our youth.

I have never seen so many brats who feel entitled to a free ride through life as today.

We are partly to blame because we want them to "have a better life" than we did.

Unfortunately, today that means that the kids go to school till they get kicked out, then live with their parents until the parents die, then live in the house that mom and dad worked all their lives for, until it's foreclosed for lack of paying the bills.

I am- sorrowfully- agree with you. However, the young fellows are not guilty, in my opinion. The reward for long training and study is very low and continuously decreases.

I think will be better to use a metal-enclosed substation-switchgear connected with transformer- and use busbars in order to supply and distribute the currents.

If the switchgear is located far from the transformer in an underground run-for instance- you should have to employ 21 parallel cables of 3*300 mm^2 copper/xlpe in pvc ducts .

See-for instance:

https://library.e.abb.com/public/86ce3b71c32e5e01c1257417004c3d3c/Kline%20Switchgear%20TB%203.1.2-1B.pdf

Julius, was wondering whether there are some certain criteria or points to judge the the preference or necessity of busways to cables. I do know that busways are more expensive.

It is wrong for anybody to supply the kid with answers !! He is in over his head and going to kill people! Screw the equipment and himself being destroyed, it people I'm worried about

Consult the applicable electrical code for your site for the correct information.

In the USA the needed information will be in the NEC/NFPA tables.

Not sure about other critical details of the installation however ambient mean temperature, moisture, length, and duty cycle should be factored in.

Better let your electrical consultants to do all the calculation and sizing for the cables needed for the 33KV side. Don't take the risk getting some one killed with 33KV voltage.