Earthing Current Limiting

It won't as the current won't reach 200A, recalculate using the figures you were given.

BTW what are your plans for the 150kW of heat?

dear ,

what do you mean by 150 kw of heat??

also confused how to calculate the max fault current with this resistor. i need value of fault current as i have to give it to client. calculated value.

Why are you using 125A instead the value you were told to use?

"now, what i am confused is, if putting this value resistance, how do i justify that this 63 ohms will limit earth current upto 200 amps." I'm sorry but it is up to you to justify your incompetence. Don't look to CR4 for an excuse.

You have started in the right direction to solve your problem. However, you are using the wrong current. Do not calculate based on the load current of the transfomer, but use the 200A fault current limit.

You can get some good direction on choosing resistance grounding equipment from the Post Glover web site (they manufacture & sell grounding resistors). Download the following free document:

http://www.postglover.com/download/neutral-grounding-resistors-technical-information/

It tells how you select the resistor, and it appears that you only need to specify to them the line-to-ground voltage, the fault current rating you want to limit to, and the time duration the resistor should be able to withstand the fault current.

As for TonyS's question, the resistors are designed to dissipate the heat of that fault current for the specified time. They are usually just convection cooled, but they can have added fans for extra air flow.

thanks for the link, you made my day...

one confusion,

what does this means, i mean "too great"???

Go back to your college AC circuit analysis class notes. What happens when you close the switch on an AC source feeding a load that has reactive (inductive and/or capacitive = X) as well as resistance R components? There are transient effects on the voltage before you come to steady state.