Calculating Resistance Values

Kindly describe the method or calculation for calculating the value of Resistance in NGR with respect to the rating of transformer/Generator and also respect to the voltage.

Dear pandebinod.....

pls click the following address...

http://www.postglover.com/Literature/HR003-05_High_Resistance_Ground_Gde.pdf

www.benderrelay.com/datasheets_US/Mining book _FULL PAGES_6c.pdf

http://www.startco.ca/library/papers/PowerTestPaper.pdf

Goodluck

Rgds

Sis

What's an NGR?

NGR = Neutral Grounding Resistor = Device used to limit current to ground in the event of a short to ground.

Pandabinod,

From the definition of power; S [VA] = U [V] * I [A] and U [V] = I [A] * Z [Ohm] => Z[Ohm] =(U^2)/S, where S = apparent power, U = voltage, I = current, Z = impedance, R = resistance; [..] being the respective units of measurement.

If only active (real) power is involved, Z = R and so R = U^2/S.

I am not sure what that formula is all about but what you have to determine is what amount of current can be safely shunted to ground that will allow all of your safety breakers to trip if they are upstream of the short but not damage any transformers or motors that are in the circuit. R=E/I, whereas E (voltage) is a given, I (current) is your perceived limit according to your equipment ratings, and R (resistance rating) is to be solved for. I am sure that if you want help you can contact the manufacturer of a commercial NGR for much better help than you have received here.

Try this one: http://www.avtron.com/neutral_grounding_resistors.htm