XFMR Neutral GNDg Resistor sizing
XFMR Neutral GNDg Resistor sizing
(OP)
I am working on a project where we are replacing two (2) three winding 13.8-4.16kV-480 3750kVA XFMRs with two (2) two winding 13.8-4.16kV 7500kVA XFMRs. I found a one line that shows the neutral resistors for the old 3750kVA XFMRs to be 8kV 30 ohm for 300A for 10secs. Should these resistors be replaced with the new XFMRs? If so how do I size the new XFMRs neutral resistors? Is there a IEEE std on this?






RE: XFMR Neutral GNDg Resistor sizing
Isc = 3V/(3Rg+(R1+R2+R0) + j(X"1+X2+X0)
Isc is maximum FC in amperes
V is phase to neutral voltage
Rg is the grid resistance to earth in ohms
R1 is positive seq in ohms
R2 is negative seq in ohms
R0 is Zero seq in ohms
X"1 is positive sequence subtransient reactance in ohms
X2 is negative sequence system reactance in ohms
X0 is zero sequence system reactance in ohms
Now I have to detemine my power system's symmetrical components. Once I come up with this data am I trying to evaluate whether or not this selected Neutral Resistor will limit the ground fault current to protect the XFMR? I have the ABB XFMR drawings and do not see any SC Ratings.
RE: XFMR Neutral GNDg Resistor sizing
As for calculating the current, for resistance grounding, just divide the line-to-neutral voltage by the resistance. Nothing else in the system is going to make much difference.
"The perfect is the enemy of the good." -- Voltaire
RE: XFMR Neutral GNDg Resistor sizing
RE: XFMR Neutral GNDg Resistor sizing
Don't see a reason to wait unless there is some application that is new to me. If so will you please enlighten me.
Thanks
Alan
Democracy is two wolves and a sheep deciding what to have for dinner. Liberty is a well armed sheep!
Ben Franklin
RE: XFMR Neutral GNDg Resistor sizing
RE: XFMR Neutral GNDg Resistor sizing
RE: XFMR Neutral GNDg Resistor sizing
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It may be like this in theory and practice, but in real life it is completely different.
The favourite sentence of my army sergeant
RE: XFMR Neutral GNDg Resistor sizing
There is a paper that addresses neutral-grounding-resistor selection specifically. I'll add a link to it below.
Ground-Fault Detection, Charging Current and Neutral-Grounding Resistor Selection
I would suggest, however, that if the resistors are intact, their replacement may not be necessary. An appropriate neutral-grounding-resistor monitor will verify the entire neutral-to-ground connection. A second paper detailing why neutral-grounding-resistors should be monitored can be retrieved from the IEEE website; I'll add a link to it below.
Why Neutral-Grounding Resistors Need Continuous Monitoring
Cory Anderson
http://startco.ca/
RE: XFMR Neutral GNDg Resistor sizing
"The perfect is the enemy of the good." -- Voltaire
RE: XFMR Neutral GNDg Resistor sizing
Alan
Democracy is two wolves and a sheep deciding what to have for dinner. Liberty is a well armed sheep!
Ben Franklin
RE: XFMR Neutral GNDg Resistor sizing
Alan
Democracy is two wolves and a sheep deciding what to have for dinner. Liberty is a well armed sheep!
Ben Franklin