Neutral Grounding Transformer and Resistor Sizing

It is not possible for any other CR4 reader to know the exact reasoning, so the best advice is to go back to the original design documents for the installation and look up the answer there.

Neutral grounding transformer/resistor/protective relaying combinations are used to limit the magnitude and duration of the ground fault current to some acceptable values to reduce the internal damage and/or for protective relaying purposes.

Your job is to find the engineer that can choose what those values are and for how long you want it to flow, once you do that then it is a simple matter to use the transformer turns ratio and Ohm's laws to size your resistor, then choose the resistor and transformer short term ratings based upon the amount of time before your protective relaying operates.

Get a copy of the GE Protective Relaying Manual for the actual formulas if you have no experience in these calculations.

The neutral grounding transformer and resistor size and voltage rating is a decision based upon the original generator design criteria/specifications and is dictated by the Original Equipment Manufacturer.

There are many considerations such as but not limited to:

Machine insulation temperature rating.

Cooling type and size.

Generator winding conductor size and composition.

Type and speed of generator protection scheme.

Generator application (Base load, demand-swing,ETC.)

Altitude at installation location.

Ambient mean temperatures.

As I stated theses are some of the considerations however you need to contact the original generator manufacturer to identify their reasoning and requirements.

Am I the only one who gets the crap scared out of me every time there's another "Hello everyone, I am working on a several-killovolt power station, and I apearantly have no qualifications for the job I'm in, because I'm asking a bunch of semi-annonymous people on the internet to advise me on how to set up and run dangerous equipment when they cannot see the equipment, or even know where the equipment is located" thread started?

Call me crazy but if you're going to be setting up a High Voltage electrical supply/substation, shouldn't you be TRAINED in how to work with High Voltage? That means you would either know the answer to these questions, or you would know how to find the answer in the safety regulations for your area, or at least have some contact information on your instructor or whichever agency is responsible for electrical safety in your area? If you're trained and qualified to work with Kilovolt-range circuits, you should have better sources for safety info than the bunch of jabronies who post here, myself included.

No you're not, I believe there's a fair percentage of responders who wonder how some of the questioners even have the cojones to expose their ignorance. In this case though I suspect OP is a newbie designer sitting in an office and will never get to see the actual equipment in service.

I asked the same question when I was a coop student in a major utility, my supervisor immediately sent me on a paper chase through three departments where I was finally able to piece together the "hows and whys" of the various neutral grounding schemes before I went to see them in action. They're usually in a cage so there's no direct danger unless you ignore the "High Voltage Do Not Enter" sign.

Of course being in a generating station has its own myriad risks, but less than 1% of office personnel ever get into one anyhow.

"I asked the same question when I was a coop student in a major utility, my supervisor immediately sent me on a paper chase through three departments where I was finally able to piece together the "hows and whys" of the various neutral grounding schemes before I went to see them in action."

Ohh that sounds like it was fun, ask a question get sent on a 'snipe hunt' to learn the answer for yourself, with the side effect that you get to meet people from all the departments, and they get to meet you and test out your sense of humor.

Too bad that's considered 'harassment' these days. Did it REALLY hurt people to be sent out for a 'left handed smoke bender,' or for a '200 foot coil of shore line'? The point was to get the new guy introduced around, teach him where the department offices were, and show him that the working world isn't as try and boring as school portrayed it.

I can has megavolts and resistives?