HRG on Medium Voltage Systems?

What's HRG stand for in your part of the world?

Although you did not ask me specifically, that never stops me from butting in anyway.

High Resistance Grounding is my understanding.

Here are some links that can give you additional info on resistance grounding. I have more commonly seen low resistance grounding at medium voltage levels (15kV), and high resistance grounding used at Low voltage and the lower end of medium voltage (480V up to 2400 or 4800V). Your decision of which to choose has much to do with what level you want (or need) to limit the fault current.

HRG generally depends on having some means for detecting the flow of (the limited ground fault) current in the resistor, and then some means of tracing that current back to its source (the fault) so that it can be shut down and repaired under your timing and control. LRG instead limits the fault current enough to prevent equipment damage before protective relays automatically can trip the supply to the faulted equipment.

If you are concerned that the long cable runs will limit the fault current at remote locations to a value difficult to discriminate, then you may need to go to a low resistance grounded or solidly grounded system with more sensitive ground fault detection. You will have to consider what that means for the ratings of your equipment, though.

https://ecmweb.com/content/choosing-grounding-options-electrical-power-systems

First of all, I am having difficulty to understand what your question is.

The comment provided by PeterT is good (GA), especially the second link is very informative.

In a past thread, I wrote this comment (http://cr4.globalspec.com/comment/589279) which I pasted here. Comment in another thread (http://cr4.globalspec.com/comment/642965) also helps.

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NGR protects the electrical system and equipment by limiting the ground fault currents. Because of the use of resistance between the neutral and the ground, the ground fault current is minimized for the single line to ground fault (most common type of fault) and hence there is less damage to the system as well as the faulty equipment. By limiting the fault current, NRG also improves the arc flash of the system.

There are two types of NGR: High Resistance Grounding (HRG) and Low Resistance Grounding (LRG)

High Resistance Grounding (HRG): It is used where service continuity is vital, such as process plant motors. With HRG, the neutral is grounded through a high resistance so that very small current flows to the ground if ground fault occurs. In the case of ground fault of one phase, the faulty phase goes to the ground potential but the system doesn't trip. This system must have a ground fault monitoring system. The use of line to neutral (single phase) is prohibited (NEC, 250.36(3)) in HRG system, however, phase to neutral is used with using the additional transformer having its neutral grounded. When ground fault occurs in HRG system, the monitoring systems gives alarm and the plant operators start the standby motor and stop the faulty one for the maintenance. This way, the process plant is not interrupted.

Low Resistance Grounding (LRG): This is used for limiting the ground fault current to minimize the impact of the fault current to the system. In this case, the system trips for the ground fault. In this system, the use of line to neutral (single phase) is prohibited here as well.

See these links for further help:

http://ecmweb.com/power_quality/electric_ground/?smte=wl

http://www.wwcctraining.com/pdf/overland_park/Arc_Flash_Understanding_and_Preventing.pdf (page 19 and 20)

http://www.labplan.ufsc.br/congressos/Powertech/papers/472.pdf

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- MS

My apologies in that I should have been more specific...

I understand the types and uses for each. I have worked and specified them previously.

My issue is moreso a client trying to spec one on a MV system. The reason this seems almost impossible to me is due to the systems capacitive charging current. Most standards have rough ranges to assume depending on the MVA of the system.

It becomes almost impossible to spec an HRG on a MV or higher system, due to the amount of current that will just be flowing at all times (hard to limit or alarm when its alarming 24/7). Long cable runs contribute nicely, as do surge arresters and any other fun uses of capacitance.

My question is... Has anyone had experience where it was done/works? an MV system with an HRG? I am guessing it can only be done on a very small plant thats tightly packed, but I might be missing something, hence my question.