High Resistance Grounding Units

[SparkyJunior]

I have a project that involves the connection of a stand alone high resistance grounding unit to a 12KV Generator Switchboard. I realize the intent of the HRGU is to limit fault currents and limit damage to equipment and personnel. I have little to no practical experience with these units and was wondering if I could get some hele here. What wiring is connected between the Switchboard and HRG? Is this a simple three phase feed to the HRGU so it can monitor for fault current? Is there any control wiring involved?

If anyone has general knowledge and has seen this type of application, your input would be appreciated.

Thanks

 

[dpc]

We'll need to know more about the 12 kV system and how it is presently grounded.

If it is solidly grounded, this grounding unit is basically just a resistor that connects between the transformer neutral and ground.

If it is presently ungrounded, the grounding system has to include a zig-zag or delta-wye transformer to create a neutral and a resistor to limit the fault current.

I am assuming this is not an incoming utility feeder that you are trying to high-resistance ground, because that will probably not work.

 

[oldfieldguy]

In the units I've dealt with in the past, You'll have a few connections to deal with.

The major one from the system integrity and safety standpoint will be the connection from your system's neutral point. This will have to be rated for the system phase to ground voltage. It connects to the neutral grounding resistor or the neutral grounding transformer. The ampacity of this conductor is dependent on the design ground current allowed by the high resistance grounding system. Coincident with this conductor is the need for a GOOD ground between the system grounding resistor and your station grounding grid.

The remainder of the connections are metering, relaying and control voltage level stuff and should be covered in the engineering package.

old field guy

 

[CoryA]

There is an online schematic diagram showing how to high-resistance ground the neutral of a delta transformer as dpc suggested. I'll add the link below.

Implementing Resistance Grounding on Ungrounded Systems

You could skip the zigzag if you're grounding the neutral of a wye-connected transformer. It is possible to purchase neutral-grounding-resistor packages that include monitoring relays and CTs installed - the kinds of connections old field guy may be referring to.

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Cory Anderson

http://startco.ca/