high resistance ground device installation

[oranjeep]

I have a question about high resistance ground device installation.
Does the device have to be connected to the main bus, or can it be connected to a branch circuit, which in turn, is connected to the main bus?
The application is for a 3Ph., 1500KVA ungrounded delta-delta feeding a 600V bus, that in turn has 3 branch circuits. One person says that it has to be bolted on to the main bus, another says all the branch circuits go back to the main bus anyway, so it does not matter.
Is there something fundemental about HRG systems that I am missing that stipulates where they are installed on the system?

 

[weh3]

It will be connected on one side to the grounded circuit conductor (neutral) bus at the service equipment, and on the other side to the grounding electrode.

Its purpose is to limit fault currents, but not to limit them to the point of not tripping a GFD. On an ungrounded system, the first fault will cause no fault currents anyway.

Regards,
William

 

[PWR]

In most applications, the HRG unit would be connected to the main bus because you don't want the system to change to ungrounded because one of the branch circuits is taken off line for any reason. On a wye system, there is typically just a small wire connecting the resistor to the neutral. Since you have a delta, you must create a neutral some way. In your situation, there is typically a dedicated disconnect of some type upstream of the URG unit.

 

[RalphChristie]

Can you just clarify? Do you want to ground your system (like the high resistance suggests) or do you want to install a ground detection scheme on a ungrounded system? (like the delta connection suggests)

But in either way, it should be connected on the main bus, for the reason PWR mentioned.

 

[oranjeep]

Ground detection on ungrounded system.
It is a critical process with no available equiped space on the main bus, which, I am told, is not really like a main bus-it is a "lattice" network. Either way, we can't take a shutdown, so I am going to have to put it on one of the branches until the next scheduled shutdown. Since the branch is tied to the "main", then it-I am told-will do what it was intended to to-detect grounds in the system. We never intentionally take that branch down anyway. If we lose the branch the hrg happens to be on-thereby losing ground detectionin the rest of the system-we have much "bigger fish to fry" than losing our ground detection system.

 

[RalphChristie]

If you are not going to loose your branch-feeder your protection will be fine. However, I would not recommend it, but it will be better than nothing for the time being.

How long before the next shutdown? And can you take the branch down without a shutdown to the system? (to install the device)

What kind of device are you going to use? A voltage operated device or an Insulation Monitoring Device?