GIS Circulating Shell and Grounding Current

[tomasDgreat]

Hi. First time posting here and I just badly needed your professional insights. We have 500kV Gas Insulated Substation catering 600MW of power. We measured the current in grounding cables around the area and we got 70A at most.

It was reported in the managers, and they were alarmed by this. But I conducted research and found research conducted by Research Institute in China. They conducted simulations and got shell and grounding currents flowing in GIS system.

I also looked for related standards like IEEE, NEC and ANSI but they don't have the regulating standards regarding GIS cases.

I'm asking if you guys have experience similar with this? What are related standards that govern GIS system? Is it safe having currents flowing like that casually? Basically, anything that can be useful related to the topic. Thanks guys.

 

[FPelec]

Hello,
In GIS installations, currents of similar order of magnitude as those in the phase conductors are induced in the enclosures. These induced currents become larger as the enclosure thickness increases; consequently, they tend to be higher in EHV switchgear. When multiple grounding points of the same enclosure and enclosures of different phases are present, part of these induced currents return through the grounding connections.

The sizing of those grounding connections is generally carried out considering short-circuit currents, which are several orders of magnitude higher than circulation currents. As long as the sizing has been done correctly, there should be no issues.
You can find some information (hopefully reassuring) here:

Practical lesson in grounding and bonding of Gas-Insulated Switchgear (GIS) | EEP

With the exception of SF6-to-air bushings terminals, all active portions of gas-insulated switchgear (GIS) are contained within grounded

electrical-engineering-portal.com