Geomagnetically Induced Currents
Geomagnetically Induced Currents
(OP)
Does transformer connection make a difference in GIC currents and their mitigation such as delta wye 345kv-69kv vs a typical Wye Grd auto? Also are GSUs effected by GICs such that it needs to be evaluated?






RE: Geomagnetically Induced Currents
Our GSUs are mainly delta (low side) to wye-grd (high side). In the U.S., a New Jersey utility had a GSU failure because of GIC. This has been maybe 20 years ago.
RE: Geomagnetically Induced Currents
RE: Geomagnetically Induced Currents
The flow of GIC is a dc current that tries to go to earth. With a wye-grounded connection on one side of the transformer and a relatively low impedance to earth, the dc flow produces lots of harmonics in the transformer.
There are a number of rules of thumb and generalizations about GIS, including
- locations closer to the earths's magnetic poles are at higher risk
- long transmission lines running east-west are most suceptible. North-south transmission lines are relatively immune to GIC.
There's a number of free EPRI reports available on the subject of GIC and I'd encourage you to look at some of them. Just search EPRI reports on GIC.
RE: Geomagnetically Induced Currents
I doubt there would be much voltage across most distribution lines.
RE: Geomagnetically Induced Currents
RE: Geomagnetically Induced Currents
RE: Geomagnetically Induced Currents
RE: Geomagnetically Induced Currents
RE: Geomagnetically Induced Currents
RE: Geomagnetically Induced Currents
RE: Geomagnetically Induced Currents
Bare with me here- in regards to detla wye vs auto- say there were GICs on the 345kv system- they would not pass straight through to the 69kv system- correct? Rather current would have to find a wye secondary at one point of the 69kv system, up through the 69kv system- then out another wye point X distance away, correct?
RE: Geomagnetically Induced Currents
RE: Geomagnetically Induced Currents
RE: Geomagnetically Induced Currents
The thing that is odd about GIC is that the transformers aren't damaged if they go into hard saturation. If they saturate, they will trip on saturation current. The damage is done if they semi-saturate. Just enough to not trip but enough to cause damage if sustained.
The best solution in my opinion is to just shut the system down. The world doesn't end if the power is out for a few hours and that is cheaper and preferable than trying to ride it out.
RE: Geomagnetically Induced Currents
Placing an inductor in series just introduces more impedance, so not much help.
Needless to say, delta systems don't have a GIC problem.
If one were to not load a transformer fully it is possible to not saturate the core during a GIC event.
RE: Geomagnetically Induced Currents
RE: Geomagnetically Induced Currents
I meant to use an additional inductance to cancel out the series capacitance so you wouldn't change the fault current. Xc = Xl, Xc*(-i) + Xl(i) = 0.
Transformers are the least saturated when heavily loaded. I don't know if loading them more or less would help. Less loading would mean they would more likely trip out due to further saturating. Heavy loading might help pull them out some of saturation. You don't want them to sit in the region of semi-saturating.
RE: Geomagnetically Induced Currents
RE: Geomagnetically Induced Currents
The blocking capacitors on transformers neutrals include an arc gap/surge arrestor bypass that activates during fault conditions. This one from Siemens looks to be in cabinet of 1 m by 1 m by 2m. https://w3.siemens.com.br/topics/br/pt/EM/Document...
A military EMP event is totally different; the typical mitigation actions for a solar flare GIC provide negligible mitigation against an EMP attack.
There is little consensus as to what level of solar flare will cause enough GIC to damage large portions of the power grid. It would be interesting to figure out prearranged criteria for making a decision to shut down the grid. Intentionally shutting down the grid trades off the possibility of saving the grid from long term damage, with the certainty of death and severe economic damage from a temporary blackout. According to Wikipedia, the US east coast blackout in 2003 contributed to almost 100 deaths.
RE: Geomagnetically Induced Currents