Solar Storms
Solar Storms
(OP)
I'm curious who in the utility world is concerned and what is normally done to advert damage?
When was the last time you drove down the highway without seeing a commercial truck hauling goods?
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RE: Solar Storms
My limited understanding is that transformers (often generator step up transformers) are subject to a relatively high DC off set current that causes overheating. For a small amount of overheating the generator/circuit load can be reduced. Particularly vulnerable transformers can have a resistor added to the earth connection to reduce the DC current flow at times of high solar activity.
If you google geomagnetically induced currents you should get more info.
RE: Solar Storms
There was talk at one time about using capacitors instead of resistors. But I don't think that was ever done.
Also in areas of low impedance soils this is not as much of a concern.
I would think series capacitors can be used in transmission lines to reduce DC flows.
RE: Solar Storms
RE: Solar Storms
My only guess is that the transmission lines are not the only source of induced current in the system that would cause an overload. The transformers themselves, due to the presence of their windings, also induce current. That fact, in and of itself, would render the transformers vulnerable even in the presence of disconnects.
Mike McCann
MMC Engineering
http://mmcengineering.tripod.com
RE: Solar Storms
The problem with leaving the neutral open or high impedance grounded is it reduces the ability to flow ground fault currents, and thus the ability to detect a ground fault on the line. And because ground faults can transition into phase to phase faults we do want to clear them fast.
The transmission lines are not the only inducable conductor. In most of these cases the earth also acts like an inducable conductor, which is why the DC potential in the earth causes current in some lines.
Also note there can also be current flow in shield wires, pipelines, etc, although they go un-noticed because there are no seen effects.
RE: Solar Storms
I believe Hydro Quebec or Hydro Ontario had some serious issues back in a large event about 1990 or so. I seem to recall they did install some protection in the transformer neutral to ground path.
RE: Solar Storms
RE: Solar Storms
Effect of GIC on Power Transformers", by Dr. Ramsis Girgis (ABB Inc.)
"Simulating GIC flow in power systems, and the evaluation of potential impact of VAR swings on voltage stability and harmonics on system protection", by Dr. Emanuel Bernabeu (Dominion)
"GIC monitoring and examples of actual GIC signatures", by Dr. David Fugate (Electric Research & Management, Inc.)
"An overview of the NERC GMD TF activities, conclusions, and recommendations", by Mr. Frank Koza (PJM Interconnection)
"Processes / procedures presently used by utilities in North America to mitigate the effects of GIC", by representatives of North America utilities
You can have all these presentations from IEEE site after 15th ie
http://www.transformerscommittee.org/
RE: Solar Storms
We recently installed a new transformer onto our line that is most likely to be affected by GIC which has a solidly-earthed neutral. I also have a box of special CT's and relays sitting at my desk waiting to be installed on this and several other soon-to-be-purchased transformers. These will measure the DC component of the neutral current, and provide an alarm for our system operator to take action if the DC current starts to become high. It looks like we'll miss out the present solar storm, which would have been a good test to see how it all works.
Adding to my misery - it's cloudy and snowing out, so no Northern Lights show!
RE: Solar Storms
Specail CTs and relays?? Do you mind sharing the wiring schematics/settings of how these will be implemented? Just curious and want to learn about these types of protection schemes.
I worked in a utlity that is pretty far south so I haven't had the opportunity to see something like this before.
RE: Solar Storms
RE: Solar Storms
They are by Flexcore (http://www.flex-core.com/). I don't have the schematics in front of me, but I don't recall there being anything unusual in how they're connected - just a CT into a transducer which gives a 4-20mA output to SCADA.
RE: Solar Storms
At least that is what I have seen in Canada (Prince George to points 300km North).