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Subject:
NERC GIC Application Guide regarding shunt devices
From:
"Juricek, Michael" <[log in to unmask]>
Reply To:
Planning Geomagnetic Disturbance Task Force <[log in to unmask]>
Date:
Mon, 23 May 2016 13:02:28 +0000
Content-Type:
multipart/mixed
Parts/Attachments:
text/plain (2413 bytes) , text/html (34 kB) , GIC Application Guide 2013_approved.pdf (1 MB) 
PGDTF,

Larisa extracted the following information from the NERC Application Guide.


Shunt Devices
The bulk power system generally uses two types of shunt elements to help control system voltage: shunt capacitors and shunt reactors. Shunt capacitors present very high impedance to the flow of GIC, and are consequently excluded in the dc analysis. Shunt reactors connected directly to the substation bus or transmission lines, on the other hand, can provide a low impedance path for GIC and should be included in the analysis. The dc model of a grounded-wye shunt reactor is the same as that of a grounded-wye winding of a GSU. If dc winding resistance values are unknown, they can be estimated using an assumed X/R ratio. Note that X/R ratio of a typical dead-tank shunt reactor can be far greater than the X/R ratio of a typical transformer of the same MVA rating. It is not uncommon for the X/R ratio of large shunt reactors to exceed 1000.


The preceding calculation methods use two particular assumptions in order to simplify the calculations: 1) the magnetic field variations are uniform over the area of the power system and 2) the earth conductivity structure only varies with depth (i.e., there are no lateral variations in conductivity). To improve the accuracy of the calculated geoelectric fields both the structure of the source magnetic field and the lateral variations in conductivity should be considered.

Regards,


Michael Juricek, P.E.

Chairman Planning Geomagnetic Disturbance Task Force



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