Cable Fill in a Ground / Zero Sequence CT?

[mbk2k3]

If I have a window type ground/zero sequence CT, with a 7.5" window diameter, are there any standards for how much cable can be passed through this CT?

I have 12 conductors (4x3Cx___MCM) [can't remember gauge exactly], and the cables are a very tight fit. I'm worried about the pressure this causes on the CT, and potential overheating in that small area due to thermal dissipation from the cables.

Thoughts?

 

[mbk2k3]

i found my answer.

if you read the last paragraph on this technical doc. by Siemens:

http://www.energy.siemens.com/us/po...oducts/TechTopics/ANSI_MV_TechTopics50_EN.pdf

The cables should be located toward the center of the
CT opening, and should not be allowed to contact the CT
case. If the cables are directly against the CT case, it could
lead to localized saturation of the CT core under throughfault
conditions, leading to false operation. Typically, the
mounting plate for the zero-sequence ground CT can be
used to restrict the cables so that they pass through the
approximate center of the CT window.​

 

[randyman]

The Siemens article is referring to placement of conductors in general when there is plenty of space which is not really same as in your condition. In your case however, all conductors fill the window area and as long as the conductors are rated for the CT class, 0.6kV for example, then you should be OK electrically. Keep the phases grouped. As for what could happen to CT in terms of damage depends on what the CT construction is, and exactly how much force you will be putting on it both mechanically and thermally.

Might be best to select a larger ID sensor, but please beware of the type of sensor you have, or will order. If it is just a simple 50:5 or 100:5 CT for example, then placement of cables can be critical. If the sensor is designed for zero-seq in true core balance scheme, then placement of conductors is not so important. There are not many CT suppliers who recognize this or offer different type winding for core-balance application.

Hope this helps....