Zero Sequence CT

[Bugman1400]

I would like to clarify a few items. The 2000:1 CTs mentioned previously are not typical CTs that are connected to the GE Multilin. The CTs mentioned in the Multilin manual is a specialized Ground Fault CT and has a small twisted pair secondary wire that is connected to the back of the Multilin. I think this CT is typical red or orange in color. This is in contrast with typical window type 50:5 CTs that have a true 5A secondary. For both types, you need to make sure the phase conductors go through the CT and the ground wire does not.

 

[joep2k]

I would like to clarify a few items. The 2000:1 CTs mentioned previously are not typical CTs that are connected to the GE Multilin. The CTs mentioned in the Multilin manual is a specialized Ground Fault CT and has a small twisted pair secondary wire that is connected to the back of the Multilin. I think this CT is typical red or orange in color. This is in contrast with typical window type 50:5 CTs that have a true 5A secondary. For both types, you need to make sure the phase conductors go through the CT and the ground wire does not.

Hi, I wanted to follow up on this. We have specified using 50:0.025A ZSCTs, however the options on Multilins F750 and 469 for ground CT is either 1A or 5A per the brochure when selecting the model number.

This is what I extracted from the GE brochure.
Ground Current Input
Source CT: 1 to 50000 A primary / 1 or 5 A secondary

In this case which input value is used?

 

[arrehman1]

Hi, I wanted to follow up on this. We have specified using 50:0.025A ZSCTs, however the options on Multilins F750 and 469 for ground CT is either 1A or 5A per the brochure when selecting the model number.

This is what I extracted from the GE brochure.
Ground Current Input
Source CT: 1 to 50000 A primary / 1 or 5 A secondary

In this case which input value is used?

If you are using 50:0.025A zero sequence CT, you have a high impedance 4 wire system. Which means that ground fault current will be very small due to the high impedance in the neutral of the power transformer.

Check out the relay manual here for the Multilin 469: https://www.gedigitalenergy.com/app/ViewFiles.aspx?prod=469&type=3 - page 316 has information on the 50:0.025A zero sequence CT rating.

In section 5.3.1 of the manual (page 162) - there are several options for "ground CT" - one option is 50:0.025A -- this is the one you want if you have 50:0.025A zero sequence CT.


If you're programming the relay, this specific setting will be found under --------> SETTINGS --> S2 SYSTEM SETUP --> CURRENT SENSING

 

[arrehman1]

The 50:0.025A CT?s (for example GE part number 140-SD-13526) and 50:5A CT?s (for example GE part # 143-500) have 600V insulation. As they only contain ground fault current, so can they be used on 4160V high resistance grounded (25A) system?

One of the advantage of a high impedance 4 wire system is that you don't have to worry about CT saturation. Ground fault current is severely limited by the high impedance/resistance in the transformer neutral.

I believe the 50:0.025A and 50:5A CTs should not saturate as far as ground fault currents are concerned.

 

[zxfabb]

Hi, I have a project containing a 600V ac system that is high-resistance grounded, the ground fault current is limited at 5A. In each feeder there is a zero sequence CT with ratio 5:5 and an analog ammeter to display the fault current. I've asked GE/ITI, but they don't have such stuff. Do you know where can I find a 5:5 ZSCT? Thanks.

 

[Bugman1400]

Hi, I have a project containing a 600V ac system that is high-resistance grounded, the ground fault current is limited at 5A. In each feeder there is a zero sequence CT with ratio 5:5 and an analog ammeter to display the fault current. I've asked GE/ITI, but they don't have such stuff. Do you know where can I find a 5:5 ZSCT? Thanks.

You need to know the size of the window you need and how to mount it among other things. You can get one-off type CTs made at ITEC based out of Charlotte, NC. Check out www.itec-ctve.com.