Zero Sequence (neutral) CT Wiring

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mbrooke said:
If I'm wiring a group of CTs in order to read neutral current, would I use option A or option B? What would happen if I went with option B? Under what conditions would option B be used?

https://imgur.com/EmgXVBF
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One is star and one is delta but the delta should be the real ground current times 1.732. Not much use.

The big thing here is you can get both phase and zero sequence currents with just three CTs. The downside is that the zero sequence (ground) current will have the error of all three CTs combined. It is the same as using a multifunction relay or meter that adds all three currents together in software. This is just the analog (wired) equivalent.

A better method is to use a single CT with a larger window. The downside is they tend to be fairly expensive,
 
paulengr said:
One is star and one is delta but the delta should be the real ground current times 1.732. Not much use.

The big thing here is you can get both phase and zero sequence currents with just three CTs. The downside is that the zero sequence (ground) current will have the error of all three CTs combined. It is the same as using a multifunction relay or meter that adds all three currents together in software. This is just the analog (wired) equivalent.

A better method is to use a single CT with a larger window. The downside is they tend to be fairly expensive,
Click to expand...

Would you not mean broken delta?
 
One drawback of B is that current transformers are designed to feed a short circuit or at least a resistance lower then the specified burden.

Putting CTs in series will result in higher than normal voltages on the secondary winding and could, in the worst case, lead to saturation errors.
Just as PTs with different voltages should not be paralleled, CTs with different currents should not be put in series.
 
GoldDigger said:
One drawback of B is that current transformers are designed to feed a short circuit or at least a resistance lower then the specified burden.

Putting CTs in series will result in higher than normal voltages on the secondary winding and could, in the worst case, lead to saturation errors.
Just as PTs with different voltages should not be paralleled, CTs with different currents should not be put in series.
Click to expand...


You know your stuff. Only one seasoned engineer pointed this out on another forum.
 
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