CT

[babambu]

Does the voltage rating of the Current Transformer matter if you are measuring on the neutral side?

 

[buzzp]

Yes I would think the rating matters. I assume your are referring to the isolation rating of the CT. Standard practice is to place around ONE hot leg. It will not matter if you put it around ONE neutral. The isolation rating would still need to be as high as that for use on a hot leg. Maybe you are referring to something else?

 

[230842]

I agree with buzzp. As far as I know the only rated voltage specified for a CT is the insulation voltage that must be higher than the voltage of the line the current of which is to be meassured. In case of neutral you need to be sure that neutral voltage value is always less than the rated insulation voltage value. In case of a fault phase to neutral, neutral voltage increases and in some cases can rich line voltage value. Julian

 

[jbartos]

Suggestion: It may be a good idea to follow some suitable industry and or manufacturer's standard(s), e.g. ANSI/IEEE C57.13-1978 "An American National Standard IEEE Standard Requirements for Instrument Transformers" to be on a safe side.

 

[230842]

To jbartos: Please let us know what such an standard says about that matter. Julian

 

[jbartos]

Here are some related data:
Table 7 Basic Impulse Insulation Levels for Current Transformers
Nominal Voltage (kV) BIL and Full Wave Crest (kV)
0.6 10
2.4 45
etc.
Suggestion: As electrical engineers, experts, specialists, etc., the standards are good to have accessible.
Next, for example, 600V CT may have BIL 10kV
however, when applied over conductor or cable insulation, this insulation BIL counts and adds to the CT BIL. Therefore, on the 69kV system voltage the CT over an insulated cable can be 600V with BIL 10kV under an assumption that the cable insulation would provide the remaining 340kV BIL to agree with Table 7 CT BIL 350kV.

 

[230842]

Jbartos, my question was in relation to babambu query, i.e. what Standards say about insulation requiermentes for CT meassuring on the neutral line Julian

 

[jbartos]

Suggestion: Normally, the neutral line is considered part of the system voltage installation since in case of a certain fault or faults, it can have the line to line voltage impressed.