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CT theory

Johno12345
Im just reading about CTs, just for interest really. I have always known that you short CTs when they arent connected, but assumed it was just so you couldn't get a shock from the cable which would rise to the voltage on the cable its clamped around. I know this isn't quite right now.


Evidently, the voltage can rise to thousands of volts and damage the CT, I assume this happens instantly, rather than a gradual rise


The other thing, and this is my question really, if one side is grounded and commoned, as the drawings of them show, and the other side is open, does the voltage rise still occur? I just cant quite fathom it in my head
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    As Mike has said, it depends on the core size and material whether you are talking hundreds ov volts, or thousands of volts. With a decent amount of magnetic material in the core, the secondary voltage will be limited by the core saturating, or something flashing over. The latter may be within the CT secondary winding itself, or within the equipment / cable connected to it. 


    We had an ammeter go open circuit on an 11kV circuit during a fault last year. The arc filled the case of the instrument, totally destroying the coil and covering the inside of the instrument in carbon. I will post pictures as an example when I find them. 


    To sum up, an open circuit CT secondary is a very bad and dangerous thing to have on a power system.
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  • 0
    As Mike has said, it depends on the core size and material whether you are talking hundreds ov volts, or thousands of volts. With a decent amount of magnetic material in the core, the secondary voltage will be limited by the core saturating, or something flashing over. The latter may be within the CT secondary winding itself, or within the equipment / cable connected to it. 


    We had an ammeter go open circuit on an 11kV circuit during a fault last year. The arc filled the case of the instrument, totally destroying the coil and covering the inside of the instrument in carbon. I will post pictures as an example when I find them. 


    To sum up, an open circuit CT secondary is a very bad and dangerous thing to have on a power system.
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