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Registered Member #15
Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068
Just a quick question on cascaded current transformer design.
I'm having some quality issues with the company that built some of my custom cascaded current transformers. The issue is that the loop that connects the two transformers is about 1" long (you can pull the loop 1" above the cores) and not tight against the cores.
Do you think this could pose a serious problem with the performance of the CT, or could it just be ignored for now and just mostly cosmetic in nature?
If schedule wasn't an issue, I would send them back have the vendor rework them, but with such a tight schedule, I need to either decide to keep them as is, even if they don't "look as nice", or spend the time to rework them myself.
Registered Member #72
Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659
First some upper and lower bounds
If the core had unit permeability, then the position of the wire is the *only* thing that affects the coupling. If the core had infinite permeability, then the position of the wire is totally irrelevant.
So ...
For huge but finite permeability, there will be a tiny effect. For a first hand-waving approximation, if the core is ur = 2000, then you might expect an upper bound on the change of sensitivity of 1/ur, 0.05% for iron at 2000, say if you move the wire from one side of the core to the other. Changing the size of a loop will have less effect than that. Going from one core-symmetric arrangement to another one of the same size will have no effect (so you might use several turns on each core equally spaced round the toroid to approximate to this).
If your accuracy/repeatability is larger than 1/ur, then you should be OK. Approaching that, you might want to do some careful testing.
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Cascaded Current Transformer Question
