use of RCD`s in thyristor power controller circuits
use of RCD`s in thyristor power controller circuits
(OP)
I have an application that uses thyristor power controllers to heat up a "melting pot". The supply is 415v 2 phase that is fed through a stepdown transformer giving a secondary voltage of 240v centre tapped. This is fed to thyristor power controller which has a resistive load . If a wire is broken @ the o/p of the thyristor and shorts down to earth i need to detect a current of 30mA or more and "trip" out the supply. I have tried using an RCD but this does not work. Anybody any ideas please?






RE: use of RCD`s in thyristor power controller circuits
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If we learn from our mistakes I'm getting a great education!
RE: use of RCD`s in thyristor power controller circuits
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If we learn from our mistakes I'm getting a great education!
RE: use of RCD`s in thyristor power controller circuits
RE: use of RCD`s in thyristor power controller circuits
Sorry if it's a dumb question, I seem to be asking more and more of them...
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If we learn from our mistakes I'm getting a great education!
RE: use of RCD`s in thyristor power controller circuits
RE: use of RCD`s in thyristor power controller circuits
RE: use of RCD`s in thyristor power controller circuits
Does the RCD trip when it is not supposed to, or refuse to trip when it should? On re-reading your original post I suspect that it is not detetcting the fault but presumably is not experiencing a false trip.
I suspect this is a DC offset problem because with a broken wire from one thyristor you will have an assymetric output and there will be a net DC component. RCDs use a toroidal core with a multi-turn sense winding to trip the device. If there is DC present then the toroid will saturate and the current in the sense winding will not be a accurate replica of the primary current, causing mis-operation or non-operation of the RCD. I think the RCDs which are tolerant of DC must use an air-gapped core although I admit I've never looked.
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If we learn from our mistakes I'm getting a great education!
RE: use of RCD`s in thyristor power controller circuits
RE: use of RCD`s in thyristor power controller circuits
RE: use of RCD`s in thyristor power controller circuits
----------------------------------
If we learn from our mistakes I'm getting a great education!
RE: use of RCD`s in thyristor power controller circuits
RE: use of RCD`s in thyristor power controller circuits
RE: use of RCD`s in thyristor power controller circuits
http://hvacity.danfoss.com/pdf_files/rcd.pdf
The same logic would apply to DC drives.
However, 30mA would be too low for an AC drive due to the inherrent leakage current from filters, cabling, switching frequency etc. Not sure if this is the case with DC drives.
RE: use of RCD`s in thyristor power controller circuits
Bill
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