Open Circuit Condition

A

Thread Starter

Abel

How long will a 50:1 ratio (0-250Amp/0-5Amp) CT be able to withstand the open circuit condition? I'm switching in a short with a relay at the same time I open circuit the CT, but it takes the relay 10-25 milli seconds max to switch in the short. I'm trying to avoid damaging the relay and CT without using any timing circuitry
 
Abel... The instant the secondary is open-circuited, the primary current Ampere-Turns will be substituted for the normal excitation AT. Thus producing extremely high secondary voltages in just a few milliseconds!

Regards,
Phil Corso
 
R
I take it you are using a N/O N/C contact on the same relay;
It doesn't seem like a good idea to me but then I was taught never to open a CT because the voltage can spike to KV range.

It would be best to short out before opening the load circuit.
What are you doing, multiplexing? I have often wondered if something like a MOV or back to back zenner diodes would protect the CT against open circuit

Roy
 
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