All this talk about HV fuses got me wondering how quickly a fuse will blow.
After some time googling, I realize this simple question is not so simple
after all.
So, is there a good reference that will answer the question as related to
our typical need to protect amplifier hv components and tubes?
I have a specific application for protecting a non-obtainable twt if
damaged. This particular tube is supplied with 4400vdc at 400 mA through a 500
ohm limiting resistor. The resistor is purposely made this high to limit
fault current to a value that will not kill the tube in case of an internal
arc. This technique works ONLY if the fault current is interrupted very
quickly, like 2 or 3 milliseconds.
So, I am thinking that a 1 A fuse will survive turn on surges ok but will
it open in 2 or milliseconds with 8.8 A fault current?
The existing protection circuit uses a simple current sensing circuit in
the ground side of the hv supply that operates a small latching relay that in
turn opens the control circuit to a vacuum relay in the hv lead. This
scheme works reliably but there is no way the two relays can kill the high
voltage in 2 or 3 milliseconds.
Any information, comments or suggestions are greatly appreciated!
73,
Gerald K5GW
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