[Amps] HV fuses

[Roger (K8RI)]

On 10/27/2013 12:54 AM, Jim Thomson wrote:
> Date: Fri, 25 Oct 2013 05:38:56 +0000
> From: "Fuqua, Bill L" <wlfuqu00 at uky.edu>
> To: Jim Garland <4cx250b at miamioh.edu>, "Amps at contesting.com"
> <Amps at contesting.com>
>
> Subject: Re: [Amps] HV fuses
>
>     This does not sound right. I assume you are saying that they are glass fuses.
> I suspect if you blow one in a HV powe rsupply it will shatter or explode into pieces if
> you have a reasonable value of filter capacitor.  Do you have a data sheet on these
> fuses?

High voltage fuses can be glass or ceramic. Even the high voltage fuses 
in power substations are often glass.  The only ones I've seen were 
about 4" in diameter 1/4" to 5/16ths " wall,  and they appeared to be 
about 16-18 inches long (Might have been 2 feet) . IIRC they had several 
parallel elements and were packed with fine sand.  The PS HV fuses had a 
glass tube around a 1/4 to 5/16ths inch in diameter and were packed with 
a very fine, white, quartz sand.

The engineers forgot to remove the shorting cables after we PM'd a sub. 
  those small, HV wires with about a #16 conductor vaporized so 
violently there was not a sign of them left. The entire sub cabinet was 
8' high X 12 ft wide X 6' deep were completely coated with a copper 
film. The doors were about 3' wide , had an inch and a half formed edge 
and were made of 1/8th inch steel.  I was looking at the sub when it 
blew.  The center of those doors arched out between 1 and 2 feet.

It blew the fuses, but they remained in tact.

The cables feeding the subs were larger than 500 MCM, but I don't 
remember the actual size.

Sure was loud, expensive, and embarrassing!

73

Roger (K8RI)


> 73
> Bill wa4lav
>
> ##  why would they explode ?   Mine don’t.    The 50 ohm glitch R  LIMITS the current..and the
> HV fuse  INTERRUPTS the fault current.   BTW,  you always put the HV fuse B4
> the  glitch R.   Reason is, if the glitch was damaged, and dangling down  onto the chassis,  you
> want the HV fuse INBOARD  of any glitch, so the fuse will open.
> Yes, you can parallel em  for more current..and you can also  series em for more HV.
> You can also wire em series-parallel  for more current + Voltage.
>
> ##  another useful place to insert a HV fuse is between EITHER plate xfmr secondary.....and the
> FWB  or FWD.   Then if any B+ shorts  in the filter caps, or any problems inboard of the B+ fuse,
> then you are still protected.   Dirt cheap insurance.   I have seen the AC  HV fuse blown open twice
> and the B+  HV fuse blown several times... while de-bugging a new hb RF deck.
>
> Later....    Jim   VE7RF
>
>
>
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