Can you two get back to earth and keep it somewhat relative to ham amps in
the under 20KW range (-;
Carl
KM1H
----- Original Message -----
From: "James R Carr" <n7fcf@hctc.com>
To: "Roger (K8RI)" <sub1@rogerhalstead.com>; <amps@contesting.com>
Sent: Saturday, January 08, 2011 7:21 PM
Subject: Re: [Amps] Fuses
> Down in prosser, WA about 30 years ago they had a problem with a pottato
> processing plant and a mechanic came running into the panel room and
> before
> anyone could stop him threw the main 480v 3 phase breaker. The plant was
> under full load with motors up the cazoo. When the back emf hit it blew
> the
> breaker out of the panel. The guy was lucky he wasn't hurt.
> I retired in 2000 and there is a whole raft of devices that have come on
> line since.
> Jim
> N7FCF
> ----- Original Message -----
> From: "Roger (K8RI)" <sub1@rogerhalstead.com>
> To: <amps@contesting.com>
> Sent: Saturday, January 08, 2011 2:38 PM
> Subject: Re: [Amps] Fuses
>
>
>>
>>
>> On 1/8/2011 5:22 PM, James R Carr wrote:
>>> Agreed, The first instant in time you have the full output of Bonnyville
>>> Dam
>>> on the fault. But then the impedance of the system kicks in and limits
>>> it.
>>> But still depending on the size of the utility transformer, it's
>>> eficiency,
>>> the length and size of the service conductors, you can still have
>>> several
>>> thousand amps at the main panel and down the line. About 20 25 years ago
>>> they had to increase the fault clearing ability all the breakers in the
>>> panels from 5000 amps to 20000 amps due to the increased use of low loss
>> Our mains weren't quite that large, but they were big...It's been too
>> long for me to remember the actual size.
>> They used magnetic quenching in arc chutes. They could open under full
>> load without self destruction, BUT with big transformers down stream
>> (Inductive loads) the "kick back" was so bad that reverse EMF would take
>> out almost any thing attached to the line. So, if you blew one of the
>> mains you knew it was going to be an expensive day.
>>
>> 73
>>
>> Roger (K8RI)
>>> transformers by the utilities. basically the breaker can clear it
>>> without
>>> exploding. It probably will be terminally damaged though. I have seen
>>> buss
>>> bars twisted into pretsels by a dead short and a breaker that didn't
>>> clear
>>> quick enough.
>>> Jim
>>> N7FCF
>>> ----- Original Message -----
>>> From: "Jim Thomson"<jim.thom@telus.net>
>>> To:<amps@contesting.com>
>>> Sent: Saturday, January 08, 2011 2:18 AM
>>> Subject: [Amps] Fuses
>>>
>>>
>>>> Date: Sat, 8 Jan 2011 08:34:30 +0000
>>>> From: Ian White GM3SEK<gm3sek@ifwtech.co.uk>
>>>> Subject: Re: [Amps] Fuses
>>>>
>>>> James R Carr wrote:
>>>>> Where pray tell do you get a hydraulic breaker? I have installed
>>>>> several thousand over the years but have yet to see one filled with
>>>>> oil. As for current limiting devices, the fastest breaker will hold in
>>>>> for three to seven full cycles. To be current limiting, a fuse has to
>>>>> clear in less
>>>>> than 1/2 cycle.
>>>> A fuse provides NO current limiting until it blows; and a breaker
>>>> provides NO current limiting until it breaks.
>>>>
>>>> A lot of damage can be done in those first few milliseconds, which is
>>>> why the fuse/breaker is only PART of the solution.
>>>>
>>>> We always need a surge limiting resistor in the B+ as well, to provide
>>>> instantaneous current limiting until the fuse/breaker takes over and
>>>> finally breaks the circuit.
>>>>
>>>>
>>>> --
>>>>
>>>> 73 from Ian GM3SEK
>>>> http://www.ifwtech.co.uk/g3sek
>>>>
>>>> ## Agreed. The purpose of the mag-hydraulic breaker is [A] handy
>>>> dandy
>>>> way of opening off the 240 v line, without having to kill the dedicated
>>>> breaker in the
>>>> main 200A panel. [B] eliminate any follow on current.
>>>>
>>>> ## On my latest 7700 vdc supply, I use a Buss HVU series, sand
>>>> filled
>>>> HV fuse..rated at 3A..in series
>>>> with the B+ lead. The HV fuse gets inserted just prior to the kw
>>>> rated
>>>> glitch R, which consists of 4 x
>>>> parallel globar type AS energy absorbing type resistor's, 1.5" diam x
>>>> 18' long. [ 4 x 200 ohm in parallel= 50 ohms]
>>>> 7700/50 ohms = 154A. max fault current. Now 154 A of fault current,
>>>> flowing through a 3 A rated
>>>> fuse, will open VERY fast. [ the fuse is running at 5100% of it's
>>>> rating]. I use a 50 ohm glitch R on the
>>>> smaller supplies as well... with the provisio that a smaller rated HV
>>>> fuse
>>>> is used..like 1A, etc.
>>>>
>>>> ## I also use a 2nd Buss HV fuse, in the sec of the plate xfmr, [one
>>>> leg
>>>> only], between sec and input to
>>>> FWB. In normal operation, with any B+ to chassis fault, the B+ HV
>>>> fuse
>>>> alway's blows open 1st..so the
>>>> breaker used in the 240 v line is sorta a moot point. That B+ fuse
>>>> concept has been tested 34 x times
>>>> now, and nothing ever happens..except a blown HV fuse. Once, some of
>>>> the
>>>> blown HV fuses were
>>>> 'refurbished' with a single strand, soldered on the outside..and
>>>> wrapped
>>>> with 88 tape. In one case, the
>>>> wire ga of the single strand refurbished job was too big.. and the end
>>>> result was the parallel pair of 100
>>>> ohm, 225 W- WW's were literally incinerated, burnt to a crisp. That
>>>> was
>>>> with a 165 uf filter cap..and a 253 lb
>>>> dahl hypersil xfmr. That particular glitch R was replaced with 4
>>>> parallel 200 ohm, 225 W, wirewounds
>>>> [ $12.00 each, from mouser],and the correct size HV fuse. Zero
>>>> problems
>>>> since then, and you can literally
>>>> cro-bar it all day long. I would not trust any of these glitch R's,
>>>> even
>>>> big ones..without a prior series HV fuse,
>>>> not with big uf caps, huge amount's of joules involved, and then trying
>>>> to
>>>> rely on a breaker [ or even the
>>>> 2nd HV AC fuse].
>>>>
>>>> ## In one instance, one of the hv lytics [ 3900 uf @ 450 vdc] towards
>>>> the hot end of the string, arced through a
>>>> crack in the plywood, and launched itself. Since the fault was before
>>>> the B+ fuse.... the 2nd HV fuse blew.
>>>> [ the one located between sec of xfmr and FWB]. The 96 x 6A10's in
>>>> the
>>>> FWB were not damaged. In 2 x instances the
>>>> 240 vac breaker popped open. Once when a screw removed from a 6"
>>>> fan..and
>>>> the AL fan swung down like a pendulum
>>>> and hit one side of the 240 vac buss. [ and blew a chunk out of the fan
>>>> casing]. The 2nd time was a B+ fault.
>>>>
>>>> ## I use a simple 50 ohm-50W WW on my L4B's..with the stock drake
>>>> HV
>>>> B+ fuse. [ consist of a .82 ohm, 1 watt carbon R ].
>>>> The stock .82 Ohm R always blows cleanly in 1/2. I have only had 2
>>>> x
>>>> ever blow open since 1977.
>>>>
>>>> later... Jim VE7RF
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