Date: Fri, 7 Jan 2011 22:11:50 -0800
From: "James R Carr" <n7fcf@hctc.com>
Subject: Re: [Amps] Fuses
Who makes it and what's the model number? I'd like to see the specs on it
especially the UL test results. When I retired in 2000 the only way they
were able to get a breaker to clear a fault in less than three full cycles
was to put 18" of wire between it and the buss bars. And even then it didn't
get down to 1/2 cycle. Fuses were tested as a bolted fault across the buss
bars.
## per all the eng notes from airpax, and a host of other breaker
manufacturers,
a good quality Thermal breaker should trip in 35 msecs. [this was with a gross
overload,
like several hundred percent, IE; dead short]. There is also a breaker known
as a
'thermal-magnetic' and also the 'hydraulic magnetic'. The hydraulic-magnetic
is the
fastest of the bunch. The hy-mag breakers have loads of options, to handle
everything from
medium in-rush currents, to heavy motor start inrush. You can also get em with
optional
cam followers to tweak the trip characteristics even more. Other options
included
various arc chutes, aux contacts, lighter duty alarm contacts, etc. You can
also get them
with no breaker at all, and configure them as an on-off switch. You can also
obtain them with external
sense leads, and manually adjust the exact trip point, both thermally, and
over trip, and even various
timing schemes for max % of overload.
There is 2 x ways to open off the mag-hydraulic breaker. one was with a slight
overload, like 125%...
in which case the hydraulic portion of it functions. With gross overloads,
like several hundred percent,
the magnetic portion would take over. Internally, there is a fluid reservoir.
Per the eng notes, to change the
basic trip curves, ['instant trip' , normal, more lag, even more lag, then
motor start, etc... they changed the
viscosity of the oil used inside the reservoir. The 'instant trip' versions
had no oil in the reservoir at all, were the
most sensitive to any kind of overload, and are only recommended for use in
delicate circuits. These instant
trip versions are way faster than the typ 35 msecs you get from a plane jane
thermal house breaker. Thermal
breakers are typ 35-116 msecs... depending on % of overload.
Their are several caveats/eng notes when using ....'instant trip'
...mag-hydraulic breaker's, esp when used in conjunction with
any kind of... 'pulse train' type supplies. IE: switching supplies. The
original pulse train, is of course, any ham type
High C , B+ supply. By pulse train, they mean super high current
pulses..every 8.3 msecs, like you get from any FWB
and a high C filter. The mag hydraulic breaker makers say the individual
pulse every 8.3 msecs can't be any longer than
10 msecs max in duration..or the duration of the pulse will be long enough to
fool the magnetic portion of the mag-hydraulic
breaker...and cause it to trip, cause of a combo of high peak current and pulse
duration. Using Duncan's PSUD, plus various
experiments with scopes and current probes, the AVERAGE current during each
pulse is still
pretty low. The peak current, of course is sky high, depending on Z of
primary/sec of plate xfmr..and all wiring back to the
main 200A panel, drop wire, all switch's, contactor's etc.
Interesting enough, in my quest to lower the Z from plate supply back to main
panel... by using bigger ga wire, and thus
lowering the peak V drop, results in mixed results. With small ga wire, and
higher Z, the peak current every 8.3 msec
are slightly lower.. and peak V drop is still bad. With bigger ga wire, the Z
is lower, and now the peak current pulses are a lot higher.
Trbl is, the higher peak current pulses times the lower Z wire, still results
in a big V drop on peaks. The pulse width will vary too,
as though it's trying to compensate. With a lower Z source, the width of each
pulse gets a little wider. Overall results are still better
with bigger ga wire, esp with bigger VA xfmr's and bigger C filters. Peak
current's can still be anywhere from 2-5 times average, it's
all over the map, depending on how many uf used, ga and length of wire, how
many va the xfmr is, etc. I didn't want to take a chance,
so sized my mag-hydraulic breaker up by one notch, since it was a one shot
purchase, and a custom order..and no refunds. With fixed
breakers like these, you don't want em on the hairy edge. With the breakers
that incorporate an external, adjustable trip level, no big
deal. As I mentioned b4, with a pair of HV fuses, the type of breaker in the
240 line is sorta a moot point. The thought here was..initially
if a breaker is used, lets use the fastest one made.
BTW, we had a bad fire in on of our bigger telco's just a few yrs back, in the
huge panel that contained all the motor control stuff
for the HVAC in the building. [ 6 x separate units]. The entire panel burned
up. The cause was one of those adjustable external trip
sensors. It malfunctioned, and would not send the control signal to the big 3
phase contactor it controlled. Something had shorted,and
the wiring just sat there and burned up. A real mess, the fire spread, and
burnt everything..including the 1st 20' of all wires that exited the
panel, via 17 x conduits on top of the same panel. Insides of the conduits
just charred black. IMO, these adjustable trip devices should still have
to use supplemental breakers, which these did. Trbl was, the supplemental
breakers/fuses I believe, were further downstream. The larger upstream
breakers for the burnt up panel, were located in another panel, across the
room. With a 4000 lb, 450 kva vault xfmr, you can burn stuff to a crisp..fast.
It's almost like having a 15A breaker fail shut in your main panel, then trying
to rely on the 200A breaker to do the job, it won't.
Later... Jim VE7RF
----- Original Message -----
From: "Paul Kraemer" <elespe@lisco.com>
To: "AMPS" <amps@contesting.com>
Sent: Friday, January 07, 2011 6:50 PM
Subject: Re: [Amps] Fuses
> It is a terminology thing as in magnetic / hydraulic trip
> Also, we routinely use supplemental IEC protection devices that have an
> adjustable thermal trip plus a near instantaneous overcurrent trip
> Actual tests in our shop have demonstrated to us that they will in fact
> trip
> faster than a fast semiconductor fuse will blow
> That is why we frequently install them ahead of motor drives to protect
> the
> expensive semiconductor protection fuses.
> Paul K0UYA
> ----- Original Message -----
> From: "James R Carr" <n7fcf@hctc.com>
> To: "Jim Thomson" <jim.thom@telus.net>; <amps@contesting.com>
> Sent: Friday, January 07, 2011 8:01 PM
> Subject: Re: [Amps] Fuses
>
>
>> 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.
>> Jim
>> N7FCF
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