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'[EE] Shunt Trip Continued'
2007\02\02@103626 by Mark Peterson

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Responses to comments/questions:

I do understand what the client is demanding.  The client is the U.S.
Navy and they are very clear.  I'm with you that there are other ways to
do this, and other people and I have proposed and recommended other
means, but this is what they want.

I agree that this is different than the normal meaning and application
of shunt trip; tripping a breaker with a control signal.  I had many
years of experience in that world designing relaying protection schemes
for 12.5kV through 345kV systems.  Do know that not all breakers have
shunt trip capability.  The 2000 Amp breaker in this case is exclusively
load current/magnetically actuated.  It is very similar in function to
the main breaker in your house panel.

Forcing a remote breaker to trip by the application of a forced fault is
nothing new and has been done in the utility industry for decades.  It
is an implementation of a transfer-trip scheme.  The method is crude but
very simple and effective.  The preferred method of doing this utilizes
piloted relaying schemes that communicate the desired tripping or
blocking action via power line carrier, radio, fiber, or leased phone
lines.  The shunt trip method is not implemented using a big
screwdriver, but rather appropriately designed and sized switches.
Stuff in the utility world is designed to normally handle hundreds of
thousands of volts at tens of thousands of amps, and to do so safely.  I
knowingly stood 30 feet from one as it was switched across a live 34.5kV
line with several thousand amps of available fault current that resulted
in the remotely located 10kA breaker opening, and it was actually rather
uneventful.  There were no flames or large arcs at all, as would be the
case if an attempt was made to use the same switch to open the circuit,
which is a very different situation.  There would be a ball of fire in
that case and I have witnessed that situation.  

A couple things that lessen the requirements of the contactor is that
the 3000 amp load only needs to be carried for approximately 10 cycles,
which is the maximum time it will take for the upstream breaker to open.
So the contactor needs to handle a momentary 3000A current rather than a
continuous 3000A load current.  The other thing is that it does not need
to interrupt that high current since that will be done by the breaker.

FYI, there are SCRs available that can handle currents of this
magnitude.  Semikron SKT 1600/16E devices are rated 1600 volts at 2500
amps.  For a 150 ms pulse, they can handle 10,000 amps.  They run about
a grand apiece, which would be acceptable for this project.

Good discussion, folks.  Great minds here, for sure.
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2007\02\02@112038 by Howard Winter

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Mark,

On Fri, 2 Feb 2007 09:30:49 -0600, Mark Peterson wrote:

>...
> A couple things that lessen the requirements of the contactor is that
> the 3000 amp load only needs to be carried for approximately 10 cycles,
> which is the maximum time it will take for the upstream breaker to open.

So you're giving it 3kA for 166mS (assuming 60Hz)...

>...
>  
> FYI, there are SCRs available that can handle currents of this
> magnitude.  Semikron SKT 1600/16E devices are rated 1600 volts at 2500
> amps.  For a 150 ms pulse, they can handle 10,000 amps.

That looks really marginal - A continuous rating of 2.5kA and a momentary 10kA for 150mS doesn't specify how long it can handle 3kA, so you'd need
to check their graphs.  And for something this dramatic, I'd want some serious headroom!  :-)

As a matter of interest, why do they want to trip a 2kA breaker at 500A?  Wouldn't it have been better to get the right rating in the first place?  :-)

Cheers,


Howard Winter
St.Albans, England


2007\02\03@110123 by Vasile Surducan

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I haven't any doubt you have experience. The problem was clear described
and the potential solutions where also named.
But the request was unusual.

Unfortunately I don't know too much about the american power
distribution system (except that is weird and aparently without any
rule).
What I know,  the number one technology in the Europe in switching on
20KV is a russian vacuum patented system bought by many european high
voltage breaker producers (in fact by almost all).

See here: http://www.tavrida.com/page.php?id=products
and take a look "low voltage vacuum contactor"
Buy one and take a look :)
it's a 4KA breaker with 50mS turn on and 80mS turn off.

greetings,
Vasile


On 2/2/07, Mark Peterson <spam_OUTmpetersonTakeThisOuTspamcannontech.com> wrote:
{Quote hidden}

> -

2007\02\04@061924 by Lee Jones

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>> I do understand what the client is demanding.  The client is the U.S.
>> Navy and they are very clear.  I'm with you that there are other ways to
>> do this, and other people and I have proposed and recommended other
>> means, but this is what they want.

> But the request was unusual.
>
> Unfortunately I don't know too much about the american power
> distribution system (except that is weird and aparently without
> any rule).

Look at the client -- the US Navy.  I'm wondering if some of the
unusual requirements are dictated by ... fault tolerance ... like
working reliably while being blown up or having bullet holes added.
I could easily see an AEGIS cruiser or an aircraft carrier needing
this sort of power handling capabilty while combat conditions would
introduce uncommon constraints.

                                               Lee Jones

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