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Joined: Jul 2004
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These can't be very large contacts to fit inside a meter and opening a fairly large inductive load will create quite an arc. Will these have room to move enough to put the fire out?


Greg Fretwell
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Perhaps the contacts are backup for a solid state switch. IGFET turns off the load, mechanical contacts are the "and stay off!" backup in case a serious surge tries to short the FET.

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Time to talk to my utility guys for some input.


John
Joined: Mar 2013
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Please do! It's not exactly like we could just go and poke around inside of these things... eek

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I saw a picture of the contact assembly at one of those lunch meetings. It all fits in a disk about 1/2" thick and the size of the meter.
It just did not look like 200a switch gear to me.



Greg Fretwell
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I poked around to see if the picture was on the GE web site but before I got there, I saw an article about hackers.

http://krebsonsecurity.com/2012/04/fbi-smart-meter-hacks-likely-to-spread/

No matter how long these things will hold up electronically, it looks like they all need a security makeover. That sounds expensive.


Greg Fretwell
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Most smart meters use a form of Mesh network to communicate. ( the ones here in Houston do) They can talk to each other or to the local node. This assures a signal path to the node. Most use one freq. to communicate to the local node, like 900 mz and another to communicate from the local node to the host 5gz. Other meters like gas and water can communicate with a local meter. Data may make several hops before accessing the local node. My understanding is the contactor in the meter is designed to switch at zero volts at the waveform to minimize arcing.

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Originally Posted by WESTUPLACE
My understanding is the contactor in the meter is designed to switch at zero volts at the waveform to minimize arcing.


Wow! That's some precision engineering!

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I agree, the fastest relay IBM had, when we were running trigger rings with relays, had a 1 ms response time and they worked at a fraction of an amp with a wire contact that was #30 AWG or so, moving about a 32d of an inch.
Each swing of a 60z sine wave is about 8ms zero to zero. That is some good shooting with a contact that probably has a 10 MS response time or more. ;-)
They generally drop slower than they pick so that might even be more.

Then you have all of that current vs voltage stuff in reactive circuits.

My guess is they don't plan on operating these that often. If this is a grow house with a room full of HPS plant lights, the contracts might weld and not open at all.


Greg Fretwell
Joined: Jun 2004
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To repeat myself: IGBT.

Google is your friend.

Compared to IGBT the other stuff is as dated as as vacuum tubes.

IGBT can switch 1000 Amps at 1000 VDC in microseconds -- with the device about the size of a cubic inch. 120 Hertz is eons to such a device.

Next, because of sampling speed and the quality of Poco sine waves, predicting the next commutations/ 0 volt cross-overs is a snap. Unlike most switches we deal with, the Poco can wait a couple of cycles to shut off the juice. That option opens the door to cheap switching.

This is the technology that permits wave synchronization for PV inverters.

Take it as Gospel: the Poco can switch your smart meter on and off remotely. The hacking of infrastructure that we read of in the news revolves around gaff-tastic zero-day vulnerabilities in this net.

Before the decade is out, all of these meters will have to be replaced. They're all wide open to even primitive hacks.


Last edited by Tesla; 03/27/13 07:51 AM.

Tesla
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