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Author Topic: Testing MOV surge protectors Joules of energy absorption  (Read 2331 times)

Nathan Riddle

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Re: Testing MOV surge protectors Joules of energy absorption
« Reply #10 on: April 17, 2018, 08:42:47 pm »

Something like this?  Don't have time to calculate joules right now...

http://www.compwest.com/image/catalog/Datasheets/MegaPulse%201.2x50-8x20-12-2ohm.pdf

Honestly this is a better tester as it follows ANSI/IEEE surge ratings (8x20).

Mike, I see much research in your future of lightning surge protection ;)

http://www.ecmweb.com/archive/putting-10350-under-microscope

http://www.electrical-installation.org/enwiki/Characterization_of_the_lightning_wave
« Last Edit: April 17, 2018, 08:45:17 pm by Nathan Riddle »
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Jonathan Johnson

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Re: Testing MOV surge protectors Joules of energy absorption
« Reply #11 on: April 17, 2018, 09:59:46 pm »

I was thinking of all the hi-pot testers out there that can produce calibrated high voltages.  But a dedicated surge unit is exactly what the doctor ordered.

Something tells me that with the way MOVs degrage, that this would be a one shot test.  Work your way up with a fresh device each time until you start getting failures.  Then do enough around that voltage to get a statistical sampling.  Then you can decide where to rate on the curve from first failure to the mean.

I also wonder if MOVs have a variable failure pattern. For example, it might fail at 500 joules in one shot. But it might withstand a hundred 10 joule shots -- for a durability of 1000 joules.

I don't know in detail how MOVs work -- or fail -- either.
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Nathan Riddle

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Re: Testing MOV surge protectors Joules of energy absorption
« Reply #12 on: April 17, 2018, 10:41:27 pm »

I also wonder if MOVs have a variable failure pattern. For example, it might fail at 500 joules in one shot. But it might withstand a hundred 10 joule shots -- for a durability of 1000 joules.

I don't know in detail how MOVs work -- or fail -- either.

You're on the money.

I had to do some surge research for work since our site gets hit by lightning all the time.

SPD's come in different types and all have advantages and disadvantages. The big 3 are: MetalOxideVaristor (MOV), Gas Discharge Tube (GDT), Silicone avalanche diode (SAD)

https://ieee.li/pdf/viewgraphs/selecting_the_appropriate_circuit_protection_component.pdf
https://www.linkedin.com/pulse/comparison-contrast-between-gdt-mov-newman-liang
https://www.atis.org/peg/2017/CompaingCircuitProtection_TimHowell.pdf
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Mike Sokol

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Re: Testing MOV surge protectors Joules of energy absorption
« Reply #13 on: April 18, 2018, 03:02:26 am »

Something tells me that with the way MOVs degrage, that this would be a one shot test.  Work your way up with a fresh device each time until you start getting failures.  Then do enough around that voltage to get a statistical sampling.  Then you can decide where to rate on the curve from first failure to the mean.

Not exactly, but sorta kind-of.The MOV based surge protectors for RVs can be rated for up to 5,000 Joules or so. See https://rvlivingnow.com/best-rv-surge-protectors/. And MOV devices are basically sacrificial elements, so a 5,000 Joule rating implies one hit of 5,000 Joules, or five hits of 1,000 Joules each, and then the MOV is dead and a little indicator light comes on or off or whatever to tell you to buy a new one.

In my test I'll want to be able to do multiple strikes at lower Joules, while monitoring the health of the MOVs. I would then take a fresh surge protector and do one BIG spike at the rated Joules max to see if it actually protects the circuit from the rated spike. And finally, on another fresh unit one REALLY BIG test of maybe 10K to 20K Joules to simulate more of a direct lighting hit scenario to see what all will be destroyed.

Like I said, it needs a serious scatter shield with a remote video camera seeing the action. I'll know in a few weeks if this project has a budget. Right now I'm just figuring out how to build it. But I think it's just a really big capacitor rated for rapid discharge, and rally big Thyristor bank rated for these peak voltage and currents, a variable DC power supply for charging it up, and a current transformers and high voltage probe on a digital storage scope along with a video camera to monitor what happened. Just brute force testing until something blows up. 
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Nathan Riddle

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Re: Testing MOV surge protectors Joules of energy absorption
« Reply #15 on: April 18, 2018, 09:04:47 am »

You may have to work with the Tesla Coils.

Tesla Coils don't have enough current to simulate real lightning.

Marx Generators are really what would be used.
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Frank DeWitt

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Re: Testing MOV surge protectors Joules of energy absorption
« Reply #16 on: April 18, 2018, 09:06:02 am »

There are some You Tube videos put out by Surge-X where they let the smoke out of MOVs  You might get some hints from them as to what equipment they are using to do it.
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Nathan Riddle

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Re: Testing MOV surge protectors Joules of energy absorption
« Reply #17 on: April 18, 2018, 09:07:37 am »

Not exactly, but sorta kind-of.The MOV based surge protectors for RVs can be rated for up to 5,000 Joules or so. See https://rvlivingnow.com/best-rv-surge-protectors/. And MOV devices are basically sacrificial elements, so a 5,000 Joule rating implies one hit of 5,000 Joules, or five hits of 1,000 Joules each, and then the MOV is dead and a little indicator light comes on or off or whatever to tell you to buy a new one.

In my test I'll want to be able to do multiple strikes at lower Joules, while monitoring the health of the MOVs. I would then take a fresh surge protector and do one BIG spike at the rated Joules max to see if it actually protects the circuit from the rated spike. And finally, on another fresh unit one REALLY BIG test of maybe 10K to 20K Joules to simulate more of a direct lighting hit scenario to see what all will be destroyed.

Like I said, it needs a serious scatter shield with a remote video camera seeing the action. I'll know in a few weeks if this project has a budget. Right now I'm just figuring out how to build it. But I think it's just a really big capacitor rated for rapid discharge, and rally big Thyristor bank rated for these peak voltage and currents, a variable DC power supply for charging it up, and a current transformers and high voltage probe on a digital storage scope along with a video camera to monitor what happened. Just brute force testing until something blows up.

Yeah methinks you need a 10k budget for the 10k joules test... unless you can find somewhere to rent a capacitor bank....

Also, get a high speed camera please. Maybe even hire the slow mo guys from Youtube. This will be sooo much cooler with 240+fps videos :)
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frank kayser

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Re: Testing MOV surge protectors Joules of energy absorption
« Reply #18 on: April 18, 2018, 11:12:29 am »

Hi Mike,


I wondering a bit about your process.


Hitting it with measured joules, and then increasing steadily until fail.


MOVs as I understand them, have a limited amount they can absorb, then fail.  That is your test.
Why would not just keep hitting it with the same joule level over and over till failure?
What would be the purpose of constantly increasing the shock level?


Would it be a better test (or multiple tests) using one value till fail, then 2x value till fail, 4x... until shock equipment is maxed out or the MOV fails on a single hit, then compare whether total number of joules absorbed are the same (or similar)?


Would it also provide useful data to monitor the temp of the MOVs during the test?  Maybe there is a correlation between heat dissipation versus premature failure (providing there is premature failure).


Just idle thoughts...


frank
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Stephen Swaffer

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Re: Testing MOV surge protectors Joules of energy absorption
« Reply #19 on: April 18, 2018, 01:02:12 pm »


Like I said, it needs a serious scatter shield with a remote video camera seeing the action. I'll know in a few weeks if this project has a budget. Right now I'm just figuring out how to build it. But I think it's just a really big capacitor rated for rapid discharge, and rally big Thyristor bank rated for these peak voltage and currents, a variable DC power supply for charging it up, and a current transformers and high voltage probe on a digital storage scope along with a video camera to monitor what happened. Just brute force testing until something blows up.

I'm still jealous of the guys at the Milbank UL lab I got to visit a few years back.  Nice little prototyping lab (3D printer and all) and 4 cinder block rooms with steel doors & bullet proof windows in them to test their protoypes to see if they blew up.  They had a serious dedicated service to the building so they could test breakers & service equipment for up to 50,000 amps available fault current-it never used much in the way of KWhours, just huge, short surges.  They kept the paint toouched up when the cinder blocks got chipped...
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