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Title: Testing MOV surge protectors Joules of energy absorption
Post by: Mike Sokol on April 17, 2018, 02:01:39 pm
I just had a manufacturer contact me about designing a test for their MOV based surge protectors. I need to build a test rig that will allow me to keep raising the voltage/joule spike I'm hitting it with until it fails or blows up or whatever. And of course I need to monitor the Joules of energy being absorbed. Sounds like my kind of gig.

I'm thinking this is very similar to how the original defibrillators worked with a pair of paddles and some big capacitors you can charge up with varying amounts of energy. Then you hit the big red button and shock the patient back to life. In this case I would keep raising the joules of energy until the circuit failed.

Anyone here have any experience with this sort of thing? I think I know how to do this in my head, but if there's a piece of gear in existence that I could hack to make it work for this application, so much the better.

I have too much fun with this, don't I? ;D
Title: Re: Testing MOV surge protectors Joules of energy absorption
Post by: Nathan Riddle on April 17, 2018, 02:35:54 pm
Equipment in existence I don't know.

There's this thing: https://www.erico.com/part.asp?part=MGATESTER

But you could build a buckboost transformer and do the voltage calculation with capacitors. You have a very easy way to determine the current joules in the system. Run an o-scope on the leads to determine current & voltage. You can do all sorts of calculations from that :)

W= 1/2 * C * V^2
w = joules
C = capacitance
v = voltage

https://www.engineeringtoolbox.com/capacitors-energy-power-d_1389.html
Title: Re: Testing MOV surge protectors for Joules of energy absorption
Post by: Mike Sokol on April 17, 2018, 02:41:26 pm
I'm thinking one of each of these with a variable voltage charging circuit and a way to monitor the peak current/voltage. This will cost a few thousand dollars to build, but I might get a serious budget.

However, to get full power I would need a big capacitor with less voltage and more capacitance, or a big SCR with more voltage capability. I do need to get up above 2,000 Joules per spike, and even 5,000 Joules would be better. Probably need to build a scatter shield for this thing, eh?
Title: Re: Testing MOV surge protectors for Joules of energy absorption
Post by: Mike Sokol on April 17, 2018, 02:51:32 pm
Looks like I need one of these things designed for locomotive engine DC switching. http://www.power-thyristor.com/pulse-power-supply/

I'll have to work on my ghoulish laugh...  ::)

Title: Re: Testing MOV surge protectors for Joules of energy absorption
Post by: Dave Garoutte on April 17, 2018, 03:08:44 pm
Looks like I need one of these things designed for locomotive engine DC switching. http://www.power-thyristor.com/pulse-power-supply/

I'll have to work on my ghoulish laugh...  ::)

We definitely need a MWah-ha-ha emoji.
Title: Re: Testing MOV surge protectors for Joules of energy absorption
Post by: Nathan Riddle on April 17, 2018, 03:13:10 pm
I'm thinking one of each of these with a variable voltage charging circuit and a way to monitor the peak current/voltage. This will cost a few thousand dollars to build, but I might get a serious budget.

However, to get full power I would need a big capacitor with less voltage and more capacitance, or a big SCR with more voltage capability. I do need to get up above 2,000 Joules per spike, and even 5,000 Joules would be better.

Note that voltage is squared so it is non linear. To get more joules it is much better to double voltage than double capacitance.

Quote
Probably need to build a scatter shield for this thing, eh?
That's an emphatic YES!

By the way, i'm jelly about your project :) I've always wanted to build a coil gun or rail gun or something sciencey ;)
Title: Re: Testing MOV surge protectors for Joules of energy absorption
Post by: Marc Sibilia on April 17, 2018, 05:37:41 pm
  Probably need to build a scatter shield for this thing, eh?

And be sure to make it from polycarbonate (Lexan), not acrylic (Plexiglas) which is brittle and sharp.  Almost lost a grad student I knew to that mistake in a combustion lab at school.

Marc
Title: Re: Testing MOV surge protectors for Joules of energy absorption
Post by: Corey Scogin on April 17, 2018, 05:38:45 pm
This is very interesting. Keep us updated.

Knowing very little about how surge protectors are supposed to work, I have numerous questions:

At what point do the MOVs begin absorbing energy? At +10% of nominal voltage? +20%?
Can the energy absorption and the voltage peak be measured by separate tests? ie: Can you supply a steady 300V until the MOV is 'saturated' or are they not rated for continuous power absorption?
What is the determining criteria for when a MOV is worn out? ...when they are unable to maintain the rated voltage at the output?
Title: Re: Testing MOV surge protectors Joules of energy absorption
Post by: Stephen Swaffer on April 17, 2018, 05:54:16 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

Title: Re: Testing MOV surge protectors Joules of energy absorption
Post by: Stephen Kirby on April 17, 2018, 06:53:07 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
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.
Title: Re: Testing MOV surge protectors Joules of energy absorption
Post by: Nathan Riddle 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
Title: Re: Testing MOV surge protectors Joules of energy absorption
Post by: Jonathan Johnson 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.
Title: Re: Testing MOV surge protectors Joules of energy absorption
Post by: Nathan Riddle 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
Title: Re: Testing MOV surge protectors Joules of energy absorption
Post by: Mike Sokol 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. 
Title: Re: Testing MOV surge protectors Joules of energy absorption
Post by: Jerome Malsack on April 18, 2018, 08:48:25 am
https://www.boeing.com/commercial/aeromagazine/articles/2012_q4/4/

https://www.scientificamerican.com/article/what-happens-when-lightni/

https://www.nasa.gov/larc/lightning-tests


You may have to work with the Tesla Coils.
Title: Re: Testing MOV surge protectors Joules of energy absorption
Post by: Nathan Riddle 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.
Title: Re: Testing MOV surge protectors Joules of energy absorption
Post by: Frank DeWitt 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.
Title: Re: Testing MOV surge protectors Joules of energy absorption
Post by: Nathan Riddle 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 :)
Title: Re: Testing MOV surge protectors Joules of energy absorption
Post by: frank kayser 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
Title: Re: Testing MOV surge protectors Joules of energy absorption
Post by: Stephen Swaffer 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...
Title: Re: Testing MOV surge protectors Joules of energy absorption
Post by: Mike Sokol on April 18, 2018, 01:16:45 pm

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)?

frank

Methinks I need to do both types of tests. Of course, doing 1/10 of the 5,000 rated joules test (500 joules) at least 10 times would be important. But they also want to know if their product can absorb a single 5,000 joule spike without vaporizing. The first multi-test will confirm that the MOVs are sufficiently robust, and the second overload test will confirm that the wiring can withstand the peak current without vaporizing. And yes, I need a high-speed camera and such. I'll be talking to their engineers about this in a few weeks, so I just need as many ideas swimming in my head for the initial consult. Then it will be down to budget and timing.
Title: Re: Testing MOV surge protectors Joules of energy absorption
Post by: John Roberts {JR} on April 18, 2018, 01:45:46 pm
I could tell you everything I know about MOV testing in a very short post... I'm finished.  8)

Can I ASSume they are buying somebody else's off the shelf MOV? How about asking the MOV manufacturer for advice?

A couple decades ago I had a difficult problem troubleshooting behavior of a triac based power switch. In that case the triac manufacturer was zero help. The difficulty may be reaching the person or people at the firm who know, to ask.

JR

PS: A friend who manufactured a high voltage capacitor discharge strobe flash for photography, built a protective thick plastic(?) shield for manufacturing QA to deal with exploding capacitors. 
Title: Re: Testing MOV surge protectors Joules of energy absorption
Post by: Jonathan Johnson on April 18, 2018, 02:57:43 pm
Methinks I need to do both types of tests. Of course, doing 1/10 of the 5,000 rated joules test (500 joules) at least 10 times would be important. But they also want to know if their product can absorb a single 5,000 joule spike without vaporizing. The first multi-test will confirm that the MOVs are sufficiently robust, and the second overload test will confirm that the wiring can withstand the peak current without vaporizing. And yes, I need a high-speed camera and such. I'll be talking to their engineers about this in a few weeks, so I just need as many ideas swimming in my head for the initial consult. Then it will be down to budget and timing.

So it's not only determining the durability of the MOV, it's also about determining the failure modes under various circumstances.

Knowing the failure modes is important, so the manufacturer can know how to best contain a failure and ensure the devices protected by the MOV remain protected in the event the MOV fails.

There are a lot of (cheap) surge protectors out there with a "protected" LED that's just connected across line and neutral -- it doesn't actually tell you that the MOVs are working. And if the "protected" LED is being truthful, it still doesn't tell you that the MOV has only one joule of protection left... and when the MOV does fail, there's nothing in there to break the circuit.
Title: Re: Testing MOV surge protectors Joules of energy absorption
Post by: Mike Sokol on April 18, 2018, 03:56:15 pm
So it's not only determining the durability of the MOV, it's also about determining the failure modes under various circumstances.

I think so. This is a new surge protector that will be built by an OEM supplier to the market. And yes, my first plan is the contact the MOV manufacturer once I know who it is, and talk to the engineer designing this product, etc...

Part of the design issue is likely that just because a single MOV behaves a certain way in a circuit, how do you know how a ten of them will react. The peak shunting currents would go up by a factor of 10. Heating on the circuit would go up by 10 times the watt energy, other weird things I don't know about could occur. For instance, just how closely matched are these MOV's. You just can't slap 10 transistors in parallel and expect them to share the load equally.

The RV industry is in a period of consideration that all RVs should have some sort of surge protection, likely because of me writing so much about it. But I'm really promoting the idea of everyone getting an "intelligent" surge protector with a relay that can disconnect your RV from a power source that's too high, too low, or has lost its ground. Gonna be interesting to figure out exactly what's happening. I'll be under an NDA so I would be able to post the nitty gritty here. But at least I can post the scientific parts. 
Title: Re: Testing MOV surge protectors Joules of energy absorption
Post by: Mike Sokol on April 20, 2018, 10:51:51 am
Just doing a little armchair engineering. I can get a 16 piece lot of capacitors that are 450-volt / 5600 uF. I can stack them 8 high for 3,600 volts, which also divides the individual capacitance by a factor of 8 for 700 uF per stack. Now I run the two stacks in parallel for a big capacitor of 1,400 uF at 3,600 volts. According to my quick Joule calculator at https://www.electronics2000.co.uk/calc/capacitor-charge-calculator.php that works out to just over 9,000 joules of storage. Am I thinking about this correctly or is it the French wine talking?
Title: Re: Testing MOV surge protectors Joules of energy absorption
Post by: John Roberts {JR} on April 20, 2018, 11:44:53 am
When stacking capacitors in series you need to provide some strategy to force them to share the voltage equally. The common technique is parallel resistors forming a voltage divider. Without a resistor string higher and/or lower leakage in individual caps will create over voltage across non leaking caps. One shorted capacitor could cause overvoltage in all the other series capacitors. High voltage power supply needs to be current limited to protect against such faults.

 I would be nervous (careful) when working around this much energy potential. Probably worthwhile budgeting a robust resistor divider string power budget. The good news is this will discharge the caps when power is removed. 

JR

PS: Perhaps active devices would provide the parallel divider string using less power consumption but this ups the complexity/cost.
Title: Re: Testing MOV surge protectors Joules of energy absorption
Post by: Stephen Swaffer on April 20, 2018, 12:55:29 pm
I spent yesterday studying arc flash as it relates to electricians.  I'm not going to pretend to know how to calculate an arc flash incident rating from the information given-but if I am doing quick calculations correctly, you could be looking at arc energy equivalent to a short at 3.6 kV, protected by a 75 amp fuse, or 480 volts protected by a 600 amp fuse (based on the device opening the circuit in 2 cycles).  From experience using software to do some arc flash calculations, I am guessing this would put you into at least a 2 rating-requiring FR clothing at appropriate incident ratings, faceshield, etc. Most electrical installs have transformer impedance as well as wire run impedance to limit short circuit current. I have seen bus plug covers bent from that kind of energy-you have both a thermal and concussive hazard.  I could be being overly cautious-but better to consider this before you build it.
Title: Re: Testing MOV surge protectors Joules of energy absorption
Post by: Mike Sokol on April 20, 2018, 01:21:25 pm
When stacking capacitors in series you need to provide some strategy to force them to share the voltage equally. The common technique is parallel resistors forming a voltage divider. Without a resistor string higher and/or lower leakage in individual caps will create over voltage across non leaking caps. One shorted capacitor could cause overvoltage in all the other series capacitors. High voltage power supply needs to be current limited to protect against such faults.

 I would be nervous (careful) when working around this much energy potential. Probably worthwhile budgeting a robust resistor divider string power budget. The good news is this will discharge the caps when power is removed. 

JR

PS: Perhaps active devices would provide the parallel divider string using less power consumption but this ups the complexity/cost.

I built this exact same storage bank about 40 years ago for a 2K Joule (2,000 watt-second) surplus airport landing strobe. I stacked enough capacitors to get up to the 3,000 volts or so I was producing from a commercial microwave transformer, and used a car ignition coil to initiate the strike on the strobe lamp. The lamp itself was HUGE, with an outer Pyrex shield the size of a soda can, and the coiled lamp inside was finger size IIRC. It drew a full 20-amp from the 120-volt line for at least 2 seconds to reach full charge, and when we flashed the thing it could completely overwhelm 48KW of conventional tungsten PAR cans. Good times in the mid-70's.

Yes I know this is really dangerous to build, and really dangerous to use. But if the company has a serious enough budget I'll make it really safe with a remote control outside of the blast zone. This is serious mojo and not to be taken lightly. I can't believe I built and tested my 2KWS strobe on an open bench without killing myself. And it was really dangerous to set off as well since it was as bright as an arc welder. So don't worry, I'll be super safe and triple-check my work. This thing will have as much stored energy as a small bomb and I don't take it lightly.

But it is interesting, isin't it?
Title: Re: Testing MOV surge protectors Joules of energy absorption
Post by: Jonathan Johnson on April 20, 2018, 04:45:28 pm
Yes I know this is really dangerous to build, and really dangerous to use. But if the company has a serious enough budget I'll make it really safe with a remote control outside of the blast zone. This is serious mojo and not to be taken lightly. I can't believe I built and tested my 2KWS strobe on an open bench without killing myself. And it was really dangerous to set off as well since it was as bright as an arc welder. So don't worry, I'll be super safe and triple-check my work. This thing will have as much stored energy as a small bomb and I don't take it lightly.

But it is interesting, isin't it?

Maybe the folks at the Bonneville Power Administration's high voltage lab (located in Vancouver, Washington) could offer some advice. They've got a lot of experience discharging huge amounts of stored energy safely.

http://www.today.com/video/today/55754864

http://www.columbian.com/news/2013/dec/09/high-voltage-bpa-lab-a-rare-asset-ross-complex/

https://www.bpa.gov/
Title: Re: Testing MOV surge protectors Joules of energy absorption
Post by: Mike Sokol on April 23, 2018, 06:56:11 am
Maybe the folks at the Bonneville Power Administration's high voltage lab (located in Vancouver, Washington) could offer some advice. They've got a lot of experience discharging huge amounts of stored energy safely.

http://www.today.com/video/today/55754864

http://www.columbian.com/news/2013/dec/09/high-voltage-bpa-lab-a-rare-asset-ross-complex/

https://www.bpa.gov/

That's a great idea. I've talked to one of their engineers two years ago about induced voltage from overhead power lines, and they were very helpful. I'll give them a call about this project and see what kind of research they've done already.
Title: Re: Testing MOV surge protectors Joules of energy absorption
Post by: Jerome Malsack on April 23, 2018, 10:00:20 am
Another consideration would be flash burns.  if the arc would flash burn your eyes, welding glasses ??? 
Title: Re: Testing MOV surge protectors Joules of energy absorption
Post by: Mike Sokol on April 23, 2018, 10:21:59 am
Another consideration would be flash burns.  if the arc would flash burn your eyes, welding glasses ???

I have a 6-ft tall lead-lined gobo on wheels with a lead-glass window that came out of a 1950's doctor's office when they had their own X-ray machines. No kidding. That will be my last line of defense along with a welding face shield and ear plugs. Since the idea is to keep raising the power level until something breaks, I have to assume it will be north of the product's rated 5,000 joules of spike protection which is nothing to take lightly. I'll design this thing for up to a 10,000 joule  discharge, start low, and take it up a bit at a time.   
Title: Re: Testing MOV surge protectors Joules of energy absorption
Post by: Stephen Swaffer on April 23, 2018, 12:21:15 pm
I should have made the distinction in my earlier post-the "faceshield" I mentioned was intended to be one made for arc flash-they have UV protection as well as being designed not to melt  in the event of an arc flash.  Presumaby this is a paying job-charge enough to cover the cost for the correct PPE.  It's cheaper than an ER visit.
Title: Re: Testing MOV surge protectors Joules of energy absorption
Post by: Mike Sokol on April 23, 2018, 01:49:24 pm
I should have made the distinction in my earlier post-the "faceshield" I mentioned was intended to be one made for arc flash-they have UV protection as well as being designed not to melt  in the event of an arc flash.  Presumaby this is a paying job-charge enough to cover the cost for the correct PPE.  It's cheaper than an ER visit.

Yes, this would be a well paying job, so I'll get the correct PPE and be super safe. I've had a few serious burns in my youth and saw a few arc-flashes from a distance, so I'm very respectful of what can go wrong with this type of experiment. Kids, don't try this at home....
Title: Re: Testing MOV surge protectors Joules of energy absorption
Post by: Mike Sokol on May 27, 2018, 08:16:39 pm
I now have a second client asking about a test that could use my big bug zapper. Let's see: 5,000 volts, 10,000 joules and a few thousand peak amperes. Oh baby!
Title: Re: Testing MOV surge protectors Joules of energy absorption
Post by: Michael Ardai, N1IST on May 28, 2018, 08:16:41 pm
We use an ECAT line transient tester at work (made by Thermo Fisher Scientific).  It's more than just a big cap; there's some form of LC pulse-shaping network in there.  There's a specific test sequence that we use (if I recall, 3 pulses 30 seconds apart at +/-6kV 200A  every multiple of 30 degrees from zero crossing of the AC line).  That's for indoor stuff; when we did a device that mounts to street lighting poles, we had to send it out to a site that could do much higher power.

As for failure modes, MOVs tend to fail shorted, and since they are across the AC line, then tend to go bang...  So yes, the blast shield is needed :-)