High Voltage Megger Used To Check Capacitors
HTML-код
- Опубликовано: 29 ноя 2022
- I have recently needed to measure leakage current in high voltages devices like transformers and purchased a modern digital Megger. This video is about the high voltages that are at the tips of the megger probe and how you should be Very Careful if you use it to measure capacitors.
BTW - these meggers can be used to check very high ohmage resistors (Gig ohm level resistors) just like any ohm meter. Just remember you have some HV at the probe tips that can bite you...Be Safe... 
Развлечения
David, this is the first time I've been glad you're in Texas and I'm in Australia ;-)
EJP
The hf whistle during charging of the capacitors reminded me of the old camera flashguns. 👍
I didn't hear it but I know that sound of the older type camera flash charging. I guess my hearing is deteriorating more than I thought.
Just wanted to check in with you. I hope you are doing o.k.?
Take care and thank you for all your videos! Interesting, informative and fun!
Thanks for the video!
Feel like not many people into these videos even though they play guitar or do any kind of music hard for me to understand little by little , not only I'm learning from your video but by your viewers & these comments to see what they have to say unbelievable came from uncle Doug , rock on
Actually, Uncle Doug started posting on my channel before he started his own and did exceptionally well with many more subscribers than me.
been doing this for years. works great
wow! That was SHOCKING! DOOH!
I use an old hand-crank motor insulation tester to test caps, it's very inaccurate but if it doesn't read open circuit I know that it is leaky. Very safe, only outputs around 100V max, but with like 0 current, the meter goes to 1GOhm
you could just put 400V or whatever the rating is across the capacitor, and put an ammeter between to measure the leakage, just put a resistor between the cap and some diodes across the ammeter so if the cap shorts it doesnt blow up your meter
Absolutely - you just verified what I asked some of my amateur radio friends about using the series resistor. I have the 1G ohm resistor that will limit, even 5KV, to 5 uA and I actually measure it as 4uA on the old Triplette meter. Love the old meters. I have some standalone sensitive uA meters to use and will do some testing tonight. And I will protect my sensitive uA meter with diodes. Thank You for reminding me... I looked at some of the beautiful General Radio meggers and wanted one but, it sure seems to me, this inexpensive foreign made meter does the job and they ask a fortune for the old meggers on Ebay. This meter was $61. I have a new toy to play with and maybe it can't kill me like my transmitter 5KV supplies... 🙂
Very informative as always. I was wondering if floating the transformer was going to be a permanent repair.
It was intended to be permanent but it arced again, probably this time to the primary so I gave up on it. I did not previously realize that I had an adequate replacement transformer but had to completely redo the voltage-doubler rectifier to a bridge. The "new" transformer fit nicely and gives me 3700 VDC instead of 4KV as I originally had but it is just something that I have to live with.
Hey hope you’re doing well, haven’t seen a new post in a while.
We use fancy testers for the field work I do, the most portable of which puts out up to 5kV DC. I have used it to test capacitor banks (at a lower voltage) for harmonic filters and UPS systems. Usually they’re Megger or AEMC.
I also learned the hard way that medium voltage cables (2.4 to 69kV in the power distribution world) not only retain charge, but they will have a rebound charge after discharging much like an actual capacitor. Grounding and testing before touch will keep you alive.
That is interesting about the power lines retaining a charge - it can make sense to me although I have never worked around it and I understand the rebound in capacitors. I can only imagine the special issues with long transmission lines and dealing with them safely. I have seen movies where guys would work on the very first 2KV lines (probably DC from Edison stations) and they would work on them bare handed with hardly a clue of what they were dealing with and many were killed. Thanks for sharing your experience and posting.
@@ElPasoTubeAmps Fascinating stuff - I am appalled every time I look into early electrical work and line practices. The charge issue can be a concern with isolated and ungrounded utility lines, but most of what I’ve run into with charge issues is with insulated cables. Most medium voltage (1kV to 69kV) to high voltage (70kV+) power cables use a slightly semiconducting layer to dissipate electrical charge gradients between the live conducting core to the insulating and grounding layers. If you think about having one inch of rubber and imagine, say, 120kV of potential difference across it - you’ll get pin arcing and treeing since the charge gradient is simply too many volts over too small a distance at too high an insulation value. Having that gradual change in potential between live and ground makes the cable last much longer.
Problems arise from losses and cable capacitance introduced, especially with longer cables and higher voltages. This also lends to extra hazards with testing - although “semiconducting” in fact and theory, the discharge time is enough that the cable becomes a huge capacitor with any kind of DC testing. Sometimes DC testing (or Line freq testing) isn’t even possible due to massive inrush current to charge the cable, so we use low frequency (0.1Hz, one cycle per ten seconds) VLF AC testing.
If you look up okolene and enjoy that rabbit hole, that’ll tell you far more than I could about cable construction.
@@Dukers2300 What you say is so interesting to me and I can see how the capacitance in lines could hold a charge. Even the little megger I was using was constantly pumping a charge, at 1 mA, into the large capacitors that could turn our deadly from an enormous charge. Your experience and understanding of HV cables is beyond anything I have any knowledge of and goes to show there is always much more to a situation than is known by those that are not in the field - whatever it may be.
I have always just assumed that the insulation is for all practical purposes "infinite" in the windings of transformers although I know there is going to be eventually a break-down voltage where things arc. I bought the megger as I was dealing with a power transformer of 1800 volts into a doubler which requires capacitors in the doubler circuit and ended up with 4KV - exactly what I wanted for the 833A. However... remember reading how the CT of transformers meant for FWCT connections may have a CT that is too close to ground to leave floating? Well... that is what I did and it worked for a few years until it arced to the case of the transformer - I then "floated" the transformer above chassis ground and it worked a little longer but probably went to the primary. Floating chokes actually works by keeping the case of the choke well insulated as there is no primary to internally arc to.
I appreciate you posting your experience and knowledge -
I go shooting in the New Mexico desert where the lines from an El Paso Electric plant provides power to Las Cruces, NM. The poles and lines are huge right from the power plant and sizzle and crackle all the time being under them. Once I was under them with a shotgun and moving it around and got a small bite. I have no idea what the voltage and current and wire size is. I would love to know. Another thing hard to believe is there are some people that actually shoot the wooden poles and some poles have been strengthened by metal straps in an attempt to repair some of this damage. I can not conceive of someone shooting away at these poles. Heaven help if they fell - it would probably shut off Las Cruces... I do know the plant is gas powered as the lines are marked in the BLM area we go shooting at. It is all legal to shoot there. I have met the BLM rangers out there with my 45 strapped to my side and all is fine. Mostly what they patrol is illegal dumping. It is disgusting how people will take sofa's, TVs, whatever and throw them in the desert and auroras where the water runs after a nice rain. The desert is beautiful after a nice rain. I have brought truck loads of trash home to put in proper disposal but it is like trying to clean up the oceans with a hand fish net.
Thanks again - stay safe 🙂
@@ElPasoTubeAmps That’s awesome! I also go shooting under power lines - the run between Grand Coulee and Seattle offers a lot of nice spots. Crazy hearing that you got bit out there - there ARE measurable and hazardous amounts of induced and step potential you can get near HV lines. They SHOULD be safe to be around - the towers are grounded, clearance from hanging lines to ground have a minimum distance etc - but as you found out, dealing with extreme currents and voltages can cause some weird side effects. I’m always wary of huge distribution yards, just like the event you described even holding metal objects around energized parts can induce some voltage. I think we were out in eastern Montana at the Fort Peck dam and I felt a tingle on more than one occasion.
I’ll have to send you some pictures of a relatively low voltage cable fault, 2400 volts to an underground splice. There was a very well defined ashen circle about four feet around where the earth was energized and on fire.
I honestly believe and I’ll even tell people that once you exceed a certain threshold of voltage and/or current, electricity will ditch perceived physical limitations and do “freaky scary magic stuff.” There’s something insane and awe-inspiring about how we can create and transfer power over great distances, and manipulate EM fields for radio - at a minimum with just a few components and glass tubes. I don’t think the intrigue will ever go away, it’s witchcraft with math and science behind it.
The southwest is lovely. Shame hearing that folks leave trash out there. We have the same problem here with some of the old logging roads and forests. People go up and dump their trash out and don’t clean up after a “range day”. I’m glad you clean up their mess, it’s frustrating as hell and they always come back with more.
😻🐾🐾🐾
Could you give me a link to where you bought that STmeter megger tester?
I have one of the old hand cranked ones... Just out of interest, what is a safe isolation resistance value in a transformer between primary and secondary, and between the frame and primary, and the frame and secondary? If I pick up a transformer at a hamfest. I always check continuity in the primary and secondary and check there's no short in either. But I guess isolation is a very good measure as well.
73 de VK4QP
Here is a link to what I bought off Ebay. I think it is prudent to be careful with these meggers. Not in the sense of being deadly from electrocution as the short-circuit current is only 1 mA but it could break down insulation in capacitors and between windings of transformers from the simple pressure of the voltage that can be raised to 5000 volts. What I mean by this is it would not be wise to test a small audio transformer at 5000 volts or a 450 volt capacitor at 5000 volts from a Megger as it could puncture the insulation and damage/destroy a good component.
As for HV transformer testing, I think the same thing applies. I have some large 3500 volt transformers that I have respectfully tested with this megger and find the leakage resistance between windings to be in the Gig ohm range and it makes sense but I would not use the megger to test insulation between windings in a transformer way beyond the actual rating of the transformer. That is the way I look at it. I think these megger instruments should be used with some caution so as not to damage components that are otherwise good and within their proper range of operation. Hope this makes sense.
I do a similar thing by checking for obvious shorts with an ohm meter between primary and secondary on transformers and go from there.
I think I made this video as a warning that even a small current device like this that is relatively safe as it is, can charge a capacitor, over time, to a deadly charge.
www.ebay.com/itm/363613989089?epid=26054971064&hash=item54a91528e1:g:mxsAAOSwZd9hZp~X&amdata=enc%3AAQAIAAABILQxhslsNXBoCpzIAgNPw7Z%2B9BykgfcxJRBa%2FDcctkLVUivxqfDPID64tLxMh0Cx2W%2FuORUesskS%2B%2BJ3mPah42aZRlpmd0ciZt%2FThRpNkrfkSBzyLAgD4tT76fvZc7Xv2Ophi%2FLsH%2FAoBcf1tO9C7TyiOvKcAlAUv6dN4QZQb3uTfhPPzgkxduwNynDJt6irwTFkhucs4t2S%2B3hwDLArhdPH80xR4dhABu66VLqHCdHJZz3FTri5gnNEdkIBKzfH6ZzrhuJL15wudJBfg3QcebebWLHxrfy8f0JYTGGIAdTOZX%2BEwu%2FjSsioFMeGLQIHKqUAL50Z8etNvW%2BIImSCv8DGHiFvnx8bRKkmHcF4OU9HZUyY0tgO2RvMRggM1RMArA%3D%3D%7Ctkp%3ABFBM-qXIvoJi
Greetings I enjoy watching your videos I have learned quite a lot from them. I was wondering about the literature you shared from Lilienthal Engineering 100 Amplifiers parts 1 through 4. Is this still available? Any help would be appreciated thank you! Robert Ke7jys
I can Google them and get a list but I don't find them like I used to in a simple downloadable PDF form. A few years ago I downloaded everyone of them and printed them. I figured that someone was going to mess it up and make them unavailable and I think that has happened. I have four separate books printed on a laser printer and I am glad I did. I think you have to pay to see them online nowadays.
@@ElPasoTubeAmps I work at WSU I will see if the Libraries here can get access to them. I will let you know what they find.
@@ElPasoTubeAmps The WSU Library is requesting more information for their search. Any ideas what else to give them?
@@robertbrooks5176 Besides the author's name and the titles of the books, I can't think of anything else. I don't assume they have an ISBN. I will look and see if I can find what I downloaded in PDF. Not sure if it is legal for me to sent them nowadays and most of all, I have changed all my computers in the last year so, who knows if I still have them. If I find them in PDF I will let you know.
How much resistance did the meter show on that oil filled 6mf capacitor?
As I remember the short current current was 1 mA on all the scales so on the 5000 volt scale that would be 5 megohm.
I use a Heathkit it-11 or it-28 cap checker. you get up to 600vdc to test for leakage. Also a sencore lc75 probably the most.
Have you checked your grounding rod? I was always told to have my left hand in my pocket as it is closer to the heart, but at 5K it most likely wouldn't matter which matter which hand was in your pocket. You would not have a 100k ohm at least 5 watts linear rheostat in your bench stock. I have to repair my cap tester - an old EICO.
The heart is almost exactly in the center of the chest (SLIGHTLY to the left, for a right-handed person, to the right, for a lefty). The reason for keeping one hand in your pocket, is if you get zapped, the current will flow down that side of your body, to ground, and not from one hand to the other, through your chest (and heart).
@@Pootycat8359 It was what I was told about 60 years ago and I have followed it every since whether 100 percent accurate or not. It has seemingly served me well. I still need that rheostat. I cannot believe what they want for one now. They were never really common, but wow, the prices now days are just insane.
@@JosephLorentzen It is the 5 watt rating that is going to be difficult to find - possibly also, it may need to have better insulation than a standard pot ?
The insulation on those yellow leads is surely not rated for 5 kV?
Yes, that was what I thought.
How are you I hope everything is ok
Hi Jim,
I am doing OK. Needless to say, it has been hard living alone but I have a few very good friends that I stay in contact with here locally. I haven't been making any significant videos lately but I haven't given up yet. Thanks for asking and caring.
Can you tell us the make and model? For the record, not for me, you'll never catch me in four-figure voltages.
Here is the link. I see them all over RUclips and they come in very color. Is it worse to get shocked by a purple one or an orange one?
www.ebay.com/itm/363613989089
How many are thinking that this is how Photon at PHOTONICINDUCTION got started? Probably at 10 y/o 😆.
Actually, currents greater than 15-20 ma can kill. I think 1 ma is barely perceptible.
I assume the megger is "safe" as it does not come with any death-warnings... It really got my attention when I saw it charging that large capacitor and I knew I had to mention that all that HV charge and potential energy it is storing in the capacitor could end up being a deadly situation. This is my first experience with a megger. Without forethought and care, it could damage components being measured.
@@ElPasoTubeAmps I had an interesting experience regarding a charged HV capacitor, in the 1980s. I was the transmitter engineer for a TV station. Because the transmitter site was on a mountain peak, I would live up there, during my shift, which included sleeping. Around 5 PM, I was aroused from my slumber, by a loud "POW!" coming from the xmmtr room. It was about as loud as a .38 going off. The xmttr kicked off the air. I then heard the "chunk-chunk," as the overload reset, and it came back on. I made a mental note to check it out, after sign-off, which was when my real work was done. Lying at the base of a P.S. filter cap was a little mousey. Mousey's front and rear legs were charred. The char mark went the length of his underside, and his guts were hanging out. That was a 12 uF cap, charged to 8 KV. "WOW!" I thought. "That would make an EXCELLENT mouse trap!"
I was nervous. Don't do that again, super very dangerous.
Chuck Norris Capacitors.... they will whup your butt if you cross them.
Meh - childs play. Try working on a 36" Sony television with a glass CRT and anode voltage of ~50Kv. Burns a hole through skin right down to the bone - gives ya instant arthritis for the next 24 hours
I think a 36" TV with 50KV on the anode is called an full-body X-Ray machine... 🙂 I would want to keep it at a distance. Thanks for your comments.