Megohmmeters (Full Lecture)

In this lesson we'll learn to use a special purpose instrument designed to measure unusually high resistance connections called a megohmmeter. Megohmmeters are commonly used to test integrity of insulation. This lecture will feature an application exercise where a megohmeter is used to test the insulation resistance of a motor’s windings.
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For more FREE online technical training check out the following playlists available at the bigbadtech channel:
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Motor Control • Motor Control
Motors and Generators • Motors and Generators
Motor Drives/Variable Frequency Drives (VFD) • Motor Drives
Programmable Logic Controllers (PLCs) • Programmable Logic Con...

[@RineboBohead]

Wow, very helpful and scientific 🧪! Thank you!

[@javierferrer4634]

Thank you for the lecture on megger meter!

[@jeffreystroman2811]

Finnally, a video worth my attention and time

[@rodgraff1782]

One short high voltage pulse is not enough. You need to maintain high voltage for a time specified by the motor manufacturer. Hand crank megohmmeters are not old technology. They can still be purchased new. The instructions say the voltage is to be applied for a period of time, not just an instantaneous pulse. I would use a hand crank megohmmeter over one of these battery powered ones any day.

[@burnedupsparkytipsandrevie9597]

Neta and ieee recommend a 1min test, have to have time to allow the Voltage and current to stabilize

[@davidpalmer963]

Awesome education ..as always

[@davidhaines4173]

Thanks Jim.

[@JaimeGarciaX]

Awesome. Thank you so much! Succinct and thorough!

[@Automationacademytv]

nice one

[@ghostdog662]

Thank you!

[@themotofixery]

Woah to those indeed!

[@Alejandro14300]

Thanks Jim. 4:50 Based.

[@michaelcostello6991]

Did you ignore the 3rd path in parrallel cause it has very little effect on your megger reading and so can be ignored

[@bibblical]

4:50 I'm rolling 😆😆😆

[@bigbadtech]

Amirite?

[@bibblical]

@@bigbadtech you're not wrong.

[@jeffreystroman2811]

Is that the juggalo refrence he threw in there? Yea, I caught that one

[@cama5259]

Always saving my a$$

[@someguy9431]

Holy crap, Juggalo spotting in the most unlikely of places! Shaggy2Dope and ViolentJ comin at ya!

[@edbass2769]

Jim, I'm shopping for a MEGGER Model # MIT410. I see 410/2 and 410-TC/3. Not much cost difference. Perhaps you could share your contact at MEGGER.

[@jasonjohnsonHVAC]

I have a Fluke 1587 that i use. DMM and Megohmeter in one

[@scruffy4647]

On a 9 lead motor, i separate all the connections and check each winding to ground (4,5,6 - 1,7 - 2,8 - 3,9). Then I check winding to winding. Infinity or dead short is easy, what is your threshold reading for "no go".

[@bigbadtech]

If I answer this with any other than "check the motor manufacturer specifications" I'm probably going to get in trouble! This being said customarily 100megaohms of resistance between windings is considered the low threshold for motors below 1000V. For everything you ever wanted to know about insulation testing check out Megger's "A Stitch In Time" at: www.testequipmentdepot.com/media/pdfs/electrical-insulation-testing_guide.pdf

[@AB-yu2tj]

How can turn to turn short on the same winding be detected? and consider this question when you don't have three phases to compare to the other two and no other motor to compare the resistance too.

[@bigbadtech]

If you've got access to one phase, when would you NOT have access to the other 2 phases for comparison purposes? If you want to be handicapped by this challenge one way of determining an issue is an ammeter. Ideally a motor is a balanced load and each line current will be equal in magnitude (although phase shifted by 120). Given equal line voltages any difference in current is a sure sign of an impedance difference.

[@mikeadler434]

👍👍

[@michaelcostello6991]

If both leads of A1 coil were not labelled and hanging loose how would you determine which end was 1 and which end was 4. If you did not get this right would they be out of phase and cause a short etc I have see a video elsewhere which discussed this type of thing but i did not fully understand what they were saying.

[@bigbadtech]

Check out the the electromagnetic interaction lecture at: kzbin.info/www/bejne/nKeYZWxqobeEd9U Long story short if you swap the direction of current the magnetic field changes direction. If only one winding was backwards the motor might still run but exhibit some wonky behavior. I might actually do this with my students for an upcoming lab! I pity my lab motors, they're often abused in the most creative ways.

[@bigbadtech]

By the way ... the detection method you're most likely referring to involves analog (ie: needle) volt meters. Analog meters are hopelessly old school ... however ... needle deflection (left or right) is more noticeable than some digits flashing on a screen. As mentioned in the electromagnetic interaction lecture, induced polarity is direction dependent. By momentarily applying voltage to a nearby winding with a specific polarity one can determine if the resultant induced polarity is in the same (or opposite) direction. I watched a demonstration of this at AWEA 2011 as well as a motor winding demo. Part science ... part art!

[@nickledimez4012]

Jim Pytel thank you for that explanation!!

[@larryfine6394]

Hey Jim, how can I get a hold of you?

[@bigbadtech]

I'll email you in a bit.

[@JohnnyJr396]

Thanks. Do you select a voltage that’s twice the operating voltage for testing?

[@bigbadtech]

Great question. Yes, the test voltage is dependent upon the intended operational voltage of the motor in question. There's a lot of generally accepted rules to determine the appropriate test voltage however I find it better to refer to the Megger document "A Stitch in Time". Download here: us.megger.com/promotion/vf/social-media/stitch-in-time-instant-download

[@JohnnyJr396]

@@bigbadtech thanks! Enjoyed the video and this helps make things more clear.

[@michaelcostello6991]

Hi, When you put it in the low voltage Y configuration and megger between L1 and L2 you do not just have B1 and A1 in parrallel with B2 and A2 ?? Isnt there a 3rd path ?? I am not an electrician but i drew out the circuit on paper . Please advise

[@bigbadtech]

Check out the ohmmeters lecture at: kzbin.info/www/bejne/jnPNfamsmrOCi5o Resistance is a 2 point measurement and the megohmmeter sensing current will only travel in one path.

At which voltage should be set to test motor windings ?

[@bigbadtech]

Depends on the motor manufacturer's specifications. Note testing above 1kV necessitates special training and safety precautions. Here's a link to some guidance produced by Megger: www.instrumart.com/assets/Megger-Insulation-Testing-Above-1kV-Brochure.pdf

[@TEHSTONEDPUMPKIN]

I mean ya ain't wrong about Juggalo's, but there good people.... A bit out there and unusual.... BUT good people! WHOOP WHOOP! MMFCL!!!!

[@muhammadtalha5432]

Plz 1 video generate PI test

[@bigbadtech]

That's actually a great topic for a lecture. Stay in touch.

[@lonewolf1647]

4:52 lol what??

[@larryfine6394]

Your emails keep bouncing back?

[@bigbadtech]

I just sent you one to your @megger.com account. CGCC changed their extension to "cgcc.edu" check out the CGCC webpage faculty links.

[@doperider85]

Probably wont be seeing you at the gathering

[@bigbadtech]

I see what you did there.