megging readings

[Mule]

In order to do a PI test you'd need a megger with a 1000G or 1Tera ohm max range. Many handhelds won't even come close to that.

His readings are not near that high, and unless his PI would be way over a 2.0 or 3.o would he need a that kind of equipment....

I have ran PI's with a crank, although not minute accurate, and your arm gets mighty tired, it will give you a definite indication of the capacitance values. Its really pretty simple the resistance values are either getting better or going south.....

I cant remember, what's the 3 mintute test called? It's a decent test for go/nogo

 

[wptski]

His readings are not near that high, and unless his PI would be way over a 2.0 or 3.o would he need a that kind of equipment....

I have ran PI's with a crank, although not minute accurate, and your arm gets mighty tired, it will give you a definite indication of the capacitance values. Its really pretty simple the resistance values are either getting better or going south.....

I cant remember, what's the 3 mintute test called? It's a decent test for go/nogo

Megger with a built in PI/DAR test with a low range will error out early if the max range is hit. It calculates value change over time, so if the max is met, it errors out. This is a problem using the Fluke 1507 for one. You need to measure insulation that's not too good to begin with or the PI/DAR test will error out for max range exceeded.

 

[zog]

Megger with a built in PI/DAR test with a low range will error out early if the max range is hit. It calculates value change over time, so if the max is met, it errors out. This is a problem using the Fluke 1507 for one. You need to measure insulation that's not too good to begin with or the PI/DAR test will error out for max range exceeded.

Right, at certian IR (high) values the PI result is worthless.

 

[wptski]

Right, at certian IR (high) values the PI result is worthless.

Not sure if it's worthless. The PI/DAR tests are ratios that can be limited to the point of not even functioing because of the maximum limits of your tester. I'm starting to wonder why the Fluke 1507 even has the built in PI/DAR test because 99% of the time it errors for maximum limit even at 1000V.

 

[zog]

Not sure if it's worthless. The PI/DAR tests are ratios that can be limited to the point of not even functioing because of the maximum limits of your tester. I'm starting to wonder why the Fluke 1507 even has the built in PI/DAR test because 99% of the time it errors for maximum limit even at 1000V.

IEEE Std 43-2000 states If the 1 minute insulation resistance is above 5000 Meg-Ohms, the calculated PI may not be meaningful. In such cases, the PI may be disregarded as a measure of winding condition."

 

[wptski]

IEEE Std 43-2000 states If the 1 minute insulation resistance is above 5000 Meg-Ohms, the calculated PI may not be meaningful. In such cases, the PI may be disregarded as a measure of winding condition."

Some of the Fluke 1507 max resistances are:

250V-220M
500V-550M
1000V-11G

If you were testing a 120V or 240V motor, you can't even come close to that standard's maximum. If a one minute test reads 220M at 250V on Fluke 1507, the PI test will error. If you were tracking a new, your first PI will error for sure.

 

[Mule]

IEEE Std 43-2000 states If the 1 minute insulation resistance is above 5000 Meg-Ohms, the calculated PI may not be meaningful. In such cases, the PI may be disregarded as a measure of winding condition."

Now, we're getting some where !! Good info

 

[zog]

Some of the Fluke 1507 max resistances are:

250V-220M
500V-550M
1000V-11G

If you were testing a 120V or 240V motor, you can't even come close to that standard's maximum. If a one minute test reads 220M at 250V on Fluke 1507, the PI test will error. If you were tracking a new, your first PI will error for sure.

That is why I dont use the 1507, too limited. Dont get me wrong, good meter for megging 600V cables and those kinds of things but not much of a meter for testing guys.

 

[wptski]

That is why I dont use the 1507, too limited. Dont get me wrong, good meter for megging 600V cables and those kinds of things but not much of a meter for testing guys.

It's not just Fluke as many handhelds are limited too! Although the bigger Fluke 1550B goes up to 5000V, its lower end still doesn't have a much higher range. What brand/model of megger do you use?

 

[mickeyrench]

Please excuse my ignorance on megging. My question is my meter range ends at 1999.9 , is that next number going to put the scale at gigaohms ? 2 gigs?
I believe the meter scale is 19.99, 199.9, 1999.9. I have not a good understanding with this ,ohms , megaohms or gigaohms.
Thanks for your help.

 

[ohmhead]

Well some say i dont know what iam talking about but you really dont need that high a reading gig ga megging on high for a motor , its not going up that high anyway and a hand held is fine we never had any problems in 50 years of electric work . And i think most service work is all needless work in my way of thinking you can test but it really doesnt help to me its a waste of time and money ? comments weve been in the field work for many years and i think from what i see here is just book talk your motors are fine and thats from a electrician not a engineer . best to ill be here after work today cant wait for comments ?

 

[mickeyrench]

ohm , i am trying to find out if giga ohmis the next reading after 1999.9 on the scale. My readings went up to 1999.9 on the megger and i am trying to find out what reading that would be. I megged for 60 seconds and that was the value i got on the meter. thanks

 

[ohmhead]

Well when we megg its a minute or more if we have a issue but thats your reading after , megging . Lets say gear SQ D req say 25 meg ohms on bus GE says 100 meg ohms motors are different but not really a wire is a wire wound or not and magnet wire is not much different ,dont take what i say as the bible but your ok we test motors new on ever job havent had one blow up yet . take care got to go to work .

 

[zog]

It's not just Fluke as many handhelds are limited too! Although the bigger Fluke 1550B goes up to 5000V, its lower end still doesn't have a much higher range. What brand/model of megger do you use?

I have about 5 meggers, all for different uses. From a small AVO 1000V handheld to a 10kV AEMC model with a printer, USB port for downloading results and scales up to T-Ohms (50 I think)

 

[zog]

Well some say i dont know what iam talking about but you really dont need that high a reading gig ga megging on high for a motor , its not going up that high anyway ?

For LV motors, yes. For larger MV motors you need higher scales. Remmember, it is not so much the value you get but the trend analysis over many years of testing so you can predict the expected life of the insulation. If you record >something (High scale of your megger) or worse yet "Infinity" you dont know what the real value is and wont know over time how fast the insulation is deteriating. Thats why having a megger that can record an actual value, even if it is way about your minumum spec is important.

 

[brian john]

kilo- k 1,000
mega- M 1,000,000
giga- G 1,000,000,000
tera- T 1,000,000,000,000

 

[wptski]

IEEE Std 43-2000 states If the 1 minute insulation resistance is above 5000 Meg-Ohms, the calculated PI may not be meaningful. In such cases, the PI may be disregarded as a measure of winding condition."

Using that standard wouldn't the chances of a new motor measuring >5G be pretty good? Yet it may not be meaningful! Isn't that the point of the PI test to trend over time from the day it's new?

 

[zog]

Using that standard wouldn't the chances of a new motor measuring >5G be pretty good? Yet it may not be meaningful! Isn't that the point of the PI test to trend over time from the day it's new?

Yes, and the IR values can still be used for trending. There is a lot more to this standard, anyone doing motor testing should be familiar with it.

 

[ohmhead]

Electric motors megg

Electric motors megg

well tests generators & motors should pass the following tests.per IEEESTD112-1995 115 or ANSI/NEMA MG1-1993 a temperature rise under full load , dielectric strength of insulation , overload capacity as specified , cold resistance of all circuits , electrical balance , mechanical balance vibiration . IEEE STD 45 1998 covers this in detail .kind of found this today in old book 460 volt moto = 500 /1000meg test voltage , 2400 volt moto = 1000/2500 meg test voltage , 4160 moto = 2500 test voltage 6900v = 5000 volts at test .PI = IR at 10 minutes divided by IR at one minute . just a little input to test by .Best to yas

 

[mickeyrench]

what type of megger would be needed to test 480 v 100-200 hp motors ?

I have a crank that goes up to 1000v and over 2000m
also a fluke 1587 and amprobe dm-3

Ihave been using 1000v for my 480 v motors.
thanks.