megging readings

[zog]

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.

1000VDC is fine for 480V motors. you can use any type but you might get sick of craking for 10 minutes for every test to get your PI's. I would recommend either the AEMC 1050 or 1060, depending on how many motors you test. The 1060 has some good data storage and you can download your results to your computer for reporting. Both read up to 4T Ohms, have built in safety features so you cant test an energized circuit, and have the best cases you will find anywhere. I use my 1060 more than any one of my meggers, always in the trunk of my car. http://www.aemc.com/products/pdf/2130.03.pdf

 

[ohmhead]

Well not to be a expert but a large motor say 200 hp or 500 hp what we do is a step test at 500 volt increments holding this you can see current on a micro amp meter up or down on tester . you can use a regular hand held just watch the voltage drop or charge not the same but its close . on a smaller motor 2hp or 30 hp we just bump test not a issue really . large motors are slow start then full run we test then same way it works at a lower voltage longer and watch current we never test directly after a run or hot motor , we test cool down and ground all leads before test for 20 minutes it effects the insulation if you dont . its called polarization or PI TEST kind of . step voltage is good for your insulation and tells you alot over time when she going to blow , In the navy we tested with the kelvin tester its the best way .best to ya

 

[zog]

Well not to be a expert

Dont worry....

but a large motor say 200 hp or 500 hp what we do is a step test at 500 volt increments holding this you can see current on a micro amp meter up or down on tester .

Sounds like a hipot

you can use a regular hand held just watch the voltage drop or charge not the same but its close . on a smaller motor 2hp or 30 hp we just bump test not a issue really . large motors are slow start then full run we test then same way it works at a lower voltage longer and watch current we never test directly after a run or hot motor , we test cool down

Huh??

and ground all leads before test for 20 minutes it effects the insulation if you dont .

i recommend you remove your ground leads before your test, make the reading a little better

its called polarization or PI TEST kind of . step voltage is good for your insulation and tells you alot over time when she going to blow ,

PI has been discussed at length already in this thread

In the navy we tested with the kelvin tester its the best way .best to ya

Huh? you tested insulation resistance with a "kelvin tester"?

 

[wptski]

Huh? you tested insulation resistance with a "kelvin tester"?

I've never heard of a Kelvin Tester! Kelvin leads, yes, I have a milliohm meter that uses them.

 

[wptski]

1000VDC is fine for 480V motors. you can use any type but you might get sick of craking for 10 minutes for every test to get your PI's. I would recommend either the AEMC 1050 or 1060, depending on how many motors you test. The 1060 has some good data storage and you can download your results to your computer for reporting. Both read up to 4T Ohms, have built in safety features so you cant test an energized circuit, and have the best cases you will find anywhere. I use my 1060 more than any one of my meggers, always in the trunk of my car. http://www.aemc.com/products/pdf/2130.03.pdf

I got a AEMC 1060 last week. Very nice, good maximum range and features. The DataView software is a bit weird.

I can run a PI/DAR test even at 250V, where that couldn't be done with the Fluke 1507 at 1000V because of its limited range.

 

[RHJohnson]

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.

You mentioned 3 small 480vac motors. That crank megger you mention above should be good for the job you need to do. If it has a 500 volt scale use that one and not the 1000 volt scale.

This discussion of what you need do to megger those inexpensive and not technically involved squirrel cage motors has become much more involved than what you need. You do not need to make any 10 minute tests, and you do not need to spend a fortune in time or money, not for THOSE motors. The engineering group and testing company guy's on this forum are willing to spend much more time and money than those of us with good sense - There comes a time to keep it simple.

Check my 1st post on what you need do ( # 18 ) - to do more is simply not necessary. And if you do try to do more management may very well decide you are over reacting to a simple job and wasting time. And time is money.

 

[ohmhead]

Well we used a kelvin tester to check from mcc center to motor or directly at motor for winding resistance not insulation resistance , it checked taps connections and more it dryed up motor windings we use a dc power soucre to dry a wet or damp motor before a insulation test in the navy and it was done everytime .It is important to understand that grounding for 20 minutes the leads on your motor before any testing this is for polarization of the insulation the molecules must align inside your insulation ill find you a article Zog on that if needed. comments ? take care see ya after work

 

[zog]

You mentioned 3 small 480vac motors. That crank megger you mention above should be good for the job you need to do. If it has a 500 volt scale use that one and not the 1000 volt scale.

Every IEEE and ANSI spec requires a minimum of 1000VDC for 600V rated motors. Please state your reference that says to use 500V, I would like to see it.

 

[zog]

.It is important to understand that grounding for 20 minutes the leads on your motor before any testing this is for polarization of the insulation the molecules must align inside your insulation ill find you a article Zog on that if needed. comments ? take care see ya after work

No need, i have actually written an article on Domain Theory that you may come across.

 

[wptski]

Well we used a kelvin tester to check from mcc center to motor or directly at motor for winding resistance not insulation resistance , it checked taps connections and more it dryed up motor windings we use a dc power soucre to dry a wet or damp motor before a insulation test in the navy and it was done everytime .It is important to understand that grounding for 20 minutes the leads on your motor before any testing this is for polarization of the insulation the molecules must align inside your insulation ill find you a article Zog on that if needed. comments ? take care see ya after work

What is a Kelvin Tester? Did a search and all I came up with is a Kelvin test jig for checking contact resistance and Kelvin test leads which I knew about.

 

[zog]

What is a Kelvin Tester? Did a search and all I came up with is a Kelvin test jig for checking contact resistance and Kelvin test leads which I knew about.

I believe he is talking about a Kelvin Bridge, which we did use in the navy, but to measure contact resistance. Most microhmeters (Ductors, DLRO's, etc) use this principle.

 

[wptski]

You mentioned 3 small 480vac motors. That crank megger you mention above should be good for the job you need to do. If it has a 500 volt scale use that one and not the 1000 volt scale.

This discussion of what you need do to megger those inexpensive and not technically involved squirrel cage motors has become much more involved than what you need. You do not need to make any 10 minute tests, and you do not need to spend a fortune in time or money, not for THOSE motors. The engineering group and testing company guy's on this forum are willing to spend much more time and money than those of us with good sense - There comes a time to keep it simple.

Check my 1st post on what you need do ( # 18 ) - to do more is simply not necessary. And if you do try to do more management may very well decide you are over reacting to a simple job and wasting time. And time is money.

Could a Fluke insulation tester be used or their more expensive megohmmeter? I ask because in another thread you stated that engineering will not accept the results if a Fluke was used. I asked why but you never replied to the post! Can you respond now about the Fluke's now? Cheap motors need only require cheap testers?

I've seen some pretty expensive assembly machines driven by ordinary cheap motors. When they die the whole machine is dead!

 

[ohmhead]

Electricians

Electricians

No need, i have actually written an article on Domain Theory that you may come across.

Well we would like to read that article Zog can you post a reference to it ? That unknown kelvin tester was uesd to dry up windings also transformer windings it shot dc at low or high current thur windings yes you could use a micro ohmmeter or DLR but its not the same the kelvin tester was a dc power source itself which could be current adjustable voltage adjustable to test resistance of windings lower than one ohm and could dry up the test winding object which was important in a wet area . Resistance is a major issue with vibration of motor dont you think ? the polarization was for the other guys who may not know about it zog so i brought it up i was posting for the benifit of others who may not know what you know . I always thought the forum was to learn from others but iam new here speaking as a electrician for many years in the trade we all have special things we do i mostly run large projects but we test also . Sorry for my input we will not post anymore i guess most will be happy but to most of the moderators who were rude and attack every post i made it was fun . take care best to ya

 

[zog]

Well we would like to read that article Zog can you post a reference to it ?

I wrote it when I worked for another company so I dont have it anymore, I will see if i can find it online somewhere.

That unknown kelvin tester was uesd to dry up windings also transformer windings it shot dc at low or high current thur windings yes you could use a micro ohmmeter or DLR but its not the same the kelvin tester was a dc power source itself which could be current adjustable voltage adjustable to test resistance of windings lower than one ohm and could dry up the test winding object which was important in a wet area .

I think you are confused about what a Kelvin Bridge is, a DLRO or Microhmter is the exact same thing. http://en.wikipedia.org/wiki/Kelvin_Double_bridge

the polarization was for the other guys who may not know about it zog so i brought it up i was posting for the benifit of others who may not know what you know . I always thought the forum was to learn from others but iam new here speaking as a electrician for many years in the trade we all have special things we do i mostly run large projects but we test also . Sorry for my input we will not post anymore i guess most will be happy but to most of the moderators who were rude and attack every post i made it was fun . take care best to ya

Please dont get discouraged, it is easy to do so here sometimes, your inputs and experience is greatly appreciated here.

 

[ohmhead]

Kelvin tester dc resistance

Kelvin tester dc resistance

Well were not confused about how a Kelvin Bridge works. We stated that in the navy we used a dc power source to heat the windings up in a motor for damp or wet issues . This kelvin tester used dc power to not only heat up the motor windings to dry them up but was used to test contact resistance from the starter or drive controller to the motor it would eliminate conductors or terminations from point of connections by measuring less than one ohm . You can not use a micro ohm meter to do this or a dlr because the batt and power source in these electronic testers dont have what it takes to drive that dc power to go that long distance from point A to point B . Yes its a kelvin connection voltage sent = two leads and current measured = two leads as a 4 wire kelvin test lead connection is normally design to work so we called it a dc kelvin test set . after a cool down period the test was made You test the connections also windings can short and a insulation test cant tell but dc test can find a resistance unbalance. There are different test methods just thought i would add this . But we maybe just making this up so comments ?

 

[RHJohnson]

Could a Fluke insulation tester be used or their more expensive megohmmeter? I ask because in another thread you stated that engineering will not accept the results if a Fluke was used. I asked why but you never replied to the post! Can you respond now about the Fluke's now? Cheap motors need only require cheap testers?
I've seen some pretty expensive assembly machines driven by ordinary cheap motors. When they die the whole machine is dead!

Bill, I am not sure what thread you refer to - I did say in a thread that I am not familar with some of the Flukes mentioned in this and other threads - and some other manufacturers.
I've got a high $ Fluke that I would never think to use for recording a megger reading, cost a lot more than my megger - I do use it to verify something has not changed in the very recent (past few hours?)
I have an inexpensive? Biddle Megger which was $1200 about 18 years ago.
I have no idea what you could buy a good megger for today. I seldom do price shopping, when I need something I get it.
I don't think the Biddle hand crank is a cheap megger. They cost more than those small motors. Cheap motors? Not much to a squirrel cage motor - the
price is determined more by enclosure type, mounting method, and shaft style.
Sorry I didn't answer your post sooner. Occupied with other things.

 

[wptski]

Bill, I am not sure what thread you refer to - I did say in a thread that I am not familar with some of the Flukes mentioned in this and other threads - and some other manufacturers.
I've got a high $ Fluke that I would never think to use for recording a megger reading, cost a lot more than my megger - I do use it to verify something has not changed in the very recent (past few hours?)
I have an inexpensive? Biddle Megger which was $1200 about 18 years ago.
I have no idea what you could buy a good megger for today. I seldom do price shopping, when I need something I get it.
I don't think the Biddle hand crank is a cheap megger. They cost more than those small motors. Cheap motors? Not much to a squirrel cage motor - the
price is determined more by enclosure type, mounting method, and shaft style.
Sorry I didn't answer your post sooner. Occupied with other things.

In this post I'm refering to where you made the Fluke comment.

 

[zog]

Well were not confused about how a Kelvin Bridge works. We stated that in the navy we used a dc power source to heat the windings up in a motor for damp or wet issues . This kelvin tester used dc power to not only heat up the motor windings to dry them up but was used to test contact resistance from the starter or drive controller to the motor it would eliminate conductors or terminations from point of connections by measuring less than one ohm . You can not use a micro ohm meter to do this or a dlr because the batt and power source in these electronic testers dont have what it takes to drive that dc power to go that long distance from point A to point B . Yes its a kelvin connection voltage sent = two leads and current measured = two leads as a 4 wire kelvin test lead connection is normally design to work so we called it a dc kelvin test set . after a cool down period the test was made You test the connections also windings can short and a insulation test cant tell but dc test can find a resistance unbalance. There are different test methods just thought i would add this . But we maybe just making this up so comments ?

My microhmeter has a 100A output (As our specs require) , most have a 10A output, some cheapo ones are less than that, itt all depends on the type you have.

 

[wptski]

My microhmeter has a 100A output (As our specs require) , most have a 10A output, some cheapo ones are less than that, itt all depends on the type you have.

The Megger brand has one that does 200A.

 

[wptski]

Well were not confused about how a Kelvin Bridge works. We stated that in the navy we used a dc power source to heat the windings up in a motor for damp or wet issues . This kelvin tester used dc power to not only heat up the motor windings to dry them up but was used to test contact resistance from the starter or drive controller to the motor it would eliminate conductors or terminations from point of connections by measuring less than one ohm . You can not use a micro ohm meter to do this or a dlr because the batt and power source in these electronic testers dont have what it takes to drive that dc power to go that long distance from point A to point B . Yes its a kelvin connection voltage sent = two leads and current measured = two leads as a 4 wire kelvin test lead connection is normally design to work so we called it a dc kelvin test set . after a cool down period the test was made You test the connections also windings can short and a insulation test cant tell but dc test can find a resistance unbalance. There are different test methods just thought i would add this . But we maybe just making this up so comments ?

You called it a DC Kelvin Test Set but is it just a high amperage micohmeter with Kelvin leads?