New Digital Megger

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mull982

Senior Member
We are looking to replace our handcrank analog megger that has been damaged. I have been looking around at different digital type meggers and wanted to check with the experts here to see what recomendations others had for good digital type meggers.

I was looking at some from Fluke and AMEC that appear to be able to calculate PI, DAR, and even temperature correct. They also had software which I'm assuming is for trending.

We have several 4.16kV motors here on-site. Is it beneficial to purchase a megger that is capable of testing at 5000V in order to test some of these larger motors. These larger capacity meggers seem much more expensive so I was hoping to hear opinions as to weather or not they were worth it.
 
zog

zog

Senior Member
Location
Charlotte, NC
mull982 said:
We are looking to replace our handcrank analog megger that has been damaged. I have been looking around at different digital type meggers and wanted to check with the experts here to see what recomendations others had for good digital type meggers.

I was looking at some from Fluke and AMEC that appear to be able to calculate PI, DAR, and even temperature correct. They also had software which I'm assuming is for trending.

We have several 4.16kV motors here on-site. Is it beneficial to purchase a megger that is capable of testing at 5000V in order to test some of these larger motors. These larger capacity meggers seem much more expensive so I was hoping to hear opinions as to weather or not they were worth it.
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You bet they are worth it, not to mention you need a minimum of 2500VDC to megger a 4160V motor and a scale in the high Gigaohm or Tetraohm range to get any valueable info.

Unless you use Powerforms or other reporting software you wont need that feature, depending on how many tests you do a day will determine if you should shell out the extra $ for data storage.

My favorite megger in this class is the Megger MIT series
 
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mull982

Senior Member
zog said:
You bet they are worth it, not to mention you need a minimum of 2500VDC to megger a 4160V motor and a scale in the high Gigaohm or Tetraohm range to get any valueable info.
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I was not aware of the requirement for 2500VDC for 4.16kV motors. I'm assuming then that 5000VDC will only make a more reliable test and should be used to do a PI on these motors as you would with a LV motor. I've seen tests on MV motors and cables go as high as 25kVDC for 15min.

I guess folks here will have to understand that you cannot use the 5000V setting on the 600V low voltage cables or motors we have in the plant.
 
Pierre C Belarge

Pierre C Belarge

Senior Member
Location
Westchester County, New York
mull982 said:
I was not aware of the requirement for 2500VDC for 4.16kV motors. I'm assuming then that 5000VDC will only make a more reliable test and should be used to do a PI on these motors as you would with a LV motor. I've seen tests on MV motors and cables go as high as 25kVDC for 15min.

I guess folks here will have to understand that you cannot use the 5000V setting on the 600V low voltage cables or motors we have in the plant.
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Not that you cannot use one, you should not use one. ;):grin:


Which model and expense you use, is dependant upon your needs. Check out the functions and if you are trying to be cost effective, you will be able to choose based on the necessary functions.
 
76nemo

76nemo

Senior Member
Location
Ogdensburg, NY
mull982 said:
I was not aware of the requirement for 2500VDC for 4.16kV motors. I'm assuming then that 5000VDC will only make a more reliable test and should be used to do a PI on these motors as you would with a LV motor. I've seen tests on MV motors and cables go as high as 25kVDC for 15min.

I guess folks here will have to understand that you cannot use the 5000V setting on the 600V low voltage cables or motors we have in the plant.
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25kVDC "Hi-Potting".
 
zog

zog

Senior Member
Location
Charlotte, NC
mull982 said:
I was not aware of the requirement for 2500VDC for 4.16kV motors. I'm assuming then that 5000VDC will only make a more reliable test and should be used to do a PI on these motors as you would with a LV motor. I've seen tests on MV motors and cables go as high as 25kVDC for 15min.
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Yep, 2500VDC is the minimum test voltage for 4160V equipment. I suggest you get your hands on the NETA testing specs for all the tests to be run on MV motors.

25kVDC is a hipot, tan delta, or PF test, not a megger test as pointed out by nemo.
mull982 said:
I guess folks here will have to understand that you cannot use the 5000V setting on the 600V low voltage cables or motors we have in the plant.
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If they don't know that they shouldnt have a megger in thier hands in the first place :)
 
M

mull982

Senior Member
zog said:
Yep, 2500VDC is the minimum test voltage for 4160V equipment. I suggest you get your hands on the NETA testing specs for all the tests to be run on MV motors.
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So what if we had only been using 1000V to perfrom insulation tests on all of our 4.16kV motors for all this time? Would this not be a worthwhile test or produce results worth anything. Usually we just perfrom a test to see if windings are shorted and is more of a go / no-go test.

Pierre C Belarge said:
Which model and expense you use, is dependant upon your needs. Check out the functions and if you are trying to be cost effective, you will be able to choose based on the necessary functions.
Click to expand...


Basically on the maintnance side of things we only use the megger when we suspect a motor is bad or tripping a breaker or something. We usually just meg it at 1000V and determine if the motor is shorted or not. We currently do not have a PM or any routine in place to periodically check insulation readings of our motors. I would like to maybe start inplementing one and thought purchasing a worthwhile meter would be a step in the right direction.

We also once in a while us the megger for acceptance testing of new motor we recieve. We try to do a P.I. for these tests.
 
zog

zog

Senior Member
Location
Charlotte, NC
mull982 said:
So what if we had only been using 1000V to perfrom insulation tests on all of our 4.16kV motors for all this time? Would this not be a worthwhile test or produce results worth anything. Usually we just perfrom a test to see if windings are shorted and is more of a go / no-go test.
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Well 1000VDC should tell you if the winding are shorted, but you are not stressing the insulation enough. 4160V while the motor is in service will find more failures on its own than a 1000VDC test.

mull982 said:
Basically on the maintnance side of things we only use the megger when we suspect a motor is bad or tripping a breaker or something. We usually just meg it at 1000V and determine if the motor is shorted or not. We currently do not have a PM or any routine in place to periodically check insulation readings of our motors. I would like to maybe start inplementing one and thought purchasing a worthwhile meter would be a step in the right direction.

We also once in a while us the megger for acceptance testing of new motor we recieve. We try to do a P.I. for these tests.
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The trending of the megger readings over time is a more vaulable peice of info than the actual reading itself. Of course you need to temperature correct the readings for them to mean anything (40 Degrees C for inductive equipment like a motor).

Predictive maintenence is a big money saver over the band aid maintenence you are describing (Dont feel bad, most plants do it your way). There are entire conferences, magazines, heck a whole industry out there about predictive maintence cost savings. (Uptime magazine is the "EC&M" of that industry)
 
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mull982

Senior Member
Is a digital meter better than the old analog handcrank type megger I am trying to replace? The digial meter seem easier to use (no cranking) but are we giving up anything by choosing digial over the analog?
 
tom baker

tom baker

First Chief Moderator
Staff member
Location
Bremerton, Washington
I have used the Fluke digital insulation tester and I was not sure at first, but now I am going to sell the hand crank megger.
One of the flukes is a DVM and insulation tester in one, great for a service truck.
 
zog

zog

Senior Member
Location
Charlotte, NC
mull982 said:
Is a digital meter better than the old analog handcrank type megger I am trying to replace? The digial meter seem easier to use (no cranking) but are we giving up anything by choosing digial over the analog?
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A PI test requires application of the test voltage for 10 minutes. You can get sick of cranking pretty quick when testing a pile of motors.
 
Fulthrotl

Fulthrotl

~Autocorrect is My Worst Enema.~
Location
HB, CA (19 Hrs. 22 Min. from Winged Horses)
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mull982 said:
Is a digital meter better than the old analog handcrank type megger I am trying to replace? The digial meter seem easier to use (no cranking) but are we giving up anything by choosing digial over the analog?
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there really isn't any comparison.

spinning a crank is great if you are trying to get night crawlers to fish with,
but if you want something that can give you repeatable readings that mean
something, get a digital, like fluke or similar.
 
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wptski

Senior Member
Location
Warren, MI
As mention above, I have the AEMC 1060 which I got after being frustrated with the Fluke 1507 lack of max range for PI/DAR tests. I don't think that the Fluke 1550B has that great of max range either!
 
76nemo

76nemo

Senior Member
Location
Ogdensburg, NY
netaguy said:
we purchased one of these last year and bought two more of them this year.

Nice product and handles well for field work.

http://www.hioki.com/product/pdf/3455E3-59M-00P_web.pdf
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Nice link man. I have never used Hioki test equipment. That tester looks pretty impressive. It also shows current leakage. That has me baffled. Hi-pot shows current leakage. I don't know the difference in circuitry between megohmeter testers and hi-pot testers and how they work exactly, but is it possible this tester performs both tests? Is it just DC hi-pot, or is it just a conversion?

Anyone else want to chime in on Hioki equipment? I have heard some good things on their PQA equipment, and I would like to hear more opinions.


Anyone????????
 
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