Megger a compressor on a City Multi

[Daz man]

Hi all,

very simple question which I would be grateful if any one could assist or provide the correct advice on the below question -

when 'Meggering' an hermetic compressor on a Mitsubishi City Multi condenser which setting on my Megger is best suited to check the windings?

250v
500v
1000v

?

Many thanks

[install monkey]

500 typically
dont forget to disconnect the leads from the inverter board- and make sure ur testing phase to earth:confused:

[Daz man]

500 typically
dont forget to disconnect the leads from the inverter board- and make sure ur testing phase to earth:confused:

Will do, much appreciated.

thanks for the reply.

[Tayters]

Hi Daz.

Stuff I've read generally says to megger at twice the operating voltage.
In that case a 3 phase inverter you'd megger at 1kV.

Still, read a lot of stuff, not sure how much is true but I've not meggered anything to death. Yet...

Cheers,
Andy.

[nike123]

http://www.fluke.com/fluke/uses/comunidad/fluke-news-plus/articlecategories/insulation-resistance/hvac+insulation+test.htm

[FreezerGeezer]

Never have used more than 500V as I was taught that 1000V may blow the winding klixons - on comp's where the beads are in the windings.

[moideen]

http://www.fluke.com/fluke/uses/comunidad/fluke-news-plus/articlecategories/insulation-resistance/hvac+insulation+test.htm

nike, thanks your link.more info, good information about meggering.

[nike123]

Here is another thread:
http://www.refrigeration-engineer.com/forums/showthread.php?11604-Compressor-insulation-measuring

[Daz man]

Cheers all for the feedback. - common question really but wanna make sure before I mess up potentially a perfectly good compressor.

[Daz man]

Compressor tested out okay to be honest. With my Megger set on the 500v range, connected my black lead to the oil equalising line (copper pipe, which I cleaned with emery cloth) my red lead to each terminal U,V&W on each winding it took its time (about 40 secs) I got to >1Mohm. After speaking to Mitsi they suggested a replacement inverter pack. Cheers blokes

[install monkey]

u can test the inverter circuit but pulling the leads off the comp, flick a dip switch on the inverter pcb - not the comms board- test your getting 180v ac on any 2 phases

[nike123]

For compressors with modern insulation (manufactured after 1975) 100 Mega-ohms is value for pass/fail judgment.
I would say that your is "mature" for replacement.

New compressor have insulation resistance more than 10 Giga-ohms at 500V test voltage (OL indication on my megger or out of range, which is 10 Gohm at 500V).
Check it on new one, you will see.

1 Mega-ohm or similar mean 10000 times weaker insulation than it was when manufactured. Certainly not good, by my judgment.;) And, I would say, clear indication that whindings are not in good shape.

[nike123]

Some insulations in use since 1975 have improved insulating values that may not readily allow leakage current, may have insulation-resistance-testing values near 20,000 megohms (20 gigohms), and may be unacceptable for use if insulation-resistance-testing values are below 100 megohms, regardless of whether or not the windings have surface contaminants.

http://flic.kr/p/jAZe2W

http://hpac.com/motors-drives/testing-hvac-motors-0509

http://www.pearl1.org/standards/Tables-Section-6000/6002%20Table%202%20Insulation%20Resistance%20Test%20Values%20for%20Electrica.pdf

http://www.ewh.ieee.org/cmte/pes/materials/WorkingGroups/P43/P43-2000_Draft_May-08R1.pdf