vaccum

[venkatesan]

what happens when a refrigeration system holds the vaccum for 24hrs whether it cause a damage to compressor winding

[ktm]

Don't think it would do anything to the windings but I have heard realy realy deep vacuums can do something to oils but never come across it to be honest.

[stufus]

You should not megger a compressor whilst under vacuum.I think
Not entirely sure why but it's something to do with arcing across the winding's or arcing to the shell.
It's one of those thing's someone said in passing years ago and it stuck with me.
Never really gave it too much thought until now
Must look into it .
Cheers
Stu

[Grizzly]

I have left many many systems in a prolonged vacuum. 12 or 24hrs is the norm when proving systems for the Royal Navy.
In fact it is still one of the best ways of proving the system has neither leaks nor moisture content.
Nonickname posted earlier today that the only practice that can cause damage.
Is to Megga a system whilst under Vacuum because as Stufus also states. Electrical discharge across the internal motor windings can occur.
So no, a vacuum will not damage a motor only someone who is not trained can do that!
Grizzly

[Tesla]

Don't think it would do anything to the windings but I have heard realy realy deep vacuums can do something to oils but never come across it to be honest.

When I spoke to an oil manufacturer they told me that at around and below 300 microns the oil will start to boil and then start to decompose loosing it's ability to lubricate. Also I have seen the oil expand like 1.5 times it's original volume under a deep vacuum.

[mikeref]

Tesla, would that be for new oil or used oil? For used oil one would expect this with refrigerant and other nasties that may be mixed in..Mike.

[Tesla]

Hi mikeref
This was for brand new oil going into a very old 19DA chiller.

[dan22]

The reason is arcing, caused by lack air. Air offers electrical insulation or resistance, when in a vacuum the electricity will take the path of least resistance to ground, an arc to caseing or winding to winding vs. traveling the whole winding.

[xxargs]

in very high vakuum you can have very high voltage without arcing - but in range 10 mBar to 0.01 mBar is high risk to arcing even with low voltage.

rule of how this works often called Paschen's law and more infomation about it, look http://en.wikipedia.org/wiki/Paschen%27s_law

[cktoy]

I have left many many systems in a prolonged vacuum. 12 or 24hrs is the norm when proving systems for the Royal Navy.

In fact it is still one of the best ways of proving the system has neither leaks nor moisture content.

Nonickname posted earlier today that the only practice that can cause damage.
Is to Megga a system whilst under Vacuum because as Stufus also states. Electrical discharge across the internal motor windings can occur.
So no, a vacuum will not damage a motor only someone who is not trained can do that!
Grizzly

vacuum only proves you can hold about 15psia.not a good method of leak checking a system,not even low pressure system.vacuum only good for dehydration and removal of noncondesables.ref. oil can boil below 300 microns.energizing windings ,whatever method ,while in vacuum ,will damage windings.

[Grizzly]

CKtoy.
I should of explained.
Prior to a Vacuum test which would prove leaks (below 15psi if you insist!) You pressurize the system to check for positive pressure leaks.
The length of time for each is Dependant upon the designated practices for those systems.

In fact it is still one of the best ways of proving the system has neither leaks nor moisture content

Is correct even if only to 15psi
There are lots of systems that run at below that pressure.
But hey! If you want to be pedantic!
Grizzly