oil film conductivity

[Tmoose]

We have some big dump resistors that may get whacked with several hundred volts during an "event".
They are mounted on G10 insulating standoffs.
Some sections of that machine are now covered with a light oil film. Probably some cutting or grinding oil.

We plan to degrease things, but I'm interested in confirming there is no conducting film left on the surfaces that might allow a shorting and carbon tracking.

Someone suggests a resistance check is sufficient. An electrical amateur (me) a modified hi pot test is required.

So far GOOGLE has returned almost no info re: oil film condcutivity and resistance.

 

[Skogsgurra]

Probably no problems with the oil film per se.

But you will have dust, flies, mosquitos and what have you stuck in the oil film. Flies and mosquitos may be a minor problem - but accumulating dust is not to be taken lightly.

So you have to remove the oil film. I would not use hipot test. If the surface feels dry to the touch, you probably have got rid of the oil. Do the white glove test and make sure the glove is white after going through all insulators.

Gunnar Englund

http://www.gke.org

 

[Comcokid]

I once worked at a place where in production they had thermoform machine that was controlled with 220V relay logic. They had a vacuum pump/tank right next to the controls. The vacuum pump had bad rings and would blow a oil mist in the air which coated heavly the relay controls.

The maintainance guy was told to clean the controls. He disconnected power, sprayed the controls with "Gunk" engine degreaser, and hosed it down. The degreaser melted the plastic relay housings and sockets. It left a white film over everything. It was a big mess to rework. Gunk is a kerosene and soap base which leaves a soap film behind.

Be careful with how you degrease your devices!

 

[logbook]

I don't think this is a big deal to test. Just "open" both ends of the resistor chain and use a hand-held insulation tester at 500V or 1000V DC/AC to do the test. If it doesn't arc over and has a resistance in the megohm region then it is fine.

 

[Zogzog]

I agree, shouldnt be a problem, oil is a pretty good insulator. Follow the above advice for cleaning and a megger test, you should be fine.

 

[VEBill]

Big (kw-class) RF Dummy Loads are often (intentionally) submerged in oil for cooling purposes.

Google 'Cantenna'.

I suspect that the amateur radio community has used every oil known to man in this application. Cooking, motor, gear... - I'll bet they've used every last one.

A dirty coating is different than a bucket of clean oil.

 

[waross]

I think you may have two issues here. Oil on the resistors may not be as conductive as the resistors them selves even if it is contaminated. If there is sufficient oil it may be a fire hazard, but I don't think you have that much oil film.
Oil on the supporting insulators may be a conduction issue. You will have to disconnect your resistors from ground and from the system before hi-potting. Then, if you have enough oil to be a problem the hi-pot test may be succesful but in a few months enough dust may build up to cause issues.
I would say "Skip the electrical tests and go with skogskurras' 'White glove' test."
respectfully

 

[MikeHalloran]

One small and possibly relevant factoid, okay two:

Under thermal or electrical stress, petroleum oil decomposes ... into carbon, among other things.

Under themal or electrical stress, silicone oil decomposes ... into incredibly fine white sand.



Mike Halloran
Pembroke Pines, FL, USA