Could you provide a description or maybe a link to the Rution test you mention - I do work in a place with an HV test facility, and I suspect it is a test I might know by another name.
Meanwhile in general the breakdown voltages of gas filled gaps between conductors fall as the pressure is reduced, and increase as the pressure rises.

This in turn is because the mean free path between the molecules determines the run-up distance that charged particles get between collisions that in effect bring them to a dead stop. The accelerating voltage over whatever that distance happens to be sets the collision energy, it also may, or may may not be  enough to trigger impact ionisation. When it is, that is to say when the E field is such that the voltage drop across a distance of one mean free path is comparable to or exceeds the ionisation energy, then catastrophic avalanche breakdown ensues. Mean free path may be estimated by the no of molecules per cubic metre at the pressure involved, and a bit of geometry.

This does not work when electrodes are closer than the gas mean free path but that is only an issue for very low pressures and or very close spacing. Unless you are designing a particle accelerator or a CRT, this is not normally a consideration.
Mike.

Thanks for discussion, Mike

In IEC 61869-1 there is the routine test  7.3.1 Power-frequency voltage withstand test on primary terminals.

It is said that the test voltage shall have the appropriate value given in table 2.

In our national standards (RU) we want to introduce in the test methods possibility to do Power-frequency voltage withstand test on primary terminals with reduced pressure (not with rated pressure) during routine test only for gas-filled Instrument transformers without solid insulation inside.

Do you have any experience with such kind of tests, is it standardisised?

Olga.

It is not my day job, and 61869 is a complex standard - and some of it is being revised, so we expect a 2022 or 2023 version of part 1  soon which I did not look at the DPC when it was available, so I am not sure what is changing. (the interrelation of the parts of the standard  is described in this white paper.)

However in general a reduced pressure test of anything gas-filled is a harder test to pass than when fully pressurized. BUT it only reduces the thresholds for the breakdown paths through the gas - things like tracking across external bushes will of course be unaffected by internal pressure, but perhaps less obviously so will some of the internal breakdown mechanisms though things like solid insulation pr trapped particles as well, so a reduced voltage test at a reduced pressure does not provide the same confidence that all possible mechanisms have been properly exercised. (This paper, although about gas insulated switch gear shows this) test at reduced voltage, and reduced pressure are, as far as I know, dependent on knowledge of the internal failure modes- which is maker specific.
Mike

Thank you Mike.

I am the vice-chair of TC38 and IEC 61869-1 close to the FDIS stage. I even checked the CDV and new reduction in the WG but there is no any information even at what kind of pressure to do the test, rated or reduced. I will ask the convenor.

(This paper, although about gas insulated switch gear shows this) test at reduced voltage, and reduced pressure are, as far as I know, dependent on knowledge of the internal failure modes- which is maker specific. - what clause of the article is it?

Thank you Mike.

I am the vice-chair of TC38 and IEC 61869-1 close to the FDIS stage. I even checked the CDV and new reduction in the WG but there is no any information even at what kind of pressure to do the test, rated or reduced. I will ask the convenor.

(This paper, although about gas insulated switch gear shows this) test at reduced voltage, and reduced pressure are, as far as I know, dependent on knowledge of the internal failure modes- which is maker specific. - what clause of the article is it?

Ah well, you probably know much more about the standards side of it than I do, my only experience of anything even remotely like that is nearly 20 years ago for 3gpp, where for a while I was asst convenor to a small group looking at 3G handset performance verification.

But if your group is anything like that was, then if folk are bringing technical CRs to change test limits or processes, and expect them not to be thrown out almost unread, then surely they should also be providing the justification and supporting data either to the committee members under NDA, or in the form of open publications. IEC process may be a bit different of course.

Technically, not procedurally, I can say that in other areas of gas filled high voltage stuff I have seen, which is NOT the sort of thing covered by IEC (experimental lab kit, laser triggered gaps, for TR switching and components of accelerators etc, all very custom design) it is common to do production test at nominal gas pressure and some agreed over-voltage, and/or 75-80 % of nominal gas pressure and nominal voltage, and gas leak test at 120-125% of nominal pressure, maybe with or without voltage at all, but also that in practice during development all sorts of other things such as partial discharges versus slowly increasing voltages are tested. I'd expect gas filled transformers to be similar, but I'd be very happy to be corrected - as I said above it is not really my area.

Production test is much simpler as it only needs to catch defective parts or incorrect assembly - you are verifying the thing is built to meet the plan, not that the design on the plan is fit for purpose - someone else did that during development. 
Mike

Thanks Mike