Oil Filtration vs. Vacuum Oil Purification Transformers

Yes many of us Know .So what? Are you taking our interview? Please do not waste others time by putting such threads.

Some folks ask a question in the form of what seems like a statement. One thing I can not stand is some idiot who knows just enough to THINK he knows everything and wants to be a jackass about it. This Forum is to share ideas. You seem to think you know everyting and do not want to share what you know if in fact you know anything.

You say you do. Lets hear it. Else why be on this or any forum?? Very Rude. I also say that you are a liar. I would bet a lot of $ on the fact that you are a liar.

Jim

I'm sorry, but, I have to agree with V. I. To ask that broad of a question indicates to me a complete lack of knowledge of the subject in question. It only seems reasonable to at least look a few places and get a general idea of what you need to know first. Then ask for help on what one may need to know that is not covered.

While Peter T deserves a GA for the info he gave, my concern would be what the OP is going to do with the info that may cause problems and dangerous conditions down the line.

P. S. Would have thought Lynn or Cat would have beat V. I. to his right on response, even if "Off Topic". To me, the question was "Off Topic". -- JHF

Wiki do.

And I does!

...and the oil manufacturer does.

...and what is needed may be found either in the User Manual supplied with the equipment or, in its absence, by telephoning the equipment manufacturer directly.

Two type of impurities to be removed from oil to make it suitable.

1. Fatty acids (salicylic acid - good for massage and relieve pain) : produced as a result of oxidation of mineral oil in contact with bare Cu under heat. These can be removed through filter press.

2. Moisture: Picked up due to breathing under load cycling when Silica gel is near end of its cycle - this comes out by subjecting oil to vacuum at room temperature.

A simple filter press has heating and filters. Though it removes moisture along with sludge, but heating in presence of oxygen in air deteriorates oil properties.

Therefore best is to purify/ treat oil through a filter press which also has vacuum chamber and can purify oil without heating it.

In case the transformer is in service for more than 20 years and have fed line faults, it become necessary to dismantle same, clean all windings of deposit sludge, inspect windings of symmetry, inspect surge coils, tap changers, any damage to coil insulation, tightness of clamps of coils, and check insulation of core clamping bolts etc. etc.

Once exposed to atmosphere, the insulation of coils, which is paper, is very hygroscopic and hence absorbs lots of moisture (one can find that a 15 - 17.5MVA transformer may soak in 40 to 50kg of water once left open for one week for inspection job listed above). To remove this moisture, after assembly back of transformer in its tank, it is subjected to vacuum. To evaluate moisture removed and remaining in winding the exhaust of vacuum pump is circulated through a cooler to condense moisture. For efficient removal of moisture the pressure inside the tank is of just few tors. (Before subject to vacuum, important to check if the transformer tank is designed for vacuum.) The oil is filled in slowly from bottom, with tank still under vacuum to ensure no air trap.

Above comments are from my very old experience of 1972-80. Since that time, I have not got in to any maintenance activity of Transformers. Thus above can be out dated. Other knowledgeable members may contribute more accurately to this topic

Removing water from insulating oil without heating it and keeping it under vacuum is just not possible to the required degree . . . parts per million, that is.

It is possible to remove moisture under vacuum without heating. It is reverse of pressure cockers. The Boiling Temperature of any fluid is function of its vapour pressure over its surface. Thus if we increase pressure the boiling temperature increases (Pressure Cooker in the kitchen) and conversely we decrease vapour pressure the boiling point decreases.

In late 70, I had dried out transformer at ambient temperature using two vacuum pumps in series - one reciprocating and another Momentum (vapour jet ejector) to achieve a vacuum of order of 2.5 to 4 torr.

It is all game of vapour pressure corresponding to temperature. If you can create a pressure lower than the vapour pressure of particular liquid at a given temperature the liquid will evaporate to create its equilibrium pressure to stop further vaporisation. In drying out via vacuum, we remove moisture efficiently without much heating by creating low enough pressure below its natural vapour pressure at the ambient temperature.

In case of portable Oil Filter Press, slight heating is done, which depends upon efficiency of vacuum pump installed. But it is not to that level as in press without vacuum pump.

The temperature in Vacuum Press is of the order that it is below the boiling point of Oil at that Vacuum, so that oil does not boil in sufficient quantity at that temperature and pressure - thus not putting much load or increasing capacity of vacuum pump.

Word of caution - Drier the paper insulation, more brittle it is and would tend to crack under residual tension left during manufacturing (we are aware that insulation tape used is mostly Crepe paper tape so that it does not rapture when wrapped around conductor under tension). HENCE ONCE DRIED OUT THE TRANSFORMER SHALL NOT BE SUBJECT TO SHOCKS OR JERKS ETC., BEFORE IT IS FILLED WITH OIL.

I am on vacation in US at the moment, thus do not have access to my notes on transformer maintenance. I am commenting on memory of maintenance work carried out in late 70s and based on reasoning and fundamental of science and engineering which I suppose should remain true.

What in the world are you talking about . . ? . . . dry paper insulation . . ? ? !!! Paper insulation is NEVER DRY, . . . it is properly impregnated with oil as soon as it is finished, . . . and hopefully maintained impregnated for the rest of its life!

Oil filtration will remove contaminants from the fluid, however the oil has the ability to hold water in suspension which cannot be removed with ease.

Vacuum oil purification will remove water (and some gaz and acids) from the oil at a low temperature (and will not harm the oil additives) and the filters in this circuit will also remove contaminants, the resulting product offers longer life for the oil.

Yes, that is right, . . . oil will hold water unless you heat it and hold under vacuum. A temperature of 100C is desirable to 'boil off' ALL water. And such a temperature NEVER WILL harm the oil, . . . the ASTM standard specifies the oil to be heated to 100C for testing purposes.

I beg to disagree. There are excellent hydrophilic filters available these days that will (with adequate number of passes through the filter element) reduce dissolved water in the oil to less than 15-20 ppm. We use them regularly in our business. It is not always necessary to vacuum treat a transformer to reduce the water content, unless it is extremely high, or there are other impurities to remove such as dissolved gases.

That said, when filling a new, large power transformer (or refilling one that has had all the oil removed), it should be done under vacuum due to what was posted - the paper insulation tends to absorb and hold a lot of moisture if it is exposed to air.

Peter, I did not dispute your comments regarding Hydrophilic filter element.

My reply was to comments of olewhi, " Removing water from insulating oil without heating it and keeping it under vacuum is just not possible to the required degree . . . parts per million, that is"

Sometime we have to work in circumstances where neither sophisticate Filter Vacuum press or hydrophilic filters are available. Below is one of my experience (Members please do not take it as a biodata)

In 1982, my firm Belfour Kilpatrick faced with restore or replace 2400kVA Distribution Transformer of Al-Hassan Palace in Salalah (then a small city in Sultanate of Oman, Middle East) which was damaged by a painter, who accidently moved off load tap changer while painting. I opted to Manager, Perry Benet, that I could try to repair the transformer.

Nothing conventional was available to repair, for example,

- Insulation tapes of jointing kits of PILC cables, available in our store,were used to re- insulate damaged insulation.

-Open Paint shed (without any crane) was converted to rewinding shop.

- Steel scaffolding structure and chain block was used to lift damaged 11kV coil.

- Fabricated wooden mandrel for unwinding and winding damaged coil.

After repairing the coil and assembly of Transformer I had challenged of drying out of Transformer. Salalah goes through 3 months of Monsoon season and coils had absorbed lot of moisture. Below is the detail of make shift dryer - hope it will interest members

- Built oven frame of slotted angles and Al sheet and covered with Asbestos cloth as heat insulation. (these items were available in Salalah)

- Fabricated duct of Al sheet and installed in duct Thermostat and electric heaters. These were removed from water heaters lying in Junk yard (connected in series to lower temperature).

- Blower fan of discarded window AC was used to circulate hot air between Over and duct. The original plastic impeller of blower was replaced from one fabricated out of Al sheet - just balanced it statically. Blower sucked air from bottom of oven, heated it through duct and push back in to oven near top.

- A window AC was installed in the oven wall opposite to location of air duct. Of the two impellers of window AC, the impeller on Evaporator side was removed, so that we did not blow cold air on windings and could just pick up the moisture out of oven coming in contact with cooling coils (evaporator).

You won't believe that we used to collect up to 12 to 15 litres in 24 hours of water from drain of window A/C. It took us about 20 days and at the end when the collection was just half litre per 24 hours for 4 to 5 days - I considered this being due to leakages of make shift oven and considered the coils dried out.

The hot windings of transformer was sprayed with new transformer oils, boxed up in the tank and slowly filled up with oil under gravity oil rising from bottom. allowed to settle for 24 hours for any air pocket to escape.

Transformer was tested for IR, HV test and finally back charged with 3 phase 415V Main supply soaked for 48 hours. No abnormality, it was commissioned back in service - at that time I was a young boy of 31-32 years age and got bonus for repairs from Belfour Kilpatrick (Zubair Kilpatrick in Oman).

So necessity is the mother of invention - one can exploit resources using basic principles of science and achieve desired results. In above case I did not use any vacuum pump to reduce water vapour pressure - in stead air-conditioner to absorb water vapours - lowering vapour pressure and letting more water to come out of insulation. Heating further assisted in vaporisation.

My good luck was that I had a very good Millwright Fitter, Papachan, who could weld, fabricate etc. as desired.