Hot oil filteration in transformers

[prc]

In some utilities, as annual routine, they conduct hot oil circulation in transformers in service ( may be for 3-4 days). Taking oil from bottom of transformer tank, circulate through a filter machine(with a shrouded electrical heater to raise oil temperature to 70C + vacuum chamber to remove moisture in oil) Is this the universal practice? Is it really necessary? Is it effective in removing moisture from paper insulation? Will oil get deteriorated by this, as oil pass over the hot heater?

 

[edison123]

I think it's an odd practice, peculiar to India. Like doing annual 'overhaul' of motors that have been running perfectly well and then dumping loads of varnish on the windings to 'improve their life'. Have been fighting against such beliefs with my clients for years now. A few have been reformed but still a lot left stuck to their beliefs which are passed on from seniors to juniors.

Muthu

http://www.edison.co.in

 

[ScottyUK]

Hi prc,

I've organised this task on a handful of occasions when we had problems with oil quality on specific transformers, but not as a routine maintenance requirement across the fleet. It certainly removes water from the oil, so it must reduce the water content in the paper to a degree because a new equilibrium point will be reached. I don't think for a moment that it fully dries the paper.

 

[prc]

Thank you Edison and Scotty for the inputs. Edison, my views are same as yours. I wanted to know the practice followed in US and Europe.In India,at least in some places,they are doing it to satisfy the electrical inspector also with out knowing that water ppm values will regain to original figures within couple of weeks as the water will migrate from paper to oil to keep up the equilibrium.

 

[stevenal]

Not at all routine, but we have had a similar service done. Generally a week long dryout as described, but with the oil passing through fullers earth as well. It helps with moisture and other oil quality indicators. To dry the paper, suggest using the Velcon approach.

 

[prc]

Thank you stevenal- Flow over fullers earth is required only for reclamation of oil ie to treat aged oils to recover to original properties and then supplemented with oxidation inhibitors to stabilize the properties. Annual reconditioning is done only to remove water, dust and dissolved gases.On line driers are painfully slow and may be useful only for moderate wet conditions.

 

[bacon4life]

Certainly not routine on an annual basis. One complication with annual degasing transformer oil is that you cannot trend dissolved gasses. Trending DGA results is a good way to detect developing problems in a transformer.