Transformer Oil Analysis -worrisome results 3

[ruble3]

We recently completed our annual oil analysis on seven transformers- 4 of them showed a significant rise in dissolved gases from last years results. We were somehat baffled because we've never seen a sudden increase like this. Someone then mentioned that several months ago the utility increased the incoming voltage by 2% ( 800v). Three of the transformers are fairly old but one was installed in 1997 and it too showed a sudden increase so my question is ( and I'm not an EE)- would the increased supply voltage ( to 44kV from 43.2)be one of the reasons for the sudden increase?

 

[ruble3]

Subtech; thanks for the great post- I'll be able to answer a couple questions- the transformers are all pad mount, located outside in a fenced in area- they are subject to extreme weather conditions;+30 deg C in summer and (like last week -30deg C in winter)- the tanks are not n2 pressurized-they are not being sprayed by vehicles
(especially now that there is 3' of snow on the ground)
the loads on two of the transformers has not changed significantly since the last set of tests- one transformer(3.0 MVA/600V has peaked at 2.6 mva in the last year- the load is variable since it supplies power to a bank of 6 air compressors that are sequenced on demand-450 hp each);the load on another transformer has not changed at all
I looked at the numbers again , in one case, the Oxygen numbers are lower but CO2 has risen quite a bit; in the other case 02 numbers have risen slightly, but the CO2 numbers are fairly constant? Temperatures were not recorded at the time of the tests, but looking at them this morning they look ok- max temp rise is 65 deg C; one gauge has a red pointer at 60 deg C so I'm not sure if thats a 'set' point or thats the max temperature the oil rose to- I'll ask around
I'll pass your post on to a 'higher authority' and get his opinion- we are scheduled to retest within the next month