Dangerous Effects Of Moisture on Transformers life

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What do you mean by Transformer Life Span ?Trafo life span is nothing but life span of Insulation(Cellulose insulation)It Depends on Cellulose bonds between cellulose cells.Cellulose in the paper is made up of glucose molecules strung together in long chains. The longer these polymer chains are, the stronger will be the insulation.

Major sources of moisture in transformer Residual Moisture in Thick Structure element(Ex: PCPB blocks, End Blocks, Permali wood, core guiding block)Incomplete drying.Ingress of moisture during transportation & erection(poor handling).Poor gasket sealing,poor quality of oil seal.Ageing Decomposition of Cellulose & Oil.

Existence of Water in transformer in different form

Free water at bottom of tank.Water can be in the form of Oil emulsion.Dissolved Water (Can be measured by DGA).Chemically bound Water.

Usual moisture contents as shipped from factory

Avg oil TempSuggested Max. Water Content in Oil & Corresponding paper moisture when shipped from factory < 69 kV69 230 kV >230 kV50 deg C7 ppm2 ppm2 ppm60 deg C12 ppm4 ppm4 ppm70 deg C20 ppm7 ppm7 ppm% Water Saturation6 %2%2%Paper Moisture1 % M/DW0.5% M/DW0.5% M/DW

Interpretation of absolute saturation of solid Insulation

Percent M/DWClassification< 0.5 %New Trafo>0.5 1.5 %Dry Insulation>1.5 2.5%Medium Wet Insn.>2.5 4% Wet Insulation.> 4% Very Wet Insulation.

How much water is 1% M/DW?That depends on the size of the transformer and some other factors.Example:10000 kVA Trafo with 3000 gallons of oil will have approximately 3510 pounds of paper insulation. So, 1% M/DW calculates to 35.1 pounds of water. Thats 4.20 gallons!

Max.Water Solubility in Oil with Increasing Temp as per (IEEE P57.106TM/D5, Oct.2005)

Oil Temp in C Water Content in Oil PPM1036308360242100772

What is Relative Saturation ?Relative Saturation= Water Content in Oil Max. Water Content the Oil can hold at that temp.

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Dielectric BDV

RS% at 22 Deg C

Delelectric BDV

Dielectric Breakdown V/s Relative Saturation(RS)

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Dielectric BDV3634322826221815104

RS % at 22 Deg C102030405060708090100

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Dielectric BDV

RS% at 22 Deg C

Delelectric BDV

Dielectric Breakdown V/s Relative Saturation(RS)

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How Does Moisture affect the Dielectric System

TimeM/DWPPMTemp. Deg COil BDVMax. Water Solubility in OilRelative SaturationRemarks11.30 am1.5%20ppm7050 kV220 ppm10%No Problem11.30Pm1.5%20ppm5035 kV140 ppm20%A bit high11.30 am1.5%60ppm9045 kV>242 ppmApprox10%No Problem11.30Pm1.5%60ppm5035 kV140 ppm>40%Very High

Example for Loss of Insulation life

% Moisture by Dry Weight(M/DW)Expected life of Transformer0.5 to 0.75(New Trafo)50 Years1.525 Years312 Years

Degree of PolymerizationDP should be 800-1000 for a brand new transformer.DP will decline as the transformer ages.

Insulation AgeingTwo Processes:Oxidation: will produce carboxylic acids (Ex: formic, acetic, levulinic acid) & water at lower temperature.Hydrolysis: This is due to Carboxylic acids dissociated in water catalyses, which will affect or dominates at higher temperature.

Effects of water on transformerDissolved water is a problem for Cold Transformer.(BDV may go upto 0.2 to 0.4 kV/mm which was observed).Bubble evolution is a Problem for Hot Transformer.

EFFECTS OF AGEING OF CELLULOSE Reduction in paper strength.Reduction of BIL & Short Circuit withstand capability.Reduction in solidity of windings.Reduction in capability of withstanding normal movement & disruption of service life.

Wrong Practices in present daysMeasuring the Concentration of water when trafo is out of service or at ambient.At ambient or temperature

Measurement of Moisture content in Transformer.Concentration of water in Oil will be high at High temperatures.Sample of Oil to be taken in Hottest period of a day & high temperature.Sample of Oil to be taken in Syringe, in order to avoid contact with atmosphere.

Preventive Action found nowadaysImplementing online moisture sensors.