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“Ageing Phenomenon of Paper oil insulation in power transformer”

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Presentation on theme: "“Ageing Phenomenon of Paper oil insulation in power transformer”"— Presentation transcript:

1 “Ageing Phenomenon of Paper oil insulation in power transformer”
By: Ahmad Arslan

2 Composition of Insulation Paper-OIL
Ageing: Irreversible changes in one or more properties as a consequence of normal use or as a result of electrical, thermal, mechanical, and environmental stress over time To be able to use the real capacity of transformer, Its important to know the duration & level of stress , a transformer can withstand. Thus liquid and solid insulation is equally important with regard to the operating capacity and overloading capability. Composition of Insulation Paper-OIL CELLULOSE PAPER Cellulose fibers (Chains of Hydrocarbons) Long chain with similar molecular structure. Strength (Chain connections + Hydrogen Bonding) OIL Paraffins, Naphthenes & Aromatics ………(Simply Hydro carbons ) Hydrocarbons but with different molecular structure. Degree of Polymerization (DOP): No. of monomeric units in a Macromolecule, or polymer. (unaged cellulose DOP is usually glucose rings )

3 Degradation of hydrocarbon structure in paper-oil
Ageing performance of insulation (oil/paper) is influenced by “DEGRADATION OF HYDROCARBONS”. Three types of degradation Hydrolysis degradation (By Product: Sugar Glucose Chain Breakdown) Oxidative Degradation (Chain scission, By produces: Carboxyl Groups) Pyrolysis Degradation (Boosts H+O degradation, DOP/strength, opening of Glucose Ring, H2O & C-O) Factors Leading to Degradation The process of degradation (ageing) is influenced by following factors. Thermal ageing process Electromechanical & Combined Electro-thermal ageing process

4 Thermal Ageing Process
Temperature changes Electrical & Mechanical properties of the Oil/cellulose insulation. Thermally supplied vibration energy is more concentrated on C-C, C-H & C-O Bonds. Leading to Breakdown CO2 ,CO , H2O, CH4 Chemical reactions Sludge , Acid , etc. Moisture + Water is absorbed by cellulose and causes further decomposition Oxygen: Predominant in oil Oxidation of Oil/cellulose Acids, CO/CO2, H2O Acids: Further decomposition of oil by dissolving the copper & iron Mathematical Model of Thermal degradation Montsinger’s Law: “Increase or decrease of operating Temperature by 6-10K results in doubling or halving of ageing rate”. Dakin’s Equation calculation: 𝑑 𝑑𝑡 𝑥 0 −𝑥 =𝐶 𝑇 .𝑥 X0= Material Characteristics at Time t=0 x= Material characteristics at time t t=time in days C= Aging rate T=Absolute temperature in K

5 Dakin’s equation with “α” as general order reaction (α>0) 𝑋 𝑡 = 𝑥(𝑇) 𝑥 0 𝑑𝑥 𝑑𝑡 =−𝐶 𝑇 . 𝑥 α where 𝑥 𝑡 = 𝑥 0 .exp [-C(T).t] for boundary condition 𝑥 𝑡=0 = 𝑥 0 Arrhenius Equation: Explains temperature dependence of ageing rate constant C(T) 𝐶 𝑇 = 𝐶 𝐴 . exp − 𝐸 𝑅.𝑇 CA=Constant [1/time] E=activation energy [J/mol] R=gas constant [J/K.mol]

6 Thermal Ageing process under influence of h2o & o2
Breakdown voltage of liquid insulation depends upon water content in that liquied. > If water is dissolved in the oil, breakdown voltage is quit higher (i.e 65KV) >If water is emulsified in oil, Break down voltage falls. Majority of Moisture in paper & pressboard, a small portion in oil. Oxyegn: reacts with oil molecule to form water, CO/CO2 (mainly, by oxidation) H2O+CO2 Thermo hydrolytic decomposition of cellulose.

7 Electrical +combined electrical &thermal ageing
Electrical stress has little direct effect on ageing of liquid insulation. Electrical Discharges By products Thermal Energy Ionic & Gaseous reactions Electric field strength Separation of Ions (Preventing form combining)

8 Diagnostic methods. Oil Test
>Moisture Contents: sample >Surface Tension Cohesive forces among liquid molecule >Neutralization Number -Amount of base needed to neutralize the acids in sample >Dielectric Strength Voltage Withstand level >Dissolved Gas Analysis -Composition of generated gas Paper Test >DOP Mechanical Strength of Paper >Furfural Analysis -Permanent byproducts >Moisture Content Sample >Tensile Strength Mechanical Stress Dielectric Test >Voltage Test Electrical withstand strength of insulation >Partial Discharge Test Detect and locate harmful local discharge >Dielectric Response Diagnostic measurement, Moisture content

9 Thank you


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