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