Contents

Chapter 1: Unused Mineral Insulating Oil

1.2..... Mineral Oil 2

1.3..... Classification of mineral oil based on application 3

1.3.1...... Transformers oil 4

1.3.2...... Switchgear oil in low temperatures 4

1.4..... Additives. 9

1.5..... Special cases. 11

1.6..... Analysis of potentially corrosive sulphur 11

1.7..... Oil contamination 12

References. 12

Chapter 2: In-service Mineral Insulating Oil

2.2..... Oil monitoring and purification 14

2.3..... Oil ageing and degradation 15

2.4..... Oil tests. 15

2.4.1...... Color and appearance 15

2.4.2...... Breakdown voltage 16

2.4.4...... Water in the insulation system 17

2.4.5...... Acidity. 21

2.4.7...... Additives and oxidation stability 24

2.4.8...... Sludge and sediment 25

2.4.9...... Interfacial tension 25

2.4.10.... Particle content 25

2.4.11.... Flash point 27

2.4.13.... Pour point 28

2.4.14.... Density. 28

2.4.16.... PCB.. 28

2.4.17.... Corrosive sulphur 28

2.4.18.... Dibenzyl disulphides (DBDS) 29

2.4.19.... Passivators. 29

2.5..... In-service oil monitoring 30

2.5.1...... Uninhibited oil monitoring 30

2.5.2...... Inhibited oil monitoring 30

2.6..... Time schedule of sampling and testing in-service oil 31

2.7..... Available on-site tests 31

2.8..... Classification of operating oil 32

2.9..... Corrective actions 32

2.10... Purification. 32

2.10.1.... Physical purification 33

2.10.2.... Chemical purification (refinement) 35

2.10.3.... Substitution of additives 36

2.10.4.... Cleaning PCB contaminated oil 36

2.11... Replacing oil in electrical equipment 36

2.12... Adding passivators 37

2.13... Determining water concentration in the oil 38

References. 39

Chapter 3: Chemical Indicators

3.1..... Introduction. 42

3.2..... Insulation paper life determination 42

3.3..... Cellulose. 43

3.4..... Cellulose molecular structure 44

3.5..... Cellulosic insulation 44

3.6..... Degree of polymerization 46

3.7..... Oil impregnated insulation paper 47

3.8..... Ageing of oil impregnated insulation paper 47

3.9..... Ageing mechanism.. 48

3.9.1...... Pyrolysis. 49

3.9.3...... Oxidation. 51

3.10... Influence from acids 52

3.11... Ageing of oil 52

3.12... Oil oxidation. 53

3.13... Degradation products in oil impregnated insulation systems 53

3.14... Degradation products from cellulosic insulation 54

3.14.1.... Water 54

3.14.2.... Acids. 54

3.14.4.... Carbon oxides 55

3.14.5.... Hydrocarbons 55

3.15... Degradation products of oil 56

3.15.1.... Acids. 56

3.15.2.... Sludge. 56

3.16... Chemical indicators 56

3.17... Furan compounds 57

3.17.1.... Furans origin. 57

3.18... The relationship between DP and furans 57

3.19... Stability. 58

3.20... Furans disadvantages 59

3.21... CO₂ and CO.. 59

3.22... The combination of CO₂/C