Experiences in Service with New Insulating Liquids

Transcription

1 Experiences in Service with New Insulating Liquids Cigre Brochure 436 A2 & D1 JOINT COLLOQUIUM, KYOTO 2011 R.Martin Cigre Kyoto Sept 2011 Experiences in service with new insulation liquids - R.Martin Slide 1

2 Content Introduction Insulating fluids - their properties & applications Physical properties of fluids as a function of temperature Fire safety Moisture behaviour Environmental behaviour Oxidation stability Design considerations In service testing methods Diagnostic testing DGA Fluid standards Retrofilling with alternative s to mineral oil Use of fluids with solid insulation Impregnation behaviour Cigre Kyoto Sept 2011 Experiences in service with new insulation liquids - R.Martin Slide 2

3 Cigre Kyoto Sept 2011 Experiences in service with new insulation liquids - R.Martin Slide 3

4 Insulating Fluids Properties and Applications Cigre Kyoto Sept 2011 Experiences in service with new insulation liquids - R.Martin Slide 4

5 Insulating Fluids Mineral Oil Synthetic Ester Natural Ester Silicone Liquid Newer Fluids Cigre Kyoto Sept 2011 Experiences in service with new insulation liquids - R.Martin Slide 5

6 Mineral Oil Mixture of different hydrocarbon structures Refined from crude oil Most widely used fluid in transformers Can be inhibited or uninhibited Cigre Kyoto Sept 2011 Experiences in service with new insulation liquids - R.Martin Slide 6

7 Silicone Liquid Manufactured from chemicals Repeating part of structure shown in box Viscosity depends on the chain length Cigre Kyoto Sept 2011 Experiences in service with new insulation liquids - R.Martin Slide 7

8 Synthetic Ester Manufactured by reaction of acids with an alcohol Can have 2 to 4 ester groups, depending on raw materials Ester linkage in boxes All R chains in synthetic esters are saturated for oxidation stability Cigre Kyoto Sept 2011 Experiences in service with new insulation liquids - R.Martin Slide 8

9 Natural Ester Made from seed oils Triglyceride with three ester groups R chains can be saturated or unsaturated Viscosity depends on saturation of carbon chains Oxygen stability depends on saturation of carbon chains Cigre Kyoto Sept 2011 Experiences in service with new insulation liquids - R.Martin Slide 9

10 Properties Property Mineral Oil Silicone Liquid Synthetic Ester Natural Ester Flash Point C 160 >300 >250 >300 Fire Point C 170 >350 >300 >350 Fire Classification O K K K Oxidation Stability Medium High High Low Moisture Tolerance Low Low V.High High Biodegradability Low Low Readily Biodegradable Readily Biodegradable Corrosive Sulphur Possible None None None Pour Point C - 50 < to -25 Breakdown Strength IEC mm (kv) >70 >50 >75 >75 Cigre Kyoto Sept 2011 Experiences in service with new insulation liquids - R.Martin Slide 10

11 Applications Mineral oil Silicone fluid Synthetic ester Vegetable oils (natural ester) Power transformers A X B B Traction transformers A A A X Distribution transformers A A A A Instrument transformers A X X X (Key: A = Largely used, B= Less commonly used, X = Currently not used) Cigre Kyoto Sept 2011 Experiences in service with new insulation liquids - R.Martin Slide 11

12 Physical Properties of Insulating Fluids as a Function of Temperature Cigre Kyoto Sept 2011 Experiences in service with new insulation liquids - R.Martin Slide 12

13 Kinematic Viscosity 300 Viscosity cst GBN Mineral Oil 561 Silicone Fluid Low viscosity silicone fluid Midel 7131 FR3 Biotemp Temperature (C) Cigre Kyoto Sept 2011 Experiences in service with new insulation liquids - R.Martin Slide 13

14 Log Viscosity Plots 3 10 GBN Mineral oil Log 10 Kinematic viscosity Silicone fluid Low viscosity silicone fluid Midel 7131 FR3 Biotemp Temperature (C) Cigre Kyoto Sept 2011 Experiences in service with new insulation liquids - R.Martin Slide 14

15 Density Synthetic ester Mineral Oil Natural Ester Silicone Liquid 940 Density (kg/m 3 ) Temperature ( C) Cigre Kyoto Sept 2011 Experiences in service with new insulation liquids - R.Martin Slide 15

16 Specific Heat Capacity 2500 Specific Heat Capacity (J/ kg K) Synthetic ester Mineral Oil Natural Ester Silicone Liquid Temperature ( C) Cigre Kyoto Sept 2011 Experiences in service with new insulation liquids - R.Martin Slide 16

17 Thermal Conductivity Thermal Conductivity (W/m K) Synthetic ester Mineral Oil Natural Ester Silicone Liquid Temperature ( C) Cigre Kyoto Sept 2011 Experiences in service with new insulation liquids - R.Martin Slide 17

18 Fire Safety Cigre Kyoto Sept 2011 Experiences in service with new insulation liquids - R.Martin Slide 18

19 Why Increase Fire Safety? Mineral oil fires are common occurrence Risk to human life Extremely costly in terms of damage and clean up ( m s) Knock on effects e.g. Blackouts Down-time cost Transformer replacement Increased insurance premiums Damage to reputation Smoke hazard to victims and rescue service Cigre Kyoto Sept 2011 Experiences in service with new insulation liquids - R.Martin Slide 19

20 Significance of Flash and Fire Point Flash Point - temperature at which vapour ignites, but will not sustain burning when flame is removed Fire Point - temperature at which vapour ignites and sustains burning for at least 5 seconds when source of ignition is removed Class Fire Point C Class Net Calorific Value O MJ/kg K >300 2 <42MJ/kg L No Measurable Fire Point 3 <32MJ/kg Fluid Fluid Flash Point C Fluid Fire Point C Class Mineral Oil O Silicone Liquid >300 >350 K3 Low Viscosity Silicone Fluid K3 Natural Ester >300 >350 K2 Synthetic Ester >250 >300 K3 Cigre Kyoto Sept 2011 Experiences in service with new insulation liquids - R.Martin Slide 20

21 Fire Safety Advantages of Using K Class Fluids High degree of fire safety Fluids extremely difficult to ignite Very low risk of pool fires (none reported) Very low risk of smoke hazard Lower installation costs Possible insurance benefits Cigre Kyoto Sept 2011 Experiences in service with new insulation liquids - R.Martin Slide 21

22 Moisture Behaviour Cigre Kyoto Sept 2011 Experiences in service with new insulation liquids - R.Martin Slide 22

23 Where Moisture Originates The atmosphere Can ingress through headspace in breathing transformers Through leaks in sealed units During maintenance The paper As paper ages due to oxidation it releases water Cigre Kyoto Sept 2011 Experiences in service with new insulation liquids - R.Martin Slide 23

24 Why is Moisture Tolerance Important? Wet transformers Have a shorter life Prone to dielectric faults Require maintenance Can suffer from condensation problems (free water) Dielectric Strength Withstand strength of fluid and paper decreases with increasing moisture Rate of paper ageing Ageing rate increases with increasing moisture content Condensation Mineral oil can release water when going from hot running to cold Cigre Kyoto Sept 2011 Experiences in service with new insulation liquids - R.Martin Slide 24

25 Superior Moisture Tolerance with Esters Fluid Mineral Oil Silicone Liquid Natural Ester Synthetic Ester Ester Linkages Water Saturation at Ambient (ppm) Esters are able to absorb much larger quantities of water than mineral oil through hydrogen bonding Cigre Kyoto Sept 2011 Experiences in service with new insulation liquids - R.Martin Slide 25

26 Moisture Saturation Limit Moisture Saturation [ppm] Synthetic MIDEL 7131 Ester Mineral Oil Natural Ester Silicone Liquid Temperature [ C] Ref: H. Borsi Schering Institute Cigre Kyoto Sept 2011 Experiences in service with new insulation liquids - R.Martin Slide 26

27 Breakdown Voltage vs. 20 C Breakdown Voltage (kv) Mineral Oil Natural Ester MIDEL 7131 Synthetic Ester 10 Silicone Liquid Moisture Content (ppm) Cigre Kyoto Sept 2011 Experiences in service with new insulation liquids - R.Martin Slide 27

28 Relative Moisture Content Defined by the equation below W rel W abs = x 100 W sat W abs Moisture content of fluid in ppm W sat Saturation limit at a given temperature Gives an indication of safety margin Midel IEC limit 400ppm, W C = 15% Mineral Oil IEC limit 30ppm, W C = 55% Cigre Kyoto Sept 2011 Experiences in service with new insulation liquids - R.Martin Slide 28

29 Breakdown Voltage vs. Relative Moisture 100 Breakdown Voltage (kv) IEC Breakdown Voltage Limit Mineral Oil Synthetic ester Natural Ester 1 Natural Ester 2 Natural Ester 3 Silicone Liquid Relative Moisture Content (%) Ref : S Tenbohlen, Stuttgart Cigre Kyoto Sept 2011 Experiences in service with new insulation liquids - R.Martin Slide 29

30 Solid Insulation H O H O O H O O H O H O O H O O H O H O O H O n-2 O H Chemical Structure of Cellulose O H Cellulose pressboard and paper is the most commonly used solid insulation in fluid filled transformers Cellulose is a natural polymer made up of glucose rings linked together in chains After drying new cellulose has 1000 to 1200 glucose rings in each chain the DP value is equal to the number of rings Cigre Kyoto Sept 2011 Experiences in service with new insulation liquids - R.Martin Slide 30

31 Cellulose Degradation in Transformers Paper strength is often indicated by Degree of Polymerisation or DP value Water attacks the links connecting glucose units in cellulose reducing the polymer chain length As paper ages the DP value reduces, through depolymerisation Depolymerisation of paper weakens the winding mechanically Once the winding is weakened short circuit stress can cause mechanical failure Reducing the rate of depolymerisation extends the life of the transformer Increasing moisture & temperature accelerates ageing of paper Short circuit faults will cause failure Cigre Kyoto Sept 2011 Experiences in service with new insulation liquids - R.Martin Slide 31

32 Moisture Distribution Paper Insulating Fluid Synthetic Ester At 60 C and 200ppm the cellulose contains 1.4% water Mineral Oil At 60 C and 20ppm the cellulose moisture is 2,6% Cigre Kyoto Sept 2011 Experiences in service with new insulation liquids - R.Martin Slide 32

33 Environmental Behaviour Cigre Kyoto Sept 2011 Experiences in service with new insulation liquids - R.Martin Slide 33

34 Why Greater Environmental Protection? Legislation Corporate Social Responsibility Cost of containment for fluid Clear up costs for spills Recycling Potentially lower insurance premiums e.g. FM Global Preserving the Planet Cigre Kyoto Sept 2011 Experiences in service with new insulation liquids - R.Martin Slide 34

35 Biodegradation Biodegradation is a measure of how readily fluids are consumed (removed) by natural microbes Biodegradation Recognised measurement of environmental behaviour Environmentally friendly fluids are very biodegradable Readily Biodegradable is the best classification Standard & stringent measurement methods Cigre Kyoto Sept 2011 Experiences in service with new insulation liquids - R.Martin Slide 35

36 Comparative Biodegradation Rates Biodegradation (%) Natural Ester Synthetic MIDEL 7131 Ester Mineral Oil Silicone Liquid Time (Days) Cigre Kyoto Sept 2011 Experiences in service with new insulation liquids - R.Martin Slide 36

37 Comparison of 28-Day Biodegradation Mineral Oil Synthetic Ester Natural Ester Silicone Liquid 28-Day Biodegradation 9.7% 89% 94% 3.1% OECD Status Nonbiodegradable Nonbiodegradable Readily biodegradable Readily biodegradable IEC Not tested to 301 C/F Fully biodegradable Fully biodegradable Not tested to 301 C/F Cigre Kyoto Sept 2011 Experiences in service with new insulation liquids - R.Martin Slide 37

38 Advantages of Readily Biodegradable Fluids Safer for the environment Does not persist Possibility of reduced bunding FM Global - larger volume before containment required for biodegradable fluids Use demonstrates commitment to social responsibility Cigre Kyoto Sept 2011 Experiences in service with new insulation liquids - R.Martin Slide 38

39 Oxidation Stability Cigre Kyoto Sept 2011 Experiences in service with new insulation liquids - R.Martin Slide 39

40 Importance of Oxidation Stability Transformer fluids are expected to perform reliably for many years & for some oils oxidation can seriously affect dependability Critical for breathing transformers where fluid is exposed to oxygen from the air Oxidation degrades the performance of transformer fluids Increases acid content Can increase viscosity Produces sludge in mineral oil Can lead to gelling in natural esters At high temps the effects are accelerated & even in sealed systems, oil can age Cigre Kyoto Sept 2011 Experiences in service with new insulation liquids - R.Martin Slide 40

41 Oxidation Stability Test Pressurised Vessel Oxidation Test Oil + Copper Catalyst + 90psi Temperature = 140 C Time for Pressure = 65psi DOBLE Engineering USA ASTM D2112 Cigre Kyoto Sept 2011 Experiences in service with new insulation liquids - R.Martin Slide 41

42 Oxidation Stability Test Results Silicone fluids > 450 Synthetic esters 421 RBOT Test (Mins) Mineral oils 300 High Oleic Natural esters Typical Natural esters < 40 0 Fluid Types Cigre Kyoto Sept 2011 Experiences in service with new insulation liquids - R.Martin Slide 42

43 Natural Ester Oxidation Susceptibility The unsaturated parts of the chain, circled, are available for oxidation Mono-unsaturated (oleic) = one double bond in chain Di-unsaturated = two double bonds in chain Poly-unsaturated = three double bonds in chain Saturated oils have a higher pour point Cigre Kyoto Sept 2011 Experiences in service with new insulation liquids - R.Martin Slide 43

44 Comparative Fatty Acid Chain Structures and Oxidation Steric (18:0) Oleic (18:1) Linoleic (18:2) Linolenic (18:3) Relative rates of oxidation Cigre Kyoto Sept 2011 Experiences in service with new insulation liquids - R.Martin Slide 44

45 Comparison of Natural Esters 100% 90% 80% Poly Mono Saturated Oil Melt Point C 70% Coconut 25 60% 50% 40% HO Sun Rapeseed % Soya % 10% 0% Coconut HO Sun Rapeseed Soya Sunflower Linseed Oxygen Stable % Fatty Acids Oxygen Unstable Sunflower Linseed Solid Liquid Cigre Kyoto Sept 2011 Experiences in service with new insulation liquids - R.Martin Slide 45

46 Design Considerations Cigre Kyoto Sept 2011 Experiences in service with new insulation liquids - R.Martin Slide 46

47 Properties for Thermal Design Viscosity Measure of fluid s resistance to flow, (how thick is it) A low value is desirable for cooling Specific Heat Capacity Gives indication of fluid s ability to absorb energy without increasing in temperature Thermal Conductivity Indicates a fluid s ability to conduct heat A higher figure is better for cooling Expansion Coefficient Expansion of fluid per degree Kelvin rise in temperature Density Variation of density affects siphoning force in naturally cooled systems, directly related to Thermal Expansion Coefficient Pour Point Expansion Coefficient Important for cold starts Cigre Kyoto Sept 2011 Experiences in service with new insulation liquids - R.Martin Slide 47

48 Properties for Electrical Design Considerations include Operating voltage and power rating Operating load pattern Operating temperature range Electrical stresses present Fluid considerations Breakdown voltage Partial discharge behaviour Impulse behaviour pour point Cigre Kyoto Sept 2011 Experiences in service with new insulation liquids - R.Martin Slide 48

49 Other Design Considerations Whether the transformer is sealed or free breathing Type of cooling (forced or natural) Operating temperatures Hazards fire and environmental Type of solid insulation (cellulose or aramid) Other materials present (mat comp) Cigre Kyoto Sept 2011 Experiences in service with new insulation liquids - R.Martin Slide 49

50 In Service Testing Methods Cigre Kyoto Sept 2011 Experiences in service with new insulation liquids - R.Martin Slide 50

51 Typical Parameters for Fluid Condition Monitoring Appearance The colour of the fluid gives a quick indication of condition Neutralisation Value / Acid Value Acid content is a key indicator of fluid ageing Acid value will increase with ageing Water Content Measure of the dissolved water in the fluid AC Breakdown Voltage Measured at various gap sizes, depending on the standard method chosen, typically in the range 1-2.5mm A higher figure is better Dielectric Dissipation Factor Measure of the dielectric loss in the fluid. A lower figure is better, although has little impact on transformer operation Flash Point Measure of temp at which fluid vapours ignite, but extinguish when the source of ignition is removed Fire Point Measure of temp at which fluid vapours ignite and sustain burning for 5s when the source of ignition is removed Cigre Kyoto Sept 2011 Experiences in service with new insulation liquids - R.Martin Slide 51

52 Fluid Testing Methods Properties Mineral Oil Synthetic Ester Natural Ester Silicone Fluid Acidity IEC / IEC ASTM D974 IEC / IEC ASTM D974 IEC Appearance ISO 2049 ISO 2049 ASTM D1524 Visual, ISO 2049 Breakdown Voltage IEC / ASTM D1816 IEC ASTM D877 / ASTM D1816 IEC Colour ISO2049 / ISO 2211 / ASTM D1500 ISO 2211 ASTM D1500 ISO 2211 Corrosive Sulphur IEC / ASTM D1275 ASTM D1275 Dielectric Dissipation Factor IEC / IEC ASTM D924 IEC ASTM D924 IEC Density ISO 3675 / ISO / ASTM D1298 ISO 3675 ASTM D1298 ISO 3675 DGA Analysis IEC ASTM D2945 / ASTM D3284 / ASTMD3612 Fire Point ISO 2592 / ASTM D92 ISO 2592 ASTM D92 ISO 2592 Flash Point ISO 2719 / ISO 2592 / ASTM D92 ISO 2719 / ISO 2592 ASTM D92 ISO 2719 / ISO 2592 Furanic Compounds IEC / ASTM D5837 Gassing Tendency IEC / ASTM D2300 IEC ASTM D2300 IEC Key: Most commonly used IEC method / Most commonly used ASTM method / Not quoted but generally used Cigre Kyoto Sept 2011 Experiences in service with new insulation liquids - R.Martin Slide 52

53 Fluid Testing Methods.Continued Properties Mineral Oil Synthetic Ester Natural Ester Silicone Liquid Interfacial Tension ISO 6295 / ASTM D971 ASTM 971 ASTM 971 Kinematic Viscosity ISO 3104 / ASTM D445 ISO 3104 ASTM D445 ISO 3104 Kinematic Viscosity at low T IEC Lightning Impulse Breakdown (IEC 60897) / ASTM D3300 ASTM D3300 Oxidation Stability IEC / IEC / ASTM D2112 / ASTM D2440 IEC PCB Content IEC / ASTM D4059 ASTM D 4059 Permittivity IEC / ASTM D924 IEC ASTM D924 IEC Pour Point ISO 3016 ASTM D97 ISO 3016 ASTM D97 ISO 3016 Refractive Index ISO 5661 ISO 5661 ISO 5661 Resistivity IEC IEC ASTM D1169 IEC Specific Heat ASTM D2766 ASTM D2766 Stray gassing CIGRE Brochure n 296 Thermal Conductivity ASTM D2717 ASTM D2717 Thermal Expansion Coef. ASTM D1903 ASTM D1903 Visual Examination ASTM D1524 ASTM D1524 Water Content IEC / ASTM D1533 IEC ASTM D1533 IEC Cigre Kyoto Sept 2011 Experiences in service with new insulation liquids - R.Martin Slide 53

54 Diagnostic Testing - DGA Cigre Kyoto Sept 2011 Experiences in service with new insulation liquids - R.Martin Slide 54

55 Dissolved Gas Analysis DGA is still possible with esters & silicone fluid The same key gasses can be used to identify faults Acetylene = arcing Hydrogen = partial discharge Methane, Ethane, Ethylene = thermal fault Interpretation methods may need modification New Duval triangle available Ratio methods may give misleading diagnosis Cigré group due to publish in near future IEEE team has been set up to provide further guidance Cigre Kyoto Sept 2011 Experiences in service with new insulation liquids - R.Martin Slide 55

56 Cigre Kyoto Sept 2011 Experiences in service with new insulation liquids - R.Martin Slide 56

57 The Duval Triangle for Non Mineral Oils PD = partial discharges D1 = discharges of low energy D2 = discharges of high energy T1 = thermal faults of temp <300ºC T2 = thermal faults of temp 300ºC < T < 700ºC T3 = thermal faults of temp >700ºC DT = mixtures of electrical / thermal faults The Triangle coordinates corresponding to DGA results in ppm Source: Michel Duval IEEE Electrical Insulation Magazine 2008 Cigre Kyoto Sept 2011 Experiences in service with new insulation liquids - R.Martin Slide 57

58 The Duval Triangle for Silicone and Midel Cigre Kyoto Sept 2011 Experiences in service with new insulation liquids - R.Martin Slide 58

59 The Duval Triangle for FR3 and Biotemp Cigre Kyoto Sept 2011 Experiences in service with new insulation liquids - R.Martin Slide 59

60 Fluid Standards Cigre Kyoto Sept 2011 Experiences in service with new insulation liquids - R.Martin Slide 60

61 Fluid Standards Mineral Oil IEC New Mineral Oil IEC / BS5730 In Use Mineral Oil Synthetic Ester IEC New Ester Fluids IEC In Use Ester Fluids Silicone Liquid IEC New Silicone Liquid IEC In Use Silicone Liquid Natural Ester No IEC standards exist American Standard ASTM D Cigre Kyoto Sept 2011 Experiences in service with new insulation liquids - R.Martin Slide 61

62 Retrofilling with Alternatives to Mineral Oil Cigre Kyoto Sept 2011 Experiences in service with new insulation liquids - R.Martin Slide 62

63 Why Retrofill with Alternatives to Mineral Oil Retrofilling is the replacement of fluid in a transformer Why? Circumstances change Area built up Population density increase Cost of maintaining other protection measures Regulation changes Benefits Considerably improves fire & environmental safety Increases moisture tolerance May have insurance benefits Both synthetic & natural esters are fully miscible with mineral oil Cigre Kyoto Sept 2011 Experiences in service with new insulation liquids - R.Martin Slide 63

64 Miscibility of Transformer Fluids Miscibility gives an indication of the compatibility between fluids Non miscible fluids will separate into two distinct layers It is important to note that although mineral oil and silicone liquid are miscible a mixture may cause foaming under vacuum Synthetic Ester Mineral Oil Natural Ester Silicone Liquid Synthetic Ester - Fully Miscible Fully Miscible Not Miscible Mineral Oil Fully Miscible - Fully Miscible Miscible Natural Ester Fully Miscible Fully Miscible - Not Miscible Silicone Liquid Not Miscible Miscible Not Miscible - Cigre Kyoto Sept 2011 Experiences in service with new insulation liquids - R.Martin Slide 64

65 Use of Fluids with Solid Insulation Cigre Kyoto Sept 2011 Experiences in service with new insulation liquids - R.Martin Slide 65

66 Use of Different Fluids with Solid Insulations Cellulose Most common solid insulation Uses at low to moderate temperatures Wide range of applications Aramid paper More robust than cellulose Used with high temperature fluids (K class) Used in demanding applications e.g. Traction Cigre Kyoto Sept 2011 Experiences in service with new insulation liquids - R.Martin Slide 66

67 Fluid Solid Insulation Impregnation Rates Height of oil (m Mineral oil Synthetic est er Nat ural est er Square root of time (s^0.5) Height of oil (m M ineral oil Sy nthetic ester Natural ester Square root of time (s ^0.5) Capillary Action 20 C Capillary Action 60 C Source : Prof Z Wang, University of Manchester, UK Cigre Kyoto Sept 2011 Experiences in service with new insulation liquids - R.Martin Slide 67

68 Fluid Solid Insulation Impregnation Rates 100% Impregnation length (mm) Mineral oil (20 degree C) Synthetic ester (60 degree C) Natural ester (60 degree C) Time (minute) 80% 60% 40% 20% 0% Testing has shown that at 60 C synthetic ester impregnation rate is equivalent to mineral oil at 20 C Source : Prof Z Wang, University of Manchester, UK Cigre Kyoto Sept 2011 Experiences in service with new insulation liquids - R.Martin Slide 68

69 Summary The new fluids have been in service for some years now Much is already known about their properties Research continues to gain further insights as to their uses There are many applications where they are preferable to mineral oil for a variety of reasons. Cigre Kyoto Sept 2011 Experiences in service with new insulation liquids - R.Martin Slide 69

70 Thank-you for listening Dr. Russell Martin Technical Manager for M&I Materials Ltd Tel: +44 (0) Cigre Kyoto Sept 2011 Experiences in service with new insulation liquids - R.Martin Slide 70