Transformer fluid options and condition monitoring STLE Toronto Section September 2016

Transcription

1 Transformer fluid options and condition monitoring STLE Toronto Section September 2016 Products of M&I Materials Ltd.

2 Topics Covered Transformer Fluid classes & Options Comparison of Fluid Properties Fire Safety Environmental Protection Fluid Moisture Tolerance Oxidation Stability Retrofilling With Alternative Fluids Interaction of Transformer Fluids with Solid Insulation Dissolved Gas Analysis Fluid Standards

3 Transformer fluid classes & Options Products of M&I Materials Ltd.

4 Fluid Filled Transformer Electrical insulation in a transformer consists of fluid and solid materials As a state of art one can have different options of fluid and solid materials in a transformer to make the transformer fit for purpose Picture shows a general construction of a transformer

5 Fundamental purpose of the insulating materials Fluid Function as a coolant and electrical insulation Solid Function as an electrical insulation with or without a liquid As a current state of the art liquid & solid insulation combination provides the best technically adept and and economically viable solution in transformers for most applications Common fluids in transformers Mineral oils, Esters, Silicone liquid Common solid insulation materials Cellulosic Paper, Aramid, other synthetic materials

6 Fluid Classes IEC IEC has replaced previous standard IEC Classifies fluids by fire point and net calorific value Mineral oil is class O Synthetic esters class K Natural esters class K Silicone oil class K Fire Point Net Calorific Value O 300 C 1 42 MJ/kg K > 300 C 2 < 42 MJ/kg L No Measurable Fire Point 3 < 32 MJ/kg

7 Mineral Oil Chemical Structures

8 Mineral Oil from Crude Oil Typical Transformer Oil C Mineral oil is a distillation cut from crude oil which is further hydrotreated to reduce aromatics and to remove impurities such as sulphur.

9 Paraffinic and Naphthenic Mineral Oils Paraffinic Oil Contains substantial quantities of naturally occurring n-paraffins Has a relatively high pour point and may require the inclusion of additives to reduce the pour point Properties include higher resistance to oxidation, more viscous, and less volatile Paraffinic oils oxidise slower than naphthenic oils The oxidation product (or sludge) is insoluble & will precipitate at the bottom of the tank and may obstruct the transformer cooling system.

10 Paraffinic and Naphthenic Mineral Oils Naphthenic Oil Contains lower level of naturally occurring n-paraffins Has a low pour point and requires no additives to reduce the pour point Provides better viscosity characteristics Has more polar characteristics than paraffinic oil Naphthenic oil is more easily oxidised than paraffinic oil The oxidation product (sludge) in the naphthenic oil is more soluble than in paraffinic oil, hence is less likely to be precipitated in bottom of the transformer, and thus is less likely to obstruct convection circulation of the oil.

11 Additives Added to delay the oxidation of oil. Uninhibited oils: Must be free of additives to improve oxidation stability. In the USA, IEEE accept that < 0.08% inhibitor can be classified as uninhibited Inhibited oils: are insulating oils which have antioxidants

12 Synthetic Ester The building blocks for synthetic esters are alcohols and acids 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

13 Key Properties of Synthetic Ester High fire point Low pour point Biodegradability High oxidation stability Superior moisture tolerance Paper lifetime enhancement Suitable for breathing and sealed transformers Suitable for cold climates

14 Natural Ester Made from vegetable sources 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

15 Properties of Natural Ester Fluids Increased fire safety Greater environmental protection Superior moisture tolerance No corrosive sulphur Lower oxidation stability More suited to temperate climates & indoor locations Suitable for sealed systems (+ bagged conservators) High pour point Cost effective solution for managing risk

16 Applications of Ester Fluids Electrical Utility Power Distribution Retrofilling / retrofitting Wind Energy Offshore / Onshore Offshore Substation Oil & Gas Rail Traction / Trackside Underground Marine

17 Silicone Liquid Manufactured from chemicals Repeating part of structure shown in box Viscosity depends on the chain length

18 Properties of Silicone Fluids Increased fire safety Poor environmental protection - not biodegradable No corrosive sulphur High oxidation stability Suitable for breathing and sealed transformers

19 Overview of Transformer Fluid Applications Mineral Oil Silicone Liquid Synthetic Ester Natural Ester Power Transformers Traction Transformers A X B B A A A X Distribution Transformers A A A A Instrument Transformers A B B B Key: A = Largely used, B= Less commonly used, X = Currently not used

20 Comparison of Fluid Properties Products of M&I Materials Ltd.

21 Transformer Fluid 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 to -31 Breakdown Strength IEC mm (kv) >70 >50 >75 >75

22 Fire Safety Products of M&I Materials Ltd.

23 Fire Safety Advantages of Using Alternative 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 (esters) Lower installation costs Potentially lower fire protection costs Possible insurance benefits

24 Ignition Resistance Mineral Oil 3 mins Mineral Oil 4 mins Synthetic ester 3 mins Synthetic ester 70 mins

25 Environmental Protection Products of M&I Materials Ltd.

26 Environmental Protection Legislation Demonstrates social responsibility Reduced or simplified containment Reduced clear up costs for spills Potentially lower insurance premiums Preserving the planet

27 Environmental Impact of Fluids Impact can be assessed by laboratory testing OECD classifies Readily Biodegradability (at least 60% degradation in 28 days and this must happen within 10 days after a sample exceeds 10% biodegradation. Very stringent test standard It is assumed that compounds will rapidly biodegrade in aquatic environments under aerobic conditions (in the presence of micro organisms)

28 Comparison of 28-Day Biodegradation

29 Advantages of Readily Biodegradable Fluids Safer for the environment Does not persist (decomposed by living organisms) Possibility of reduced or simplified containment FM Global - larger volume before containment required for biodegradable fluids Use demonstrates commitment to social responsibility

30 Fluid Moisture Tolerance Products of M&I Materials Ltd.

31 Fluid Moisture Tolerance Moisture can ingress through headspace in breathing transformers Through leaks & during maintenance Oxidation aging of paper releases water Wet transformers Have a shorter life rate of paper aging increases with increasing moisture content Prone to dielectric faults Require maintenance

32 Moisture Content Limits (IEC)

33 Oxidation stability Products of M&I Materials Ltd.

34 Oxidation stability Oxidation Fluid degraded by reaction with Oxygen from the air Leads to increase in acid value Can increase fluid viscosity Produces sludge in mineral oil Can lead to polymerisation or gelling in natural esters Short chain acids (2-5C) due to oxidation is soluble in water and affects transformer life

35 ASTM D2112 Oxidation Stability Testing Pressurised Vessel Oxidation Test Oil + Copper Catalyst + 90psi Temperature = 140 C Time for Pressure = 65psi DOBLE Engineering USA

36 ASTM D2112 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

37 Retrofilling with Alternative Fluids Products of M&I Materials Ltd.

38 Retrofilling with Alternative Fluids Retrofilling is the replacement of the fluid in the transformer with an alternative fluid. Can be done on site. Increased fire safety - Significantly improves fluid fire point Greater environmental protection - Replaces a poor environmental fluid with a much better one Asset Life - Retrofilling also enhances moisture tolerance & extends paper life - Reduces maintenance - In particular synthetic ester is very oxidation stable and is suitable for breathing transformers

39 Pre-Retrofill Checks Used to establish if the transformer is suitable for retrofill Visual check of the transformer Check of previous oil testing results Furan analysis can give guide to paper condition

40 Interaction of Transformer Fluids with Solid Insulation Products of M&I Materials Ltd.

41 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 -

42 Solid Insulations Cellulose Most common solid insulation Wide range of applications Used at low to moderate temperatures Aramid paper More robust than cellulose Used with high temperature fluids (K class) Used in demanding applications e.g. Traction

43 Cellulose 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 (DP value)

44 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

45 Dissolved Gas Analysis with Alternative Fluids Products of M&I Materials Ltd.

46 Fault Gas Formation in Mineral Oil Bond Bond Energy kj/mol C - H 413 C - C 348 C - O 358 C = O 799 C = C 614 Si - O 368 Si - C 301 Hydrogen H + H = H - H Methane CH 3 + H = CH 4 Ethane CH 3 + CH 3 = C 2 H 6 Also C 2 H 4 (Ethylene) C 2 H 2 (Acetylene)

47 Synthetic Ester Fault Gas Formation Hydrogen H + H = H H Methane CH 3 + H = CH 4 Ethane CH 3 + CH 3 = C 2 H 6 C 2 H 4 (Ethylene) C 2 H 2 (Acetylene) Also CO (Carbon monoxide) CO 2 (Carbon dioxide)

48 Key Indicator Gasses High Energy (Temp >700 C) Acetylene C 2 H 2 Medium Energy (Temp C) Ethylene C 2 H 4, Ethane C 2 H 6 Lower Energy (Temp <300 C) Hydrogen H 2, Methane CH 4 Cellulose Degradation Carbon Monoxide CO, Carbon Dioxide CO 2 Esters also give off CO and CO 2 without paper

49 Fault Diagnosis Methods Ratio methods Rogers Ratio Doernenburg Ratio Optimised for mineral oil seem to be falling out of fashion Duval Triangle commonly used Uses C 2 H 2 + C 2 H 4 + CH 4 in triangular plot Michel Duval has published triangles for Mineral oil, silicone fluid, synthetic esters and natural esters

50 How to use the Duval Triangle PD = Partial Discharge T1 = Low thermal fault (<300 C) T2 = Medium thermal fault ( C) T3 = High thermal fault (>700 C) D1 = Low energy electrical discharge D2 = High energy electrical discharge DT = Intermediate thermal fault or electrical discharge EXAMPLE Gas ppm Ratio % C 2 H / CH / Methane Ethylene C 2 H / Total 150 TRENDING IS IMPORTANT Acetylene

51 Duval Triangles Mineral oil and synthetic ester fault boundaries have been modified

52 The Duval Triangle for Silicone and SE

53 Importance of Good Sampling Ideal sampling method is syringe with tap Gasses can be lost in transit Especially CO and H 2 Gasses can be introduced from atmosphere O 2, N 2, CO 2 Galvanic reactions can cause high H 2 in samples Galvanised fittings must be avoided on sample port

54 CO 2 / CO Ratio With MINERAL OIL Can be used to indicate if cellulose is involved in fault. CO 2 /CO ratio 3-11 is normal, average around 7 <3 indicates a local high temperature fault A large quantity of CO produced in degradation of paper >11 indicates general overheating With ESTERS More care is needed as esters can produce CO and CO 2 without paper Cigre WG 47 (M.Duval) looking at this more closely

55 Conclusions DGA can be performed using non mineral oils (Non-MO) The range of gases from Non-MO are the same as for MO DGA key gasses are similar for esters and mineral oil Duval Triangle fault boundaries changed for each fluid type Synthetic esters, Natural esters. CO/CO 2 ratios need extra care

56 Fluid Standards Products of M&I Materials Ltd.

57 Fluid Standards Mineral Oil IEC New Mineral Oil IEC In Use Mineral Oil Synthetic Ester IEC New Ester Fluids IEC In Use Ester Fluids Natural Ester IEC New Ester Fluids American Standard ASTM D Silicone Liquid IEC New Silicone Liquid IEC In Use Silicone Liquid

58 Q & A and Discussions Manjunath Ramakrishna M&I Materials Hibernia Way, Trafford Park Manchester M32 0ZD United Kingdom Products of M&I Materials Ltd.