POWER TRANSFORMER OIL PROCESSING SPX TRANSFORMER SOLUTIONS, INC.

Transcription

1 Regional Technical Seminar POWER TRANSFORMER OIL PROCESSING SPX TRANSFORMER SOLUTIONS, INC. June 20, 2018

2 Agenda 1. Oil Processing Theoretical Information Transformer Drying Theory Insulation Media 2. Equipment 3. Vacuum Filling Instructions Preliminary processes Oil Filled Transformers Vacuum filling processes 4. Maintenance Oil Processing 5. Transformer Storage Considerations SPX Transformer Solutions, Inc. June 20,

3 Glossary of Common Terminology Degasify Removal of air and other gases from transformer oil and transformer by applying high vacuum Dehydrate Removal of water from the transformer oil and transformer by high vacuum SPX Transformer Solutions, Inc. June 20,

4 Transformer Drying Theory Degasifying Oil absorbs air up to its saturation point (about 12% by volume) by exposure to air Benefits of Degasifying Removal of oxygen reduces oxidation deterioration of oil Degasified oil better impregnates cellulose insulation Remaining bubbles trapped under surfaces as oil fill progresses are absorbed into the oil Removal of any combustible gases generated during transformer use Improves insulating quality of the oil (air is a better conductor than oil) SPX Transformer Solutions, Inc. June 20,

5 Transformer Drying Theory Dehydration - Importance of Removing Water from the Insulation If water is removed from the oil only: a large percentage of the total water in the system will still remain After the transformer is returned to service, water in the insulation will migrate to the drier oil until equilibrium is met and the transformer will test wet The rate of aging of the cellulose materials is directly proportional to the water content. That is if water content is doubled from 1 to 2 percent, the life is halved. Low water content of the solid insulation permits greater extremes in temperature cycling without impairing the dielectric integrity of the system. SPX Transformer Solutions, Inc. June 20,

6 Transformer Drying Theory Dehydrating At atmospheric pressure, you must heat the water in the transformer to higher than 212 Deg F (100 Deg C) to boil it off. When lowering the pressure by pulling vacuum, we can boil the water off without heating it at all (as long as it s above freezing) SPX Transformer Solutions, Inc. June 20,

7 Transformer Drying Theory Why Add Heat For the water in the transformer to turn into vapor (change phase) heat is required just to allow the phase change. The steam leaving the transformer takes this heat with it. SPX Transformer Solutions, Inc. June 20,

8 Transformer Drying Theory Why We Add Heat The heat required for the phase change comes from the surrounding oil and transformer parts. As heat moves from the oil into the water, the temperature of the oil and transformer drops. Therefore replacement heat is added by continuously reheating the oil and pumping it into the transformer. If the heat is not replaced, eventually freezing can occur. SPX Transformer Solutions, Inc. June 20,

9 Insulating Fluids

10 Transformer Oil Purpose of Insulating Oil To provide a dielectric insulation between sources of voltage and ground. To provide cooling to the transformer windings. Contaminants in the oil reduce its ability to perform these two essential functions. SPX Transformer Solutions, Inc. June 20,

11 Transformer Oils Various fluids are used in transformers and electrical components. They all have a tendency to absorb moisture and air when exposed to atmosphere. Inadvertent mixing of one oil type with another can cause severe foaming under vacuum. SPX Transformer Solutions, Inc. June 20,

12 Transformer Oils Some of the Major Transformer Oil Types Mineral Oil R-Temp (higher viscosity) Silicone based oil Natural Ester Fluid SPX Transformer Solutions, Inc. June 20,

13 Equipment

14 Equipment Requirements The purpose of vacuum purification equipment is to Remove water and gas vapors from solid insulation within the transformer Reduce the moisture content of the insulating fluid Remove solid particulate from the fluid Reduce soluble gasses from the insulating fluid SPX Transformer Solutions, Inc. June 20,

15 Equipment Requirements Equipment performance must be capable to Reduce total gas content to less than 0.2% Lower dissolved water content to less than 10 PPM Remove 96% of all particles greater than the nominal pore size of discharge filter Operate at temperatures ranging from 50 F to 180 F Achieve flow rate of 1200 GPH Achieve blanking pressure of less than 50 microns SPX Transformer Solutions, Inc. June 20,

16 Vacuum Oil Purification Equipment SPX Transformer Solutions, Inc. June 20,

17 Oil Processing Equipment Vacuum Dehydration Water is removed from the oil by: Spreading into a thin film and exposing it to vacuum. Water in the oil will boil at the low pressure for the same reasons discussed earlier. Water vapor is then pumped away by the vacuum pumps. The higher the vacuum, the better the degree of water removal. SPX Transformer Solutions, Inc. June 20,

18 Oil Processing Equipment Vacuum Degasification Gases are removed from the oil by: Spreading into a thin film and exposing it to vacuum. Gas in the oil will flow out to the low pressure much like a soda with the lid removed. Gases are then pumped away by the vacuum pumps. The higher the vacuum, the better the degree of gas removal. SPX Transformer Solutions, Inc. June 20,

19 Oil Processing Equipment Gas Ballast Water vapor and oil mist can condense in the vacuum pump during compression When handling wet oil or vacuum drying a transformer, admitting air through the gas ballast on the pump: Extends vacuum pump oil life Extends vacuum pump life Reduces pump efficiency slightly at high vacuum SPX Transformer Solutions, Inc. June 20,

20 Oil Processing Equipment Cold Trap Dry Ice and Acetone / Liquid Nitrogen Can be mounted on top of transformer Uses either liquid nitrogen or a slurry or dry ice and acetone to cool the thimble. Water freezes to the thimble and therefore can be collected for measurement. Protects vacuum pumps from water contamination and makes them more efficient since water is removed from the air stream before going through the pump. SPX Transformer Solutions, Inc. June 20,

21 Oil Processing Equipment Cascade Cold Trap Cascade Cold Trap Usually mounted in the trailer, in a separate trailer or sits on the ground. Uses electric power and refrigeration to chill freeze plates. Water freezes to the plates providing the same benefits as the previous trap but without need for liquid N2, dry ice or acetone. Heated defrosting allows rapid ice thawing and speedy measurement. SPX Transformer Solutions, Inc. June 20,

22 Oil Processing Equipment Mechanical Filtration Solid Particles are removed from the oil by: Passing the oil through treated paper elements that have a pore size that allows the oil to pass through but stops solid particles larger than the pore size. These elements are typically disposable and are replaced when they begin to plug with trapped particles. SPX Transformer Solutions, Inc. June 20,

23 Oil Processing Equipment Fullers Earth Treatment Sludge is removed from the oil by: Flowing hot oil that has already been dehydrated through a bed of bulk fullers earth. Sludge particles are too small to be filtered with paper filters. Fullers earth removes these and other polar contaminants by adsorption which is the attraction of polar contaminants and release of non-polar compounds. SPX Transformer Solutions, Inc. June 20,

24 Oil Processing Equipment Fullers Earth Treatment Acid is removed from the oil by: Flowing hot oil that has already been dehydrated through a bed of bulk fullers earth. The amount of fullers earth that is required to alter the Neutralization number from a given value back to within specification can be estimated from this chart. SPX Transformer Solutions, Inc. June 20,

25 Oil Processing Theory Fullers Earth Treatment Oil color is corrected by: Flowing hot oil that has already been dehydrated through a bed of bulk fullers earth. Color, Acid Number and IFT are related and are all corrected with fullers earth. SPX Transformer Solutions, Inc. June 20,

26 Equipment Requirements Beyond the vacuum purification system, other required material include Dew pointer Oil test equipment Vacuum gauges Vacuum and oil hoses Oil storage tanks Miscellaneous pipe fittings SPX Transformer Solutions, Inc. June 20,

27 Oil Processing Procedures

28 Preliminary Processes Prior to beginning vacuum filling operations, some items must be verified Setup Recommendation Determination of insulation moisture content Verification of tank leakage rates Field dry out methods Low ambient processing SPX Transformer Solutions, Inc. June 20,

29 Vacuum Preparations When preparing for vacuum filling operations, there are several recommendations. Complete preliminary testing Ground transformer tank, storage tanks, purification unit, and bushing terminals Disconnect any bushing terminations Cover transformer cover with tarp Isolate all devices not rated for vacuum Balance pressure on terminal boards or barriers Leave mechanical relief device in position SPX Transformer Solutions, Inc. June 20,

30 How Do We Know When the Transformer is Dry? Dryness measurement methods Vapor Pressure Power Factor Rate of Water Collection in a Cold Trap Water Content of the Oil Dewpoint SPX Transformer Solutions, Inc. June 20,

31 Transformer Dryness Determination Vapor Pressure measurement consists of isolating the transformer while under vacuum and monitoring vacuum decay over time (often 30 minutes) then using a Piper Chart to estimate water content. Pros and Cons Useful because can be made while a transformer is being processed using vacuum gauges. The measurement is an average for the entire system which may not be a good indicator if the system is not in equilibrium Not always a good indicator of the dryness of the most inaccessible locations in the insulation. SPX Transformer Solutions, Inc. June 20,

32 Transformer Dryness Determination SPX Transformer Solutions, Inc. June 20,

33 Transformer Dryness Determination Power Factor has been used for many decades to assess the drying process of transformers using low voltage test or by the use of probes and models to assess the condition of the solid insulation. Pros and Cons Can be used for acceptance testing and at completion of field drying after oil filling to ensure a dry unit. Can be used to detect pockets of water that may be deeply imbedded that may be missed by other methods that rely on equilibrium conditions to be accurate. SPX Transformer Solutions, Inc. June 20,

34 Transformer Dryness Determination Rate of Water Collection in a Cold Trap The Cold Trap method involves measuring the amount of water collected in a trap over a four-to-six hour period and the amount of water collected per hour is calculated. If the amount of insulation and its initial moisture content are known, the amount of water removed can provide a sense of the insulation dryness. Pros and Cons Sometimes initial dryness and mass of insulation is difficult to ascertain. Must have a cold trap available that efficiently traps the majority of the water so it can be measured. Collecting the water in a trap prevents it from collecting in the vacuum pump. SPX Transformer Solutions, Inc. June 20,

35 Transformer Dryness Determination Moisture Equilibrium Curve Water Content of the Oil is typically determined using a Karl Fischer tester or Panametrics hygrometer. Pros and Cons Requires equilibrium conditions. The operating temperature has a tremendous effect on the water content of the oil, and therefore, PPM values may be inadequate to determine the overall dryness of the insulation system. SPX Transformer Solutions, Inc. June 20,

36 Moisture Equilibrium Curve Water in the transformer will seek equilibrium throughout the entire insulation system including the oil and the insulation Data shows that there is a relationship between the amount of water in the oil and the amount in the paper insulation Although this relationship exists, the paper has a higher tendency to hold water than the oil so more of the water resides there. SPX Transformer Solutions, Inc. June 20,

37 Transformer Dryness Determination Dew Point measurement of the gas inside the transformer is used to provide an estimate of the average surface water content of the insulation after reaching steady state (equilibrium) conditions. Pros and Cons Requires equilibrium conditions. Is done without oil in the transformer so must be done on a new unit or after vacuum drying a unit. SPX Transformer Solutions, Inc. June 20,

38 Insulation Moisture Content Dew point measurement Introduce dry gas and stand idle for hours Measure dew point of gas Record tank pressure Record insulation temperature Utilize Pieper curve information to calculate moisture present Acceptance range is less than 1.0% SPX Transformer Solutions, Inc. June 20,

39 Calculation of Percent Moisture Tank pressure = 3 PSI Gas Temperature = 31 C Dewpoint of Gas = -30 C Insulation Temperature = 31 C What is the percent moisture? SPX Transformer Solutions, Inc. June 20,

40 Dewpoint V C = V P ( T P ) 14.7 V C = 300 ( ) 14.7 V C = SPX Transformer Solutions, Inc. June 20,

41 Dewpoint Moisture content is.9%. SPX Transformer Solutions, Inc. June 20,

42 Field Dry Out Methods There are multiple methods for field drying of a transformer if the moisture content is found to be above an acceptable limits. Vacuum Vacuum with Hot Air Short circuit and Vacuum Vacuum with Hot Oil SPX Transformer Solutions, Inc. June 20,

43 Transformer Dryout Method Vacuum Good method for removing small amounts of residual moisture Transformer is subjected to high vacuum and held for a period of time Cold traps can be used in vacuum line to measure moisture extraction Vacuum with Hot Air Efficiency of method is increased at higher temperatures SPX Transformer Solutions, Inc. June 20,

44 Low Ambient Processing Vacuum is ineffective when the insulation temperature approaches the freezing point. Therefore, the temperature must be elevated Evacuate tank to 10 Torr of less While maintaining vacuum, introduce oil with inlet temperature of 70 C + 5 C Do not go below oil volume to 10% of total (36 of oil head) or enough to establish oil circulation Circulate oil under vacuum until outlet oil temperature reaches a minimum of 10 C Drain oil from transformer SPX Transformer Solutions, Inc. June 20,

45 Transformer Dry Out Methods High vacuum and hot oil circulation Process is more effective when heat is introduced to increase the vapor pressure of the moisture. Evacuate tank to 2 torr of less While maintaining vacuum, introduce oil with inlet temperature of 70 C + 5 C Oil volume to be no less than 10% of total or enough to establish oil circulation Circulate oil under vacuum until outlet oil temperature reaches 50 C SPX Transformer Solutions, Inc. June 20,

46 Transformer Dry Out Methods Monitor moisture extraction through cold trap. Cease drying when cold trap is less than 1 oz./hr. Alternatively, monitor with vapor pressure equilibrium chart. Cease when vacuum level corresponds to 0.75% at applicable temperature. Drain oil from transformer Continue to pull vacuum and monitor moisture through cold trap until moisture extraction rate achieved Confirm result via dew point measurement SPX Transformer Solutions, Inc. June 20,

47 Oil Filling Procedures Oil Filled Transformer Transformer Shipped with Dry Gas SPX Transformer Solutions, Inc. June 20,

48 Transformers Shipped Oil Filled Open bottom radiator valves and vent air through top bleeder plug Open top radiator valves If required, add make-up oil Test each individual container (drum, tanker, etc.) It is permissible to pump oil into the transformer through a filter press or degassing equipment. During filling, the added oil should be pumped in at level below current oil level in tank and should be directed horizontally over core and coil assembly. Caution: Do not pull vacuum over the oil in the transformer SPX Transformer Solutions, Inc. June 20,

49 Transformers Shipped Oil Filled Fill transformer to 25C mark through upper filter press valve or manhole. Attempt for horizontal oil flow to minimize bubbling. Adjust oil level allowing for temperature compensation per nameplate instructions Purge gas space with nitrogen. Maximum permissible O 2 is 1.2 %. Take final oil samples Observe proper set time for energizing SPX Transformer Solutions, Inc. June 20,

50 Vacuum Filling In inclement weather, take necessary precautions to prevent moisture intrusion should a leak develop. Make connections from pumping system to transformer as short as possible to increase efficiency Make sure there are no low spots in hoses for moisture to collect Use large diameter hoses (4 ) to increase pumping efficiency SPX Transformer Solutions, Inc. June 20,

51 Vacuum Filling Instructions Conduct vacuum leak test. Pull vacuum per OEM specifications Prior to adding oil to transformer, the oil should be tested to OEM specifications Moisture content - 30 PPM maximum value Dielectric strength (ASTM-877) - 30 kv minimum value Power factor 20 c maximum value Interfacial tension - 40 dynes/cm minimum value SPX Transformer Solutions, Inc. June 20,

52 Verification of Leakage Rate Leaks are detrimental to the vacuum process so it is necessary to verify tightness of transformer. Pressure Check to 5 PSI for 4 hours Vacuum Leak Check Evacuate Tank to 2 Torr Isolate Pump and Take Reading 10 Minutes Later(P1) Take Second Reading 30 Minutes Later(P2) SPX Transformer Solutions, Inc. June 20,

53 Vacuum Leakage Rate (P2 -P1) x V < OEM Value OR Tank oil volume (Gallons) Maximum allowable leak rate (mm Hg rise in 20 minutes) Less than SPX Transformer Solutions, Inc. June 20,

54 Typical Vacuum Set Up SPX Transformer Solutions, Inc. June 20,

55 Vacuum & Oil Filling Specifications (Typical OEM Specifications) Preparation Vacuum Oil Filling Voltage, kv Complete all assembly yes yes yes yes Dew point measurement yes yes yes yes Core & Coil minimum temperature, Celsius Drain all oil prior to final vacuum yes yes yes yes Close oil preservation system valve yes yes yes yes Open all cooler equipment yes yes yes yes Final Leak Test yes yes yes yes Absolute Pressure Maximum, Torr Vacuum Hold Time, Hrs Fill from Top or Bottom T/B T/B T/B T/B Oil Temp Minimum, Celsius 50/60 50/60 50/60 50/60 Oil Temp Maximum, Celsius Degasser required or Filter Press only D/F D/F D D Vacuum during filling Maximum, Torr Rate of filling, GPM Maximum Oil Recirculation, # of passes 2/3/4 2/3/4 2/3/4 2/3/4 Minimum Stand Time, hrs kv & below > 69 < 230 kv 345 KV 500 kv & above SPX Transformer Solutions, Inc. June 20,

56 Oil Filling Once the prescribed vacuum hold time is completed, the transformer is filled.. Verify proper acceptance criteria of oil Fill oil into upper fill valve or bottom fill valve Validate that inlet temperature meets minimum specification Verify positive fill pressure at fill location Fill at specified flow rate or liquid level change Monitor level through site glass SPX Transformer Solutions, Inc. June 20,

57 Oil Filling When oil reaches 6 to 8 from cover, stop filling and isolate vacuum pump For sealed or nitrogen blanketed systems, displace vacuum with dry nitrogen For COPS system, displace vacuum with dry gas or oil Fill COPS system once tank pressure reaches slight positive pressure SPX Transformer Solutions, Inc. June 20,

58 Oil Filling Adjust oil level in accordance with OEM instructions for given average oil temperature If required by OEM specification, perform oil circulation process Bleed all vent locations and reactivate devices Observe stand time Confirm oil quality SPX Transformer Solutions, Inc. June 20,

59 Processed Oil in New Transformer Test Standard Unit Voltage Value Dielectric Breakdown Neutralization Number Interfacial Tension Moisture Content ASTM-D1816 w/ 1mm gap ASTM-D974 ASTM-D971 ASTM-D1533 min, kv max, mg KOH/g min, Dynes/cm max, C Avg. Oil Temp. Power Factor ASTM-D921 max, 25 C < 69 kv kv 30 > 345 kv 35 < 69 kv kv > 345 kv 0.1 < 69 kv kv 38 > 345 kv 38 < 69 kv kv 10 > 345 kv 10 < 69 kv kv 0.05 > 345 kv 0.05 SPX Transformer Solutions, Inc. June 20,

60 Vacuum Filling Instructions Vacuum and oil filling is meant to be a continuous process. If power interruption occurs during filling process, isolate transformer. After restoring power, you can resume process if vacuum level did not exceed 10 mm of hg. If vacuum level exceed 10 mm of hg, the transformer must be drained and process restarted. If criteria is not met while filling, entire tank must be drained and process restarted beginning with dry vacuum. SPX Transformer Solutions, Inc. June 20,

61 Maintenance Oil Processing Procedures

62 Maintenance Processing Requirements During the life of a transformer, the insulating fluid may need to be processed as the result of deterioration or in conjunction with maintenance to transformer. Reconditioning Reclamation Degasification Oil Handling Associated With Repairs or Component Replacement SPX Transformer Solutions, Inc. June 20,

63 Service Aged Oil Service aged oil is grouped into one of four categories Group 1 Oils acceptable for continued use Group 2 Oils that require minor reconditioning due to high moisture content or low dielectric Group 3 Oils that are in poor condition and should be reclaimed due to IFT, power factor, or neutralization number limits Group 4 Oil to be disposed SPX Transformer Solutions, Inc. June 20,

64 Classification of Service Aged Oils Test Standard Unit Voltage Group 1 Group 2 Group 3 Group 4 Dielectric Breakdown ASTM-D1816 w/ 1mm gap min, kv < 69 kv 23 < kv 28 < > 345 kv 30 < Neutralization Number ASTM-D974 max, mg KOH/g < 69 kv >0.2 > kv >0.15 >0.5 > 345 kv >0.10 >0.5 Interfacial Tension ASTM-D971 min, Dynes/cm < 69 kv 25 - <25 < kv 30 - <30 <18 > 345 kv 32 - <32 <18 Moisture Content ASTM-D1533 max, C Avg. Oil Temp. Power Factor ASTM-D921 max, % < 69 kv 35 > kv 20 > > 345 kv 12 > < 69 kv >0.5 > kv >0.5 >1.0 > 345 kv >0.5 >1.0 SPX Transformer Solutions, Inc. June 20,

65 Degasification Degasification of oil is required when elevated levels of dissolved gas concentrations are observed TDCG concentrations approaches IEEE category 4 (4630 PPM) TDGC approaches solubility limits for sealed systems Process can be done on line or off line Degasification by recirculation may not remove all gases from insulation. SPX Transformer Solutions, Inc. June 20,

66 Oil Handling Associated with Repairs Often repairs and component changes will require the handling of oil. Some repairs can be completed with only partial draining of the transformer. If OEM specifications permit, it is possible to refill the transformer through vacuum oil purifications system. Oil should not be lowered below active part of transformer Do not pull vacuum of partially filled transformer. Transformer should be refilled at atmospheric pressure. Bleed all vent openings Allow transformer to remain idle for specified time SPX Transformer Solutions, Inc. June 20,

67 Oil Handling Associated with Repairs It is recommended to refill unit in accordance with original OEM filling instructions if Oil is drained below active part Transformer is rated 345 kv or above There is extensive exposure time for repairs SPX Transformer Solutions, Inc. June 20,

68 Transformer Storage Considerations

69 Transformer Storage Considerations First Things First - Make sure the unit is grounded - Cabinet heaters should be energized Control Cabinet and Tap Changer Cabinet - Accessories - Mounted to the transformer - Stored Inside Determining Duration of Storage - Starts the day of shipment - All transit time as well as all time consumed in the receiving process should be included in storage time SPX Transformer Solutions, Inc. June 20,

70 Transformer Storage Considerations Storage less than 90 days Dry Air (Good) To be connected to the transformer via regulator. Pressurize to 2-3 PSI Monitored Daily for 7 days at the same time each day If holding consistent pressure then monitoring cycle may be extended. Nitrogen (Better) To be connected to the transformer via regulator. Pressurize to 2 PSI - If above 80F pressurize to 3 PSI Oil Fill (Best) Monitored Daily for 7 days at the same time each day If holding consistent pressure then monitoring cycle may be extended. Transformers received with oil from the factory can be kept as received for 90 days SPX Transformer Solutions, Inc. June 20,

71 Transformer Storage Considerations Storage 90 days to 18 months (Good) Accessories stored in covered location Unit filled with oil to the proper lever Cops tank unit filled to within 20 inches from cover. Pressurized with dry air or Nitrogen (Best) Fully assemble and fill transformer. SPX Transformer Solutions, Inc. June 20,

72 Transformer Storage Considerations 18 months or Longer Fully Assemble and Fill Transformer Start maintenance program as if in service Removal from Storage During storage moisture may accumulate in nthe transformer insulation if it is not properly stored. Stored Dry Measure Dew Point 1% moisture or better Stored Oil Filled Oil Sample Water Content Test 15ppm SPX Transformer Solutions, Inc. June 20,

73 Wrap Up Important Points 1. Vacuum Logs 1. Indicate if you have leaks 2. Indicate that Vacuum has been held at acceptable levels during filling 2. Never Achieving a good vac leak test 3. Dry Air systems 4. Flash Vac at end of Long Exposure days 1. Especially with high Humidity. 5.Proper storage prevents moisture SPX Transformer Solutions, Inc. June 20,