Presentation on theme: "PRESENTED BY - M/s VISHVAS POWER ENGINEERING SERVICES PVT. LTD. NAGPUR"— Presentation transcript:
1 PRESENTED BY - M/s VISHVAS POWER ENGINEERING SERVICES PVT. LTD. NAGPUR SEMINAR ONPREVENTIVE MAINTAINANCE AND CONDITION MONITORING FOR POWER TRANSFORMERSPRESENTED BY -M/s VISHVAS POWERENGINEERING SERVICES PVT. LTD. NAGPUR
2 INFORMATION ABOUT COMPANY NAMES OF DIRECTORS :Mr. R. M. Bhave : Mr.S.V.D’mello :Mr.Kiran JoharapurkarPRODUCT SKILLS OF DIRECTORS :HT switchgrars : Transformers (all make) :On load tap changers (all type)No. of engineers/site managers:10Office staff:04Other staff/skilled workers:80
3 INFORMATION ABOUT COMPANY AREAS OF BUSINESS INTERESTCapital overhaul/servicing of power transformersServicing of SF6 breakersServicing of on load tap changers.Annual maintenance contracts for substation and control room maintenance.Testing of oil and bushings.RLA studies on power transformers.Installation services for power transformers, HT switchgears and substation equipmentsRetrofitting of LT air circuit breakersInstallion of rubber balloons in conservator of power transformers to retard oxidation of oilTesting and commising of substationsTesting of transformers
4 Doubts raised by users Whether oil filteration or dry out Criterions of stopping dryout/filterationWhether overhauling/reinsulationFrequency of condition monitoringOil mixing preconditionsDissolved Gas Analyis
5 PLEASE LET ME KNOWWHAT YOU EXPECT FROM THIS SESSION?
6 Areas of concern OIL PAPER Wood (treated / parmali WINDING TANK LEADS OLTCBUSHINGCOOLING BANKS/ HEAT EXCHANGERAUXILIARIES
7 IMPORTANT STANDARDS TRANSFORMER USER SHOULD KNOW IS 335IS 12463IS 1866IS 2099IS 2026
48 IEEE guidelines for Internal Inspection Oil Odour Color Moisture Free WaterDiscoloration- Tank walls Bushing Terminals Corona shields Copper connectors Bus bars
49 Vacuum drying is based on the principle of Thermodynamics Boiling point of moisture in insulation is reduced by way of Pressure Reduction PrincipleThermal energy needs to be imparted externally for achieving faster and better moisture extraction
54 Continue to heat tillCore_< 70 cMed _< 75cWdg _<70c
55 COMPARISON OF HEATING METHODS OI LREQUIRES OLD OIL FOR HEATINGREQUIRES FILTER PLANT OIL RESERVIORSREQUIRES LESS MONITORINGNITROGENREQUIRES NITROGEN GASREQUIRES EXTRNAL HEATING ELEMENTS SUCH AS HEATERSREQUIRES MORE VIGILLANT MONITORING
56 DRY AND NON SOAKED INSULATION RELEASES MORE MOISTURE AND IN FASTER WAY OIL SOAKED INSULATION DOES NOT RELEASE MOISTURE VERY FASTIF OIL IS ACIDIC THEN IT CAN AFFECT INSULATION PAPERTHIS METHOD IS NOT CONSIDERED PRESENTLY AS USER FRIENDLY METHODDRY AND NON SOAKED INSULATION RELEASES MORE MOISTURE AND IN FASTER WAYIF NITROGEN IS PURE IT CANNOT AFFECT INSULATION PAPER & COPPER
57 OILMONITORING PARAMETERS ARE OIL BDV & MOISTURE CONTENT OF OIL USED FOR HEATING PURPOSEOIL WILL LOSE/REDUCE ITS PARAMETERS SUCH AS RESISTIVITY, TANDELTA WHEN HEATED ABOVE 600CNITROGENTHIS METHOD IS PRESENTLY CONSIDERED AS USER FRIENDLY AND TECHNICALLY BETTER .MONITORING PARAMETERES ARE CONPARISON OF IR VALUE AND DRYNESS OF NITROGEN GAS USED FOR HEATING PURPOSENITROGEN HEATING DOES NOT INVOLVE OIL HEATING ABOVE 600C
58 Details of nitrogen heating Nitrogen gas: 99.6% pureDew point-40c &betterPressure gauge: 0.1 To 1.0KG/SQ.CMVacuum gauge: MM scale: Bourdentorr scale: MacleoidM-bar scale
67 N2 filling Ir. value measurement dew pt measurement Vacuum cycle ivN2 filling Ir. value measurement dew pt measurementTake vacuum and fill up oilWhile filling oil fill under vacuum and fill from top filler valve
68 Oil toppling up oil circulation Break vacuum over oilby N2/ dry airOil toppling up oil circulationOil testing at site forBDV >_ 60 kVmoisture content<- 10 ppm
75 TRENDS IN OIL Napthene based oil 1. Low pour point enabling the use in low ambient temp.areas2. Oxidation products are soluble in oil.3. High resistivity.4. High Viscosity.Paraffin based oil1. High pour point but no problem in country like INDIA.
76 ALKYL BENZENE BASED OIL 1. Low Tan Delta2. High resistivity.3. No sludge.4. Low viscosity.5. Very low pour point.6. Non hygroscopic and does not form gum and sludge.
78 SYNTHETIC OILUsed due to fire resistance property2. Contain polychlorinated biphenyl.3. Hazardous for dumping in earth or otherwise.
79 EFFECT OF MOISTURE CONTENT IN OIL ON IMPULSE STRENGTH 100%70%IMPULSESTRENGTHMOISTURE CONTENT30 ppm
80 Oil color Interpretation ASTM- color ASTM - D1500-91 Clear New conditionPale yellow Good conditionYellow Service conditionBright yellow Marginal conditionAmber Bad conditionBrown Severe bad condition
81 OIL COLOUR INTERPRITATION Dark brown - Extremely bad conditionSludge - To detect presence of pentane insoluble sludge in serviced oilTHE TEST IS not Performed unlessIFT <26 dynes/cm ACIDITY> 0.15 mg of KOH gm of oil
82 IS 335 Density o.89 gm/cm3 at 29.5º C Viscosity 27 MAX at 27º C IFT N/MFlash point cPour point cBDV KV unfiltered KV filteredTAN DELTARESISTIVITY 35*1012 ohm-cm AT 90º c *1012 ohm-cm AT 27º c
83 IS 335 Acidity 0.4(max) Sludge 0.1% (max) Corrosive sulphur No traces oxidation inhibitor % (max)Water content PPM max (unfiltered) PPM max (filtered)
84 DISSOLVED GAS ANALYSIS Most widely used and effective technique. Requires skill to draw inference.FAULTSThermal aging - overhead metallic partsPartial dischargeArcing
85 FACTORS INFLUENCING GAS PRODUCTION Meaningful assessment of a Transformer on basis of DGA is possible if information and data is considered on following factors which influence gassing rate & gassing comparisonOxygen content of oilOil temperatureAmbient temperature
86 Dissolved Gas Analysis Methodology Gas tight syringe with a 3 way stop cockStainless steel tubular bottleBottle capable of being air/gas tight with screwed cap
87 Labeling Details of transformers Date of sampling History of transformersTemp of transformerCharged/service conditionAmbient Temp.
88 STAGESCollection of oil sample.Extraction of gases in dissolved oil.Separation identification and quantitative determination of gasInterpretation.
93 Thermal degradation of insulation material =Co, Co2, H2oHealthy ratio of Co/Co2 = 5If ratio is below 3, it indicates severe overheating of paper.Oil degradation : Methane(CH4), Ethane(C2H6) Ethylene(C2H5)Partial Discharge : Occurs due to ionization in high stressed areas where gas/vapour filled voids.
94 DEGREE OF POLYMERIZATION STRATEGIC END OF LIFEECONOMIC END OF LIFETECHNICAL END OF LIFEDEGREE OF POLYMERIZATIONINITIAL : 1200POOR :AFFECTING PARAMETERSTEMPERATUREMOISTUREACIDITY
95 Comparison of Furful content in various generator transformers
97 Interpretations of impedance test Variation in short circuit impedance of a transformer winding indicates possible movement of winding/deformation within the transformerVariations upto 2% NegligibleVariations upto 3% Significant
99 AGEING OF INSULATING PAPER With advanced instruments available for technical analysis of aged insulation it is possible to determine /measure following properties of insulation paper1. Thickness2. Water content3. Tensile strength4. Degree of polymerization
100 TENSILE STRENGTH1. Determined as per IS determined in both machine direction and cross machine directions.2. Deterioration of tensile strength is further dependent on temp. factor.3. The rate of tensile strength deterioration is exponential with time.Tensile strengthAgeing (days)
101 Degree of polymerization This proves to be the most informative parameter for assessing the ageing or the process of ageing of cellulose . The connection between deterioration in material properties and formation of aging products is degree of polymerization.This is also direct decomposition of cellulose.
102 DETERIORATION OF PAPER 900 cDegree of polymerization1050c1200c150Days
103 Source documents / forums IEEEANSII.S.C.B.I.P.’s INT. ConferenceCIGRE’s working groupOur own field experience
104 Abnormalities observed during internal inspection/ capital overhauling EXTERNALPumps running in reverse directionThermosyphon blankedThimble-terminal cap fusion due to heating.heat generated due to faulty term.connector.INTERNAL1 Cotton tape used for gasket locating not removed causing leakageCore bolt insulation zeroSelector switch contact arm assy not making adequate contact
105 Abnormalities(continued) Bucholz pipeline slope not properLens screw of OLTC shaft not properly fittedOil leakges in box type stiffner, between main tank and stiffnerCore earthing melted.Part of laminations fused.
106 BUSHING TYPE TEST TAP SRBP/OIP/RIP FOR MEASUREMENT MUST BE EARTHED PROPER EARTHINGCORROSION OF THREADS ON CONNECTION CAUSES HIGH RESISTANCE AND SPARKING
107 3Measurement of mounted bushing done in UST mode , using test tap connection4Measurement of winding is done in GST mode using connections between bushing top terminal and grounded.
109 210 kV is a referred as a preferred reference voltage although usually measurements of tan delta and capacitance should not vary with applied voltage.Usually measurements at 2 KV,5KV and 10KV are taken at site.Capacitance value measurement is equally important.Tan delta value measurement may get affected by conditions such as oil. temperature, humidity, surface cleanliness and inductions in the switchyard.
111 Predictive maintenance for OLTC Contact resistance measurement .Measurement of divertor motor acoustic signals.Temp difference between oil in main tank and oil in divertor switch.Dissolved gas analysis.Deposition of solid carbon.
112 Predictive maintenance(cont...) Changes in switching time weak springs,OverhaulingContact wear
113 Precautionary steps for ensuring correct installations Paper Moisture420 KV 0.5 or less245 KV less than1.0145 KV less than 2Oil Moisture420 KV less than 10245 KV less than 15145 KV less than 20
115 Magnetic balance test is like a signature test Diagnostic tool with focus on current is more important Quality of core is not assessed if voltage distribution is in order but current are not then further analysis is required
116 Partial DischargeEffective for comparing at factory/ at site after repairs.Advanced diagnostic system used for off line PD detection.3 Background noise suppression, using a Spectrum analyzer to do selective filtration.
117 FREQUENCY RESPONSE ANALYSIS Short circuit high fault currents can lead to displacement of windings.An already weak coil or an insulation system can fail, during over voltage stress.Background.Electrical measurements are not sufficient to indicate this type of displacement of coil or insulation.
118 PrincipleDeformation results in minor changes of internal inductance and capacitance of winding.These deformations can be noted by noting a difference in response of particular winding on network analyzer when 1 signal (sinusoidal) having frequency band 50 Hz to 500 Hz is connected to bushing and response is measured through neutral bus.
119 Procedure for FRA Identify two ends of winding. Connect two cables from measuringUnit giving sinusoidal output of two V rms and one measuring inputOther end of winding is connected to measuring input.Other windings are grounded.Voltage transfer function is measured for each winding for four frequency scans between 5 Hz to 2 MHz.
120 FREQUENCY RESPONSE ANALYSIS BENEFITSImmune to Electro-magnetic interference.Easy to perform on site.Identical results for similar transformers.DRAW BACKSAbove data required effectively used more as signature
121 INDICATIONSShift in response of windingDifferences in response between phases of same transformer.Difference between responses of transformer of same design.
122 CONTROL OF LEAKAGE FLUX IN POWER TRANSFORMER NETT FLUX WHICH IS NOT LINKED BY BOTH COILSMagnetic flux which energizes core abd induces required flux density.Load flux which is balanced by load flux of secondary winding.Leakage flux which links the winding conductors and returns through a path outside the core.
123 EFFECT OF LEAKAGE FLUXLeakage flux will follow a path of low resistanceWill be attracted to magnetic steel.This induces Eddy Currents and hence generate heat.REMEDYIncrease the distance of tank wall from source of leakage flux.Continuously transposed conductor (CTC).To provide shunt plates to carry leakage flux.
124 CASE STUDY New 390 MVA generator transformer PROBLEM Core overheating Yoke overheating Tank & top cover overheatingVISIBLE EFFECTSDue To overheating caused by eddy currents flowing in top cover or bell cover visible deterioration of gasket was observedDESIGN REMEDY:To subdivide the plate width of outermost pocketsUse of nonmagnetic material for frames.Use of flux shunt plates at LV side of the tank
125 CONCEPT OF AIR CELL 1. Oil Deteriorates majorly because of Oxidation. 2. Atmospheric breathing is a continuous process.3. To avoid atmospheric breathing, rubber cell/balloon/separator is inserted in conservator.4. The balloon / air cell is INFLATED INITIALLY. The breathing of transformer is then through this cell.5. When air expands, air cell contracts.6. When oil contracts , air cell expands7. There can be a substantial reduction in oil deterioration, preserving or at least retarding its increase parameters like acidity moisture content and dielectric dissipation factor.
126 THERMOSYPHON FILTER CHAMBERS On line acidity ReductionAcidity of oil is bad for insulation.Aluminum granules can reduce acidity and Fuller’s earth can reduce acidity.Above materials are contained in cylinder chamber/chambers in wire mesh.Cylinder/ cylinders are fitted to transformer tank and connected through valves.Oil passing through the column of Alumina or fuller’s earth reduces the acidityContinuous use of facility can help in maintaining acidity low since commissioning.
127 Hydran 2011 system Continuos monitoring of key gases Alarm facility Hourly and daily changes in levelAdjustable alarm levelsSelf test systemPossibility of connection to SCADA systems
128 SF6 INSULATED TRANSFORMERS MANUFACTURING RANGE: 275KV300MVACOMPACT SIZEREDUCED SIZEEXTRA LIFEHIGHER COST ALMOST DOUBLERATE OF LOWERING DP VALUE IS RELATIVELY MUCH SLOWER IN SF6 THAN NITROGEN AND OIL