Presentation on theme: "PREVENTIVE MAINTAINANCE AND CONDITION MONITORING FOR POWER TRANSFORMERS PRESENTED BY - M/s VISHVAS POWER ENGINEERING SERVICES PVT. LTD. NAGPUR SEMINAR."— Presentation transcript:
PREVENTIVE MAINTAINANCE AND CONDITION MONITORING FOR POWER TRANSFORMERS PRESENTED BY - M/s VISHVAS POWER ENGINEERING SERVICES PVT. LTD. NAGPUR SEMINAR ON
INFORMATION ABOUT COMPANY NAMES OF DIRECTORS :Mr. R. M. Bhave : Mr.S.V.D’mello :Mr.Kiran Joharapurkar PRODUCT SKILLS OF DIRECTORS :HT switchgrars : Transformers (all make) :On load tap changers (all type) No. of engineers/site managers:10 Office staff:04 Other staff/skilled workers:80
INFORMATION ABOUT COMPANY AREAS OF BUSINESS INTEREST Capital overhaul/servicing of power transformers Servicing of SF6 breakers Servicing of on load tap changers. Annual maintenance contracts for substation and control room maintenance. Testing of oil and bushings. RLA studies on power transformers. Testing of oil and bushings. Installation services for power transformers, HT switchgears and substation equipments Retrofitting of LT air circuit breakers Installion of rubber balloons in conservator of power transformers to retard oxidation of oil Testing and commising of substations Testing of transformers
Doubts raised by users Whether oil filteration or dry out Criterions of stopping dryout/filteration Whether overhauling/reinsulation Frequency of condition monitoring Oil mixing ---------- preconditions Dissolved Gas Analyis
PLEASE LET ME KNOW WHAT YOU EXPECT FROM THIS SESSION? WHAT YOU EXPECT FROM THIS SESSION?
Areas of concern OIL PAPER Wood (treated / parmali WINDING TANK LEADS OLTC BUSHING COOLING BANKS/ HEAT EXCHANGER AUXILIARIES
IMPORTANT STANDARDS TRANSFORMER USER SHOULD KNOW IS 335 IS 12463 IS 1866 IS 2099 IS 2026
TRANSFORMER FOR OVERHAULING
PROCESS OF OVERHAULING TESTING POST SHUT DOWN OBSERVATIONS P.t.o
POST SHUT DOWN OBSERVATIONS(CONT..) OIL DRAINING DISMANTLING
125 MVA TOP COVER LIFTING
GASKET REPLACEMENT INTERNAL INSPECTION PREPARING TRS FOR EVACUATION N2 PRESSURE TEST
VIEW OF LEAD TAKE OFF
IEEE GUIDELINES INTERNAL Inspection Winding - Lead clamping Winding support system Clamping Insulation discoloration Lead distortion Lead movement Indications of hot spots
IEEE guidelines for Internal Inspection –Oil- Odour Color Moisture Free Water Discoloration- Tank walls Bushing Terminals Corona shields Copper connectors Bus bars
Vacuum drying Vacuum drying is based on the principle of Thermodynamics Boiling point of moisture in insulation is reduced by way of Pressure Reduction Principle Thermal energy needs to be imparted externally for achieving faster and better moisture extraction
DRY OUT PROCESS INVOLVING CYCLES
Vacuum drying( continued) Under vacuum (pressure reduction)boiling point of water reduces to 50 0c medium of heating can be Old oil Old oil Nitrogen Nitrogen Hot air Hot air other methods of heating are also under use.
Prepare TRS for evacuation Fill N 2 over air to get pressure 0.2KG/CM2 Attend leakages Process of dryout
NITROGEN PRESSURE PRESSURE TEST
Continue to heat till Core_< 70 c Med _< 75c Wdg _<70c
COMPARISON OF HEATING METHODS OI L REQUIRES OLD OIL FOR HEATING REQUIRES FILTER PLANT OIL RESERVIORS REQUIRES LESS MONITORING NITROGEN REQUIRES NITROGEN GAS REQUIRES EXTRNAL HEATING ELEMENTS SUCH AS HEATERS REQUIRES MORE VIGILLANT MONITORING
OIL SOAKED INSULATION DOES NOT RELEASE MOISTURE VERY FAST IF OIL IS ACIDIC THEN IT CAN AFFECT INSULATION PAPER THIS METHOD IS NOT CONSIDERED PRESENTLY AS USER FRIENDLY METHOD DRY AND NON SOAKED INSULATION RELEASES MORE MOISTURE AND IN FASTER WAY IF NITROGEN IS PURE IT CANNOT AFFECT INSULATION PAPER & COPPER
OIL MONITORING PARAMETERS ARE OIL BDV & MOISTURE CONTENT OF OIL USED FOR HEATING PURPOSE OIL WILL LOSE/REDUCE ITS PARAMETERS SUCH AS RESISTIVITY, TANDELTA WHEN HEATED ABOVE 60 0C NITROGEN THIS 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 PURPOSE NITROGEN HEATING DOES NOT INVOLVE OIL HEATING ABOVE 60 0C
Details of nitrogen heating Nitrogen gas : 99.6% pure Dew point-40c & Dew point-40c & better better Pressure gauge: 0.1 To 1.0KG/SQ.CM Vacuum gauge: MM scale: Bourden torr scale: Macleoid torr scale: Macleoid M-bar scale M-bar scale
HALOGEN HEATING OF TANK VIEW OF HEATING ARRANGEMENT
VIEW OF SHED FOR HEATING
DRY OUT IN PROGRESS
PT 100 SENSOR FOR TEMPERATURE MONITORING
Heating cycle duration will depend upon size of trs 72 hrs 48 hrs 24hrs 100-250 MVA 50 MVA 25 MVA Vacuum cycles 1 for 60/72 hrs
Vacuum cycle iv N 2 filling Ir. value measurement dew pt measurement Take vacuum and fill up oil While filling oil fill under vacuum and fill from top filler valve
Break vacuum over oil by N 2 / dry air Oil toppling up oil circulation Oil testing at site for BDV >_ 60 kV moisture content <- 10 ppm
Stop filtration if oil parameters are satisfactory as per voltage class of trs.
VIEW OF FILTERPLANT OIL TANK AND DG SET
TRANSFORMER AFTER OVERHAULING
TRENDS IN OIL Napthene based oil 1. Low pour point enabling the use in low ambient temp.areas 2. Oxidation products are soluble in oil. 3. High resistivity. 4. High Viscosity. Paraffin based oil Paraffin based oil 1. High pour point but no problem in country like INDIA.
ALKYL BENZENE BASED OIL 1. Low Tan Delta 1. Low Tan Delta 2. High resistivity. 2. High resistivity. 3. No sludge. 3. No sludge. 4. Low viscosity. 4. Low viscosity. 5. Very low pour point. 5. Very low pour point. 6. Non hygroscopic and does not form gum and sludge. 6. Non hygroscopic and does not form gum and sludge.
SYNTHETIC OIL 1.Used due to fire resistance property 2. Contain polychlorinated biphenyl. 3. Hazardous for dumping in earth or otherwise.
EFFECT OF MOISTURE CONTENT IN OIL ON IMPULSE STRENGTH MOISTURE CONTENT 30 ppm 100% 70% IMPULSE STRENGTH
Oil color Interpretation ASTM- color ASTM - D1500-91 Clear New condition Pale yellow Good condition Yellow Service condition Bright yellow Marginal condition Amber Bad condition Brown Severe bad condition
OIL COLOUR INTERPRITATION Dark brown - Extremely bad condition Sludge - To detect presence of pentane insoluble sludge in serviced oil THE TEST IS not Performed unless IFT 0.15 mg of KOH gm of oil IFT 0.15 mg of KOH gm of oil
IS 335 Density o.89 gm/cm 3 at 29.5º C Viscosity 27 MAX at 27º C IFT 0.04 N/M Flash point 140 0 c Pour point -6 0 c BDV 30 KV unfiltered 60 KV filtered TAN DELTA 0.002 RESISTIVITY 35*10 12 ohm-cm AT 90º c 1500*10 12 ohm-cm AT 27º c
IS 335 Acidity 0.4(max) Acidity 0.4(max) Sludge 0.1% (max) Sludge 0.1% (max) Corrosive sulphur No traces Corrosive sulphur No traces oxidation inhibitor 0.05% (max) oxidation inhibitor 0.05% (max) Water content 50 PPM max (unfiltered) 15 PPM max (filtered) Water content 50 PPM max (unfiltered) 15 PPM max (filtered)
DISSOLVED GAS ANALYSIS Most widely used and effective technique. Requires skill to draw inference. FAULTS Thermal aging - overhead metallic parts Partial discharge Arcing
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 comparison Oxygen content of oil Oil temperature Ambient temperature
Dissolved Gas Analysis Methodology Gas tight syringe with a 3 way stop cock Stainless steel tubular bottle Bottle capable of being air/gas tight with screwed cap
Labeling Details of transformers Date of sampling History of transformers Temp of transformer Charged/service condition Ambient Temp.
STAGES STAGES Collection of oil sample. Extraction of gases in dissolved oil. Separation identification and quantitative determination of gas Interpretation.
Key gas and fault pattern C 2 H 2 (Acetylene) :Arcing H 2 (Hydrogen) :Partial discharge C 2 H 4 (Ethylene) :Oil overheating. Co/Co 2 (Carbon monoxide & Carbon Dioxide) :Conductor overheating
Various h 2 ch 2 c 2 h 6 c 2 h 4 c 2 h 2 co co 2 Various h 2 ch 2 c 2 h 6 c 2 h 4 c 2 h 2 co co 2 sources sources IEEE 140 160 115 190 11 580 -- IEEE 140 160 115 190 11 580 -- GTR 100 120 65 50 35 350 2500 GTR 100 120 65 50 35 350 2500 CIGRE 28.6 42.2 85.6 74.6 -- 289 3771 DOBLE 100 100 60 100 5 250 -- New Trs 200 100 100 150 15 500 ---- Old trs 250 200 200 300 35 1000 -- Oil overheating c 2 h 4 c 2 h 6 ch 4 Cellulose overheating co Partial discharge in oil h 2 ch 4 Arcing in oil c 2 h 2 h 2
KEY GAS : Hydrogen ARCING : Between leads. Leads to coil. KEY GAS :Acetylene, Hydrogen
IEEE Arcing :Acetylene C 2 H 2 :Hydrogen H 2 :Hydrogen H 2 Carona : H 2 Overheated oil :Ethylene C 2 H 2 :Methane CH 4 :Methane CH 4
Thermal degradation of insulation material =Co, Co 2, H 2 o =Co, Co 2, H 2 o Healthy ratio of Co/Co 2 = 5 Healthy ratio of Co/Co 2 = 5 If ratio is below 3, it indicates severe overheating of paper. If ratio is below 3, it indicates severe overheating of paper. Oil degradation : Methane(CH 4 ), Ethane(C 2 H 6 ) Ethylene(C 2 H 5 ) Partial Discharge : Occurs due to ionization in high stressed areas where gas/vapour filled voids.
STRATEGIC END OF LIFE ECONOMIC END OF LIFE TECHNICAL END OF LIFE DEGREE OF POLYMERIZATION INITIAL : 1200 POOR : 300 AFFECTING PARAMETERS TEMPERATURE TEMPERATURE MOISTURE MOISTUREACIDITY
Comparison of Furful content in various generator transformers
Interpretations of impedance test Variation in short circuit impedance of a transformer winding indicates possible movement of winding/deformation within the transformer Variation in short circuit impedance of a transformer winding indicates possible movement of winding/deformation within the transformer Variations upto 2% --Negligible Variations upto 3% --Significant
AGEING OF INSULATING PAPER With advanced instruments available for technical analysis of aged insulation it is possible to determine /measure following properties of insulation paper With advanced instruments available for technical analysis of aged insulation it is possible to determine /measure following properties of insulation paper 1. Thickness 2. Water content 3. Tensile strength 4. Degree of polymerization
TENSILE STRENGTH 1. Determined as per IS 1924 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 strength Ageing (days)
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 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. This is also direct decomposition of cellulose.
DETERIORATION OF PAPER 150 120 0 c 105 0 c 90 0 c Days Degree of polymeri zation
Source documents / forums IEEE ANSI I.S. C.B.I.P.’s INT. Conference CIGRE’s working group Our own field experience
Abnormalities observed during internal inspection/ capital overhauling EXTERNAL 1Pumps running in reverse direction 2Thermosyphon blanked 3Thimble-terminal cap fusion due to heating.heat generated due to faulty term.connector. INTERNAL INTERNAL 1 Cotton tape used for gasket locating not removed causing leakage 2Core bolt insulation zero 3Selector switch contact arm assy not making adequate contact
Abnormalities(continued) 4Bucholz pipeline slope not proper 5Lens screw of OLTC shaft not properly fitted 6Oil leakges in box type stiffner, between main tank and stiffner 4Core earthing melted. Part of laminations fused. Part of laminations fused.
BUSHING TYPE SRBP/OIP/RIP TEST TAP FOR MEASUREMENT MUST BE EARTHED PROPER EARTHING CORROSION OF THREADS ON CONNECTION CAUSES HIGH RESISTANCE AND SPARKING
3 Measurement of mounted bushing done in UST mode, using test tap connection Measurement of mounted bushing done in UST mode, using test tap connection4 Measurement of winding is done in GST mode using connections between bushing top terminal and grounded. Measurement of winding is done in GST mode using connections between bushing top terminal and grounded.
2 10 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.
DGA OF OIL FOR BUSHING [IEC-36A]
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.
Predictive maintenance(cont...) Changes in switching time weak springs, Overhauling Contact wear
Precautionary steps for ensuring correct installations Paper Moisture 420 KV0.5 or less 245 KVless than1.0 145 KVless than 2 Oil Moisture 420 KVless than 10 245 KVless than 15 145 KVless than 20
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
Partial Discharge 1Effective for comparing at factory/ at site after repairs. 2Advanced diagnostic system used for off line PD detection. 3 Background noise suppression, using a Spectrum analyzer to do selective filtration.
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.
Principle Deformation 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.
Procedure for FRA Identify two ends of winding. Connect two cables from measuring Unit giving sinusoidal output of two V rms and one measuring input Other 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.
BENEFITS Immune to Electro-magnetic interference. Easy to perform on site. Identical results for similar transformers. DRAW BACKS Above data required effectively used more as signature Above data required effectively used more as signature FREQUENCY RESPONSE ANALYSIS
INDICATIONS Shift in response of winding Differences in response between phases of same transformer. Difference between responses of transformer of same design.
CONTROL OF LEAKAGE FLUX IN POWER TRANSFORMER NETT FLUX WHICH IS NOT LINKED BY BOTH COILS Magnetic 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.
EFFECT OF LEAKAGE FLUX Leakage flux will follow a path of low resistance Will be attracted to magnetic steel. This induces Eddy Currents and hence generate heat. REMEDY REMEDY Increase the distance of tank wall from source of leakage flux. Continuously transposed conductor (CTC). To provide shunt plates to carry leakage flux.
CASE STUDY New 390 MVA generator transformer PROBLEM Core overheating Yoke overheating Tank & top cover overheating VISIBLE EFFECTS VISIBLE EFFECTS Due To overheating caused by eddy currents flowing in top cover or bell cover visible deterioration of gasket was observed Due To overheating caused by eddy currents flowing in top cover or bell cover visible deterioration of gasket was observed DESIGN REMEDY: To subdivide the plate width of outermost pockets Use of nonmagnetic material for frames. Use of flux shunt plates at LV side of the tank
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 expands 7. 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.
THERMOSYPHON FILTER CHAMBERS On line acidity Reduction 1Acidity of oil is bad for insulation. 2Aluminum granules can reduce acidity and Fuller’s earth can reduce acidity. 3Above materials are contained in cylinder chamber/chambers in wire mesh. 4Cylinder/ cylinders are fitted to transformer tank and connected through valves. 5Oil passing through the column of Alumina or fuller’s earth reduces the acidity 6 Continuous use of facility can help in maintaining acidity low since commissioning.
Hydran 2011 system Continuos monitoring of key gases Alarm facility Hourly and daily changes in level Adjustable alarm levels Self test system Possibility of connection to SCADA systems
SF6 INSULATED TRANSFORMERS MANUFACTURING RANGE: 275KV300MVA COMPACT SIZE COMPACT SIZE REDUCED SIZE REDUCED SIZE EXTRA LIFE HIGHER COST ALMOST DOUBLE RATE OF LOWERING DP VALUE IS RELATIVELY MUCH SLOWER IN SF6 THAN NITROGEN AND OIL
FILTER PLANT HIGH VACUUM WITH DOUBLE DEGASSING CHAMBER