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PRESENTED BY - M/s VISHVAS POWER ENGINEERING SERVICES PVT. LTD. NAGPUR

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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 ON PREVENTIVE MAINTAINANCE AND CONDITION MONITORING FOR POWER TRANSFORMERS PRESENTED BY - M/s VISHVAS POWER ENGINEERING SERVICES PVT. LTD. NAGPUR

2 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

3 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. 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

4 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

5 PLEASE LET ME KNOW WHAT YOU EXPECT FROM THIS SESSION?

6 Areas of concern OIL PAPER Wood (treated / parmali WINDING TANK LEADS
OLTC BUSHING COOLING BANKS/ HEAT EXCHANGER AUXILIARIES

7 IMPORTANT STANDARDS TRANSFORMER USER SHOULD KNOW
IS 335 IS 12463 IS 1866 IS 2099 IS 2026

8 TRANSFORMER FOR OVERHAULING

9 PROCESS OF OVERHAULING
TESTING POST SHUT DOWN OBSERVATIONS P.t.o

10 POST SHUT DOWN OBSERVATIONS(CONT..)
OIL DRAINING DISMANTLING

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23 125 MVA TOP COVER LIFTING

24 PREPARING TRS FOR EVACUATION
GASKET REPLACEMENT INTERNAL INSPECTION PREPARING TRS FOR EVACUATION N2 PRESSURE TEST

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42 VIEW OF LEAD TAKE OFF

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46 IEEE GUIDELINES INTERNAL Inspection
Winding - Lead clamping Winding support system Clamping Insulation discoloration Lead distortion Lead movement Indications of hot spots

47 IEEE GUIDELINES INTERNAL Inspection
Loose connections Tap leads Bushings Terminal Boards Spacers Core bolt nuts. Physical status Contacts Operating mechanism Coupling shafts Shielding

48 IEEE guidelines for Internal Inspection
Oil Odour Color Moisture Free Water Discoloration- 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 Principle Thermal energy needs to be imparted externally for achieving faster and better moisture extraction

50 DRY OUT PROCESS INVOLVING CYCLES

51 Vacuum drying( continued)
Under vacuum (pressure reduction)boiling point of water reduces to 500c medium of heating can be Old oil Nitrogen Hot air other methods of heating are also under use.

52 Process of dryout Prepare TRS for evacuation
Fill N2 over air to get pressure 0.2KG/CM2 Attend leakages

53 PRESSURE TEST NITROGEN PRESSURE

54 Continue to heat till Core_< 70 c Med _< 75c Wdg _<70c

55 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

56 DRY AND NON SOAKED INSULATION RELEASES MORE MOISTURE AND IN FASTER WAY
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

57 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 600C 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 600C

58 Details of nitrogen heating
Nitrogen gas: 99.6% pure Dew point-40c & better Pressure gauge: 0.1 To 1.0KG/SQ.CM Vacuum gauge: MM scale: Bourden torr scale: Macleoid M-bar scale

59 HEATING ARRANGEMENT

60 VIEW OF HEATING ARRANGEMENT
HALOGEN HEATING OF TANK

61 VIEW OF SHED FOR HEATING

62 DRY OUT IN PROGRESS

63 PT 100 SENSOR FOR TEMPERATURE MONITORING

64 Heating cycle duration will depend upon size of trs
72 hrs 48 hrs 24hrs MVA 50 MVA 25 MVA Vacuum cycles 1 for 60/72 hrs

65 Heating cycles 2 :36/48 hours
Vacuum cycle 2 : 48/60 hrs Heating cycle 3 :24/36 hrs

66 Vacuum cycle 3 :36 hrs Heating cycle 4 :36 hrs

67 N2 filling Ir. value measurement dew pt measurement
Vacuum cycle iv N2 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

68 Oil toppling up oil circulation
Break vacuum over oil by N2/ dry air Oil toppling up oil circulation Oil testing at site for BDV >_ 60 kV moisture content <- 10 ppm

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70 Stop filtration if oil parameters are satisfactory as per voltage class of trs.

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73 VIEW OF FILTERPLANT OIL TANK AND DG SET

74 TRANSFORMER AFTER OVERHAULING

75 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 1. High pour point but no problem in country like INDIA.

76 ALKYL BENZENE BASED OIL
1. Low Tan Delta 2. High resistivity. 3. No sludge. 4. Low viscosity. 5. Very low pour point. 6. Non hygroscopic and does not form gum and sludge.

77 OIL COMPARISION

78 SYNTHETIC OIL Used due to fire resistance property 2. Contain polychlorinated biphenyl. 3. Hazardous for dumping in earth or otherwise.

79 EFFECT OF MOISTURE CONTENT IN OIL ON IMPULSE STRENGTH
100% 70% IMPULSE STRENGTH MOISTURE CONTENT 30 ppm

80 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

81 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 <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/M Flash point c Pour point c BDV KV unfiltered KV filtered TAN DELTA RESISTIVITY 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. FAULTS Thermal aging - overhead metallic parts Partial discharge Arcing

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 comparison Oxygen content of oil Oil temperature Ambient temperature

86 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

87 Labeling Details of transformers Date of sampling
History of transformers Temp of transformer Charged/service condition Ambient Temp.

88 STAGES Collection of oil sample. Extraction of gases in dissolved oil. Separation identification and quantitative determination of gas Interpretation.

89 Key gas and fault pattern
C2H2 (Acetylene) :Arcing H (Hydrogen) :Partial discharge C2H4 (Ethylene) :Oil overheating. Co/Co2 (Carbon monoxide & Carbon Dioxide) :Conductor overheating

90 Various h2 ch2 c2h6 c2h4 c2h2 co co2
sources IEEE GTR CIGRE DOBLE New Trs Old trs Oil overheating c2h4 c2h6 ch4 Cellulose overheating co Partial discharge in oil h2 ch4 Arcing in oil c2h2 h2

91 KEY GAS : Hydrogen ARCING : Between leads. Leads to coil. KEY GAS :Acetylene , Hydrogen

92 IEEE Arcing :Acetylene C2H2 :Hydrogen H2 Carona : H2
Overheated oil :Ethylene C2H2 :Methane CH4

93 Thermal degradation of insulation material
=Co, Co2, H2o Healthy ratio of Co/Co2 = 5 If 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 LIFE ECONOMIC END OF LIFE TECHNICAL END OF LIFE DEGREE OF POLYMERIZATION INITIAL : 1200 POOR : AFFECTING PARAMETERS TEMPERATURE MOISTURE ACIDITY

95 Comparison of Furful content in various generator transformers

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97 Interpretations of impedance test
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

98 CASE III

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 paper 1. Thickness 2. Water content 3. Tensile strength 4. Degree of polymerization

100 TENSILE STRENGTH 1. 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 strength Ageing (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 c Degree of polymerization 1050c 1200c 150 Days

103 Source documents / forums
IEEE ANSI I.S. C.B.I.P.’s INT. Conference CIGRE’s working group Our own field experience

104 Abnormalities observed during internal inspection/ capital overhauling
EXTERNAL Pumps running in reverse direction Thermosyphon blanked Thimble-terminal cap fusion due to heating.heat generated due to faulty term.connector. INTERNAL 1 Cotton tape used for gasket locating not removed causing leakage Core bolt insulation zero Selector switch contact arm assy not making adequate contact

105 Abnormalities(continued)
Bucholz pipeline slope not proper Lens screw of OLTC shaft not properly fitted Oil leakges in box type stiffner, between main tank and stiffner Core earthing melted. Part of laminations fused.

106 BUSHING TYPE TEST TAP SRBP/OIP/RIP FOR MEASUREMENT MUST BE EARTHED
PROPER EARTHING CORROSION OF THREADS ON CONNECTION CAUSES HIGH RESISTANCE AND SPARKING

107 3 Measurement of mounted bushing done in UST mode , using test tap connection 4 Measurement of winding is done in GST mode using connections between bushing top terminal and grounded.

108 1

109 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.

110 DGA OF OIL FOR BUSHING [IEC-36A]

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, Overhauling Contact wear

113 Precautionary steps for ensuring correct installations
Paper Moisture 420 KV 0.5 or less 245 KV less than1.0 145 KV less than 2 Oil Moisture 420 KV less than 10 245 KV less than 15 145 KV less than 20

114 SETTLING TIME KV Time 420 KV hours 245 KV hours 145 KV 36 hours

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 Discharge Effective 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 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.

119 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.

120 FREQUENCY RESPONSE ANALYSIS
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

121 INDICATIONS Shift in response of winding Differences 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 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.

123 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 Increase 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 overheating VISIBLE EFFECTS 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

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 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.

126 THERMOSYPHON FILTER CHAMBERS
On line acidity Reduction Acidity 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 acidity Continuous 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 level Adjustable alarm levels Self test system Possibility of connection to SCADA systems

128 SF6 INSULATED TRANSFORMERS
MANUFACTURING RANGE: 275KV300MVA COMPACT SIZE REDUCED SIZE EXTRA LIFE HIGHER COST ALMOST DOUBLE RATE OF LOWERING DP VALUE IS RELATIVELY MUCH SLOWER IN SF6 THAN NITROGEN AND OIL

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131 THANK YOU

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136 FILTER PLANT HIGH VACUUM WITH DOUBLE DEGASSING CHAMBER

137 TRANSFORMER ASSEMBLY IN PROGRESS

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