SEMINAR ON. PREVENTIVE MAINTAINANCE AND CONDITION MONITORING FOR POWER TRANSFORMERS. PRESENTED BY - M/s VISHVAS POWER ENGINEERING SERVICES PVT. LTD. NAGPUR. INFORMATION ABOUT COMPANY.
PRESENTED BY -
M/s VISHVAS POWER
ENGINEERING SERVICES PVT. LTD. NAGPUR
AREAS OF BUSINESS INTEREST
WHAT YOU EXPECT FROM THIS SESSION?
Wood (treated / parmali
COOLING BANKS/ HEAT EXCHANGER
AUXILIARIESAreas of concern
POST SHUT DOWN
PREPARING TRS FOR EVACUATION
N2 PRESSURE TEST
Winding - Lead clamping Winding support system Clamping Insulation discoloration Lead distortion Lead movement Indications of hot spots
Vacuum drying is based on the principle of Thermodynamics
Boiling point of moisture in insulation isreduced by way of PressureReductionPrinciple
Thermal energy needs to be impartedexternally for achieving faster and better moisture extraction
Under vacuum (pressure reduction)boiling point of water reduces to 500c
medium of heating can be
other methods of heating are also under use.
Fill N2over air to get pressure 0.2KG/CM2
Process of dryout
Core_< 70 c
Med _< 75c
REQUIRES OLD OIL FOR HEATING
REQUIRES FILTER PLANT OIL RESERVIORS
REQUIRES LESS MONITORING
REQUIRES NITROGEN GAS
REQUIRES EXTRNAL HEATING ELEMENTS SUCH AS HEATERS
REQUIRES MORE VIGILLANT MONITORINGCOMPARISON OF HEATING METHODS
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
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
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
Dew point-40c &
torr scale: Macleoid
HALOGEN HEATING OF TANK
Vacuum cycles 1 for
Vacuum cycle 2 : 48/60 hrs
Heating cycle 3 :24/36 hrs
Heating cycle 4 :36 hrs
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
by N2/ dry air
Oil toppling up oil circulation
Oil testing at site for
BDV >_ 60 kV
<- 10 ppm
Stop filtration if oil parameters are satisfactory as per voltage class of trs.
VIEW OF FILTERPLANT OIL TANK AND DG SET voltage class of trs.
TRANSFORMER AFTER OVERHAULING voltage class of trs.
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.
ALKYL BENZENE BASED OIL voltage class of trs.
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.
SYNTHETIC OIL voltage class of trs.
2. Contain polychlorinated biphenyl.
3. Hazardous for dumping in earth or otherwise.
30 ppm voltage class of trs.
MOISTURE CONTENTEFFECT OF MOISTURE CONTENT IN OIL ON IMPULSE STRENGTH
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
Density o.89 gm/cm3 at 29.5º C
Viscosity 27 MAX at 27º C
IFT 0.04 N/M
Flash point 1400c
Pour point -60c
BDV 30 KV unfiltered 60 KV filtered
TAN DELTA 0.002
RESISTIVITY 35*1012 ohm-cm AT 90º c 1500*1012 ohm-cm AT 27º c
Sludge 0.1% (max)
Corrosive sulphur No traces
oxidation inhibitor 0.05% (max)
Water content 50 PPM max (unfiltered) 15 PPM max (filtered)
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
STAGES voltage class of trs.
Various h voltage class of trs.2 ch2 c2h6 c2h4 c2h2 co co2
IEEE 140 160 115 190 11 580 --
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 c2h4 c2h6 ch4
Cellulose overheating co
Partial discharge in oil h2 ch4
Arcing in oilc2h2 h2
IEEE voltage class of trs.
Arcing :Acetylene C2H2
Carona : H2
Overheated oil :Ethylene C2H2
=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)
STRATEGIC END OF LIFE voltage class of trs.
ECONOMIC END OF LIFE
TECHNICAL END OF LIFE
DEGREE OF POLYMERIZATION
INITIAL : 1200
POOR : 300
Variation in short circuit impedance of a transformer winding indicates possible movement of winding/deformation within the transformer
With advanced instruments available fortechnical analysis of aged insulation it is possible to determine /measure following properties of insulation paper
2. Water content
3. Tensile strength
4. Degree of polymerization
TENSILE STRENGTH transformers
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.
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.
Degree of polymerization
Pumps running in reverse direction
Thimble-terminal cap fusion due to heating.heat generated due to faulty term.connector.
1 Cotton tape used for gasket locating not removed causing leakage
Core bolt insulation zero
Selector switch contact arm assy not making adequate contactAbnormalities observed during internal inspection/ capital overhauling
Bucholz pipeline slope not proper transformers
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.Abnormalities(continued)
Measurement of mounted bushing done in UST mode , using test tap connection
Measurement of winding is done in GST mode using connections between bushing top terminal and grounded.
420 KV 0.5 or less
245 KV less than1.0
145 KV less than 2
420 KV less than 10
245 KV less than 15
145 KV less than 20
SETTLING TIME transformers
420 KV 72 hours
245 KV 48 hours
145 KV 36 hours
Magnetic balance test is like a signature test transformersDiagnostic tool with focus on current is more importantQualityof core is not assessedif voltage distribution is in order but current are not then further analysis is required
3 Background noise suppression, using a Spectrum analyzer to do selective filtration.
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.
Electrical measurements are not sufficient to indicate this type of displacement of coil or insulation.
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.
FREQUENCY RESPONSE ANALYSIS transformers
Above data required effectively used more as signature
NETT FLUX WHICH IS NOT LINKED BY BOTH COILS
CASE STUDY transformersNew 390 MVA generator transformer
PROBLEM Core overheating Yoke overheating Tank & top cover overheating
Due To overheating caused by eddy currents flowing in top cover or bell cover visible deterioration of gasket was observed
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.
On line acidity Reduction
HIGHER COST ALMOST DOUBLE
RATE OF LOWERING DP VALUE IS RELATIVELY MUCH SLOWER IN SF6 THAN NITROGEN AND OIL
TRANSFORMER ASSEMBLY IN PROGRESS transformers