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Mineral insulating oil Petroleum origin
Other type Oil with PCB content, Synthetic oil
USES Used in HV equipments like
Transformers, Reactors , CBs, Switchgear,Cables,Capacitors.
TRANSFORMER:
An equipment to Transform power from one circuit (primary) to another circuit (secondary) normally with change in voltage and current but with no change in frequency through mutual induction;
BASIC COMPONENTS IN A TRANSFORMER
Core
Winding
Insulation Life of transformer Life of insulation
TRANSFORMER OILAn essential part of oil filled
Transformers (there are other types of Transformers like dry
type , SF6 etc)
OIL IN TRANSFORMER Acts as an insulant (paper is the
other major insulation and is termed the solid insulant).
Acts as a coolant (heat from the core and
windings dissipates through oil)
Preserves core and coil assembly
Impregnates winding Insulation
Replaces air cavities
Improves PD behaviour
DEPENDS ON CRUDE NATURE (ORIGIN OF CRUDE )
DEPENDS ON REFINING PROCESS. Hydrocracking Hydrogenation Acid treatment Clay treatment.
NATURE AND CHARACTERISTICS OF
TRANSFORMER OIL
CrudeDistillation
TOBSRefining/Treatment
(acid, hydrotreatment, solvent extrn) Clay treatment
FiltrationTransformer oil
MANUFACTURING PROCESS
NATURE AND COMPOSITION
OF OIL CHAIN OF HYDRO CARBONS (CH) 84% carbons,14% hydrogen ,1-3
% sulphur, 1% N2,O2 metals &salts
MAIN CONSTITUENT TYPES Napthenic Paraffinic Aromatic
PARAFFINIC TYPE
Derived From Crudes Having Substantial
Contents of Naturally Occurring N Paraffinic (Wax ) – require Dewaxing
Chain Structure
Most Commonly Used in India
High Viscosity, Low Resistivity
NAPTHENIC TYPE
Derived From Crudes Having very Low Naturally Occurring N
Paraffinic(wax)contents
Has Low Natural Pour Points,no Dewaxing Requirement
Cyclic Structure and Hence Stronger Bonding
Used Abroad &Now Also in India
Low Viscosity, High Quality, Costlier
IDEAL TRANSFORMER OIL
Low Density & Low Viscosity - Better Heat Transfer
Low Pour Point- Avoid Solidification
High Flash Point - Fire Resistance
Low Dissipation Factor - Less power loss
High BDV -High Voltage Application
High Resistivity - Better Insulation Resistance
STANDARDS
Important Indian Standards for Acceptance, Limit Values and
Interpretation
IS 335/1993 for New Oil IS 1866/2000 for Oil in Service IS 10593 for DGA
There Are Other Standards for Testing Methods.
CHEMICAL TESTS
Acidity Oxidation stability Water content SK value Inhibitor content Corrosive sulphur Sludge
SIGNIFICANCE AND MEANING OF TESTS
APPEARANCE
Clear, Transparent : No suspended matters and
sediments
COLOUR OF OIL:Clear pale yellow : GoodBright yellow : O.K.
Amber,Brown: Start of deterioration/Sludge
Green :Dissolved Cu or metallic contaminants;
Investigate and Repalce oil
Bad smell oil : Investigate and replace oil
Applicable Standards: IS 335, 1866
DENSITY
Mass per unit volume;
Higher Density Means Higher Viscosity
Which Will Reduce Oil Flow and
Hence Affects Heat Dissipation.
Transformer Oil Density Max =0.89g/cm3
Applicable Standards : IS 1448 ,335, 1866/2000
VISCOSITY
Resistance to Flow; High Viscosity Means Higher
Resistance to Flow.
Hence Low Viscosity Oils to Be Preferred.More heat transfer;Value-27 cstApplicable Standards : IS 335, 1866
POUR POINT
Temperature at Which Oil Begins to
Solidify
Lowest temperature at which oil flows
Cold weather application
Value : -6°c
Applicable Standards : IS 1448 , 1866
FLASH POINTFLASH POINT
The minimum temperature at which oil when heated gives off enough vapour to form a flammable mixture with air.
This test assumes significance after an arcing fault inside a transformer.
If FP is low -- Fire risk
Flash point can reveal presence of volatile and flammable materials
in oil
APPARATUS :
Fully Automatic Flash Point Test Kit has Been Procured Recently for the Chennai R&D Lab.
LIMITS:
New oil: 140 C (Min)
Transformer New Before commissioning 140 C
(Min)
In service 125C (Min) and should not to decrease by
more than 15 C from previous value.
Applicable Standards : IS 1448 ,335, 1866
The flame is automatically dipped for every 3 deg(settable value), starting from 105 deg till the flash point occurs. The flash point is displayed automatically.
IFTInterfacial tension between oil and water surface.
It is the force necessary to detach a planar ring. IFT is a good indicator of oil quality and it should
be high. Very low IFT oil indicates sludge and deterioration. IFT helps in the detection of polar contaminants . Apparatus: KRUSS / German makeLimits: New oil :0.040 N/m Transformer New before commissioning : 0.035
N/m For in service Transformer : min 0.015 N/m Applicable Standards : IS 6104,335,1866
CORROSIVE SULPHUR
To detects corrosive and free sulphur compounds in oil.
If present they are hazardous and deteriorates metal parts of transformer .
Requirement – Non corrosive
Applicable Standards : IS 335
AcidityThe acid content in the oil and plays a major part in oil contamination.
High Acidity: Metal parts corrosion, Insulation deterioration,Sludge formation.
Limits: New oil:0.03 mg KOH / gm(Max) Transformer New before commissioning : 0.03 mg KOH / gm (Max) For in service Transformer : 0.3 mg KOH /
gm(Max) Applicable Standards: IS 1448, 335, 1866
OXIDATION STABILITY
Stability of oil under oxidation .
Acidity & Sludge are tested after subjecting oil to ageing .
Acidity max: 0.4 mg KOH/g
Total Sludge : Max 0.1%
Applicable Standard : IS 335
WATER CONTENTAmount of dissolved water in oil.
The test is carried out using automatic
coulomatric titration and expressed in PPM. If high, affects BDV,IR value/winding PF.
Apparatus
Automatic water content test kit swiss make
Inject the oil in the syringe into the Automatic Titrator kept ready; Titration is started and goes on until end point is detected;
Weigh the empty syringe to find the weight of oil alone; The weight of oil is automatically transferred to the titrator for calculation;
The software does the necessary calculations and the water content is displayed automatically in ppm.
Limits : New oil 50 (max) New Tr. In
service Tr.
For V >170KV 10ppm 20 ppm For V between 72.5 to 170 KV 15 ppm 40 ppm For V < 72.5 KV 20 ppm 50 ppm Applicable Standards : IS 13567, 335, 1866
Before commg
SK VALUE
Degree of refining of oil .Optimum H2SO4 dosage during refining
results in good quality oil.No limits prescribed in standards Preferable value 2 to 4%Very low over refining, natural anti
oxidation are killed.Very high under refined.Applicable Standards: IS 335
BDV Why oil should have high BDV? Transformer insulation composite insulation --
Paper and oil Electrical stress = 1/Dielectric constant Dielectric constant of cellulose = 4.5 Dielectric constant of Transformer oil : 2.1 – 2.2 Electrical stress on Transformer oil is double for
the same thickness. Hence oil should have high BDV .
The Breakdown Voltage value of oil in KV measured across 2.5mm gap electrodes.
It is the min. voltage at which the oil breaks down when subjected to an electric field with a continuously increasing voltage, contained in a specified apparatus.
Low BDV indicate presence of contaminants such as water , dirt, cellulose fiber or conducting particles
Limit value :New oil 30 KV , min (un filtered) 60 KV min (filtered) Minimum requirement New Tr. Before
commg Inservice Tr.For V >170KV 60 KV 50 KV
For V between 72.5 to 170 KV 50 KV 40 KV
For V < 72.5 KV 40 KV 30KV
Applicable Standards: IS 6792, 335, 1866
DDF
Quality of oil
Measure of dielectric loss in oil and hence the amount of energy dissipated as heat.
Low DDF – Good oil, as it indicates low dielectric losses and and low level of soluble polar ionic or colloidal contaminants.
The dielectric dissipation factor and is a measure of the quality of oil. It is the tangent of the angle (delta) by which the phase difference between applied voltage and resulting current deviate from 90° when the dielectric of the capacitor consists exclusively of the insulating oil. Will be high if oil has conducting impurities, moisture, ageing products like acid and sludge.
LIMITS:
New oil 0.002 (max) at 90°C (filtered oil) Transformer new before commissioning Max : 0.010, for v > 170 KV Max: 0.015, for v <170 KV In service Transformer (max) : 0.2, v > 170 KV (Max): 1, for v < 170
KV Applicable Standards: IS 6262, 335, 1866
RESISTIVITY
RESISTANCE PER UNIT VOLUME RESISTANCE BETWEEN OPPOSITE FACES OF A CENTIMETRE CUBE OF OIL - - CM.MEASURE OF ELECTRICAL INSULATING PROPERTY , HIGHRESISTIVITY – LOW FREE ION AND CONDUCTING CONTAMINANTS. WILL BE LOW IF OIL HAS CONDUCTING IMPURITIES, MOISTURE AND FREE IONS. AFFECTS IR VALUE.
LIMITS:
For new oil : 35x1012 Ohm--cm (min) at 90 °C
1500x1012 Ohm-cm (min) at 27 °C
For Transformers New before commissioning : 6x1012 Ohm-cm
For In service Transformers : 0.1x1012 Ohm-cm
Applicable Standards: IS 6103, 335, 1866
SLUDGE
For all voltages should be Nil
About 40ml of oil is taken in the oil cell and the entire test is carried out as per the IS with the help of built in software ;
The results are displayed as shown;
TEST PROCEDURE
BUCHHOLZ GAS COLLECTION TEST
Test with Silver Nitrate –solution1(AgNo3) COLOR: No color – Air – investigate air
collection WHITE BLACK : Presence of CO –
Deterioration of solid insulation – DGA , Furan tests .
WHITE : Presence of Acetylene – Arcing – Hi temp oil degradation – DGA – Internal Inspection.
TEST WITH AMMONIACAL SILVER NITRATE SOLUTION
Color : No color – air Red brown to black with Silver gray
intermediate – CO Green Yellow – Acetylene Combustibility Test: Collect portion of Gas in a test tube and apply
a lighted match stick to check combustibility of the gas.
If not combustible -- Air
Most commonly carried out test on oil Test Equipment Modern Fully Automatic KitSTEP BY STEP PROCEDURE 1. Gap between electrode of 2.5mm +/- 0.01
2. Take sample oil, Rinse twice the electrode and container
3. Take oil in the container sufficiently to immerse the
electrodes4. Switch on the BDV equipment, keeping in place the
oil container.
BDV TEST
5. Allow 10 minutes initial time (as per IS)
6. Raise voltage at 2KV/sec rate and the oil breaks at a voltage.
7. After the first break (it may be a low value but still has to be taken), stir oil using magnetic stirrer for 2 minutes and allow stand time of two minutes. Then raise voltage to get second trip (breakdown) value.
8. Repeat the above for 6 readings. Take the average
of 6 readings for the BDV value of the oil
Note:
1. Oil for BDV test from the transformer should be taken from the bottom sampling valve with due precautions.2. Care should be taken to avoid air bubbles3. BDV test should always be done at ambient temperature.
4. Humidity should not be more than 50%
5. Spheres must be cleaned of deposits preferably by steel wool. Never use cotton, fibrous materials.
6. Sampling vessel to be dry, clean; Hands also to be dry and clean; atm. to be dry;
7. Sample to be protected from light, air and moisture
8. Sample to be drawn very quickly and tested within a few hours
TEST PROCEDURE
Observing proper precautions, take about 400ml of sample oil in the test vessel;
The gap set is 2.5mm
• The oil is kept in the test kit and the preset test procedure as per Indian Standard is activated;
• The BDV value is displayed automatically at the end of the test;
OIL QUALITY TEST (all the
above tests determine oil quality)
OIL TEST
DGA TEST (determines
transformer healthiness)
AGEING AND DETERIORATION OF TRANSFORMER OIL
CAUSES OF DETERIORATION Thermal stress Electrical stress Chemical contamination Gaseous contamination
ARRESTING DETERIORATION Procuring good quality oil Proper maintenance Prevention of moisture/air entry through
leak points, sealing and breather etc.
How to know oil condition and level of deterioration?
by periodical testing and comparing the characteristic with prescribed limit values
Why take action if oil is deteriorated? Deteriorated oil
can transfer moisture to paper and lower IR value (resistivity, water content)
can reduce heat dissipation (IFT, sludge) can affect other components of the
transformer (water content, acidity) can contribute to transformer failure
What action to be taken if oil is deteriorated? --- depends on degree of deterioration
Corrective actions available ---- Reconditioning, Reclamation and Replacement.
Reconditioning---- When the following characteristic becomes bad
on a sustained basis: BDV, water content, IFT and sludge.Also for degassing oil.
Reconditioning normally cannot improve acidity,
resistivity and tan delta significantly.
Reclamation Promising area
Currently carried out only in Distribution Transformers
Re refining
some apply refining and filtering to used oil as is done in the same way transformer oil is manufactured from crude oil. This involves no addition of inhibitors.
Replacement
Resorted to when Acidity, Resistivity, Tan delta and IFT are very
poor Served more than 10 years After confirming deteriorating trend Resistivity less than 0.03*1012 with very low
IR/PI value or high winding tan delta value
On line Filtration techniques Moisture absorbing cartridges
Oil quality summary
We have so far seen
Type and composition of oil
Oil quality parameters
Significance
Why we should preserve the oil characteristics throughout the life of the transformer