1. Welcome to the Presentation on Transformer Oil Characteristics Filtration & Reclamation techniques
Operation & Maintenance of Distribution Transformers, Prevention of Failures & Repairs (C&D employees)
(DIST TFs)

2. TRANSFORMER OIL CHARACTERISTICS
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3. TRANSFORMER OIL CHARACTERISTICS
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4. TRANSFORMER OIL CHARACTERISTICS
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6. TRANSFORMER OIL CHARACTERISTICS
1. Appearance: A representative sample - of the oil shall be examined on a 100-mm thick layer at 27°C
Clear transparent free from suspended matter or sediments
2. Density at 27°C g/cm3 (Max)
0.89
3.Kinematic Viscosity: Cst.at 27ºC
27 (Max)
4. Interfacial Tension, Newton/M at 27°C (Min)
0.04
5.FlashPointbyPanskyMartens apparatus (closed cup method), °C (Min)
140
6.Pour Point, ºC (Max)
-10

7. TRANSFORMER OIL CHARACTERISTICS
7. Neutralization Value
(a) Total Acidity, mg KOH/gm(Max}
(b ) Inorganic Acidity
0.03
Nil
8. Dielectric dissipation factor (Tan –delta) at 90° C (Max.)
0.005
9. Breakdown voltage (Min.)kV(rms)
New untreated oils
After treatment 30 50

8. TRANSFORMER OIL CHARACTERISTICS
11.Specific Resistance (Resistivity),Ohm-cm
(a) At 90°C(Min)
30x1012
(b) At 27°C (Min)
500x1012

9. TRANSFORMER OIL CHARACTERISTICS
Recommended limits for mineral oils filled in new Power Transformer:
Property
Highest voltage of equipment (kV)
<72.5
72.5 to 170
>170
Appearance
Clear free from sediment and suspended matter
27°C (g/cc) max
0.89
27°C max cSt 27
Flash point °C (min)
Pour point °C (max)
140
-10

10. TRANSFORMER OIL CHARACTERISTICS
Recommended limits for mineral oils filled in new Power Transformer:
Property
Highest voltage of equipment (kV)
<72.5
72.5 to 170
>170
Neutralization value (mg KOH/g) max
0.03
Water content PPM max
0.01
Interfacial tension dynes/cm 20
>20
Dielectric dissipation factor at 90°C
0.005

11. TRANSFORMER OIL CHARACTERISTICS
Recommended limits for mineral oils filled in new Power Transformer:
Property
Highest voltage of equipment (kV)
<72.5
72.5 to 170
>170 Appearance
Resistivity at 90°Cohm-cm min
6x1012
Breakdown voltage kV min 40 50 60
Oxidation stability of uninhibited oil (after oxidation)
Neutralization value (mg KOH/g) max
0.4
Sludge % by mass Max
0.1
Oxidation stability of inhibited oil
Similar values before filling

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13. OIL FILTRATION-STREAM LINE FILTER
The filter unit comprises a number of edge- type filter elements mounted in a chamber and totally enclosed in a vessel.
Each element consists of a stack of thin paper discs compressed by springs on metal rods to form filter columns (See Fig)
When cleaning becomes necessary it is achieved simply and quickly, without dismantling the plant, by passing compressed air through the filter in the reverse flow direction. The dislodged particles are then removed via a sludge drain valve.

14. Principle of Stream-Line Filter Pack

15. OIL FILTERATION-STREAM LINE FILTER
To obtain maximum operating efficiency the temperature of the oil to be treated has to be raised. This is achieved by an integral heat exchanger incorporating electrical heaters thermostatically controlled and interlocked with the re-circulating pumps to prevent accidental overheating of the oil.
The heater elements can be replaced without the need to drain the oil from the heat exchanger.

16. OIL FILTERATION-STREAM LINE FILTER
Basically the dehydration and degassing chamber is a vacuum receiver fabricated throughout from mild steel and fitted with a detachable cover to from a chamber capable of withstanding medium or high vacuum conditions.
Air, water and any gaseous contaminants are evacuated from the top of the chamber by vacuum pump and exhausted to the atmosphere.
A high level float switch protects the vacuum pump against oil rising to the level of the pump inlet and a vacuum gauge is fitted to the chamber.

18. OIL FILTERATION-STREAM LINE FILTER
The unit is completely self-contained and oil entering the plant passes through a metering pump designed to give the specified rated flow of oil.
Before entering the filter chamber the oil is heated to approximately 70o C in the heat exchanger which is located below the filter chamber in order to reduce heat losses.

19. OIL FILTERATION-STREAM LINE FILTER
The oil being filtered passes from the outside to the inside of the Stream- Line filter columns through the minute interstices formed between the paper filter discs leaving even the smallest solids on the outside edges. As the oil flows through these very small spaces, it is dispersed into very thin films thereby providing the maximum area for moisture to evaporate and it is this thin film effect which produces the required filtration.
The oil passing from the filter chamber directly into the vacuum chamber flows over the outside of the filter chamber allowing further gas and moisture to be extracted to atmosphere.

20. OIL FILTERATION-STREAM LINE FILTER
The treated oil accumulates at the base of the vacuum chamber and is drawn off by a multi-stage centrifugal pump which maintains an oil seal between vacuum chamber and outlet pipeline.
Cold oil filtration is recommended where heat soluble contaminants such as varnish are present in the oil. Under this condition they remain out of solution and can more easily removed during passage through filters.

21. THANK YOU