1. Insulating and Cooling Medium
Transformer Oil
Insulating and Cooling
Medium

2. Silica Gel
oil Sample 2
Taking Oil Sample
Interfacial Tension Test
Omicron Oil Training

3. Dielectric breakdown (ASTM D-877 & D-1816)
The dielectric breakdown is an indication of the oil’s ability to withstand electrical stress. The most commonly performed test is ASTM D-877, and because of this, it is more readily used as a benchmark value when comparing different results. The oil sample is placed in a test cup and an AC voltage is impressed on it. The electrodes are two discs, exactly 1 in. in diameter and placed 0.10 in. apart.
The voltage is raised at a constant rate, until an arc jumps through the oil between the two electrodes. The voltage at which the arc occurs is considered the dielectric strength of the oil.
For systems over 230 kV, this test is performed using spherical electrodes spaced 0.04 or 0.08 in. apart (ASTM D-1816). Portable equipment is available for performing both levels of this test in the field.

4. Dielectric breakdown Dielectric breakdown (ASTM D-877 & D-1816)
The dielectric breakdown is an indication of the oil’s ability to withstand electrical stress. The most commonly performed test is ASTM D-877, and because of this, it is more readily used as a benchmark value when comparing different results. The oil sample is placed in a test cup and an AC voltage is impressed on it. The electrodes are two discs, exactly 1 in. in diameter and placed 0.10 in. apart.
The voltage is raised at a constant rate, until an arc jumps through the oil between the two electrodes. The voltage at which the arc occurs is considered the dielectric strength of the oil.
For systems over 230 kV, this test is performed using spherical electrodes spaced 0.04 or 0.08 in. apart (ASTM D-1816). Portable equipment is available for performing both levels of this test in the field.
D-1816 is for transformer oil spherical (round) electrodes

5. Interfacial tension Interfacial tension (ASTM D-971 & D-2285)
The interfacial tension of an oil is the force in dynes per centimeter required to rupture the oil film existing at an oil-water interface. when certain contaminants, such as soaps, paints, varnishes, and oxidation products are present in the oil, the film strength of the oil is weakened, thus requiring less force to rupture. For in-service oils, a decreasing value indicates the accumulation of contaminants, oxidation products, or both.
ASTM D-971 uses a platinum ring to physically break the interface and measure the force required. ASTM D-2285 measures the volume of a drop of water that can be supported by the oil without breaking the interface.

6. Acidity Neutralization number (ASTM D-974)
Acids are formed as by-products of oxidation or sludging, and are usually present any time an oil is contaminated.
The concentration of acid in an oil can be determined by the amount of potassium hydroxide (KOH) needed to neutralize the acid in 1 g of oil. Although it is not a measure of the oil’s electrical strength, it is an excellent indicator of the pressure of contaminants. It is especially useful when its value is monitored over a number of sampling periods and trending data is developed.

7. Power factor of Oil Power factor (ASTM D-924)
The power factor is an indication of the amount of energy that ls lost as heat to the oil. When pure oil acts as a dielectric, very little energy is lost to the capacitance charging. Contaminants will increase the energy absorbed by the oil and wasted as heat. The power factor ls a function of the phasor angle (the angular displacement) between an AC potential applied to the oil and the resulting current.
The test is performed by passing a current through a test cell of known gap, and “sing a calibrated capacitance or resistance bridge to separate and compare the reactive and resistance portions of the current passing through the oil.

8. Color
Color (ASTM D-1500)
The color of a new oil is generally accepted as au Index of refmement. For in-service oils, a darkening of the oil (higher color number), observed over a number of test intervals, is an indication of contamination or deterioration.
The color of an oil is obtained by comparison to numbered standards. Although there are charts available, the most accurate way to determine the oil’s color is by the use of a color wheel and a comparator. An oil sample is placed in the comparator, and the color wheel is rotated until a match is obtained. This test is most effective when results are compiled over a series of test intervals, and trending data is developed.

9. Moisture Content of Oil
Moisture content (ASTM D-1533)
Moisture content is very important in determining the serviceability of an oil; the presence of moisture (as little as 25 parts per million) will usually result in a lower dielectric strength value. Water content is especially important in transformers with fluctuating loads. As the temperature increases and decreases with the changing load, the transformer’s oil can hold varying amounts of water in solution.
Large amounts of water can be held in solution at higher temperatures, and in this state (dissolved) the water has a dramatic effect on the oil’s performance.
Water contamination should be avoided.
(1) Water content is expressed in parts per million, and although water will settle to the bottom of the tank and be visible in the sample, the presence of free water is not an indication of high water content, and it is usually harmless in this state.
The dissolved water content is the dangerous factor; it is usually measured by physical or chemical means. A Karl Fischer titrating apparatus is one of the more common methods of measuring the dissolved water content.
New oil at 25°c can hold 66 PPM of water, at this point the oil is saturated.

10. Dielectric Fluid Mineral Oil – Dominant in power transformers
Vegetable Based Oil, High Temperature, Less Flammable
Synthetic Oil
Dimethyl Siloxane
Polyalphaolefins

11. Transformer Oil Testing
DGA - Dissolved Gas Analysis
Color - Can give an indication of condition
Dielectric Strengths
Oil (New) > 30.0 kV
Oil (In service) > 28.0 kV
Color - This test means nothing by itself. However, it is very significant when there is a marked change.Two tests are provided by ASTM.
D Lab test: Conducted by comparing a sample of oil to some color standards and applies to all types of oils, not just transformer oil.
D Field test: Used form mineral oils that have been used in electrical apparatus. Oil is compared with a series of standard colored disk filters in a hand-held comparator.
Visual Examination - As it is used in determining the color classification, the same is simultaneously checked for cloudiness, turbidity, metallic contaminants, particles of insulation, carbon, or other suspended materials. Good oil should be clear, bright and sparkling. Cloudiness indicates moisture, carbon, and/or sludge.
Dielectric Strength - The dielectric test applies an AC voltage at a controlled rate to two electrodes immersed in the dielectric fluid. This gap between the two electrodes is set at a specified distance. When the current arcs across this gap, the voltage recorded at that instant is the dielectric breakdown strength of the liquid. New oil 35,000 volts (35kv or above) Used oils would not be accepted below 23 kv. P
Flat disk ASTM D877 - Not reflective of transformer conditions and not sensitive enough to test the oil in units above 69 kv, where very dry oil is required. Generally accepted that dissolved moisture will not be detected at all by the D877 unless the oil is at least 60% saturated with moisture.
VDE (ASTM D 1816) A small motor driven, nylon impellor is immersed in the oil to stir the liquid.

12. Transformer Oil Testing
Acid/Neutralization Number
(TAN - Total Acid Number)
Maximum 0.1mg KOH/gm
Interfacial Tension (IFT)
Minimum 18 Dynes/Cm in Maintenance Manual
New Standards will increase (Approximately 24 Dynes/Cm)
Acid/Neutralization Number
An increase in the neutralization number is an index to the rate of deterioration of the oil. Sludge will be the inevitable product of an acid situation that is neglected.
The acid content is expressed as the number of milligrams of potassium hydroxide (KOH) that it takes to neutralize the acid in a one-gram sample of oil.
Interfacial Tension (IFT)
Measures the tension at the interface between two immiscible liquids, oil and water and is expressed in dynes per centimeter.
This test is extremely sensitive to the presence of oil decay products and soluble polar contaminates from solid insulating materials.
The surface tension of clean, pure water is strong enough to hold a small needle carefully placed on top without it sinking in the water. Adding detergent to the water will reduce the surface tension and the needle will sink.
Oil of course floats on top of water. The surface tension between oil and clean water falls in the range of 40 to 50 dynes/cm. Oil oxidation contaminates will lower the IFT.
A sign of sludge in solution may be an IFT in the range of dynes/cm. Badly deteriorated oil has an IFT of 18 dynes/cm or less.

13. Transformer Oil Testing
Power Factor of the oil
Water content of the oil
Depends on Temperature
Inhibitor (Oxygen Inhibitor) content
Power Factor - Whereas the dielectric test measures the level of current necessary to strike an arc through the oil, the power factor test measures the percent of current that leaks through the oil in a test cell. The test cell consists of two metal shells with a small gap between them. The gap is filled with a thin layer of oil to be tested. When the test cell is connected to the test instrument and energized, a small amount of current “leaks” through the oil film. The instrument measures the leakage. Usually tests are made at 25 °C and 100 °C. Any substance in the oil that resists/conducts electricity differently than the oil will affect the power factor reading. Common contaminants include gasoline, kerosene, diesel fuel, lubricating oil, water as well as the oxidation by-products found in heavily oxidized oil. New, properly refined transformer oil has an extremely low power factor. Oxidation, aging, moisture, and other contamination all serve to elevate the power factor.
Water Content of the oil - Temperature versus PPM
Oxygen Inhibitor Content - Easy and inexpesive chemical additative.
Specific Gravity - Relative Density - D This is simply a ratio of the mass of a given volume of oil to the mass of an equal volume of water at a specified temperature. The test is normally conducted by floating a hydrometer in the liquid and taking the reading at the meniscus (curved upper surface). If the reading would be over 0.91, then the oil probably is contains some contaminant - quite possible askarel (PCB); if less than 0.84, then the oil may be a paraffinic oil. (contains parrafins). Nevertheless, specific gravity is useless for detection of accidental mixing wilth lubricating, hydraulic or fuel oil, or pot head compounds as the specific gravities fall into the same range.
Viscosity - The degree to which a liquid resist flow.
Sludge-free life - **********************
Power Factor Valued Oxidation - *************************

14. Transformer Oil Test
Di-electric breakdown

18. New Oil @ 25ᴼ C Saturates with 66 PPM of moisture