EE 3092 Laboratory Practice V
Breakdown Characteristics of Oils
Instructed by: Mr N.P.N.P Premarhathne
Name Index No. Group Field Date of Performance Date of Submission
: : : : : :
S.P.M Sudasinghe 100523G G - 12 EE 2013/09/30 2013/10/21
Name: S.P.M Sudasinghe Index No: 100523G Group: G – 12 Date of Performance: 2013/09/30 Date of Submission: 2013/10/21 Instructed by: Mr. N.P.N.P Premarathne
1. Breakdown of coconut oil Gap (mm)
Breakdown Voltage (kV) 1
2
3
4
5
Average
1.5
9
10
9
11
11
10.0
2.0
11
12
10
12
12
11.4
2.5
12
14
13
15
15
13.8
3.0
17
17
17
17
19
17.4
3.5
24
20
19
21
21
21.0
2. Breakdown of Engine Oil Gap (mm)
Breakdown Voltage (kV) 1
2
3
4
5
Average
1.5
8
12
14
11
13
11.6
2.0
14
16
10
14
14
13.6
2.5
17
14
15
15
16
15.4
3.0
18
14
20
21
19
18.4
3.5
20
20
20
21
25
21.2
Average
3. Breakdown of Transformer Oil Gap (mm)
Breakdown Voltage (kV) 1
2
3
4
5
1.5
7
7
7
7
7
7.0
2.0
9
9
10
8
8
8.8
2.5
9
10
10
11
10
10.0
3.0
12
13
12
12
12
12.2
3.5
16
16
16
15
15
15.6
Breakdown of Coconut Oil Gap (mm)
Breakdown Voltage (kV)
1.5
10.0
2.0
11.4
2.5
13.8
3.0
17.4
3.5
21.0
Breakdown Characteristics of Coconut Oil 26
25
24
) V k ( 23 e g a t l o V22 n w o d k a 21 e r B 20
19
18
17
16
15
14
13
12
11
10
9
8 1
1.5
2
2.5
3
3.5
Gap Distance (mm)
4
Breakdown Characteristic of Engine Oil Gap (mm)
Breakdown Voltage (kV)
1.5
11.6
2.0
13.6
2.5
15.4
3.0
18.4
3.5
21.2
Breakdown Characteristic of Engine Oil 25 ) V k ( e 24 g a t l o V n 23 w o d k a e r 22 B
21
20
19
18
17
16
15
14
13
12
11
10
9
8 1
1.5
2
2.5
3
3.5 Gap Distance (mm)
4
Breakdown Characteristic of Transformer Oil Gap (mm)
Breakdown Voltage (kV)
1.5
7.0
2.0
8.8
2.5
10.0
3.0
12.2
3.5
15.6
Breakdown Characteristic of Transformer Oil 20
) V k ( 19 e g a t l o V n 18 w o d k a e r B 17
16
15
14
13
12
11
10
9
8
7
6 1
1.5
2
2.5
3
3.5
Gap Distance (mm)
4
Comparison of Breakdown Voltage of Oils Breakdown Voltage (kV)
Gap Distance (mm)
Coconut Oil
Engine Oil
Transformer Oil
1.5
10.0
11.6
7.0
2.0
11.4
13.6
8.8
2.5
13.8
15.4
10.0
3.0
17.4
18.4
12.2
3.5
21.0
21.2
15.6
Comparison of Breakdown Characteristics of Oils Coconut Oil
Engine Oil
Tranformer Oil
26
) 25 V k ( e g 24 a t l o V n 23 w o d k a e r 22 B 21
20
19
18
17
16
15
14
13
12
11
10
9
8
7
6 1
1.5
2
2.5
3
3.5
Gap Distance (mm)
4
From all graphs it is clear that the breakdown strength increases as the gap distance increases. It is clear from graph 4 that engine oil has the highest breakdown strength than other two oil samples (coconut oil & transformer oil). Hence based on this test engine oil is the best oil for transformer insulation.
1. Methods of purification of transformer oil before testing Dissolved gasses in transformer oil can cause arcing, corona discharges, and overheating reducing the electrical efficiency and lifetime of the transformer. Likewise, water contamination at levels as low as 30 ppm (parts per million) can adversely affect the insulating strength of the oil. Hence purification of oil is required for proper maintenance and before perform any test on insulating oils.
Drying method can be considered as any process that reduces and maintains at a low level the material's water vapour pressure.
Purification or Reconditioning of insulating oil is the process of removing moisture, dissolved combustible gas and particulate matter, as determined by oil and transformers' tests.
Regeneration or Reclaiming of insulating oil is the process of removal of contaminants and products of degradation such as polar, acidic or colloidal material, as determined by oil and transformer tests.
Water trapped in oil impregnated cellulose materials, indicated by increased water content (and/or de-energised winding power factor and other electrical tests), requires some form of dehydration of the transformer's insulation system. The drying procedures can only reduce the rate of loss of mechanical strength but never regain that which has been lost through neglect. Significant factors concerning the choice of drying method include the type of transformers, ambient and operating temperatures, time limitations, thickness of the insulation pieces, and the vapour pressure of moisture in the surrounding atmosphere. Moisture removal can be can be accomplished by several methods using various combinations of factors. The two general categories of drying, involves the use of heat /or vacuum performed using factory repair shop or field methods-either, power off or power on. Even with all its benefits, improper drying can result in damage to the transformer insulation. The universal demand for higher quality control has resulted in the Heat-vacuum with Coalescing filters being the preferred process. The primary advantage for dehydration of oil with high vacuum in contrast to heat alone lies in a side effect-degasification-which simultaneously occurs. This does not occur with other methods of water removal.
The value of a high degree of dehydration and degasification at the factory or in the field, prior to energising brings these benefits:
Minimizes partial discharge (corona) effect from inadequate oil impregnation.
Removal of unwanted oxygen.
Removal of combustible gases.
Extremely dry oil.
The oil degassing process begins with a pump down from atmosphere and continues until a prespecified vacuum level indicates that complete degassing has been achieved. Depending on the dissolved gas requirements, the temperature of the oil, and the method for evolving the gas; the level is typically set between 0.1 and 5 Torr. This requires a vacuum gauge that can accurately measure pressures in the sub-Torr range. Another important requirement for the gauge is that it be rugged and tolerant of the oil environment. Dial gauges are not accurate enough for the task. Also, the visual-only output of a dial gauge is inadequate for the current and future needs of this application. Functional features like electronic interfacing and settable trip-points provide integration with process controllers, reduce operator error, and enable data logging and documentation.
2. Other tests for testing transformer oil
The most important test that can be done on the liquid insulation of a transformer is an annual Dissolved Gas Analysis (DGA). This test can give an early indication of abnormal behaviour of the transformer. As the name implies, this test analyses the type and quantity of gases that are dissolved in the transformer oil.
The interfacial tension test of electrical insulating fluids is an indicator of the presence of polar compounds. These compounds are considered by some to be an indicator of contaminants of oxidation or deterioration of the materials of transformer construction.
Determination of the colour of petroleum products is used mainly for manufacturing control purposes. It is an important quality characteristic since colour is readily observed by the user of the product. In some cases, the colour may serve as an indication of aging and presence of
contaminants. However, colour is not always a reliable guide to liquid quality and should not be used as a stand-alone test for determination of contamination.
The acidity test is used to estimate the total acid value of the transformer insulating liquid. As acid values increase, (usually due to oxidation of the oil), the insulating quality of the oil decreases. In general, acidic by-products produce increased dielectric loss, increased corrosivity, and may cause thermal difficulties attributable to insoluble components called "sludge.
A power factor (dissipation factor) test measures the dielectric losses in the liquid and hence the amount of energy dissipated as heat. The laboratory normally performs this test at two temperatures,20 degrees C (68 degrees F) and 100 degrees C (212 degrees F), boiling. By testing the oil at a standard temperature, the test results can be compared to standard values. Power factor test results can help reveal the quality and the integrity of the insulation liquid. This information can form the basis for making a judgment on whether it’s suitable for a transformer to continue in service. The screen test can be used as a maintenance test for determining when a filtering or change of the transformer liquid is in need.
The water content test detects the moisture content in parts per million of the liquid insulation. The electrical characteristics of an insulating liquid are dramatically affected by its water content. A high water content may make a dielectric liquid unsuitable for some applications because a deterioration in properties such as dielectric breakdown voltage will occur. This test is suitable for evaluating filtration.
This test reveals the presence of moisture, resins varnishes or their products of oxidation in oil. For transformer rating less than 145 KV, Tan Delta should be maximum 1 and for higher voltages it should be maximum 0.2. This test can perform in two different temperatures at 27 0C and 90 0C.
The measurement of Resistivity of insulating oil is a sensitive test for detection of conducting impurities in insulating oil. The specific resistance in ohm-cm of a liquid is the ratio of the DC potential gradient in volts per centimeter to the current density in ampere per square cm at a given instant of time and under prescribed conditions. High resistance indicates good insulating oil. Resistivity of oil is improved by filtration.
It is the minimum temperature to which oil must be heated so that it gives enough vapour which can form a flammable mixture with the air under the prescribed conditions of the test. A
minimum value of flash point is specified in order to prevent the risk of fire that might result by accidental ignition. Normally a flash point should be greater than 1250C
