transformer insulating oil..

[powerjunx]

hi folks..
i would like to know; what is the passing "standard dielectric voltage breakdown of transformers"? and also, is the distance between the plates of oil tester has its definite or specific "GAP" for its corresponding Kilovolts reading? Can it be computed? then how?
i appreciate much all your opinions..
Thanks..

fbjavier

 

[Newton1Law]

I would refer to the ASTM Standards for the information your looking for. Usually 32 to 36 kV per 1/8" gap is the minimum expected for new transformer oils. The testing method used however is subject to the precondition of the oil. Attached below for your reference is information from the ASTM Standards WEB page.

Hope this helps.


D1816-97 Standard Test Method for DIELECTRIC BREAKDOWN Voltage of Insulating Oils of Petroleum Origin Using VDE Electrodes
Copyright 2002 ASTM International,
West Conshohocken, PA. All rights reserved.
1. Scope
1.1 This test method covers the determination of the DIELECTRIC BREAKDOWN voltage of insulating oils of petroleum origin. This test method is applicable to liquid petroleum oils commonly used in cables, transformers, oil circuit breakers, and similar apparatus as an insulating and cooling medium. The suitability of this test method for testing oils having viscosities of more than 19 cSt (mm /s) (100 SUS) at 40°C (104°F) has not been determined.
1.2 This test method is more sensitive to the deleterious effects of moisture in solution than is Test Method D877, especially when cellulosic fibers are present in the oil. It has been found to be especially useful in diagnostic and laboratory investigations of the DIELECTRIC BREAKDOWN strength of oil in insulating systems.
1.3 This test method is recommended for testing filtered, degassed, and dehydrated oil prior to and during the filling of power systems apparatus rated above 230 kV, and for testing samples of oil from the apparatus after filling. It is also finding increased usage for testing oils from transformers in service.
1.4 This test method is not recommended for, and should not be used for, acceptance tests on oil received from vendors in tank cars, tank trucks, or drums.
1.5 Both the metric and the alternative inch-pound units are acceptable.
1.6 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.


D877-00 Standard Test Method for Dielectric Breakdown Voltage of Insulating Liquids Using Disk Electrodes
Copyright 2002 ASTM International,
West Conshohocken, PA. All rights reserved.
1. Scope
1.1 This test method describes two procedures, A and B, for determining the electrical breakdown voltage of insulating liquid specimens. The breakdown test uses ac voltage in the power-frequency range from 45 to 65 Hz.
1.2 This test method is used to judge if the disk electrode breakdown voltage requirements are met for insulating liquids, as delivered from the manufacturer, that have never been filtered or dried. See Specification D3487, Specification D4652, and Guide D5222 for the minimum specified electrical breakdown. This test method should be used as recommended by professional organization standards such as IEEE C57.106.
1.3 Limitations of the Procedures
1.3.1 The sensitivity of this test method to the general population of contaminants present in a liquid sample decreases as applied test voltages used in this test method become greater than approximately 25 kV rms.
1.3.2 If the concentration of water in the sample at room temperature is less than 60 % of saturation, the sensitivity of this test method to the presence of water is decreased. For further information refer to RR: 327-1006.
1.3.3 The suitability for this test method has not been determined for a liquid's viscosity higher than 900 cSt at 40oC.
1.4 Procedure Applications--Procedure A is used to determine the breakdown voltage of liquids in which any insoluble breakdown products easily settle during the interval between the required repeated breakdown tests. These liquids include petroleum oils, hydrocarbons, and askarels (PCB) used as insulating and cooling liquids in transformers, cables, and similar apparatus.
1.4.1 Procedure B
1.4.1.1 This procedure is used to determine the breakdown voltage of liquids in which any insoluble breakdown products do not completely settle from the space between the disks during the 1-min interval required in Procedure A. Procedure B, modified in accordance with Section 17 of Test Methods D2225, is acceptable for testing silicone dielectric liquids.
1.4.1.2 Procedure B should also be applied for the determination of the breakdown voltage of liquid samples containing insoluble materials that settle from the specimen during testing. These may include samples taken from circuit breakers, load tap changers, and other liquids heavily contaminated with insoluble particulate material. These examples represent samples that may have large differences between replicate tests. The use of Procedure B will result in a more accurate value of breakdown voltage when testing such liquids.
1.4.1.3 Use Procedure B to establish the breakdown voltage of an insulating liquid where an ASTM specification does not exist or when developing a value for an ASTM guide or standard. Procedure A may be used once the single operator precision of 13.1 has been demonstrated.
1.5 Both the SI and inch-pound units are equally acceptable.
1.6 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.

 

[welshwizard]

In the UK doing an electric strength test using the "withstand test"
Ideal test temp 15C to 25C at atmospheric pressure

Set gap to 4mm

Fill container and start testing within 10 min
Increase test voltage in 2kV steps upto 30kV for 11kV oil sample
If test fails carry out two further tests within 20 min period of filling test cell

If sample passes two out of three then it should have passed

Dont forget to test for moisture content to!
Hope this helps

 

[jbartos]

Suggestion: Visit

http://grouper.ieee.org/groups/tran...omments on Recirculation Ballot C57.106D7.pdf

for:
The official title of the ASTM dielectric strength standards (D877 and D1816) is “Dielectric
Breakdown Voltage” so while dielecric strength may be the common usage, the correct term is
above and probably will replace his suggestions of breakdown voltage. Further, in ASTM
D2864 on definitions the term “dielectric breakdown voltage” is defined. (A similar definition
is given for “dielectric strength.” So are the two terms synonomous?) On the remaining
comments, the issues raised are direct quotes from ASTM.

 

[jbartos]

Small encore: Reference:
1. Donald G. Fink, H. Wayne Beaty "Standard Handbook for Electrical Engineers," 14th Edition,
Section: Testing for Oil Dielectric Strength on page 10-45. It also invokes ANSI/IEEE Std C57.106.

 

[electricpete]

Sounds like good answers. Some factors that could be considered in the answer of "what is the limit":

There will be a different spec for just-processed degasified oil going into a transformer than for an oil sample on a transformer in service.

There might be different requirements appropriate depending on the voltage class.

The limit you apply may depend on the test method used (different limit for 1816 than D877). Great job of newton1law of describing those methods.