What’s the Breakdown Voltage of Transformer Oil

Welcome to Lucyelec Test Equipment company. Lucyelec is the professional enterprise who is engaged in providing and export of diversified transformer oil and electrical test instruments since 2015. It’s the reliable partner and provider of China test and measurement instruments in Baoding China. In this article, we will talk about what is the Breakdown Voltage of transformer oil.

1. Transformer oil

Transformer oil, also known as insulating oil or mineral oil, serves as a dielectric and a coolant in transformers, oil type vacuum circuit breaker, cable, etc. Transformer oil has excellent electrical insulating properties and is stable at high temperatures. Transformer oil is used in oil-filled electrical power transformers to insulate, stop arcing and corona discharge, and to dissipate the heat of the transformer (i.e. act as a coolant).

2.Breakdown Voltage of Transformer Oil

The breakdown voltage (BDV) of transformer oil is also known as dielectric strength of transformer oil. Breakdown voltage is measured by observing at what voltage, sparking between two electrodes immersed in the oil, separated by a specific gap (standard 2.5mm). A low value of BDV indicates presence of moisture content and conducting substances in the oil. A good transformer can resist higher voltage.

 

As the reliable China supplier of Transformer Oil Breakdown Voltage Tester, Lucyelec can supply you diversified automatic transformer oil BDV testers

 

For measuring BDV of transformer oil, Lucyelec portable BDV measuring kit is generally available at site. In this kit, oil is kept in a pot in which one pair of electrodes are fixed with a gap of 2.5 mm between them. Now slowly rising voltage is applied between the electrodes. The rate of rising voltage is controlled at 2 KV/s and observe the voltage at which sparking starts between the electrodes. That means at which voltage dielectric strength of transformer oil between the electrodes has been broken down.

This measurement is taken 3 to 6 times in the same sample of oil, and we take the average value of these readings. BDV is an important and popular test of transformer oil, as it is the primary indicator of the health of oil and it can be easily carried out at the site.

3.Why is the transformer Insulating oil breakdown voltage test very important?

Insulating oil is widely used in liquid-filled high-voltage electrical equipment, such as power transformers, distribution transformers, transformers, bushings, oil-filled circuit breakers, oil-filled cables, oil-filled capacitors, etc. Insulating oil also acts as a coolant to dissipate electrical heat in the device. Therefore, the insulating oil should have good thermal conductivity and chemical stability at high temperatures, so before the insulating oil causes internal arcing or complete equipment failure, regular oil withstand voltage testing of transformers is an important preventive measure that will help keep the high-voltage equipment running normally, otherwise it will cause transformer failure or even casualties.
ASTM D1816, ASTM D877, and IEC 60156 are some of the popular standards that specify the dielectric strength or breakdown value and breakdown procedure for testing oil samples. The test procedure is to take a sample of insulating oil from the oil drain valve of the transformer and measure its breakdown voltage, the test voltage is applied to the electrodes immersed in the insulating oil at a constant, standard slew rate (eg 2kV/sec. The test can be carried out five to six times, and the average value of these readings can be considered as the breakdown voltage of the insulating oil under test.
The dielectric breakdown or breakdown voltage of the insulating oil should not be lower than the specified value of the recommended value. If the breakdown voltage is close to the specified limit, the sample must be subjected to further diagnostic tests such as oil resistivity and dielectric dissipation factor (tan delta) tests. As per IEEE standard, it is recommended that oil breakdown voltage tests be performed twice a year.

4.The principles and steps of the insulating oil breakdown voltage test.

When a voltage is applied to the insulating oil, as the voltage increases, the current through the oil increases sharply, causing it to completely lose its inherent insulating properties and become a conductor. This phenomenon is called breakdown of the insulating oil. The critical voltage value at which the insulating oil breaks down is called the breakdown voltage or dielectric breakdown. The electric field strength at this time, called the dielectric strength of the oil, indicates the ability of the insulating oil to resist the electric field. The relationship between the breakdown voltage U (kV) and the dielectric strength E (kV/cm) is:

 E=U/d“   d”=The distance between the electrodes (cm).

5. Test Standards of Transformer Oil Breakdown Voltage Test

There are many test standards for insulating liquids, but they are derivatives of three main standards. Two of these are from ASTM International (USA) and the other is from the IEC (Europe). These main standards are:

ASTM D877 – Standard Test Method for Dielectric Breakdown Voltage of Insulating Liquids Using Disk Electrodes.

ASTM D1816 – Standard Test Method for Dielectric Breakdown Voltage of Insulating Oils of Petroleum Origin Using VDE Electrodes.

IEC 60156 Insulating Liquids – Determination of the breakdown voltage at power frequencies – Test method.

 

Thanks for visiting our website. Lucyelec main products are Insulating oil tester, Transformer test sets, HV Hipot tester,  Switchgear analyzer, Relay test sets, Energy meter calibrator, Cable fault locator, Battery tester, and Safety Tools Test Equipment. Lucyelec products are widely used in electric power, wind solar new energy, petroleum chemical, railway, construction, and many more fields.

We also accept OEM/ODM orders and outsourcing services.

Striving for diversified test and measurement instruments, professional technical support and experienced export services. Lucyelec sincerely look forward to your cooperation. Let’s Win-win together.

 

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