ArtsAutosBooksBusinessEducationEntertainmentFamilyFashionFoodGamesGenderHealthHolidaysHomeHubPagesPersonal FinancePetsPoliticsReligionSportsTechnologyTravel

Transformer Oil and its properties.

Updated on May 5, 2016

Transformer oil is one of the very important component in oil immersed transformers. The life expectancy and satisfactory operation of transformers are mainly depend on the oil in which is immersed.

The transformer oil performs two very important functions.

1. It creates an acceptable level of insulation in combination with the insulating materials used in the conductors and coils.

2. It also acts as a coolant to extract heat from the core and the windings.

Transformer oil

The oil used in transformers is hydrocarbon mineral oil. It is mainly composed of four generic classes of organic compounds, aromatics, paraffins, napthenes and olefines. Transformer oil gives a better insulation when aromatics, paraffins, napthenes and olefines are present at the right proportion. For better insulation Transformer oil is desired to have more of saturated paraffins and less of aromatics, napthenes and olefines. For more stability, more aromatics and napthenes are necessary. To get both insulating property and stability at the same time, there must be an optimum mix of four organic components. This can be obtained by careful refining of crude oil. Vegetable and animal oils form fatty acids and attack the fibrous insulating materials and hence cannot be used in transformers.

A good transformer oil must have the following Physical, chemical and electrical properties.

Physical properties

Oil density

The maximum value of density of transformer oil at 29.5 oC must not be more than 0.89 gm/cc.

Viscosity

It is the measure of resistance to the flow of a fluid with the effect of external forces. This property of the fluids is inversely proportional to temperature. It increases with decrease in temperature. But in case of transformer oil it is necessary that viscosity remains low at low temperature. The maximum permissible level of viscosity at 27 oC is 27 cSt.

Flash point.

It is the temperature at which oil gets vaporized and when this vapor mixes with air, forms an ignitable mixture and may cause momentary flash. To prevent the risk of fire the transformer oil must have a high flash point. The flash point must be greater than 140oC.

Moisture constant

It is the amount of dissolved present in oil expressed in ppm/kg. the insulating property of the transformer oil will be degraded by the presence of moisture. The maximum allowable moisture constant is 50 ppm.

Pour point

It is the temperature at which oil just commences its flow under prescribed conditions. The specified pour point is -6oC.

Chemical Properties

Neutralization value

It is the measure of acidity of oil. It is the measure of organic and inorganic acids present in the oil. It is expressed in terms of milligrams of base required to neutralize the total force acid present in one gram of oil. The recommended maximum value of neutralization is 0.03 mg KOH/gm. Higher the neutralization value, higher the acidity leading to higher sludge formation.

Corrosive sulphur

The presence of chemicals in the transformer oil will lead to the formation of black deposits over the copper parts of the transformer. Hence the heat dissipation is highly affected. Since transformer oil is derived from petroleum it definitely contains traces of sulphur. The presence corrosive of sulphur in the transformer oil is not recommended.

Oxidation stability

The neutralization value of transformer oil increases on getting oxidised. The neutralization value must not go beyond 0.4 mg KOH/gm after oxidation and total sludge after oxidation must not be more than 0.1% of weight of oil used.

Sediment and perceptible sludge

Sludge is poor conductor of heat. Sludge deposited over the transformer parts leads to poor heat dissipation. It blocks the flow of oil in ducts and impairs cooling. Therefore once sediments or perceptible sludge are detected oil is considered as not usable.

BDV testing instrument

Transformer oil is placed between a sphere gap and the voltage across the electrodes is raised gradually till Break down of oil occurs. Break down is characterized by formation of arc between the electrodes.
Transformer oil is placed between a sphere gap and the voltage across the electrodes is raised gradually till Break down of oil occurs. Break down is characterized by formation of arc between the electrodes.

Electrical properties

Breakdown voltage (BDV)

It is the voltage is the voltage at which transformer oil losses its dielectric property and starts conducting. It represents the electrical property of transformer oil. The presence of moisture, sludge contaminating agents and sediments decreases the dielectric property of oil. For a new sample of oil the breakdown voltage of transformer oil is 30kV and for a sample after filtration must have BDV of 60kV.

Resistivity

It is one of the most sensitive properties of transformer oil. The resistivity of the oil decreases with increase in temperature. The transformer oil must have a minimum resistivity of 30 x 1012 ohm-cm at 90oC and 1500 x 1012 ohm-cm at 27oC.

Dielectric dissipation factor (DDF)

It is numerically equal to the sine of loss angle. A High value of DDF refers to poor quality of oil. The maximum recommended value of DDF factor of oil at 90oC is 0.002.

Physical constants of Transformer oil

Property
Recommended value
Permitivity
2.2
Thermal conductivity
0.12 W/m deg C
Specific Heat
2.06 kJ/kg deg C
coefficient of Expansion
0.00078/ deg C
Mean density factor
0.00065/ deg C
The above parameters are based on IS 335

The transformer is affected by its operating conditions such as operating temperature, atmospheric conditions, electric strength, moisture content and other contaminations and sludge formation. The presence of moisture or suspended particles in transformer oil affects its dielectric property. Hence transformer oil it should be tested periodically. If the oil is containing moisture or suspended particles it should be filtered or replaced by fresh oil.

Check how far you understood the topic!

view quiz statistics

Comments

    0 of 8192 characters used
    Post Comment

    • profile image

      Aloke Bhattacharyay 

      2 years ago

      Are there any rule to keep/ store oil drum by laid horizontally?

    • profile image

      manish Bajrang 

      3 years ago

      Best site of ..electrical engineers

    working

    This website uses cookies

    As a user in the EEA, your approval is needed on a few things. To provide a better website experience, hubpages.com uses cookies (and other similar technologies) and may collect, process, and share personal data. Please choose which areas of our service you consent to our doing so.

    For more information on managing or withdrawing consents and how we handle data, visit our Privacy Policy at: https://hubpages.com/privacy-policy#gdpr

    Show Details
    Necessary
    HubPages Device IDThis is used to identify particular browsers or devices when the access the service, and is used for security reasons.
    LoginThis is necessary to sign in to the HubPages Service.
    Google RecaptchaThis is used to prevent bots and spam. (Privacy Policy)
    AkismetThis is used to detect comment spam. (Privacy Policy)
    HubPages Google AnalyticsThis is used to provide data on traffic to our website, all personally identifyable data is anonymized. (Privacy Policy)
    HubPages Traffic PixelThis is used to collect data on traffic to articles and other pages on our site. Unless you are signed in to a HubPages account, all personally identifiable information is anonymized.
    Amazon Web ServicesThis is a cloud services platform that we used to host our service. (Privacy Policy)
    CloudflareThis is a cloud CDN service that we use to efficiently deliver files required for our service to operate such as javascript, cascading style sheets, images, and videos. (Privacy Policy)
    Google Hosted LibrariesJavascript software libraries such as jQuery are loaded at endpoints on the googleapis.com or gstatic.com domains, for performance and efficiency reasons. (Privacy Policy)
    Features
    Google Custom SearchThis is feature allows you to search the site. (Privacy Policy)
    Google MapsSome articles have Google Maps embedded in them. (Privacy Policy)
    Google ChartsThis is used to display charts and graphs on articles and the author center. (Privacy Policy)
    Google AdSense Host APIThis service allows you to sign up for or associate a Google AdSense account with HubPages, so that you can earn money from ads on your articles. No data is shared unless you engage with this feature. (Privacy Policy)
    Google YouTubeSome articles have YouTube videos embedded in them. (Privacy Policy)
    VimeoSome articles have Vimeo videos embedded in them. (Privacy Policy)
    PaypalThis is used for a registered author who enrolls in the HubPages Earnings program and requests to be paid via PayPal. No data is shared with Paypal unless you engage with this feature. (Privacy Policy)
    Facebook LoginYou can use this to streamline signing up for, or signing in to your Hubpages account. No data is shared with Facebook unless you engage with this feature. (Privacy Policy)
    MavenThis supports the Maven widget and search functionality. (Privacy Policy)
    Marketing
    Google AdSenseThis is an ad network. (Privacy Policy)
    Google DoubleClickGoogle provides ad serving technology and runs an ad network. (Privacy Policy)
    Index ExchangeThis is an ad network. (Privacy Policy)
    SovrnThis is an ad network. (Privacy Policy)
    Facebook AdsThis is an ad network. (Privacy Policy)
    Amazon Unified Ad MarketplaceThis is an ad network. (Privacy Policy)
    AppNexusThis is an ad network. (Privacy Policy)
    OpenxThis is an ad network. (Privacy Policy)
    Rubicon ProjectThis is an ad network. (Privacy Policy)
    TripleLiftThis is an ad network. (Privacy Policy)
    Say MediaWe partner with Say Media to deliver ad campaigns on our sites. (Privacy Policy)
    Remarketing PixelsWe may use remarketing pixels from advertising networks such as Google AdWords, Bing Ads, and Facebook in order to advertise the HubPages Service to people that have visited our sites.
    Conversion Tracking PixelsWe may use conversion tracking pixels from advertising networks such as Google AdWords, Bing Ads, and Facebook in order to identify when an advertisement has successfully resulted in the desired action, such as signing up for the HubPages Service or publishing an article on the HubPages Service.
    Statistics
    Author Google AnalyticsThis is used to provide traffic data and reports to the authors of articles on the HubPages Service. (Privacy Policy)
    ComscoreComScore is a media measurement and analytics company providing marketing data and analytics to enterprises, media and advertising agencies, and publishers. Non-consent will result in ComScore only processing obfuscated personal data. (Privacy Policy)
    Amazon Tracking PixelSome articles display amazon products as part of the Amazon Affiliate program, this pixel provides traffic statistics for those products (Privacy Policy)