ArtsAutosBooksBusinessEducationEntertainmentFamilyFashionFoodGamesGenderHealthHolidaysHomeHubPagesPersonal FinancePetsPoliticsReligionSportsTechnologyTravel

Differenet Transformers in Power Station

Updated on January 2, 2014

Generating Transformer

Generation Transformer:

Generation Transformer is employed in power plant for stepping up the voltage for transmitting the power to the grid. Electrical power is generated in the power plant at lower voltages (typically generation voltage will be between 11kV to 33kV). In order to transmit the power to long distances voltage has to step up to reduce the losses. Hence in power plants, generation transformer is employed.

Rating of the generation transformers will be almost equal to the rating of the generator (500MW generating unit will have generating transformer rating about 588MVA). Connection between the generator transformer and power plant generator will be through isolated Phase Bus Duct (IPBD).

Air Force Oil Force (AFOF) cooling is to be provided for these transformers. Generator transformers are provided with on-load tap changing mechanism to regulate the terminal voltage. Generator transformer will be Delta (LV side) and Star (HV side) connected with star connection is connected to earth through resistor to reduce the fault currents and protecting the transformer.

If Generator Circuit Breaker (GCB) is provided at the generator terminals, power from the grid can be supplied to plant auxiliary loads through generator transformer by opening the GCB when generating unit is not in operation.

Some of the points about generator transformer is given below:

  • This is the main transformer of generating unit used for stepping up the voltage from generating station for the transmission
  • In a generating plant for every generating unit one generating transformer is required
  • Rated voltage on LV side corresponds to the rated generating voltage
  • Rated voltage on the HV side corresponds to rated voltage of the HV bus
  • Usually these transformers are outdoor type
  • LV terminals are connected to the generating terminals via isolated phase bus systems
  • HV terminals are connected to the outdoor busbars by flexible ACSR conductors via overhead flexible bus

Unit auxiliary Transformer (UAT):

Power plant is provided with Unit Auxiliary Transformers (UAT) connected to the generator terminals through Isolated Phase Bus Duct (IPBD). Unit Auxiliary Transformers provides electrical power to power plant distribution buses by stepping down the voltage from 11kV to 6.6kV (example).

Unit Auxiliary Transformers are rated based on the rating of the loads it has to supply. On-load tap changing mechanism is provided to UATs. They are usually Delta (HV side) and Star (LV side) connected transformers. The neutral of the star point is connected to earth through resistor to limit the fault current during ground faults and to protect the transformer. These transformers are usually provided with Air Force Oil Force (AFOF) cooling

Some of the points associated with Unit Auxiliary Transformers are listed below:

  • The Purpose of Unit auxiliary Transformer is to feed power to generator auxiliaries of that unit
  • These transformers are connected to generators and are used as stepping down transformers. The HV side transformer voltage corresponds to the voltage of the generating unit and the LV side voltage is stepped down to 6.6KV
  • Rated KVA of Unit Auxiliary Transformers is approximately 15% of the generating rating
  • Usually these transformers are outdoor transformers
  • One Unit auxiliary transformer is present for every generating unit.

Station Service Transformer

Station Transformers are employed for supplying power to plant auxiliary loads during the event of starting of the plant or when generating unit is not generating power. Station Transformers are connected to the swichyard bus. LV side of the station transformer is connected to the auxiliary load buses.

Station transformer is normally rated for supplying power to the auxiliary loads. On-load tap changing mechanism is provided to regulate the terminal voltage of the transformer. These transformers are provided with Air Force Oil Force (AFOF) type of cooling. The star point of the station transformer is grounded through resistor.

Some the points related to station transformer are given below:

  • In general station service transformer is used for supplying power to auxiliary equipment in the power plant when the plant is not generating any power.
  • Rated HV voltage corresponds to the rated voltage of the outer busbars
  • Rated LV voltage corresponds to the auxiliary bus voltage
  • Rated KVA corresponds to the load of common auxiliaries of the station. This corresponds to the 10% to 15% of the rating of the generating power.
  • These transformers are Outdoor type.

Auxiliary Transformers

These transformers are employed in the power plants for delivering power to low voltage loads (voltage below 1kV). These transformers connects between HV distribution buses and LV distribution buses of the plant. Their rating will be around 1 to 5MVA. Natural oil cooling or air cooled transformers are used.

Some of the points related to station auxiliary transformers are listed below:

  • These transformers are located in power plant to step down voltage from 6.6KV to 415V.
  • The rating for this transformer corresponds to the rating of the auxiliary load it should be bearing.
  • These transformers are indoor type and usually dry type transformers are used.


    0 of 8192 characters used
    Post Comment

    • profile image


      11 months ago

      Very good Article. Help me very much.

    • profile image

      suidpt jena 

      4 years ago

      The above article is very much helpful to me.Thank You.

    • profile image


      5 years ago

      Love the title- love your writing style. SO FUN! YAY! another great blog to follow!

    • profile image


      5 years ago

      Very usefull.

    • profile image


      6 years ago


    • profile image


      6 years ago

      good but more matter is their means it z very good

    • profile image

      raju d l 

      6 years ago

      chanagide namage enu hechina maheti bekitu vandaneglu

    • profile image


      7 years ago is good but short notes to know about the transformer used in power plant ...


    This website uses cookies

    As a user in the EEA, your approval is needed on a few things. To provide a better website experience, 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:

    Show Details
    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 or domains, for performance and efficiency reasons. (Privacy Policy)
    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)
    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.
    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)