ArtsAutosBooksBusinessEducationEntertainmentFamilyFashionFoodGamesGenderHealthHolidaysHomeHubPagesPersonal FinancePetsPoliticsReligionSportsTechnologyTravel
  • »
  • Business and Employment»
  • Employment & Jobs»
  • Interviewing for a Job

Transformer Interview Questions Answers

Updated on January 1, 2014

During No load why the power factor of the transformer is very low ?

Current flowing through the transformer consists of two components. Magnetizing current (Im) which is in quadrature (900) to the applied voltage and in phase current which is in phase to the applied voltage. During no load condition most of the excitation current drawn by the transformer from the primary winding is to magnetize the path. Hence excitation current drawn by the transformer during no load condition mostly consists of magnetizing component of current which is used to provide magnetic field in transformer circuits (Inductive nature). Therefore as the nature of the load is inductive, hence the power factor of transformer during no load condition will by in the order of 0.1 to 0.2

What happen when Transformer is given DC supply ?

When DC supply is given to the transformer primary winding no back emf is induced in the transformer. Importance of Back emf is that it limits the current drawn by the machine. In the absence of back emf transformer starts drawing huge currents which results in burning down of primary winding.

So when dc supply is given to transformer primary windings will burn

At what power maximum efficiency of power transformer and distribution transformer is designed

Maximum efficiency of the transformer is attained at certain load factor (α) when core losses of transformer is equal to the copper losses.

PCore loss = α2 X PCopper loss

From the above equation for particular load factor (α) maximum efficiency of a transformer is designed when core loss is equal to copper loss. For a transformer core losses remain same irrespective of the load and copper losses varies based on the loading. For a transformer maximum efficiency is designed for particular load factor when core and copper losses are same. Core loss for a transformer is designed based on the application of transformer so that both core losses and copper losses will be same

For power transformer delivering bulk power employed in generating stations and other substations power it deliver will not vary round the clock and delivers full load. Hence power transformers are designed to have maximum power at full load. Whereas power deliver capacity of distribution transformers which deliver power vary with time duration of the day. Hence distribution transformers are designed to have maximum efficiency at 50% of the rated full load

What are the conditions for parallel operation of two transformers ?

Transformers which are to be operated parallel should have to satisfy the following conditions:

  • Polarities of both the transformers should be same else lead to short circuit
  • Voltage rating of the both primary and secondary of the two transformers operating in parallel should be same
  • Per unit impedance of the transformers should be same
  • Phase displacement of transformers should be same
  • Phase sequence of two transformers should be same

Why Silica gel is used in transformers?

Silica Gel is used to remove the moisture in the air entering in to the transformer. During the breathing of the transformer air enters in to the transformer. This air makes contact with the hot transformer oil in the conservator and removes the heat by convection. Air entering in to the transformer should be free from moisture else the properties of transformer oil gets degraded. Therefore silica gel crystals are provided in the breather to remove the moisture content in the air

Silica gel crystals will be in blue color initially and after absorbing moisture it turns to pink.


    0 of 8192 characters used
    Post Comment

    • profile image

      opole jared 3 months ago

      good work

    • profile image

      Roshni sahu 2 years ago

      helped me

    • profile image

      Domnic 2 years ago

      excellent questions for inrvw

    • profile image

      umesh 2 years ago


    • profile image

      nagappa hugar 3 years ago

      thanks continue sir

    • profile image

      s k sahoo 3 years ago

      Very useful for everyone

    • profile image

      john 3 years ago

      great continue frnd

    • profile image

      manish 3 years ago


    • profile image

      prabhakar 3 years ago


    • profile image

      Rajput arajanbhai 3 years ago


    • profile image

      riyaz ahmed 4 years ago

      I learn one new thing today..


    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)