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  1. What is a transformer?
    Ans: Transformer is a static device which "steps up" and "steps down" the voltage level with corresponding increase or decrease in a current at a same frequency.
  2. What is the operating principle of transformer?
    Ans: Transformer works on principle of mutual induction according to which EMF induces in coil due to change in linkage flux.
  3. Why transformer ratings in KVA?
    Ans: Transformer has mainly two losses i.e. core losses and copper losses. A core loss depends upon its voltage level and copper losses depend upon current flowing in it. As these two factors are not affected by the power factor, that's why we have transformer ratings in KVA instead of KW.
  4. What are the main components of transformer?
    Ans: Main components of Transformer are- coil (primary and secondary) and core Other Parts of Transformer:
    Conservator tank, Buchholz relay, HV and LV Bushings, Metal parts, Oil surge relay, OLTC, RTCC panel, Oil temperature indicator , Winding temperature indicator, Transformer tank, Silica gel breather, Oil level indicator, Magnetic oil level Gauge, Radiator bank etc.
  5. What is the material of core?
    Ans: Core is made up of CRGO cold rolled grain oriented silicon steel.
  6. What is the material of winding?
    Ans: Copper and aluminum is used as a winding material.
  7. What is the requirement of transformer?
    Ans: In a transmission and distribution system, there is a requirement of stepping up and stepping down the voltage for their specified purpose and so, we need a transformer in a power system which will perform these tasks efficiently without having much loss.
  8. What are the reasons of transformer failure?
    Ans: Reasons of transformer failure are as follows.
    • Transformer over loading.
    • Increase in transformer temperature.
    • Short circuit in system.
    • Heavy voltage surge
  9. How do we get transformer oil?
    Ans: We are getting transformer oil from crude distillation and by applying vacuum distillation after getting light oils like gasoline diesel etc.
  10. What is the function of transformer oil in transformer?
    Ans: Transformer oil is used in the transformer for insulation and cooling purpose.
  11. Why oil filtering is necessary in transformer?
    Ans: The oil without filtering contains water particles, gases, metal particles, etc impurities due to which the insulation level of oil goes down because the impurities are conductor of energy to remove that impurity we need to filter the oil.
  12. What is the function of Buchholz relay?
    Ans: Whenever gases developed in transformer due to any fault Buchholz relay gives signal to protecting system.
  13. What are the critical factors which affect the performance of transformer?
    Ans: Following are the factors which affect the performance of transformer.
    • Material of core
    • Material of winding
    • Quality of transformer oil
    • Quality of silica gel
    • Inside clearance of transformer etc.
  14. What is the function of breather in transformer?
    Ans: As we know transformer need a dry air for cooling the breather which allows the flow of dry air from atmosphere to transformer. Breather contains a silica gel which has property to absorb moisture. Just because of silica gel transformer gets dry air from atmosphere.
  15. What is MOG?
    Ans: MOG stands for magnetic oil level gauge, which shows us the level of oil in conservator.
  16. What are WTI and OTI?
    Ans: OTI means oil temperature indicator and WTI means winding temperature indicator which shows the temperature of oil and winding respectively.
  17. Why the shape of coils circular?
    Ans: By taking shape of coils round we can reduced air gap between core and coils. Just because of round shape we can do winding easily without any big angular banding, by taking round shape we can get more clearance between coil and tank.
  18. How many types of transformers are there?
    Ans: According to their function
    • Instrument transformer
    • Power transformer.
    • Distribution transformer
    • Phase shifting transformer
    • Rectifier transformer
    According to their supply
    • Single phase transformer
    • Three phase transformer
    • Poly phase transformer five phase transformer
    According to their cooling medium
    • Dry transformer
    • Oil filled transformer
    • Nitrogen filled transformer
    According to their cooling system
    • Oil natural air natural
    • Oil forced air natural
    • Air forced oil natural
    • Air forced oil forced.
    According to their location
    • Pole mounted transformer
    • Indoor transformer
    • Outdoor transformer
    • Underground transformer
  19. What will happen if we will apply dc to transformer?
    Ans: If we will apply a rated dc supply to transformer, it will start generating constant magnetic flux which is useless for mutual induction. If we will apply a dc supply beyond its limited voltage, transformer will be burn out.
  20. Why transformer testing is necessary?
    Ans: The various tests are done upon transformer to check the efficiency and effectiveness of the transformer.
  21. Give the basic information about routine and common performed test on transformer.
    Ans: we are performing following common testes on transformer
    • voltage ratio test- we are performing on transformer by giving supply to HV terminals and measuring the secondary voltage on secondary side to check a voltage ratio of transformer
    • Magnetic balance test- we are performing magnetic balance test on HV side at site to check the magnetic flux developed by primary coil rotating in balance sequence means is it rotating and linking well with core and secondary coil well or not.
    • Winding insulating resistance test (Megger)-we are performing winding insulation resistance test on transformer to measure the insulation resistance between high voltage to earth low voltage to earth and between high voltage and low voltage side windings. To ensure that the transformers active parts are isolated from each other properly.
    • Pi value test- this test is effective ness of winding insulation resistance test, the ratio of Megger reading in one minute and six minute gives the effective ness of Megger which tell us that is the winding providing a maximum resistance to earth at a initial time or is there any chance of flash at a starting..
    • BDV test- the BDV test is performing on transformer to check the flash point and maximum voltage withstanding capacity of transformer oil.
  22. Why we are taking voltage ratio of transformer?
    Ans: We are taking voltage ratio of transformer to check whether the primary and secondary turns are taken in correct preposition as per order specification and after overhauling we are taking that to ensure that during overhauling the active part and coils of transformer do not get affected which will be work effective at its full load.
  23. PI value: Ratio of Winding insulation resistance for 10 Min and 1 Min is called Polarize index ratio.

    Polarized index value
    PI > 1 Better
    PI = 1 Normal
    PI < 1 Very bed



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