Transformer Protection Interview Questions:

Following are the below Transformer Protection Interview Questions and Important Questions which is very useful for interviews and exams

1. Discuss the different transformer faults. What are the various protection schemes available for transformers ?

2. Describe the construction, principle of operation and application of Buchholz relay. Why is this form of protection an ideal protection ?

3. What are the various protections usually recommended for power transformers ? In what respect ‘core-balance leakage protection’ is inferior to ‘combined leakage and overload protection’ for power transformers.?

4. Explain the protection of transformer by using Merz-Price system of protection with the help of neat diagram. How many faults develop in a power transformer ?

5. Describe 3-phase transformer differential protection. Show that Y-Δ transformer differential protection CTs are connected in Δ and Y respectively.

6. Draw a neat circuit diagram of Merz-Price per cent differential protection scheme for a 3-phase Δ-Y connected transformer.

7. Explain with a neat circuit diagram the differential protection scheme used to protect Y-Δ transformers. Describe with a sketch the operation of Buchholz relay.

8. Describe the protection scheme for internal faults in a three-phase delta/star connected power transformer.

9. Draw a neat sketch and explain clearly why the CTs are to be connected in a particular fashion only.

10. For protecting a 132/33 kV, 50 MVA power transformer from internal faults, what are the different protection schemes normally used ? Discuss one of them, in brief, with sketch.

11. Discuss the special factors that are to be considered while designing the protection scheme for a large Y-Δ power transformer.

12. Describe the principle of differential system of protection applied to a power transformer. What are the shortcomings of this scheme and how are they overcome ?

13. Explain the protective scheme for the transformer that takes care of magnetizing inrush current without affecting the sensitivity.

14. Discuss the special problems of biased differential protection of a transformer. How are they overcome ? Develop a transformer differential protection scheme using the second harmonic restraint feature.

15. Why is a harmonic restrained differential relay required to be used for protecting a large size transformer? Describe the construction and working of such a relay.

16. Explain with a neat diagram the method of harmonic current restraint for protection of transformer.

17. Draw the schematic diagram of harmonic restraint differential protection scheme used for a Yd 11 transformer. Explain the scheme.

18. What is the principle of harmonic restraint relay ? Explain its application.

19. Draw the connection diagram of a differential relay for the protection a star-delta transformer. How does the bias winding of a differential relay restricts malfunctioning of the relay against (i) CT mismatch (ii) on-load tap changing and (iii) magnetising current ? What is magnetising inrush current ? What is the principle used to make a differential relay insensitive to magnetising inrush current ?

20. Write short notes on the following :

• Buchholz relay.
• Core-balance leakage protection of power transformers.
• Combined leakage and overload protection.
• Biased differential protection.
• Harmonic restraint relay.
• Restricted earth fault protection for power transformers.