1. A three-phase power transformer is provided with star-delta connections. In order to protect against fault, the connection for current transformer should be in
2. A 3-phase transformer has its primary connected in delta and secondary in star. Secondary to primary turns ratio per phase is 6. For a primary voltage of 200 V, the secondary voltage would be
- 2078 V
- 693 V
- 1200 V
- 58 V
3. Three-phase step-up transformer installed at the power house, just before the commencement of transmission line, have
- Delta-Delta connection
- Star-Star connections
- Delta-Star connections
- Star-Delta connections
4. Which of the following combination of 3-phase transformers can be successfully operated in parallel
- Δ-Y and Δ-Y
- Y-Y and Δ-Y
- Δ-Δ and Δ-Y
- Y-Δ and Δ-Δ
5. A delta/delta connected three-phase transformer can be connected in parallel with
6. Which type of connection in a 3-phase transformer is used for the substation end of the transmission line?
7. Star-star power transformer is protected by current transformer having
- Star/star connnections
- Delta/delta connections
- Star/delta connections
- Delta/star connections
8. Which type of connection is employed for current transformers for the protection of star-delta connected 3-phase transformer?
9. In electrical power transmission, the _______ configuration of transformers are extensively used.
- Neither Y/Δ and Δ/Y
- Both Y/Δ and Δ/Y
10. The Δ connection has the advantage of restricting the third harmonic components currents to
- Within star connection
- Within delta connection
- Within both star and delta connections
- Neither star nor delta connections
11. Consider the following statements regarding three-phase transformers in Open-Delta (V-V) connections:
- Being a temporary remedy when one transformer forms of Delta-Delta system is damaged, and removed from service.
- The Volt Ampere (VA) supplied by each transformer is half of the total VA, and the system is not overloaded.
- An important precaution is that load shall be reduced by times in this case.
Which of the above statements are correct
- i and iii only
- i and ii only
- i, ii and iii
- ii and iii only
12. A 3-phase transformer has 420 and 36 turns on the primary and secondary windings respectively. The supply voltage is 3300 V. The secondary line voltage on no-load when the windings are connected in star-delta is nearly
- 1908 V
- 22260 V
- 490 V
- 164 V
13. Consider the following statements concerning the utility of mesh-connected tertiary windings in star-star transformers:
- It is used to suppress harmonic voltages.
- It is used to allow flow of earth fault current for operation of protective devices.
- It facilities supply of single-phase loads.
- It provides low-reactances paths for zero-sequence currents.
Which of these statements are correct?
- i, ii, iii and iv
- i, ii and iii only
- iii and iv only
- i, ii and iv only
14. The impedance of a Δ/Y, 11000 V/400 V, transformer of capacity 100 kVA, on its name plate data base is (0.02 + j0.07) pu. The ohmic impedance pu phase referred to the primary (11000 V) side is
- (0.02+ j0.07) Ω
- (0.55 + j1.925) Ω
- (72.6+ j254.1) Ω
- (42+ j147) Ω
15. In which one of the following sets of 3-phase transformer connections will zero sequence current be present in the transformer windings?
- Primary in star, neutral grounded; secondary in star, neutral not grounded.
- Primary in star, neutral grounded; secondary in delta.
- Primary in star, neutral not grounded; secondary in star, neutral grounded.
- Primary in star, neutral not grounded; secondary in delta.
16. Which 3-phase connection can be used in a transformer to introduce a phase difference of 30° between its output and corresponding input line voltages?
17. When one transformer is removed from a Δ-Δ bank of 30 KVA transformer, the capacity of the resulting 3-phase transformer corresponding input line voltages?
- 17.3 kVA
- 11.5 kVA
- 25.9 kVA
- 20 kVA
18. A Δ/Δ connected transformer is connected to V/V connected transformer. The ratio of VA rating of V/V connected transformer and Δ/Δ connected transformer is
19. If the waveform of the voltage impressed on the primary of a Y-Δ bank contains 5th harmonics, what are the waveforms of the resultant voltages of the primary and the secondary?
20. Three single phase 11000/220 V transformers are connected to form 3-phase transformer bank. High voltage side is connected in star, and low voltage side is in delta. What are the voltage ratings and turns ratio of 3-phase transformer?
- 19052/220 V, 50
- 19052/220 V,
- 11000/381 V,
- 11000/220 V, 50
21. Possible three-to-three phase transformer connection for parallel operation is
- Δ-Y to Δ-Y
- Δ-Δ to Δ-Y
- Y-Y to Δ-Y
- Δ-Y to Y-Δ