MCQOPTIONS
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MCQOPTIONS
This section includes 16 Mcqs, each offering curated multiple-choice questions to sharpen your Electrical Machines knowledge and support exam preparation. Choose a topic below to get started.
| 1. |
Identify the correct order for the voltage transformation for the three-phase transformers. |
| A. | D-Y > D-D = Y-Y > Y-D |
| B. | D-Y > D-D > Y-Y > Y-D |
| C. | D-Y > D-D = Y-Y < Y-D |
| D. | D-Y > D-D < Y-Y < Y-D |
| Answer» B. D-Y > D-D > Y-Y > Y-D | |
| 2. |
For a star-delta three phase transformer, if the transformation ratio is x:1 , then how much percent of output will be? |
| A. | 73% |
| B. | 57% |
| C. | 173% |
| D. | 157% |
| Answer» D. 157% | |
| 3. |
For a delta-star three phase transformer, if the transformation ratio is x:1 , then how much percent of output will be improved? |
| A. | 73% |
| B. | 57% |
| C. | 173% |
| D. | 157% |
| Answer» B. 57% | |
| 4. |
In three phase supply, the voltage phases are displaced by ________ and in two phase by ___________ |
| A. | 120 , 90 |
| B. | 180 , 90 |
| C. | 120, 120 |
| D. | 120 , 180 |
| Answer» B. 180 , 90 | |
| 5. |
Operating transformers in parallel gives the advantage of ___________ |
| A. | reliable loading |
| B. | increased capacity of power system |
| C. | reducing the capacity of substation |
| D. | all of the mentioned |
| Answer» E. | |
| 6. |
Two single phase transformers A and B are operating in parallel having different impedance and identical x/r ratio. Impedance of A is Za and impedance of B is Zb, both sharing a load of Sl. Then the load shared by transformer B is? |
| A. | Sl*(Zb/(Za+Zb)) |
| B. | Sl*(Za/(Za+Zb)) |
| C. | Sl*(Zb*Za/(Za+Zb)) |
| D. | Sl*(Zb+Za/Zb)) |
| Answer» C. Sl*(Zb*Za/(Za+Zb)) | |
| 7. |
Two single phase transformers A and B are operating in parallel having different impedance and identical x/r ratio. Impedance of A is Za and impedance of B is Zb, both sharing a load of Sl. Then the load shared by transformer A is? |
| A. | Sl*(Zb/(Za+Zb)) |
| B. | Sl*(Za/(Za+Zb)) |
| C. | Sl*(Zb*Za/(Za+Zb)) |
| D. | Sl*(Zb+Za/Zb)) |
| Answer» B. Sl*(Za/(Za+Zb)) | |
| 8. |
Two single phase transformers A and B are operating in parallel having different impedance and identical x/r ratio. Also impedance of A is more than that of B, then? |
| A. | Za/Zb = Sb/Sa |
| B. | Za/Zb = Sa/Sb |
| C. | Za/Zb = 1 |
| D. | Za/Zb = (Sb/Sa)<sup>2</sup> |
| Answer» B. Za/Zb = Sa/Sb | |
| 9. |
Two single phase transformers A and B are operating in parallel having different impedance and identical x/r ratio. Also impedance of A is more than that of B, then A ___________ |
| A. | shares lesser kVA |
| B. | share more kVA |
| C. | equal kVA as of B |
| D. | total kVA |
| Answer» B. share more kVA | |
| 10. |
Two single phase transformers A and B are operating in parallel having different impedance and identical x/r ratio. Then? |
| A. | A has poorer pf than B |
| B. | B has poorer pf than B |
| C. | lesser power factor angle |
| D. | both operate at same power factor |
| Answer» E. | |
| 11. |
Two single phase transformers A and B are operating in parallel having same impedance. But the x/r ratio of them are not equal and xa > xb. Then? |
| A. | A has poorer pf than B |
| B. | B has poorer pf than B |
| C. | lesser power factor angle |
| D. | both operate at same power factor |
| Answer» B. B has poorer pf than B | |
| 12. |
Two single phase transformers A and B are operating in parallel having same impedance. But the x/r ratio of them are not equal. Then total kVA output of the output will be ___________ |
| A. | less than sum of kVA of A and B |
| B. | more than sum of kVA of A and B |
| C. | equal to sum of kVA of A and B |
| D. | any of the mentioned |
| Answer» B. more than sum of kVA of A and B | |
| 13. |
Which if the conditions is must be fulfilled for satisfactory parallel operation of transformers? |
| A. | Same voltage ratio |
| B. | Leakage impedances should be inversely proportional to kVA of the transformer |
| C. | Same pu impedance |
| D. | Correct polarity |
| Answer» E. | |
| 14. |
A 2000/1000/500 three winding transformer is to be used as auto transformer with supply of 3000 V. Two loads of 1050 kVA at 3500V and other one at 180 kVA at 1000V. The total kVA supplied will be? |
| A. | 1230 kVA |
| B. | 1440 kVA |
| C. | 1680 kVA |
| D. | 1150 kVA |
| Answer» B. 1440 kVA | |
| 15. |
Transformer operating in parallel will share a common load in the best possible manner if ____________ |
| A. | leakage impedances are proportional to their kVA rating |
| B. | pu leakage impedances are equal |
| C. | leakage impedances are equal |
| D. | any of the mentioned |
| Answer» C. leakage impedances are equal | |
| 16. |
A 2000/1000/500 three winding transformer is to be used as auto transformer with supply of 3000 V. Two loads of 1050 kVA at 3500V, and other one at 180 kVA at 1000V. The circuit representing the mentioned application is? |
| A. | <a href="https://www.sanfoundry.com/wp-content/uploads/2017/05/electrical-machines-problems-q1a.png"><img alt="Three winding transformer used as auto transformer with supply of 3000 V - option a" class="alignnone size-full wp-image-161194" height="179" src="https://www.sanfoundry.com/wp-content/uploads/2017/05/electrical-machines-problems-q1a.png" width="300"/></a> |
| B. | <a href="https://www.sanfoundry.com/wp-content/uploads/2017/05/electrical-machines-problems-q1b.png"><img alt="Three winding transformer used as auto transformer with supply of 3000 V - option b" class="alignnone size-full wp-image-161195" height="179" src="https://www.sanfoundry.com/wp-content/uploads/2017/05/electrical-machines-problems-q1b.png" width="300"/></a> |
| C. | <a href="https://www.sanfoundry.com/wp-content/uploads/2017/05/electrical-machines-problems-q1c.png"><img alt="Three winding transformer used as auto transformer with supply of 3000 V - option c" class="alignnone size-full wp-image-161196" height="181" src="https://www.sanfoundry.com/wp-content/uploads/2017/05/electrical-machines-problems-q1c.png" width="300"/></a> |
| D. | <a href="https://www.sanfoundry.com/wp-content/uploads/2017/05/electrical-machines-problems-q1d.png"><img alt="Three winding transformer used as auto transformer with supply of 3000 V - option d" class="alignnone size-full wp-image-161197" height="189" src="https://www.sanfoundry.com/wp-content/uploads/2017/05/electrical-machines-problems-q1d.png" width="300"/></a> |
| Answer» B. <a href="https://www.sanfoundry.com/wp-content/uploads/2017/05/electrical-machines-problems-q1b.png"><img alt="Three winding transformer used as auto transformer with supply of 3000 V - option b" class="alignnone size-full wp-image-161195" height="179" src="https://www.sanfoundry.com/wp-content/uploads/2017/05/electrical-machines-problems-q1b.png" width="300"/></a> | |