MCQOPTIONS
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MCQOPTIONS
This section includes 30 Mcqs, each offering curated multiple-choice questions to sharpen your Power Systems knowledge and support exam preparation. Choose a topic below to get started.
| 1. |
In the symmetrical component expression of voltages, we have\(\left[ {\begin{array}{*{20}{c}}{{V_a}}\\{{V_b}}\\{{V_c}}\end{array}} \right] = \left[ A \right]\left[ {\begin{array}{*{20}{c}}{{V_{a1}}}\\{{V_{a2}}}\\{{V_{a0}}}\end{array}} \right]\)where matrix [A] is |
| A. | \(\left[ {\begin{array}{*{20}{c}}1&\alpha &1\\{{\alpha ^2}}&\alpha &1\\\alpha &{{\alpha ^2}}&1\end{array}} \right]\) |
| B. | \(\left[ {\begin{array}{*{20}{c}}1&\alpha &{{\alpha ^2}}\\1&{{\alpha ^2}}&\alpha \\1&\alpha &{{\alpha ^2}}\end{array}} \right]\) |
| C. | \(\left[ {\begin{array}{*{20}{c}}1&1&1\\{{\alpha ^2}}&\alpha &1\\\alpha &{{\alpha ^2}}&1\end{array}} \right]\) |
| D. | \(\left[ {\begin{array}{*{20}{c}}1&1&1\\\alpha &{{\alpha ^2}}&1\\{{\alpha ^2}}&\alpha &1\end{array}} \right]\) |
| Answer» D. \(\left[ {\begin{array}{*{20}{c}}1&1&1\\\alpha &{{\alpha ^2}}&1\\{{\alpha ^2}}&\alpha &1\end{array}} \right]\) | |
| 2. |
On which among the following factors does the magnitude of the fault current depend? |
| A. | Total impedance up to the fault |
| B. | Voltage at the fault point |
| C. | Both (1) and (2) |
| D. | None of these |
| Answer» D. None of these | |
| 3. |
Possible faults may occur on a transmission line are1. 3-phase fault2. L-L-G fault3. L-L fault4. L-G faultThe decreasing order of severity of the faults from the stability point of view is: |
| A. | 1-2-3-4 |
| B. | 1-4-3-2 |
| C. | 1-3-2-4 |
| D. | 1-3-4-2 |
| Answer» B. 1-4-3-2 | |
| 4. |
A short circuit is identified by: |
| A. | No current flow |
| B. | High current flow |
| C. | Voltage drop |
| D. | Voltage rise |
| Answer» C. Voltage drop | |
| 5. |
Open circuit electrical fault is also called as _____ |
| A. | Series fault |
| B. | Shunt fault |
| C. | Short circuit fault |
| D. | Series-Shunt fault |
| Answer» B. Shunt fault | |
| 6. |
According to IEEE, “a system or a portion of a system can be said to be effectively grounded when for all points on the system or specified portion thereof, the ratio of zero sequence reactance to positive sequence reactance (X0 / X1) and the ratio of zero sequence resistance to positive sequence resistance (R0 / R1) should be __________.” |
| A. | (X0 / X1) not greater than 0.3 and (R0 / R1) not greater than 0.1 |
| B. | (X0 / X1) not greater than 3 and (R0 / R1) not greater than 1 |
| C. | (X0 / X1) not greater than 0.2 and (R0 / R1) not greater than 0.3 |
| D. | (X0 / X1) not greater than 2 and (R0 / R1) not greater than 3 |
| Answer» C. (X0 / X1) not greater than 0.2 and (R0 / R1) not greater than 0.3 | |
| 7. |
A 11 kV, 10 MVA alternator has \(X_d^{''} = 15\% ,\;X_d' = 25\% ,\;{X_d} = 80\%\). It is connected to a load through a 2-cycle circuit breaker and a transformer. At no load 3-phase short circuit fault occurs between transformer and circuit breaker. If the voltage rating of the breaker is 11 kV, its interrupting kVA is |
| A. | 46.7 MVA |
| B. | 93.4 MVA |
| C. | 140.1 MVA |
| D. | 186.2 MVA |
| Answer» C. 140.1 MVA | |
| 8. |
Due to an electrical fault, an electric line of the system is removed in a three-phase alternating current system supplying a certain electric power. If the percentage loss remains unchanged, what will be the percentage decrease in the load supplied between the conductors for the same voltage? |
| A. | 40% |
| B. | 60% |
| C. | 50% |
| D. | 30% |
| Answer» D. 30% | |
| 9. |
If A is cross-sectional area of conductor, the Bus-bar temperature rise in a DG Set is proportional to |
| A. | A |
| B. | 1/A2 |
| C. | A2 |
| D. | A3 |
| Answer» C. A2 | |
| 10. |
In per unit method of representation of a power system, the base value of |
| A. | Impedance is same for the entire system |
| B. | Voltage is same for the entire system |
| C. | MVA is same for entire system |
| D. | MVA should be in the proportion of transformer ratio |
| Answer» D. MVA should be in the proportion of transformer ratio | |
| 11. |
A 50 MVA, 10kV, 50 Hz, star-connected, unloaded three-phase alternator has a synchronous reactance of 1 p.u and a sub-transient reactance of 0.2 p.u If a 3-phase short circuit occurs close to the generator terminals, the ratio of initial and final values of the sinusoidal component of the short circuit current is: |
| A. | 3 |
| B. | 4 |
| C. | 2 |
| D. | 5 |
| Answer» E. | |
| 12. |
Identify the equipment that is used to limit short-circuit level in a substation. |
| A. | Series reactor |
| B. | Lighting switch |
| C. | Guard ring |
| D. | Line inductance |
| Answer» B. Lighting switch | |
| 13. |
A three-phase 20 MVA, 10 kV alternator has an internal reactance of 5% negligible resistance. What is the external reactance per phase required to be connected in series with the alternator so that the steady current on the short circuit does NOT excess 8 times the full load current? |
| A. | 2.38 Ω |
| B. | 1.38 Ω |
| C. | 0.38 Ω |
| D. | 3.38 Ω |
| Answer» D. 3.38 Ω | |
| 14. |
A three phase fault in a power system is |
| A. | The most common type of fault |
| B. | Usually the most severe type of fault |
| C. | Results in equal magnitude for positive and negative sequence currents |
| D. | Results in equal value for positive, negative and zero sequence currents |
| Answer» C. Results in equal magnitude for positive and negative sequence currents | |
| 15. |
In a 3-phase system, equal fault currents in the lines with 120° displacement are caused by: |
| A. | single line-to-ground fault |
| B. | symmetrical faults |
| C. | unsymmetrical faults |
| D. | unbalanced load |
| Answer» C. unsymmetrical faults | |
| 16. |
______ is a series type unbalanced fault that occurs in a power system. |
| A. | Line – to – line fault |
| B. | Double line – to – ground fault |
| C. | Single line – to – ground fault |
| D. | Open conductor fault |
| Answer» E. | |
| 17. |
In solidly grounded systems, the line-to-ground voltage during the L-G fault does not exceed _____ of the L-L voltage. |
| A. | 70% |
| B. | 60% |
| C. | 40% |
| D. | 80% |
| Answer» E. | |
| 18. |
Causes of electrical failure in rotating machines is due to ______. |
| A. | Core cross-sectional area |
| B. | Winding layer by layer |
| C. | Increase in efficiency |
| D. | Stator winding insulation failure |
| Answer» E. | |
| 19. |
If all the sequence voltages at the fault point in a power system are equal, then the fault is |
| A. | 3-ϕ fault |
| B. | Line of ground fault |
| C. | Line to line fault |
| D. | Double line to ground fault |
| Answer» E. | |
| 20. |
Irrespective of the causes, which is the fault in a 3-phase system? |
| A. | Unsymmetrical faults |
| B. | Both Symmetrical faults and Unsymmetrical faults |
| C. | Symmetrical faults |
| D. | External faults |
| Answer» C. Symmetrical faults | |
| 21. |
An equipment has an impedance of 0.9 p.u. to a base of 20 MVA, 33 kV. To the base of 50 MVA, 11 kV, the p.u. impedance will be |
| A. | 4.7 |
| B. | 20.25 |
| C. | 0.9 |
| D. | 6.75 |
| Answer» C. 0.9 | |
| 22. |
A 3-phase transmission line operates at 33 kV. It has a resistance of 5 Ω and reactance of 15 Ω. It is connected to a busbar of an alternator through a 5 MVA step up transformer which has a reactance of 0.05 pu. Two alternators rated 10 MVA, XS = 0.08 pu and 5 MVA, XS = 0.06 pu are connected to busbars. A fault between phases at HV terminals of the transformer occurs. The MVA of the fault will be |
| A. | 34.6 |
| B. | 67.6 |
| C. | 81.2 |
| D. | 91.5 |
| Answer» C. 81.2 | |
| 23. |
In a balanced 3ø system, the zero phase sequence currents are: |
| A. | maximum |
| B. | minimum |
| C. | zero |
| D. | varying |
| Answer» D. varying | |
| 24. |
In which type of fault the negative and zero sequence currents are equal to zero |
| A. | LG fault |
| B. | LL fault |
| C. | LLG fault |
| D. | 3 phase symmetrical fault |
| Answer» E. | |
| 25. |
A 30 kV, 50 Hz, 50 MVA generator has the positive, negative, and zero sequence reactance’s of 0.25 pu, 0.15 pu, and 0.05 pu, respectively. The neutral of the generator is grounded with a reactance so that the fault current for a bolted LG fault and that of a bolted three-phase fault at the generator terminal are equal. The value of grounding reactance is: |
| A. | 1 Ω |
| B. | 1.8 Ω |
| C. | 0.1 Ω |
| D. | 2.18 Ω |
| Answer» C. 0.1 Ω | |
| 26. |
Five alternators are connected in parallel to a busbar. Each alternator is rated 5 MVA, 13.2 kV and has a 25% reactance on its own base. Determine the short circuit level in MVA at the busbar. |
| A. | 50 MVA |
| B. | 25 MVA |
| C. | 100 MVA |
| D. | 10 MVA |
| Answer» D. 10 MVA | |
| 27. |
If the percentage reactance of the system up to the fault point is 30% and the base kVA is 9,000. Find the value of the short circuit kVA |
| A. | 50,000 |
| B. | 45,000 |
| C. | 30,000 |
| D. | 33,000 |
| Answer» D. 33,000 | |
| 28. |
For an unbalanced fault with paths for zero sequence currents, at the point of fault |
| A. | the negative & zero sequence voltage are minimum |
| B. | the negative sequence voltage is maximum & zero sequence voltage is minimum |
| C. | the negative sequence voltage is minimum & zero sequence voltage is maximum |
| D. | the negative & zero sequence voltages are maximum |
| Answer» E. | |
| 29. |
Match the different unsymmetrical fault currents.Unsymmetrical faultFault currenta. LG fault1. \({I_F} = \frac{{\sqrt 3 {E_a}}}{{{Z_1} + {Z_2}}}\)b. LL fault2. IF = 3Ia0 c. LLG fault3. \({I_F} = \frac{{3{E_a}}}{{{Z_1} + {Z_2} + {Z_3}}}\) |
| A. | a - 1, b - 2, c - 3 |
| B. | a - 3, b - 2,c - 1 |
| C. | a - 3, b - 1, c - 2 |
| D. | a - 1, b -3, c - 2 |
| Answer» D. a - 1, b -3, c - 2 | |
| 30. |
In case of 3 Phase Short circuit in a system, the power fed into the system is |
| A. | Mostly active |
| B. | Mostly reactive |
| C. | Active only |
| D. | Active and reactive both |
| Answer» C. Active only | |