1. A 10 MVA, 11 kV alternator has positive, negative and zero sequence reactance of 25%, 40%, 10% respectively. The resistance that must be placed in the neutral such that fault current for a single phase to ground fault will not exceed the rated line current in ohms is __________
a) 11.7
b) 12.8
c) 2.66
d) 5.2
Explanation:
2. (I) Unsymmetrical spacing configurations cause the line interference.
(II) Unsymmetrical spacing causes the voltage induction in the communication lines.
a) (I) and (II) are valid
b) Only (I) is valid
c) Only (II) is valid
d) Both are invalid
Explanation: Both the statements are correct as the unsymmetrical spacing causes the unbalanced voltage generation.
3. (I) Unsymmetrical spacing configurations cause the line interference.
(II) Unsymmetrical spacing causes the voltage induction in the communication lines.
The above problems can be eliminated by ________
a) transposition
b) parallel lines
c) three phase
d) all of the mentioned
Explanation: Transposition meaning exchange of conductors will cause the net voltage induced in the other lines to be zero as the net inductance remains constant.
4. Transposition is the mean to balance ____________
a) Inductance
b) Voltage
c) Current
d) All of the mentioned
Explanation: Transposition primarily balances the inductances in the line thus causing a constant inductance throughout the line.
5. Over the length of one transposition cycle of a power line, the total flux linkages of a nearby telephone line are zero for the unbalanced three phase currents.
a) True
b) False
Explanation: For an unbalanced supply, there will be non zero flux zero flux linkages in the telephone lines.
6. Over the length of one transposition cycle of a power line, the total flux linkages of a nearby telephone line are zero for the balanced three phase currents.
a) The above statement is valid
b) The above statement is invalid
c) It can’t be concluded
d) The above statement is valid for all conditions.
Explanation: Its valid only with balanced systems.
7.Bundled conductors used in the EHV transmission lines result into __________
a) reduced inductance
b) increase capacitance
c) increase inductance
d) increase resistance
Explanation: Bundled conductors cause the GMR to increase and thus reducing the inductance.
8. The fictitious resistance, “ r’ ” implemented in the conductors for the calculation of the inductance is _____________
a) 0.7788r
b) 2r
c) r/0.7788
d) r
Explanation: It is 0.7788r in the equivalent network configuration.
9. (i) Skin effect
(ii) Proximity effect
Which of the options are right?
a) Both (i) and (ii) cause non uniform distribution of the current
b) Neither (i) and (ii) cause non uniform distribution of the current
c) Both (i) and (ii) cause uniform distribution of the current
d) Only (i) causes the non uniformity of the current
Explanation: Skin-effect as well as the Proximity effect cause the non distribution of the flux linkages, leading to non uniform distribution of the current.
10. Ferranti effect causes the non uniform distribution of the current and voltage.
a) True
b) False
Explanation: Only the voltage regulation is affected due to the Ferranti law.