(i) Faults can cause 3-phase system to turn into unbalanced with this affects operation of 3-phase equipment.
(ii) Some faults block flow of power.
(iii) Faults usually provide rise to large currents which might damage gear in line of the system.
(iv) Large mistake current overheats system equipment.
(v) Faults can reason the system to become uneven. Q. 3. What is an unsymmetrical fault: Ans. Unsymmetrical faults occupy simply one or two phases. As an unsymmetrical liability occurs, the fault currents in lines turn into unequal by unequal phase displacement. In other words, unsymmetrical fault reason an unbalance with phases. For this reason, every phase has to be treat independently for mistake calculations. Q. 4. Which is most common fault in a power system? Ans. The mainly regular fault in a power system is single line-to-ground fault. Skill shows that among 75% and 85% of faults that happen in power system are single line-to-ground faults. Q. 5. What are fault calculations? Ans. The fault calculations are made to resolve fault currents for different types of faults at a range of locations in power system. The data obtain as of fault calculations too serves to conclude the setting of relays which control circuit breakers. Q. 6. The positive series and negative sequence impedance of a line are the similar. Why? Ans. The positive order and negative order impedance of a line are similar this value being equivalent to the normal impedance of the line. It is because the phase rotation of the currents does not create some differences in stable of the line. Q. 7. What do you mean by fault in a power system? Ans. A fault in a line is a few failures which interferes by normal flow of current in the line. Q. 8. What is dissimilarity between a short-circuit and an over load? Ans. As a short-circuit occur, voltage at fault point is condensed to zero and current of unusually elevated magnitude flows through network to point of error. On other hand, an excess means that loads more than the designed values have been forced on system. Under such conditions, voltage as the overload point perhaps loves, but not zero. Q. 9. How does circuit current work on occurrence of error in a power system? Ans. Current which flows in unusual parts of power system instantly after amount of fault is much greater than that flow a small number of cycles later. Exponential decay of error current as of an initial transient charge to a final stable state value is due to changing impedance accessible to fault through the system. Q. 10. What is the reason of fault analysis ? Ans. The reason of fault analysis is to conclude values of voltages and currents at unusual points of power system through fault. Such an analysis helps us to select accurate protection method, relays and circuit breakers in order to separate faulty sections as fast as feasible. Q. 11. Do symmetrical components contain separate existence? Ans. The symmetrical components do not contain divide existence. They are only numerical components of unbalanced currents or voltages which do exist in system. Q. 12. What is need of reactors in line of power system? Ans. With increasing trend towards consistent system, fault stage (that is the power accessible to flow into a fault) is increasing. Circuit breakers which were at first able to handle fault conditions can now be unable to do so. To restore fault level to a rate which existing circuit breakers can handle, limiting reactors are attached in series by the system at proper points. Q. 13. What is a symmetrical fault? Ans. A regular fault occurs as all the three conductors of a 3-phase line are brought jointly into a short-circuit condition. The regular faults rarely happen in power system. Occurrence shows that barely 5 of overhead line faults are regular faults. Q. 14. What are ways in which an unsymmetrical fault might happen in power system? Ans. The happen three ways in which unsymmetrical faults may occur in a power system
(i) Line-to-line fault (L-L)
(ii) Single line-to-ground fault (L-G)
(iii) Double line-to-ground fault (L-L-G) Q. 15. What are causes of faults in a power system? Ans. Fault can be happen on a power system due to a number of cause for example
(i) falling of tree on a line
(ii) lightning
(iii) snow
(iv) high-speed winds
(v) insulation failure
(vi) birds shorting the line etc Q. 16. Which is most severe fault in power system? Ans. The majority severe fault in a power system is three-phase short circuit error (that is.., symmetric al fault) as such a error occurs, main fault currents flow in lines, For this cause, ratings of circuit breakers are resolute on the basis of even short-circuit calculations. Q. 17. What is advantage of using percentage reactance instead of ohmic reactance in short-circuit calculations? Ans. The percentage reactance values continue unchanged as they are referred through transformers, dissimilar ohmic reactances which turn into multiply or separated through square of transformation ratio. This makes the process simple and permits rapid calculations. Q. 18. The positive, negative and zero phase sequence workings are call symmetrical components a/the original unbalanced system. Why? Ans. The tenure ‘symmetrical’ is suitable as the unbalanced 3-phase system has been resolved into three sets of balanced (or symmetrical) works. Q. 19. Why is zero sequence impedance (Z0) usually different as of positive (Z1) or negative (Z) sequence impedance ? Ans. Zero sequence impedance depends upon path taken through zero series current. As this is usually dissimilar as of path taken through positive and negative sequence currents, thus, zero sequence impedance is generally dissimilar from positive or negative series impedance.
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