Which of the following is a criterion used for selecting the ratio of the minimum fault current to the maximum load current in over-current protection of a transmission line?

Criterion for Selecting the Ratio of the Minimum Fault Current to the Maximum Load Current in Over-Current Protection of a Transmission Line:

In over-current protection of a transmission line, it is crucial to set the protection system such that it operates reliably under fault conditions but does not maloperate under normal operating conditions. The criterion for selecting the ratio of the minimum fault current to the maximum load current ensures that the protection system is sensitive enough to detect faults but not so sensitive that it triggers unnecessarily during normal load conditions.

Explanation of Options:

This is correct. The primary reason for selecting an appropriate ratio of the minimum fault current to the maximum load current is to ensure that the protection system does not maloperate (i.e., incorrectly trip) during normal operating conditions. The ratio must be set such that the protection system distinguishes between normal load currents and fault currents.

This is incorrect. The ratio selection is not aimed at reducing the load current but rather ensuring reliable protection.

This is incorrect. The goal is not to decrease the sensitivity to faults but to balance sensitivity to detect faults while avoiding maloperation during normal conditions.

This is incorrect. Increasing the possibility of maloperation is undesirable and contrary to the goal of reliable protection.

Conclusion:

The correct criterion for selecting the ratio of the minimum fault current to the maximum load current in over-current protection of a transmission line is:

1) To prevent the possibility of maloperation under normal operating conditions