Understanding Differential Pilot Wire Protection:

Differential pilot wire protection is a reliable method used in power systems to protect transmission lines. It primarily functions on the principle of comparing the current entering and leaving the protected section of the line.

Working Principle: The system checks for differences between the current at two ends of a transmission line. If the currents are equal under normal conditions, it indicates no fault. However, if a difference is detected, it triggers a circuit breaker to isolate the faulty section.

Why the Correct Answer is: "Fast and selective protection of short transmission feeder sections":

• Fast Protection: The differential protection systems are designed to quickly respond to disturbances by analyzing current differentials.
• Selective Protection: This mechanism ensures only the faulty section is isolated, leaving the rest of the network undisturbed. This selectivity helps in maintaining the stability and continuity of the power supply.
• Short Transmission Feeder Sections: Differential protection is especially effective for short transmission lines or feeder sections, where other protective relays may not be as effective due to lesser line impedance and limited fault current sensitivity.

Ruling Out Other Options:

• Reducing transmission line inductance: This is not a function of differential pilot wire protection. It primarily concerns itself with fault detection and isolation.
• Increasing transmission conductor diameter: Conductor diameter does not change related to protection equipment like differential pilot wire systems. This is a physical attribute unaffected by such protection systems.
• Improving illumination inside substation control rooms: This option is unrelated to electrical protection systems; it pertains to lighting and environmental factors within a substation.

Conclusion: The primary function of differential pilot wire protection is to ensure rapid and selective protection for short transmission feeder sections. It efficiently detects and isolates faults to maintain system stability and integrity.