Differential protection is used in transformer to protect transformer in case of:

Explanation:

Differential Protection in Transformers

Definition: Differential protection is a type of protective relay scheme used to protect electrical transformers from internal faults. It operates on the principle of comparing the difference between the currents entering and leaving the transformer. If the difference exceeds a pre-set threshold, it indicates an internal fault, and the protection system isolates the transformer to prevent damage.

Working Principle: The differential protection scheme utilizes current transformers (CTs) placed on both the primary and secondary sides of the transformer. These CTs measure the current flowing into and out of the transformer. Under normal operating conditions, the current entering the transformer should equal the current leaving it, considering the transformer’s turns ratio. Any significant difference between these currents indicates an internal fault. The protection relay detects this discrepancy and trips the circuit breaker, isolating the transformer from the network.

Advantages:

• Provides fast and accurate protection against internal faults.
• Reduces the risk of severe damage to the transformer and associated equipment.
• Enhances the reliability and stability of the power system by minimizing the duration of faults.

Disadvantages:

• Requires precise current transformers with accurate matching characteristics.
• Can be complex and expensive to implement, especially for large transformers.

Applications: Differential protection is widely used in power transformers, generators, and large motors to ensure the equipment's safety and reliability. It is particularly crucial in critical infrastructure and industrial applications where transformer failures can lead to significant disruptions and economic losses.

Correct Option Analysis:

The correct option is:

Option 1: Internal ground faults.

This option correctly describes the primary purpose of differential protection in transformers. Internal ground faults, or any internal fault within the transformer, cause a difference in the current entering and leaving the transformer. The differential protection scheme detects this discrepancy and isolates the transformer to prevent damage.

Important Information

To further understand the analysis, let’s evaluate the other options:

Option 2: Temperature rise.

Temperature rise in a transformer is typically monitored by thermal protection schemes, not differential protection. Thermal protection uses temperature sensors to detect overheating conditions and activate cooling systems or trip the transformer if necessary to prevent thermal damage.

Option 3: Gas formation.

Gas formation within a transformer, often indicative of internal arcing or insulation breakdown, is detected using gas detectors like Buchholz relays. These relays sense the accumulation of gas within the transformer tank and provide an early warning or trip the transformer to prevent catastrophic failure.

Option 4: Failure of cooling system.

The failure of the cooling system in a transformer leads to overheating, which is monitored by thermal protection devices. While it is critical to address cooling system failures, differential protection schemes are not designed to detect such issues.

Conclusion:

Understanding the different protection schemes and their specific applications is essential for ensuring the safety and reliability of electrical transformers. Differential protection is a specialized and highly effective method for detecting and isolating internal faults within transformers, thereby preventing severe damage and maintaining the stability of the power system. While other protection methods address issues like temperature rise, gas formation, and cooling system failures, differential protection remains crucial for safeguarding transformers against internal electrical faults.