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Differential protection of transformer is a crucial method used to detect internal faults in power transformers. It plays a vital role in the overall safety and reliability of a power system. Transformers are expensive and critical equipment. Therefore, their protection is a top priority in any electrical installation. Table of Contents Understanding Differential Protection of Transformer Working Principle of Differential Protection of Transformer Why Differential Protection is Essential for Transformers CT Connection and Polarity in Differential Protection of Transformer Types of Faults Detected by Differential Protection of Transformer Differential Protection Settings for Transformer Inrush Current and its Impact on Differential Protection of Transformer Calculation Example: Differential Protection of Transformer Advantages of Differential Protection of Transformer Challenges and Limitations Comparison Table: Differential vs Overcurrent Protection Conclusion

Differential Protection of Transformer: Working, Settings & Calculation This protection scheme operates on the principle of comparing the current entering and leaving the transformer windings. Under normal conditions, these two currents are nearly equal. But during internal faults, such as phase-to-phase or phase-to-earth faults, the difference between these currents becomes significant. This difference is what the differential protection detects and responds to.

Working Principle of Differential Protection of Transformer

The basic working of the differential protection of transformer relies on Kirchhoff’s current law. According to this principle, the incoming and outgoing currents in a closed loop must be equal. In practical terms, a transformer differential relay continuously monitors the current flowing into the primary winding and the current flowing out of the secondary winding. If the system is healthy, these currents are the same when referred to a common base. However, in case of an internal fault, the sum of these currents will not be zero. The differential relay senses this mismatch and quickly sends a trip signal to isolate the transformer. The key components in this protection scheme include: - Current Transformers (CTs) on both sides of the transformer - Differential Relay to detect current differences - Stabilizing Resistors or restraining elements to avoid mal-operation during external faults or inrush currents Know more about How Difficult Is It to Learn Programmable Logic Controller (PLC)?

Why Differential Protection is Essential for Transformers

Transformers are vulnerable to several types of internal faults such as turn-to-turn short circuits, interwinding faults, and insulation failures. External protection like overcurrent or earth fault relays may not react fast enough or may fail to detect such faults accurately. Differential protection of transformer provides fast and selective operation. It ensures that the transformer is disconnected quickly, limiting damage and minimizing system disturbance. It is the most sensitive and reliable form of protection for internal transformer faults.

CT Connection and Polarity in Differential Protection of Transformer

Correct CT connection and polarity are crucial for the successful operation of the protection system. The CTs on both sides of the transformer must be connected in such a way that during normal conditions, their secondary currents cancel each other. This is achieved by matching their polarity and considering the transformer vector group. For example, if a transformer has a Delta-Star configuration (Dyn11), the CTs on the delta side are connected in star and those on the star side are connected in delta. Also, a phase shift compensation is made in the relay settings to account for the 30-degree phase shift introduced by the transformer. Incorrect CT polarity or connection leads to unwanted relay operations or failure to trip during faults. Know more about Top 15 Variable Frequency Drive Manufacturers