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To prevent maloperation of differentially relay while energizing a transformer, the relay restraining coil is biased with
- a)Second harmonic current
- b)Third harmonic current
- c)Fifth harmonic current
- d)Seventh harmonic current
Correct answer is option 'A'. Can you explain this answer?
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To prevent maloperation of differentially relay while energizing a tra...
Preventing Maloperation of Differentially Relay
Differentially relay is an essential protection device used in power systems to protect transformers from various faults. However, during the energizing of transformers, the differential relay may operate due to the high inrush current, which can result in maloperation. To prevent this, the relay restraining coil is biased with second harmonic current.
What is Second Harmonic Current?
Second harmonic current is a type of current that has a frequency twice the fundamental frequency. In the case of a power system, the fundamental frequency is 50Hz or 60Hz, and the second harmonic frequency is 100Hz or 120Hz, respectively.
Why Biasing with Second Harmonic Current is Important?
The second harmonic current is generated primarily due to the magnetic saturation of the transformer core during energization. The magnitude of the second harmonic current is much higher than the differential current during this period. Therefore, by biasing the restraining coil with the second harmonic current, the differential relay can be prevented from maloperation during the transformer energization.
How Does Biasing with Second Harmonic Current Prevent Maloperation?
The differential relay operates when there is a difference in the current between the primary and secondary windings of the transformer. During the energization of the transformer, the second harmonic current flows through both the primary and secondary windings. As a result, the differential current becomes zero, and the relay does not operate.
Conclusion
Biasing the restraining coil with second harmonic current is a common practice used to prevent differential relay maloperation during transformer energization. This method ensures that the relay operates only when a fault occurs and not during normal transformer operation.
Differentially relay is an essential protection device used in power systems to protect transformers from various faults. However, during the energizing of transformers, the differential relay may operate due to the high inrush current, which can result in maloperation. To prevent this, the relay restraining coil is biased with second harmonic current.
What is Second Harmonic Current?
Second harmonic current is a type of current that has a frequency twice the fundamental frequency. In the case of a power system, the fundamental frequency is 50Hz or 60Hz, and the second harmonic frequency is 100Hz or 120Hz, respectively.
Why Biasing with Second Harmonic Current is Important?
The second harmonic current is generated primarily due to the magnetic saturation of the transformer core during energization. The magnitude of the second harmonic current is much higher than the differential current during this period. Therefore, by biasing the restraining coil with the second harmonic current, the differential relay can be prevented from maloperation during the transformer energization.
How Does Biasing with Second Harmonic Current Prevent Maloperation?
The differential relay operates when there is a difference in the current between the primary and secondary windings of the transformer. During the energization of the transformer, the second harmonic current flows through both the primary and secondary windings. As a result, the differential current becomes zero, and the relay does not operate.
Conclusion
Biasing the restraining coil with second harmonic current is a common practice used to prevent differential relay maloperation during transformer energization. This method ensures that the relay operates only when a fault occurs and not during normal transformer operation.
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To prevent maloperation of differentially relay while energizing a transformer, the relay restraining coil is biased witha)Second harmonic currentb)Third harmonic currentc)Fifth harmonic currentd)Seventh harmonic currentCorrect answer is option 'A'. Can you explain this answer?
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