Answer / Gyanendra Singh

1. A breather is used to allow the expansion of air in the transformer during the increase in temperature due to the electrical load or during oil filling or draining. It prevents the internal pressure from becoming too high, which could cause damage to the transformer.
2. The oil goes down in the conservator tank because it expands when heated and rises. The level of oil in the conservator is designed to stay constant by having a pipe that allows oil to flow out if the oil level gets too high, and another pipe that allows oil to flow in if the oil level gets too low.
3. We take oil samples from the bottom of the transformer because the sediment settles at the bottom and the sample from the bottom provides an accurate representation of the condition of the oil inside the transformer.
4. The IR value (I2R loss) of a transformer can be calculated using the formula: I^2 * R, where I is the current flowing through the winding and R is the resistance of the winding.
5. OLTC (On Load Tap Changer) having Buchholz trip only means that if the gas produced due to insulation breakdown reaches a certain level, it will trip the circuit breaker. There may be no alarm because alarms are typically used for fault conditions that do not necessarily require immediate action such as overload or under-voltage.
6. Off Load Tap Changer Operation Procedure: Before operating the tap changer, ensure that the transformer is unloaded (no current is flowing through it). Disconnect the high voltage and low voltage circuit breakers. Adjust the tap position as required, then reclose the high voltage and low voltage circuit breakers.
7. TR Shutdown / Isolation Procedure: Before shutting down the transformer, ensure that the transformer is unloaded and the oil level is adequate. Disconnect the high voltage and low voltage circuit breakers. Open the venting valves to allow any pressure inside the tank to be relieved. Once the pressure has been relieved, close the venting valves and isolate the transformer from the power system.
8. If three transformers in parallel, one transformer is not sharing the load – this could be due to a fault or malfunction in that transformer, or it may be out of service for maintenance. In such a case, the remaining transformers should be able to handle the full load by increasing their current output.
9. Transformers have OLTC (On Load Tap Changer) in the high voltage side because it is easier and safer to adjust the tap position while the transformer is under load. If the tap changer were on the low voltage side, it would need to be switched under no-load conditions, which could cause electrical arcing and damage to the equipment.n10. % Impedance is a measure of the opposition that a circuit offers to the flow of alternating current (AC). It is represented as a complex number with both resistance and reactance components.n11. Transformer rating in MVA (Mega-Volt Ampere) indicates the maximum power that the transformer can handle without overheating or damaging the insulation.n12. Vector Group in Transformer refers to the phase relation between the voltage and current waveforms of a three-phase transformer, which affects the connection method of the windings and the phase sequence of the input and output voltages.n13. Condition for Parallel Operation of Transformers: The transformers must have the same voltage rating, the same phase sequence, and the same vector group. They should also be connected in parallel with isolation between their windings to avoid circulating currents.n14. Tertiary winding is an additional winding on a three-phase transformer that is separate from the primary and secondary windings. It is used for specific applications such as providing auxiliary power, voltage regulation, or load balancing.n15. If TR trips on Buchholz or Tap Changer Relay, the fault condition should be investigated to determine the cause and the necessary repair or maintenance work should be carried out.n16. Difference between Oil Temperature Protection and Winding Temperature Protection: Oil temperature protection is designed to prevent excessive heating of the transformer oil, while winding temperature protection is designed to prevent overheating of the windings.n17. Winding temperature is measured in cast resin transformers using thermocouples placed at various locations along the windings.n18. Different Types of Faults in Transformers: Some common faults include insulation failure, winding short circuit, ground fault, and phase-to-phase fault.n19. If TR is charged from LV (Low Voltage), it will cause the transformer to produce a magnetic field, which may damage the windings or other components of the transformer.n20. If Megger reading shows zero between LV (Low Voltage) winding and earth, it indicates that there is an open circuit in the winding insulation.n21. Buchholz relay of Main Tank and OLTC Tank cannot be interchanged because they are designed to detect different fault conditions.n22. If the line between Breather and Conservator Tank is locked, it will prevent the expansion of air during the load cycle, which could cause an increase in pressure inside the transformer.n23. The function of Oil Seal in Breather is to prevent oil from leaking out when the breather vent is open during normal operation or maintenance.n24. Locations for Buchholz Relay fixed in Power Transformer: Buchholz relay is typically located near the transformer tank, between the conservator and the main tank.n25. Checks in Power Transformer during Maintenance: Some common checks include oil sampling and analysis, winding resistance measurement, insulation resistance measurement, and dielectric testing.n26. What is important when we check OLTC Operation during Maintenance: It is important to ensure that the tap changer operates smoothly and accurately, and that there are no leaks or damage in the mechanism.n

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