Shaanxi Hanzhong Transformer Co., ltd

What is the grounding function of oil-immersed transformer?

The grounding function of oil-immersed transformer is to provide an artificial neutral point for systems that do not have a neutral point on the neutral line. In the event of a short-circuit fault in the distribution network, use of arc suppression or low-resistance grounding can reduce grounding current and improve the reliability of the power supply system.

Grounding transformers can be divided into oil-filled and dry type transformer types based on the filling medium and three-phase transformers and single-phase grounding transformers based on the number of phases.

When an oil-immersed transformer is grounded, an equal and opposite current flows in two single-phase coils wound on the same iron core due to the flow of a certain zero-sequence current. Therefore, the zero-sequence inductive current is canceled out and the zero-sequence impedance is very small.

The neutral point of an oil-immersed transformer can generate compensating current in the event of a fault. Because the zero-sequence impedance is small, the voltage drop produced by the zero-sequence current should be as small as possible to ensure the safety of the system.

The grounding function of transformer oil immersed type is mainly to provide an artificial neutral point for systems that do not have a neutral point on the neutral line. It can be used as a factory transformer if there are extra YN wire lines.

The grounding function of oil-immersed transformers is connected to the three-phase busbar of the system, and the rated primary voltage is consistent with the system standard primary voltage. The integration of the rated primary voltage specification and the load capacity must be considered.

The rated capacity of an oil-immersed transformer must match the capacitance of the arc suppression or grounding resistor. If it contains secondary windings, the secondary load capacity must also be considered.

What are the reliability devices of oil-immersed transformer?

  • The coal gas protection device is set up for various short-circuit and oil level drop scenarios. Light gas acts instantly, while heavy gas acts when the breakers on both sides are cut off.

  • This device serves as the main protection response for longitudinal connection differential protection or current speed cutoff protection. It is used to cut off the breakers of all sides in the event of an inquest short-circuit between the coil and lead of the oil-immersed transformer.

  • Overcurrent protection is used for the oil-immersed transformer caused by external phase short circuits. Depending on the capacity of the oil-immersed china power transformer and the driving conditions and sensitivity of the oil-immersed transformer, it can work in overvoltage protection, negative current overcurrent protection, single-phase low-voltage overcurrent protection, or limited-time opening protection.

  • For neutral-grounded power grids directly above 110kV, there are zero-sequence current protection, 0-sequence voltage protection, transformer neutral point grounding and oil-immersed transformer insulation and restriction cut off.

  • Protection against overloads due to long-term use and overloads under time-limited signals.

  • The temperature rise of an oil-immersed transformer and malfunctions in the cooling system are all signaled or triggered in accordance with oil-immersed transformer standards.

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