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Three winding transformer protection

          Three-winding transformer is generally required with three laps main transformer differential protection , the main transformer high backup protection, main transformer backup protection, the main transformer low backup protection, especially in the over-voltage protection requirements of the higher three-winding transformer with high, Low-voltage three windings, if the lightning strikes high-voltage side of their operation intruded by lightning waves, will be passed through the electrostatic coupling and electromagnetic induction to the low-voltage winding over-voltage transmission. In the high and medium voltage winding operation, when the low voltage winding is open, the low capacitance of the low voltage winding has a small value to the ground, and the electrostatic induction voltage component on the winding can reach a higher value, thus endangering the insulation of the low voltage winding and limiting the harm of overvoltage , Low-voltage windings are required to be installed in the export arrester protection.

993 three main transformer differential protection device sample map.jpg

          During transformer operation, if there is an asymmetrical ground fault in the system or a non-full-phase operation of the circuit breaker and the zero-sequence voltage occurs, the voltage will be transmitted to the low-voltage winding through capacitive coupling. Because of this voltage with frequency over-voltage characteristics, the same will endanger the safety of low-voltage winding insulation. To this end, in addition to the use of circuit breakers with good performance over the same period, usually on the transformer low-voltage side bus bridge to install three Y. Wound capacitors are used to increase the capacitance of the low-voltage side to ground, which can effectively absorb and reduce the over-voltage amplitude and steepness, thereby protecting the over-voltage.

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