Do you Know the Overvoltage Protection of Transformers?

As a Transformer Winding Wire Manufacturer, share with you.

Transformers are often affected by lightning overvoltages, operating overvoltages, and power frequency overvoltages during operation. Therefore, electrostatic screens, electrostatic rings, reinforced wire cakes and aluminum foil shields are often used on the windings to improve the electric field distribution.

Transformer Winding Wire

Transformer Winding Wire

When the winding is subjected to overvoltage, because the shock wave has a steep waveform and the equivalent frequency is very high, the shock current starts to flow mainly through the capacitor path, not the inductance path. Due to the capacitance distribution relationship of the windings to the ground, the inrush current through the windings is very unevenly distributed from beginning to end, resulting in a large difference in voltage gradient.

When the transformer adopts a cylindrical winding, although the impulse voltage distribution along the entire winding is better than that of a continuous winding, the overvoltage gradient distribution of the first layer is often larger than that of the other layers. In order to reduce the over-voltage gradient of the first layer, an electrostatic screen is placed at the winding wire end, the first layer of wire is wound on the electrostatic screen, and the wire end is connected with the electrostatic screen outlet. After adding the electrostatic screen, the capacitance distribution of the winding to the ground is improved, thus reducing the overvoltage gradient of the first layer.

In order to avoid the discharge of the electrostatic screen, the electrostatic screen should not extend out of the winding end. When a continuous winding is used, when the transformer is struck by lightning overvoltage, the distribution of the overvoltage gradient along the entire winding is not uniform. The function of the electrostatic ring into the winding end is to improve the capacitance distribution of the first wire cake to ground. The electrostatic ring can also improve the electric field distribution to the ground. For the transformer windings in the middle of the line, if the tangled type is adopted, the inter-turn capacitance can be increased to improve the distribution of overvoltage. Because the electric field distribution in the middle of the winding is uniform, the tangled windings in the middle of the line may not be placed with an electrostatic ring. Although people have taken some electrostatic protection measures (electrostatic shield, electrostatic ring) and improved the structure of the winding (tangled, inner shielding capacitance, etc.), the voltage gradient of the first few turns and the first few cakes of the winding is still relatively high. In order to prevent the first few turns and the first few cakes from being broken down, and the entire winding is more economical, sometimes strengthening cakes are used, which is to strengthen the overvoltage capability of the line cakes.

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