Insulation structure of current transformer

- Jan 27, 2021-

In high-voltage power systems, the internal insulation of primary power equipment usually adopts a capacitive insulation structure. The so-called capacitive insulation structure refers to the use of insulating materials (oil-immersed cable paper) and capacitive screens (aluminum foil) to wrap the main insulation layer of the equipment, and adjust the radial thickness between the capacitive screens to achieve a uniform distribution of the internal insulation field strength purpose. Normally, the capacitive screen connected to the primary high-voltage winding is called the zero screen (high-voltage electric screen), and the capacitive screen close to the secondary winding is called the final screen (earth-electric screen). After the final screen is reliably grounded, a series capacitor bank is formed between the high-voltage winding and the ground. If there are an infinite number of capacitive screens, the field strength of each screen surface can be almost equal; but in reality, the number of capacitive screens is limited, but the field strength difference of each screen surface is strictly limited. It can be seen that if the last screen of the current transformer is poorly grounded, the last screen will generate a floating potential; and under certain conditions, it will discharge to the surrounding equipment, damage the insulation, and cause accidents such as transformer explosion or ground fault in severe cases.