The winding arrangement of a step-up isolation transformer has a direct impact on the coupling coefficient, which is manifested by changes in the magnetic flux path, leakage flux distribution, and electromagnetic coupling strength. Winding arrangement design must balance insulation performance, heat dissipation efficiency, and optimized electromagnetic coupling. The coupling coefficient, a parameter that measures the degree of magnetic field communication between two windings, ranges from 0 to 1, with values closer to 1 indicating closer coupling. The winding arrangement of a step-up isolation transformer typically follows specific principles that directly determine the coupling coefficient.
From an insulation optimization perspective, step-up isolation transformers often place the low-voltage winding inside the core, the medium-voltage winding in the center, and the high-voltage winding on the outermost layer. This arrangement minimizes the voltage gradient between the low-voltage winding and the core, minimizing insulation requirements. It also increases the distance between the high-voltage winding and the core, reducing the risk of insulation breakdown. However, placing the high-voltage winding outside the core lengthens the magnetic flux path between it and the medium-voltage winding, increasing leakage flux and resulting in a slight decrease in the coupling coefficient. Centering the medium-voltage winding balances the coupling strength with the high- and low-voltage windings, reducing overall magnetic flux leakage. However, if the spacing between the medium- and low-voltage windings is too small, local saturation may occur due to magnetic field superposition, reducing coupling efficiency.
The relationship between heat dissipation efficiency and winding arrangement also affects the coupling coefficient. Placing the high-voltage winding externally facilitates heat sink installation and oil channel design, reducing the impact of temperature rise on magnetic permeability. Temperature increases cause the core's magnetic permeability to decrease, increasing magnetic resistance and reducing the coupling coefficient. Therefore, a reasonable winding arrangement must balance insulation distance and heat dissipation requirements to avoid deteriorating coupling performance due to overheating. For example, excessive spacing between the high-voltage and medium-voltage windings increases magnetic flux leakage, while too small a spacing may hinder oil or air flow, creating heat dissipation dead zones, further affecting coupling stability.
The strength of electromagnetic coupling is directly affected by the winding arrangement. In a step-up isolation transformer, placing the low-voltage winding close to the core enhances its magnetic coupling with the core. However, placing the high-voltage winding externally lengthens the magnetic flux path between it and the low-voltage winding, increasing magnetic flux leakage. Using a staggered layered arrangement, such as a low-voltage-high-voltage-medium-voltage sequence, can reduce magnetic flux leakage by shortening the spacing between the high and low voltage windings. However, this increases the difficulty of insulating the high voltage winding from the core. In actual designs, optimization through simulation or experimentation is necessary to maximize the coupling coefficient while meeting insulation and heat dissipation requirements.
Magnetic flux leakage distribution is a key factor affecting the coupling coefficient in winding arrangement. Leakage flux that does not participate in the main magnetic circuit coupling reduces the effective coupling coefficient. When the high voltage winding is external, the leakage flux channel between it and the medium voltage winding is larger, increasing the percentage impedance voltage between the windings and reducing the coupling coefficient. Placing the low voltage winding in the center can reduce magnetic flux leakage between it and the high voltage winding. However, if the low voltage winding has too few turns, insufficient magnetomotive force may weaken the overall coupling. Therefore, winding arrangement requires a comprehensive consideration of turns ratio, voltage level, and magnetic flux leakage control.
The impact of winding arrangement on the coupling coefficient varies in different application scenarios. For precision equipment requiring a high coupling coefficient, a compact low voltage-medium voltage-high voltage arrangement may be used to reduce magnetic flux leakage by reducing the distance between layers. In high-voltage, high-capacity scenarios, to meet insulation and heat dissipation requirements, some coupling coefficient may be sacrificed, resulting in a loose arrangement with the high-voltage winding positioned externally. The design process must balance coupling performance with other parameters based on specific requirements.
Optimizing the winding arrangement to improve the coupling coefficient requires a multi-faceted approach. Using high-permeability core materials can enhance the main magnetic flux, indirectly improving the coupling coefficient. Optimizing the winding turns ratio ensures matching magnetomotive force between the high- and low-voltage windings, reducing magnetic flux leakage. Introducing shielding layers or magnetic shunts can guide leakage flux back into the main magnetic circuit, further improving coupling efficiency. These measures must be designed in conjunction with the winding arrangement to achieve the optimal balance between coupling coefficient and overall performance.
