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3. The manufacturing of an electrical power transformer involves several key steps: 1. **Core Manufacturing:** * **Material Selection:** High-quality silicon steel (often cold-rolled grain-oriented - CRGO) is used for the core. This material has high magnetic permeability and low hysteresis losses, which is crucial for efficient operation. * **Core Stacking:** The silicon steel is cut into thin sheets (lamination) and then assembled to form the magnetic core. These laminations are insulated from each other to reduce eddy currents, which cause energy loss and heating. * **Core Assembly:** The stacked laminations are typically formed into one of two main shapes: "core type" or "shell type." In a core type, the windings surround the core legs. In a shell type, the core surrounds the windings. 2. **Winding Manufacturing:** * **Conductor Selection:** Copper or aluminum wire, often insulated with a special enamel or paper, is used for the windings. The gauge of the wire depends on the current the winding will carry. * **Winding Process:** The insulated wire is wound onto formers or directly onto the core legs. For high-voltage windings, multiple layers are used, often separated by insulating paper or cardboard. The windings are carefully arranged to ensure proper electrical isolation and to minimize voltage stress between adjacent turns and layers. * **Tapping:** To allow for voltage regulation, winding taps are often incorporated. These are connection points at various stages of the winding that can be switched to change the turns ratio and thus the output voltage. 3. **Assembly:** * **Core and Winding Integration:** The manufactured core and windings are carefully assembled together. For core-type transformers, the windings are placed around the core legs. For shell-type transformers, the core is assembled around the windings. * **Insulation:** Extensive insulation is critical. This includes insulating paper, cardboard, Nomex paper, and sometimes vacuum-impregnated varnish or epoxy resins. Bushings, which are porcelain or composite insulators, are installed to provide safe external connections for the windings. * **Tanking:** The assembled core and windings are placed into a steel tank, which is then hermetically sealed. The tank is designed to contain the insulating oil and protect the internal components from the environment. 4. **Oil Filling and Testing:** * **Insulating Oil:** The transformer tank is filled with a special insulating oil, typically mineral oil or ester-based oil. This oil serves multiple purposes: it cools the core and windings by dissipating heat, it provides electrical insulation between live parts and the tank, and it helps prevent corona discharge. * **Degassing and Drying:** Before filling, the oil is often degassed and dried to remove moisture and dissolved gases, which can degrade its insulating properties. * **Testing:** After assembly and filling, the transformer undergoes rigorous testing to ensure it meets specifications. These tests include: * **Winding Resistance Test:** To check the continuity and resistance of the windings. * **Insulation Resistance Test (Megger Test):** To measure the quality of the insulation between windings and the tank. * **Dielectric Strength Test:** To verify the insulating properties of the oil. * **Voltage Ratio Test:** To confirm the correct voltage transformation. * **Polarity Test:** To ensure correct phasing of windings. * **Short-Circuit Impedance Test:** To determine the transformer's impedance. * **No-Load Losses and Excitation Current Test:** To measure core losses and magnetizing current. * **Load Losses Test:** To measure winding losses under load conditions. * **Impulse Test:** To assess the transformer's ability to withstand lightning surges. 5. **Finishing and Packaging:** * **External Components:** Components like radiators, fans (for cooling), conservators (to accommodate oil expansion), and tap changers are attached to the outside of the tank. * **Painting:** The tank is painted for corrosion protection and identification. * **Packaging and Shipping:** The finished transformer is prepared for shipping, often with its bushings removed or protected, and secured for transport.