The cooling method of a transformer is determined by the type of cooling medium used and the circulation method. Oil-immersed transformers are further categorized into internal and external cooling modes, which are typically represented using four-letter codes. These codes provide a clear indication of the cooling system's configuration and efficiency. The first letter in the code represents the cooling medium that comes into direct contact with the windings. For example: - **O** stands for mineral oil or insulating liquid with a flash point higher than 300°C. - **K** refers to insulating liquid with a flash point above 300°C. - **L** indicates insulating liquid that has an undetectable flash point. The second letter describes how the internal cooling medium circulates: - **N** means natural convection, where oil flows through the cooling device and windings without any external force. - **F** denotes forced circulation in the cooling device, with natural convection within the windings. - **D** suggests forced circulation in the cooling device and at least a guided flow in the main windings. The third letter identifies the external cooling medium: - **A** stands for air. - **W** refers to water. The fourth letter specifies how the external cooling medium is circulated: - **N** indicates natural convection. - **F** means forced circulation (using fans, pumps, etc.). Common cooling methods include: - **ONAN**: Natural convection cooling of internal oil, also known as oil-immersed self-cooling. - **ONAF**: Oil-immersed forced air cooling. - **OFAF**: Forced oil circulation with forced air cooling. - **ODAF**: Forced oil-directed circulation with forced air cooling. Understanding these codes helps in selecting the right transformer for specific applications, ensuring optimal performance and longevity under different environmental conditions.
Steel poles are commonly used to carry several types of electric power lines, distribution lines and lighting system. Distribution lines carry power from local substations to customers. They generally carry voltages from 4.6 to 33kV for distances up to 30 miles, and include transformers to step the voltage down from the primary voltage to the lower secondary voltage used by the customer. A service drop carries this lower voltage to the customer's premises.
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