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08
2024
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07
Is it necessary to install a leakage alarm device in the distribution cabinet room?
How to measure the insulation resistance of porcelain insulators in low-voltage transmission lines?
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How to measure the insulation resistance of porcelain insulators in low-voltage transmission lines?
The insulation resistance of porcelain insulators for low-voltage transmission lines should be measured before installation. The measurement method is generally using a 2500V or above megohmmeter. The shaking measurement step is: (1) Clean the insulator to be tested and place it on a dry object. (2) Place the megohmmeter steadily, shake the generator handle, and make contact between the two probes until the pointer reaches the "O" position. (3) Connect the two probes to the metal parts at both ends of the porcelain insulator of the low-voltage line being tested, and shake them evenly at a speed of 120 revolutions per minute to read the indicated number. (4) For insulators in operation, those with a resistance greater than 300M Ω are considered qualified, while new insulators with a resistance greater than 500M Ω can only be used.
What are the main reasons for flashover discharge of porcelain insulator strings in low-voltage transmission lines?
The main reasons for flashover discharge of porcelain insulator strings in low-voltage transmission lines are: (1) Lightning strikes: Overvoltage caused by lightning strikes can cause magnetic insulators in low-voltage transmission lines to flashover or even explode. (2) Internal overvoltage: Operating overvoltage, whose value is about 3-4 times the system phase voltage. Flashover under normal working voltage is mainly caused by dirty porcelain insulators on low-voltage lines and weather such as heavy fog and drizzle, commonly known as pollution flashover. (3) Long term increase in power frequency voltage: In an ungrounded neutral system, when one phase is grounded, the voltage of the other two phases increases by times. This voltage increase persists until the fault is resolved. If there is an insulation weakness in the insulator string, it may cause flashover.
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