How to measure the insulation resistance of low voltage line porcelain insulator?

How to measure the insulation resistance of low voltage line porcelain insulator?

In principle, the insulation resistance of low-voltage line porcelain insulators shall be measured before installation. The general measurement method is 2500 V and above megohmmeter.

The vibration measurement steps are:

(1) Clean the tested insulator and put it on a dry object.

(2) Place the megger stably, shake the handle of the generator to make the two probes contact and make the pointer point to the "O" position.

(3) Connect the two probes to the metal parts at both ends of the porcelain insulator of the low-voltage line under test, shake them evenly at the speed of 120 revolutions per minute, and read the readings.

(4) Insulators in operation are qualified if they are greater than 300m Ω, and new insulators can be used if they are greater than 500m Ω.

What are the main reasons for the flashover and discharge of porcelain insulator strings on low-voltage lines?

The main reasons for flashover and discharge of porcelain insulator string of low-voltage line are as follows:

(1) Lightning strike: overvoltage caused by lightning strike may cause flashover or even explosion of magnetic insulator of low-voltage line.

(2) Internal Overvoltage: working overvoltage, which is about 3-4 times of system phase voltage. Flashover under normal working voltage: mainly caused by dirty porcelain insulator of low-voltage line, heavy fog, drizzle and other weather. It is often referred to as pollution flashover.

(3) Long term rise of power frequency voltage: in a neutral ungrounded system, when one phase is grounded, the voltage of the other two phases will rise exponentially. This voltage rise will remain until the fault is eliminated. If there are weak insulation points in the insulator string, it may cause flashover.