grounding megger is also called grounding resistance megger, grounding resistance meter and grounding resistance tester
According to the power supply mode, the grounding megger is divided into traditional hand-operated type and battery driven type; The grounding megger is divided into pointer type and digital type according to the display mode; The grounding megger is divided into pile driving type and clamp type according to the measurement method
At present, almost no one uses the traditional hand-held grounding megger
Pointer type or digital grounding megger is more popular, and clamp type grounding megger is more popular in power system and telecommunications system
1、 Introduction
Megger, also known as megger, is an instrument used to measure the insulation resistance and high value resistance of the tested equipment
It is composed of a hand-operated generator, a meter head and three terminals (i
e
L: line terminal, e: grounding terminal, g:* terminal)
2、 Selection principle
(1) selection of rated voltage level
Generally, 500V or 1000V megger shall be selected for equipment with rated voltage below 500V; For equipment with rated voltage above 500V, use a megger of 1000v~2500v
(2) selection of resistance range
There are two small black spots on the dial scale line of the megger, and the area between the small black spots is the accurate measurement area
Therefore, when selecting the meter, the insulation resistance value of the tested equipment should be within the accurate measurement area
3、 Use
(1) check the meter
Before measurement, the megger shall be tested for open circuit and short circuit to check whether it is in good condition
Open the two connecting wires, shake the handle, and the pointer should point to &ldquo& infin;& rdquo; Short the two connecting wires again, and the pointer should point to “ 0” If it meets the above conditions, it is good, otherwise it cannot be used
(2) if the tested equipment is disconnected from the line, discharge the large capacitance equipment
(3) select the megger with the voltage level
(4) when measuring insulation resistance, generally only “ l” And “ e” However, when measuring the insulation resistance of the cable to the ground or the leakage current of the tested equipment is serious, it is necessary to use “ g” End, and set “ g” Terminate * layer or housing
After the line is connected, turn the handle clockwise
The shaking speed should be slow and fast
When the speed reaches about 120 revolutions per minute (zc-25 type), keep rotating at a constant speed
Read after 1 minute, and read while shaking
Don't stop reading
(5) wire removal and discharge
After reading, slowly shake and remove the wires, and then discharge the tested equipment
The discharge method is to remove the ground wire used in the measurement from the megger and short-circuit it with the tested equipment (not the megger discharge)
4、 Precautions
(1) it is forbidden to measure the insulation resistance during lightning or near high-voltage equipment
It can only be measured when the equipment is not electrified and there is no induced electricity
(2) during the shake test, no one can work on the tested equipment
(3) the megger wires shall not be twisted together, but shall be separated
(4) it is forbidden to touch the megger by hand before it stops rotating or before the tested equipment is discharged
Do not touch the metal part of the lead when removing the wire
(5) at the end of the measurement, discharge the large capacitance equipment
(6) its accuracy should be checked regularly
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