2, transformer neutral grounding resistance is not more than 4 Ω, repeated grounding resistance is not more than10 Ω.
3, lightning protection device impact grounding resistance shall not be greater than 30ω.
Extended data:
Resistance measurement method:
There are many factors that affect grounding resistance: size (length and thickness), shape, quantity, buried depth, surrounding geographical environment (such as flat land, ditch and slope), soil moisture, texture and so on. In order to ensure the good grounding of equipment, it is essential to measure the grounding resistance with instruments.
The measurement methods of grounding resistance can be divided into voltage ammeter method, ratio table method and bridge method. According to the specific measuring instruments and the number of poles, it can be divided into manual resistance meter method, clamp resistance meter method, voltage ammeter method, three-pole method and four-pole method.
When measuring grounding resistance, some factors will lead to inaccurate grounding resistance:
(1) The soil around the grounding grid has different composition, different geology, different compactness, different degree of dryness and wetness, and is dispersive. The stray current on the surface, especially the overhead ground wire, underground water pipe and cable sheath, has great influence on the test. Solution: Take different points for measurement and average.
(2) The test line is in the wrong direction and the distance is not long enough. Solution: Find out the test direction and distance.
(3) The auxiliary grounding electrode resistance is too large. Solution: splash water on the pile or use resistance reducer to reduce the grounding resistance of the current electrode.
(4) The contact resistance between the test clamp and the grounding measuring point is too large. Solution: Polish the contact points with a file or sandpaper, and fully clamp the polished contact points with a test clamp.
(5) Interference effect. Solution: Adjust the pay-off direction and try to avoid the direction with strong interference to reduce meter reading jitter.
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