Ground Resistance Test Voltage Ammeter Method Ratio Meter Bridge Method Electronic Performance Test
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Ground resistance test/voltage ammeter method, ratio meter method and bridge method
Ground resistance is an important parameter used to measure whether the grounding condition is good. It is the resistance encountered when the current flows from the grounding device to the earth and then flows through the earth to another grounding body or spreads to a distance. It includes the grounding wire and the grounding body itself. Resistance, contact resistance between the ground body and the resistance of the earth, as well as the resistance of the earth between two ground bodies or the resistance of the earth from the ground body to infinity. The size of the ground resistance directly reflects the good degree of contact between the electrical device and the "ground", and also reflects the size of the ground network. The concept of ground resistance is only applicable to small ground grids; as the ground grid area increases and the soil resistivity decreases, the inductive component of ground impedance plays an increasingly important role, and large ground grids should adopt ground impedance design.
There are many factors that affect the grounding resistance: the size (length, thickness), shape, quantity, burial depth, surrounding geographical environment (such as flat land, ditches, and slopes are different) of the grounding electrode, soil moisture, texture, etc. In order to ensure good grounding of the equipment, it is essential to use an instrument to measure the ground resistance.
Ground resistance test requirements:
a. AC work is grounded, and the grounding resistance should not be
greater than 4Ω;
b. Grounding for safe work, the grounding resistance should not be
greater than 4Ω;
C. DC working grounding, the grounding resistance should be
determined according to the specific requirements of the computer
system;
d. The grounding resistance of the lightning protection ground
should not be greater than 10Ω;
e. For shielded systems, if joint grounding is used, the grounding
resistance should not be greater than 1Ω.
Test Methods
The measurement methods of ground resistance can be divided into:
voltage ammeter method, ratio meter method and bridge method.
According to the specific measuring instrument and the number of
poles, it can be divided into: hand-operated ground resistance
meter method, clamp ground resistance meter method, voltage and
ammeter method, three-pole method and four-pole method.
When measuring ground resistance, some factors cause inaccurate
ground resistance:
(1) The soil composition around the ground network is inconsistent,
the geology is different, the density, dryness and wetness are
different, and it is dispersed. The stray current on the ground
surface, especially overhead ground wires, underground water pipes,
cable jackets, etc., has a special impact on the test. big.
Solution: Take measurements at different points and take the
average.
(2) The direction of the test line is wrong and the distance is not
long enough. Solution: Find the correct test direction and
distance.
(3) The resistance of the auxiliary ground electrode is too large.
Solution: Splash water on the ground pile or use resistance
reducing agent to reduce the ground resistance of the current
electrode.
(4) The contact resistance between the test clamp and the ground
measurement point is too large. Solution: Polish the contact points
with a file or sandpaper, and fully clamp the polished contacts
with a test wire clamp.
(5) Interference effects. Solution: Adjust the pay-out direction
and try to avoid the direction with large interference to reduce
the jump in the instrument reading.
(6) Problems with instrument use. The battery is low, solution:
replace the battery.
(7) The accuracy of the instrument decreases. Solution: Recalibrate
to zero.
The accuracy of the ground resistance test value is one of the
important factors in judging whether the grounding is good. Once
the test value is inaccurate, it will either waste manpower and
material resources (the measured value is too large), or it will
cause safety hazards to the grounding equipment (the measured value
is too small).
Ground Resistance Test Voltage Ammeter Method Ratio Meter Bridge Method Electronic Performance Test
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