Ground resistance tester structure composition

Ground resistance tester structure composition

1. Ground Resistance Tester Definition

Earth current: Current flowing in the earth or in a grounded pole.

Ground conductor: A conductor that forms a ground that connects a device, an electrical device, a wiring system, or other conductor (usually a neutral line) to a grounding electrode.

Grounding electrode: A conductor that forms a ground.

Ground connection: The connection used to make up the ground consists of a ground conductor, a grounding electrode, and ground (soil) surrounding the grounding electrode or a conductor that replaces the earth.

Ground Grid: A group of grounded poles consisting of interconnected bare conductors buried in the ground to provide common ground for electrical equipment and metal structures.

Grounding system: A system that consists of all interconnected ground connections within a defined area.

Grounding resistance: Resistance between the grounded electrode and a remotely grounded electrode with zero potential. (Note: The so-called remote refers to a distance at which the two grounded poles are essentially zero.)

Ground pole mutual resistance: refers to the ohmic unit, a grounding pole 1A DC current variable in the voltage generated by another grounding variable.

Potential: The potential difference between a certain point and an equipotential plane (usually the remote ground surface) that is considered to have zero potential.

Contact voltage: The potential difference between a grounded metal structure and a point on the ground at a certain distance. This distance is usually equal to the maximum horizontal boom distance, about 1m.

Step voltage: The potential difference between two points on the ground at a one-step distance. This distance takes the length of 1m in the direction of maximum potential gradient. (Note: This potential difference can be dangerous when a worker stands on the earth or something and current flows through the earth or the object, especially in the event of a fault.)

Grounding pole (for lightning protection of overhead lines): refers to a conductor or a group of conductors, installed below the transmission line, above the ground or above the ground, but the vast majority are underground and connected to the tower or pole foundation.

Soil resistivity: refers to the resistance between the opposite sides of a unit cube, usually in units of Ω•m or Ω•cm.

2. When the grounding resistance tester measures the grounding resistance, what factors cause grounding resistance to be inaccurate? How to avoid it?

A) The soil surrounding the grounding system (ground network) is inconsistent, with different geology, close and dry and wet degree, dispersive, ground surface stray current, especially overhead ground wire, underground water pipe, cable sheath, etc. The test has a particularly large impact. The solution is to take different points to take measurements and average them.

B) The test line is in the wrong direction and the distance is not long enough. The solution is to find the test direction and distance.

C) The auxiliary grounding electrode resistance is too large. The solution is to splash water at the ground stakes or use a resistance reducing agent to reduce the ground resistance of the current pole.

D) The contact resistance between the test clip and the ground measurement point is too large. The solution is to grind the contact point with a guillotine or sandpaper and fully clamp the polished contact with the test wire clip.

E) Interference effects. To solve the problem, adjust the direction of payoff and try to avoid the direction of large interference, so that the meter reading can be reduced.

F) Instrument usage issues. The battery is low. The solution is to replace the battery. The accuracy of the meter drops, and the solution is to recalibrate to zero.

3. When measuring high-rise building grounding, why is the resistance larger than the ground resistance? And the display data jump is serious, what causes it, how to avoid?

This is because when a high-rise building is surveyed, there is a certain resistance (R ground line) between the grounding lead of a high-rise building and the ground. In addition, the test line leading from the upper measuring point of a high-rise building to the ground meter is present in the part of the sky. Line inductance. (WL) So the resistance value measured at the ground point of a high-rise building is R=R ground +WL+R ground. Ground measurement ground resistance R = R ground.

The measurement data is more serious than the terrestrial measurement. This is because the length of the test line is extended in the air, as an antenna leads some radio and electromagnetic clutter signals in the air through the test line to the instrument, causing serious interference and making the measurement data jitter. The solution is to use a coaxial wire as the test lead, connect the coaxial cable and the core wire and connect it to the test point. Connect the shield wire at the other end of the coaxial cable to the C2 terminal of the instrument (ie the current pole), connect the core wire of the coaxial cable to the P2 terminal of the instrument (ie the voltage pole), which can better solve the high-level grounding of the measurement. Resistance due to long lead wire interference effects.

4. When the grounding resistance tester is measuring the grounding resistance, the measuring lines are required to be 20m and 40m, respectively. What is the difference between it and clamp ground resistance meter?

This is because when measuring the grounding resistance, it is required to measure the resistance between the grounding electrode and the remote grounding electrode with zero potential. The so-called remote refers to a distance at which the mutual resistance of the two grounding electrodes is substantially zero. Through experiments, the distance beyond 20m meets this requirement. If the line spacing is shortened, the measurement error will gradually increase.

Clamp-shaped ground resistance meter can only measure multi-point grounding. The measurement result is the sum of measured ground pole and parallel grounding value of multiple ground poles. When measuring single-point grounding, auxiliary pole should be connected to make the test circuit form a loop, so the measurement error Be bigger. However, it is easy to operate.

5. Is the ground of the protected electrical equipment not disconnected from the test and what is the impact on the test meter or protected electrical equipment?

Under normal circumstances, when testing the grounding resistance, the equipment of the protected appliance is required to be disconnected from the grounding terminal. This is because if the protected electrical equipment is not disconnected, the grounding resistance is too large or the contact is not good. The voltage or current of the ground terminal will flow in reverse into the protected electrical equipment. If some equipment cannot resist the reverse voltage and current of the instrument, it may cause damage to the electrical equipment. In addition, some electrical equipment will leak current through the test line and enter the instrument. Burn the meter. Therefore, it is generally required to disconnect the protected electrical equipment. In a well-grounded condition, the protected electrical equipment can be measured without disconnection.

6. Why does the grounding resistance tester block C2P2 and C1P1 of the meter and cannot switch the wiring?

Because the internal circuit design principle of ground resistance meter C2 is the test potential, it must be strictly equal to the post-reference. Therefore, it must be directly connected to the measured grounding electrode. P1 and P2 are signal paths, and the two are interchangeable. C1 is not interchangeable.

7. What factors influence soil resistivity measurements?

Soil resistivity varies not only with the type of soil but also with temperature, humidity, salt content, and soil tightness.

8. What is the difference between "1" and "1" and "OPEN" in the display when the ground resistance table is working? How to deal with?

The display shows "1" indicating that the range selected by the meter is too small. The measured value is greater than the selected range, and the appropriate range file should be selected at this time. The display shows "1" and "OPEN" at the same time indicating that the open-circuited ground or the auxiliary current-grounding resistance of the current electrode is too large, and no loop is formed with the grounding electrode (ie, open circuit). At this time, check whether the test leads of C2 to C1 are connected or bad; or reduce the current pole auxiliary grounding resistance. (Choose a suitable location for piling or watering the current poles).

9. Method for measuring soil resistivity with earth resistance measuring instrument

In the area to be measured, four underground metal needle bars are inserted at an equal distance along the straight line. The distance between them is “a” centimeters. The buried depth of the metal needle bar should be 1/20 of the distance “a”. According to the connection method shown in the figure, connect 4 metal needle bars to the four test holes C1, P1, P2 and C2 on the meter with 4 test leads. Select the appropriate range and press the test button “TEST”. The current indicator lights up. The measured ohmic value of the resistor is shown on the display.

10. Grounding resistance tester on the detection of grounding resistance reading inaccurate

(1) Causes of inaccurate ground-resistance detection or unstable indications or even negative values. Due to the grounding resistance detector is composed of many precision electronic components, there are relatively long detection lines, under the influence of adverse environments and operations, often lead to measurement error, it is difficult to confirm the exact value of the measured grounding resistance, which mainly have the following factor:

(1) There is a large potential difference at the surface, and there are multiple independent groundings. For example, transformers such as factories and complexes are grounded. Due to various reasons, the grounding resistance becomes large, the insulation of the transformer itself deteriorates, and leakage occurs. Potential differences occur around the grounding electrode. If the detection rod is placed around it, it will affect the measurement accuracy.

(2) The measured grounding electrode itself has alternating current (insulation of the power equipment is not good, and leakage due to partial short-circuiting leads to the interference of the high-voltage power supply near the downline); the structure of the previous early buildings was confusing. The wiring is messy, and sometimes even the zero line potential difference is above 100V, directly affecting the grounding resistance measurement error.

(3) poor contact (including the instrument itself): grounding resistance tester wiring connection, due to the use of often bent, easy to break, and because of the existence of the protective cover, it is difficult to find, resulting in the phenomenon of breaking time; In addition, due to The detection rods and alligator clips have a long use time, have oxidative corrosion, and can also cause poor contact; if the ground electrode to be tested is severely oxidized and badly rusted, it will also affect the measurement readings.

(4) Strong electromagnetic fields emitted by nearby transmitters, antennas, etc.: In the vicinity of high-power transmitting bases, such as mobile, microwave, and BP machines, high-voltage equipment, frequent high-voltage equipment near the high-voltage substations Starting place.

(5) Grounding devices and metal pipes buried in a relatively complex way can also cause poor or unstable ground resistance measurement, such as gas stations, chemical plants, etc., due to the complexity of the layout of underground metal pipes, in accordance with the normal inspection connection, underground metal road appearance The existence of this, in fact, changes the direction of the current at each end of the meter, often resulting in zero or negative measurements. If there is a different soil resistivity at the same site, this phenomenon can also be caused.

(6) When detecting a high-rise building, an excessively long detection line induces a voltage and causes a detection error. At the same time, the long line itself also has a wired resistance.

(7) When the soil with high resistivity and poor water absorption is used as the foundation cushion for the whole building, the measured grounding resistance is often too large.

(8) The operation is not carried out according to the method specified in the instruction manual. The instrument itself is improperly maintained, and the instrument is used to bring sickness or overdetection.

(b) Avoid methods

(1) When testing gas stations and liquefied gas stations and high-rise buildings grounding resistance and electrostatic grounding resistance, the arrangement of buried metal (oil, gas) pipes and grounding devices and metal devices is not correct on the map Marked, so detection of the grounding resistance when the detection table rod placement and distance have a great influence on the measured value, usually with the direction and distance, the value is not the same, and sometimes the measurement value may even appear negative. In particular, the detection of buried pipeline facilities such as gas stations will often occur. The solution is: to understand the layout of the underground metal pipeline before the test, not only to view the grounding device diagram, but also to view the layout of other underground metal pipelines, choose to place P, C grounding pole as little as possible.

(2) Where there is a disconnected card in the ground lead wire, disconnect the test as much as possible to avoid the impact of other devices on the test.

(3) When abnormality occurs during the test, the cause should be identified, or detected and compared at different times and in different directions and locations to obtain the correct test value.

(4) In order to avoid electromagnetic interference on the leads under high electromagnetic fields, the detection lead should be relatively shortened, and the qualified inner diameter of the lead should be used as multi-strand metal wires.

(5) When detecting the grounding resistance in the place where the high-resistivity sandstone cushion is used, the P and C ground electrodes should be placed in a place where the moisture and the ground conduct well, so that the measured grounding resistance is relatively correct.

(6) Testing should be conducted in accordance with the operating procedures. The testing equipment should be maintained frequently and regularly, and no super-inspection equipment should be used.

11. The use of DER2571B grounding resistance measuring instrument is subject to the environmental factors on the spot, the simple test method.

Due to the limitations of on-site testing, site, and geographical environment, testing cannot be performed in accordance with the instructions for use. According to the experience of us and other users, the simple test method is described as follows: After the test wire (20m, 40m) is connected with the metal probe, the metal probe is laid flat on the concrete floor, wrapped with cloth, and poured with water. With metal probes (allowing water to fully penetrate the concrete floor), measurements can now be started. If the instrument display shows the value "1" and the character "open", it means that the auxiliary grounding resistance exceeds the limit value (excluding the influence of underground geo-environmental factors), and it cannot be measured normally. It should be re-watered or replace the measuring point until the display value can be displayed normally. Numerical value. The test results are basically the same as the test data of the ground piles.

respected user:

Thank you for your attention to our products. In addition to this product introduction, the company also has insulation ladders, high-voltage insulation mats, cable fault testers, high-voltage measuring instruments, pressure test equipment for insulated boots gloves, power safety equipment cabinets, etc. If you are interested in our products, welcome to inquire. Thank you!