Principle and use of clamp-type ground resistance tester

Clamp-on ground resistance tester is also known as clamp-on ground resistance tester, and its English name is clamp-on ground resistance tester or ground resistance tester. Widely used in ground resistance measurement of telecommunications, meteorology, oil fields, construction and industrial equipment. When measuring a grounding system with a loop, the clamp-type grounding resistance meter does not need to disconnect the grounding down conductor and does not require auxiliary electrodes. It is safe, fast and easy to use. The clamp-type grounding resistance meter can measure ground faults that cannot be measured by traditional methods, and can be used in situations that cannot be measured by traditional methods, because the clamp-type grounding resistance meter measures the combined value of the grounding body resistance and the grounding lead resistance. Clamp-type ground resistance meters are available in long jaws and round jaws. Long jaws are particularly suitable for flat steel grounding applications.

Measurement principle

1. Resistance measurement principle

The basic principle of measuring ground resistance with a clamp-type ground resistance meter is to measure loop resistance. The jaw part of the clamp meter is composed of a voltage coil and a current coil. The voltage coil provides an excitation signal and induces an electric potential e on the loop under test. Under the action of potential e, a current i will be generated in the circuit under test. The clamp meter measures e and i, and the measured resistance r can be obtained through the following formula.

2. Current measurement principle

The basic principle of measuring current with a clamp-type ground resistance meter is the same as that of measuring current. The AC current i of the measured wire generates an induced current i1 through the current magnetic ring and current coil of the clamp. The clamp meter measures i1, and the measured current i can be obtained through the following formula.

Technical specifications

Power supply: 6vdc (4 AA alkaline dry batteries)

Working temperature: -10℃-55℃

Relative humidity: 10%-90%

LCD display: 4-digit LCD digital display, length and width 47×28.5mm

Jaw opening size: 32mm

Clamp weight (including battery): long jaw 1160g; round jaw 1120g

Clamp size: long jaw length 285mm, width 85mm, thickness 56mm

Round jaw length 260mm, width 90mm, thickness 66mm

Protection level: double insulation

Structural features: jaw method

Range shift: automatic

External magnetic field: <40a/m

External electric field: <1v/m

Single measurement time: 1 second

Resistance measurement frequency: >1khz

Maximum resolution of resistance measurement: 0.001ω

Resistance measurement range: 0.01-1000ω

Current measurement range: 0-20a

Measured current frequency: 50/60hz

Can store measurement data: 99 groups

Resistance alarm threshold setting range: 1-199ω

Current alarm threshold setting range: 1-499ma

Application scope

Power system applications

⑴. Measurement of ground resistance of transmission line towers

⑵． Measurement of transformer neutral point grounding resistance

⑶. Applications in power plant substations

Telecom system applications

⑴. Measurement of ground resistance in floor computer room

⑵． Measurement of ground resistance in computer rooms and transmitting towers

Application of gas station grounding system

⑴. Measurement of ground resistance of oil storage tanks and loading and unloading points

⑵． Measurement of Grounding Resistance of Oil Tanker

⑶. Measurement of the connection resistance of the fuel pump hose:

Feature comparison

The traditional ground resistance measurement method uses the voltage-current method.

a.Ease of operation

The traditional method requires unbuckling the ground wire and installing an auxiliary ground electrode. The ground electrode being measured is to be separated from the grounding system; and the voltage electrode and current electrode must be driven into the soil at a specified distance as auxiliary electrodes before measurement can be carried out.

With a clamp-type ground resistance tester, you only need to wrap the jaws of the clamp meter around the ground wire to be measured, and the ground resistance value can be read from the LCD screen.

b. Accuracy of measurement

The accuracy of traditional measurement methods depends on the position between the auxiliary electrodes and their relative position to the ground body. If the position of the auxiliary electrode is restricted and cannot meet the calculated value, it will bring about the so-called electrode placement error.

For the same grounding body, different auxiliary electrode positions may cause a certain degree of dispersion in the measurement results. This dispersion reduces the reliability of the measurement results.

The clamp-type ground resistance tester does not use auxiliary electrodes when measuring, and there is no electrode placement error. When the test is repeated, the consistency of the results is good.

The results of the comparative test between the clamp-type ground resistance tester and the traditional voltage and current method by relevant national departments show that it can completely replace the traditional ground resistance test method and give credible results for the ground resistance value.

There is a standard test ring attached. When measuring, you can measure the standard test ring first. If the reading is accurate, then the measured ground resistance value can be trusted.

c. Adaptability to the environment

The traditional method must drive two auxiliary electrodes with relative position requirements, which is the biggest limitation of using the traditional method.

The problem is that with the development of urbanization in our country, there is no soil around the measured grounding bodies, and they are all covered with cement. Even if there are so-called green belts, street gardens, etc., their soil is often separated from the soil of the earth. What's more, the traditional method of applying auxiliary electrodes has requirements on the relative position of the auxiliary electrodes. Finding soil with distance requirements is more difficult in most cases.

When using a clamp-type ground resistance tester, there are no such restrictions. Although, from the measurement principle, the clamp-type ground resistance tester must be used when there is a ground loop, but as long as the user can effectively use your surrounding environment, the clamp-type ground resistance tester can completely measure single-point grounding. system.

d.Others

In some cases, clamp-type ground resistance testers can measure ground faults that cannot be measured using traditional methods.

For example: in multi-point grounding systems (such as poles and towers, etc. In addition, some buildings also use more than one grounding body), although the grounding electrodes of their grounding bodies are qualified, the connecting lines between the grounding body and the overhead ground wire may After being used for a long time, the contact resistance will be too large or even open. Although the grounding resistance of its grounding body meets the requirements, the grounding system is unqualified. This situation cannot be measured using traditional methods. It can be measured correctly with a clamp-type ground resistance tester, because the clamp-type ground resistance tester measures the comprehensive value of the ground body resistance and line resistance.

The main technical parameters:

Display: 4-digit LCD digital display. Screen length 28.5mm, screen width 47mm

Measuring range: 0.1～1000ω

Working: 4 AA alkaline batteries

Jaw size: Long jaw 32mm×65mm

Jaw opening: long jaw 28mm

Double clamp feature

Double clamp method/ground pile method dual measurement methods:

Suitable for any grounding place, multi-point or single-point grounding, can be tested normally.

Strong anti-interference ability:

It self-generates high-frequency current to filter 50hz, 100hz and other harmonic interference currents in the mains power supply, and can accurately measure even in a 500kv environment.

Wide measurement range and high resolution:

The measuring range is from 0.01ω to 1000ω, and the resolution is 0.01ω. It can also accurately measure ground resistance below 0.7ω.

Large jaw design:

The jaw diameter is 50mm, which is suitable for using flat iron/steel as grounding lead. Special jaw size can be customized according to customer requirements.

Large capacity data storage:

Can store 200 sets of measurement data.

Double clamp parameters

1. Ground resistance measurement range:

Double clamp method: 0.01ω～1000ω

Ground pile method: 0.01ω～1000ω

2. error:

Double clamp method: ±2%±2 words

Ground pile method: ±1.5%±2 characters

3． Minimum resolution: 0.01ω

4. Jaw size: φ50mm

5. Storage capacity: 200 sets of data

6. Working temperature: 0°c～+50°c

7. Power supply: 8 AA Ni-MH rechargeable batteries or ordinary AA batteries

8. Weight: 0.8kg

9. Size: 265mm×130mm×65mm

Methods and steps for using clamp-type ground resistance tester

Before starting the machine, squeeze the trigger once or twice to make sure the jaws are closed properly.

Press the power button to enter the power-on state. First, the LCD will be automatically tested and all its symbols will be displayed. Then start the self-test. During the self-test, "cal6, al5, cal4" and "calo, ow" are displayed in sequence. When "our" appears, the self-test is completed and it automatically enters the resistance measurement mode.

During the self-test, do not press the trigger, open the jaws, or clamp any wires.

During the self-checking process, the clamp meter must be kept in its natural resting state. The clamp meter must not be turned over or external force may be applied to the jaws. Otherwise, the accuracy of the measurement cannot be guaranteed.

If ol does not appear after the power-on self-test, a larger resistance value is displayed instead. However, when using a test ring to detect, it can still give correct results. This shows that the clamp meter only has a large error when measuring large resistance values ​​(such as greater than loon), but still maintains its original accuracy when measuring small resistance values.