1、 Purpose:

 

This instrument is mainly used to test the power frequency grounding impedance, soil resistivity, contact voltage, step voltage, and other power frequency parameters of grounding devices. This instrument adopts cross frequency anti-interference technology, which can accurately measure data at the power frequency of 50Hz in strong interference environments. The instrument is equipped with a built-in lithium-ion battery, which is particularly suitable for outdoor situations without power supply, such as measuring power frequency parameters of towers.

 

2、 Overview

 

Power frequency grounding impedance refers to the ratio of the potential difference between the grounding device and the remote potential zero point to the power frequency current flowing into the ground through the grounding device. The power frequency grounding impedance was traditionally referred to as the "power frequency grounding resistance". The correction of this name is explained in the national standard GB/T17949.1-2000 "Guidelines for the measurement of soil resistivity, grounding impedance and ground potential of grounding systems Part 1: Conventional measurements" and the revised draft of the power industry standard "Guidelines for the measurement of characteristic parameters of grounding devices" (replacing DL475-92). This measuring instrument uses two frequencies of current, 45Hz and 55Hz, for testing, so the measured value should strictly be referred to as "ground impedance".

 

When measuring the grounding device, due to various interferences such as unbalanced zero sequence current and radio frequency, improper anti-interference measures can cause significant errors in the test results. In order to reduce the impact of on-site interference, there are currently two main methods used, one is to increase the test current, and the other is to use the frequency difference method. The first method is to increase the signal voltage and signal current by increasing the test current (DL/T475-2017 standard recommends not less than 50A), thereby improving the signal-to-noise ratio and reducing measurement errors. This method uses a large testing current, making the equipment very bulky, and the wiring labor intensity is high, which is time-consuming and labor-intensive. Moreover, due to the fact that the main interference is on the same frequency as the signal, it is impossible to fundamentally eliminate the impact of interference. The frequency difference rule is to avoid power frequency interference by changing the frequency of the test current. Since the signal frequency is different from the interference frequency, a filter can be used to filter out the interference and improve the measurement accuracy. Due to the use of smaller testing currents, the inter frequency method has smaller equipment and greatly reduces wiring labor intensity. Due to its advantages of stable and reliable test results, as well as time-saving and labor-saving, the frequency difference method has been widely accepted and adopted by experts at home and abroad.

 

However, according to the definition, power frequency grounding impedance refers to the impedance presented by the grounding device under power frequency current. The test current frequency used in the different frequency method is not power frequency, so the measured value will deviate from the value measured under power frequency current. Theory and practice have shown that the reason for deviation is that the grounding impedance of the grounding device is a complex impedance, which not only contains resistive components, but also inductive and capacitive components related to frequency. The farther the difference between the test frequency used and the power frequency, the worse the equivalence, that is, the greater the measurement error. To ensure the accuracy of the test, the test frequency should not differ too much from the power frequency, and the waveform of the test current should be a sine wave (other waveforms such as square waves contain rich harmonic frequencies). As early as the 1970s, countries such as the United States and Japan stipulated that the difference between the test frequency and the power frequency should not exceed 10Hz. The Chinese national standard GB/T17949.1-2000 requires that the testing current frequency should be as close to the power frequency as possible, while the industry standard DL/T475-2017 specifies that the testing current frequency should be between 40-60Hz. This instrument uses two frequencies of 45Hz and 55Hz for measurement, and then calculates the equivalent impedance at 50Hz, thus further improving the accuracy and equivalence of the measurement.

 

3、 Performance characteristics

 

1. The measured power frequency equivalence is good. The test current waveform is a sine wave with dual frequencies of 45Hz and 55Hz.

 

2. Strong ability to resist ground voltage interference. This instrument adopts the frequency difference method for measurement, combined with modern software and hardware filtering technology, making the instrument have high anti-interference performance and stable and reliable test data.

 

3. Built in lithium-ion battery. It can also be used in situations without AC power supply, suitable for outdoor use.

 

4. It can measure on-site interference, making it convenient for users to estimate measurement errors.

 

5. Easy to operate. Fully Chinese menu style operation, directly displaying measurement results.

 

6. Low wiring workload, no need for high current wires.

 

7. Can save on-site test data (shutdown data does not disappear)

 

8. This instrument is small in size, light in weight, and easy to carry.

 

4、 Technical indicators

 

1. Range: 100 Ω, 200 Ω, 400 Ω, 1k Ω, 2k Ω (optional)

 

2. Measurement error: ± (1% x reading+0.01) Ω

 

3. Test current waveform: sine wave

 

4. Test current frequency: 45Hz, 55Hz

 

5. Test current: 10mA, 20mA, 50mA, 100mA, 200mA selectable

 

6. Maximum output voltage: 50V

 

7. AC charging power supply: AC220V ± 10%, 50Hz

 

8. Built in battery: Lithium ion battery (11.1V, 2.5AH)

 

9. Usage environment: Temperature: -10 ℃ to 40 ℃; Relative humidity:<90%

 

10. Dimensions: 240 × 220 × 190

 

11. Instrument weight: 3kg

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