Ground resistance tester knowledge

With the progress of the times and the development of science, the test of ground resistance has become more and more important. The ground resistance tester is a common instrument for testing and measuring ground resistance. It is also an indispensable tool for electrical safety inspection and grounding project completion acceptance. In recent years, due to the rapid development of computer technology, the ground resistance tester has also infiltrated a large amount of microprocessor technology. Its measurement function, content and accuracy are incomparable to general instruments. At present, advanced ground resistance testers can meet all grounding measurement requirements. Using the new clamp method, there is no need to drive piles and lay out lines for direct online measurement. A powerful ground resistance tester is controlled by a microprocessor, which can automatically detect the connection status of each interface and the interference voltage and interference frequency of the ground network, and has unique functions such as value retention and intelligent prompts. Ground resistance test and development Initially, people used the volt-ampere method to measure ground resistance. This test was very primitive. Figure 1 shows the measurement method using an ammeter and a voltmeter. When measuring resistance, you must first estimate the current and select an insulated wire of appropriate cross-section. During the preliminary test, you can use a variable resistor R to adjust the current. When the formal measurement is performed, the variable resistor is short-circuited and the grounding resistance can be calculated from the values ​​obtained by the ammeter and voltmeter.

The volt-ampere method for measuring ground resistance has obvious shortcomings. First, it is troublesome, cumbersome, and has a large workload. During the test, the ground rod is 20-50 meters away from the ground, and the auxiliary ground is at least 40-100 meters away from the ground. In addition, it is greatly affected by external interference, and sometimes it is simply impossible to measure in the strong voltage area. In the 1950s and 1960s, the Soviet Union's E-type megohmmeter replaced the volt-ampere method. It was easy to carry and was a hand-cranked generator, so the workload was simpler than the volt-ampere method. In the 1970s, domestic ground resistance meters came out, such as: ZC-28, ZC-29, whether in structure, volume, weight, measurement range, graduation value, accuracy, are better than the "E" type megohmmeter. Therefore, for quite a long time, the ground resistance meter was represented by the ZC series produced by Shanghai Liubiao Factory. Due to the hand-cranked generator, the accuracy of the above instruments is not high. The use of digital ground resistance meters in the 1980s brought vitality to ground resistance testing. Although the wiring method of the test is no different from that of the ZC series, its stability is much higher than that of the megohmmeter pointer type. A real innovation of ground resistance meter is the birth of clamp-type ground resistance meter in the 1990s, which broke the traditional test method. For example, the 6411 clamp-type ground resistance tester produced by French CA company can be regarded as a major revolution in ground resistance test. The biggest feature of clamp-type ground resistance test is that it does not need auxiliary ground rod. Just clamp the ground wire or ground rod to measure its ground resistance. The above-mentioned ground resistance tester is a single-jaw type, which has its advantages of fast testing and simple operation, but it also has low accuracy, especially when the ground resistance is less than 0.7Ω, it cannot be distinguished. Besides, the single-jaw ground resistance meter is mainly used to check the multi-electrode grounding network connected above the ground, and query each ground resistance measurement through the loop ground resistance. The measurement range and accuracy of GEOX double-jaw ground resistance meter have been improved, but because the clamp method measurement adopts the principle of electromagnetic induction, it is susceptible to interference, the measurement error is relatively large, and it cannot meet the requirements of high-precision measurement. The recently introduced 234 digital display precision ground resistance meter from Italian HT Company perfectly combines the characteristics of traditional volt-ampere method measurement with the new principle of clamp method, and uses advanced computer control technology to become the leading intelligent ground resistance meter of the contemporary era. It has the characteristics of high precision, complete functions and easy operation, and can be widely used in ground resistance measurement of power telecommunication systems, buildings, airports, railways, oil tanks, lightning arresters, high-voltage iron towers, etc. At present, it has been configured in domestic post and telecommunications, power, aviation and other industries.