Analysis of Grounding Resistance of Transmission Line Towers Measured by Three-pole Method and Clamp Meter Method
1. Measuring principle of three-pole method and clamp meter method
1.2 3극 방법 측정 원리
The three-pole method (also known as the current-voltage pole method) refers to the method of testing the grounding resistance of the tower with three electrodes consisting of the tower grounding grid, the current electrode and the potential electrode. Generally, the electrodes are arranged in a straight line method (more suitable for use on the transmission line site) ). The method and principle are shown in Figure 1.
Measuring principle: The test current is injected by the grounding device G (equivalent to a hemispherical electrode), and the potential drop curve between the grounding grid and the current electrode is shown in Figure 2. 이론적으로, the resistance of the grounding device is the resistance relative to the zero potential point at infinity, then the potential difference of the grounding device relative to the zero potential plane at infinity is required, and the grounding resistance value is calculated by Ohm's law. The distribution law of the potential drop curve in Figure 2 is affected by the introduction of the current pole, causeing electric field distortion, making the zero plane at infinity move closer to P, causing electric field distortion, and making the zero plane at infinity move closer to P middle
1.2 측정 원리 of clamp meter method
측정 원리: the measurement of the clamp meter method (the overhead ground wire is directly connected to the tower), which is equivalent to the test circuit composed of the grounding resistance of the measured tower and the parallel impedance of adjacent multi-base towers. The equivalent schematic diagram is shown in Figure 4. 일반적으로, each gear The resistance and inductance of the overhead ground wire can be ignored, then the final instrument measurement result R, ten, when there are enough towers in parallel (greater than ten bases or more), is much greater than △R, then the instrument measurement result is considered to be the grounding resistance of the measured tower.
The introduction of measurement error: The impact of the shunt of the tower's natural grounding body on the measurement results is not considered. When considering the impact of the tower's natural grounding body on the test results, when the clamp meter method measures the local grounding resistance of the tower (the position of the downconductor of the tower under test), when the sum of RH and Ro (in parallel with Rj plus ΔR) and Rj When the same order of magnitude or less, the artificial grounding electrode has a greater impact on the measurement results; when the anchor bolts are directly connected to the foundation reinforcement cage (Ro=0), the natural grounding body has a greater impact on the measurement results; there are tower foundation reinforcement cages and artificial In the case of direct welding of the ground electrode (RH=0), if the anchor bolts are also directly connected to the foundation reinforcement cage at the same time, the test result will be less than 1Ω, which is essentially the metal of the grounding down-lead, anchor bolts, and reinforcement cage. loop resistance.
2. Precautions when measuring with clamp meter method
(1) First check the electrical connection of the tower under test, confirm that the overhead ground wire is directly connected to the tower, and before removing the bolts of the ground down-conductor, confirm the electrical connection status of the down-conductor one by one (use the clamp meter to confirm the connection of the metal circuit); if If all the down-conductors are connected in good condition, keep any one of 다운 컨덕터 측정 접지 저항 타워.
(2) If there is no obvious change compared with previous clamp meter measurement results, the current clamp meter measurement results are considered valid. If the measurement results of the clamp meter method are much greater than those of the previous clamp meter method, the three-pole method should be used for comparative measurement to determine the cause.
(3) 언제 조건 의 선 변경 (그의 as 교체 의 그의 번개 보호 선 및 접지 방법, 변경 의 선 방향, 등) 접지 저항 의 타워 is 비교 및 측정.
(4) 언더 그 조건 의 젖은 토양 후 비 또는 비오기 계절, 상호 저항 사이 자연 접지 몸 의 타워 및 인공 접지 전극 감소 유의하게, which will directly affect the correctness of the 측정 결과.
