Research On2-Clamps Instrument For Measuring Grounding Resistance Of Tower

Grounding devices are important equipment of electric system，which ensure electricsystem’s normal operation. Accordingly, grounding resistance measurement is a very part ofgrounding device maintenance.Firstly, in this paper the principle of grounding resistance measurement and severaltraditional measurement methods are introduced in the paper. However, there are manyshortcomings in those traditional methods. Secondly, a new online testing method isintroduced which can avoid these problems. The new method doesn’t need any groundingpole; especially, it can measure grounding resistance online.Base on this method, a new grounding resistance measurement instrument is designedin this paper. In this design, a sine-wave voltage signal is produced by single-chipmicrocomputer, amplified by a power amplifier, and then the voltage signal is injected togrounding circuit. The current in the grounding system is obtained by a current clamp. Thevalues of voltage and current are used to calculate the value of grounding resistance.Many electromagnetic interference can influence the accuracy of measurement whichincludes electromagnetic interference of the space, especially those interferences whosefrequency are near or same to the frequency of measure frequency. Therefore, severalmethods of anti-jamming are used in the design:A. All sensors are designed with shields to shield most of the space interference;B. Signal is processed with hard band pass filter;C. DFT is used to get a useful signal from compound signals;D. Two ingredients whose frequencies are the same is decomposed by the method ofcorrectitude vector.In the design, single-chip microcomputer technology, sensor technology and DSP areapplied ingeniously, in which grounding resistance can be measured without cutting offground lead, and normal operation of electric system won’t be influenced. This instrumentcan bring great application value.