Study on measuring the grounding resistance of grounding grid with short lead wire
Method of measuring the grounding resistance with short lead wire is applied to test the ground resistance of some simulated grounding grid when the resistances of the grounding conductor are considered simultaneously. The position of voltage electrode is determined through the calculation when the position of current electrode is given in advance. It is showed by test result that the method of measuring the grounding resistance with short lead wire can obtain the value of ground resistance with relatively high precision. Moreover, the length of current electrode is shortened. It provides a more scientific and suitable way for the ground resistance measurement of grounding grid in field. The relation between the position of voltage electrode and the length of current electrode is also considered.
Grounding Resistance Measurement Method Based on the Fall of Potential Curve Test Near Current Electrode
Grounding resistance is an important basic index used to ensure the safety and reliability of grounding systems. In this paper, a method for grounding resistance measurement based on the fall of potential curve is proposed that can be performed using a 2–2.5D lead wire length. In this method, the potential distribution near the auxiliary current electrode is tested and is used as the main analysis and measurement parameter. Based on the relationship between the potential distribution generated by the grounding grid and the current electrode, the grounding resistance of the grounding grid can be deduced. First, the voltages between the grounding grid and the earth surface potential near the current electrode are measured; then, the ground potential rise (GPR) of the grounding grid is calculated through theoretical analysis and numerical calculation; and finally, the grounding resistance is calculated by dividing the potential by the test current. This method avoids the complex task of accurate compensation point location required for traditional measurement methods, and can be performed easily and quickly using a short lead wire. Measurement results from spot testing show that the proposed method can meet the accuracy requirements of engineering testing.
Thermally Induced Dynamics of Satellite Solar Panels
Thermally induced structural motions are known to affect the attitude dynamics of low Earth orbiting satellites during eclipse transitions. Motions of e exible appendages such as solar panels lead to rigid body rotations of the entire satellite because the total angular momentum of the system is conserved. These potentially large attitude disturbances may violate pointing accuracy and jitter requirements. One type of thermally induced dynamics exhibited by solar panels is thermal snap. The Upper Atmosphere Research Satellite is a prominent example of a satellite that experiences thermal snap disturbances during eclipse transitions. This paper describes recent studies of thermally induced dynamicsof solarpanels, including an analysisofsatelliteattitudedynamics resulting from thermally induced structural motions and a laboratory investigation of the thermal-structural performance of a satellite solar panel. Analytical and experimental results demonstrate thermal bending deformations with acceleration transients that have characteristic thermal snap disturbance histories in response to rapid changes in heating. The studies show that solar panel thermal snap disturbances are caused by through-the-thickness temperature differences that vary at a nonconstant rate. Finite element analysis correctly predicts the thermal snap phenomenon observed in the solar panel experiments.