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.
Novel measurement system for grounding impedance of substations and power plants
A new grounding impedance measuring method based on short lead wire of current electrode and a frequency inverter AC source is proposed. The compensating site of the voltage electrode to obtain the real grounding resistance of the grounding system is analyzed according to soil structure, topological structure of the grounding system under test, and the length of current electrode's lead wire. This new method measures the ground impedance at a variety of frequencies other than power frequency, then interpolates them to reach the ground impedance at power frequency. The mutual inductance between the potential and current wires is analyzed and computed. The Intel 80C196KC cored grounding impedance measurement system is developed and the software is programmed. A field test was performed in the substation and the system worked stably.
New approach to vision-based BGA package inspection
Ball grid array (BGA) techniques have developed very fast due to the advantages of more I/O ports, small size, and so on. In this paper, a vision-based algorithm for BGA package inspection is proposed to accurately estimate center and diameters of solder-balls of BGA packages, so that defects of BGA packages, such as missing or extra balls, oversize or undersize balls, over-height or under-height balls, and pitch can be detected for ensuring the quality of BGA packages.