Vestnik MGTU (Dec 2018)
A pulse generator with inductive energy storage for measuring the grounding resistance of transmission line towers
Abstract
The pulse method may be used to measure the footing resistance of transmission towers with overhead grounding wires. Measuring systems that obtain the time dependent transient impedance may be used to measure the low-frequency resistance of transmission tower grounding devices. Current pulse generators with rectangular pulse shape are used in the measuring systems. The current pulses must have short rising time and constant magnitude during a measurement interval. Experimental investigations have shown that a pulse generator with inductive energy storage may be used in the measuring system. Generators with inductive energy storage have a number of advantages over pulse generators with capacitive energy storage. Namely, in case of unevenly distributed surge impedance along the current lead or in case of reflections from the remote end of the current lead an inductive generator allows to form a current pulse with a constant shape. Inductive pulse generators have high pulse energy. So, they may be used to measure the grounding resistance in high soil resistivity areas. Measuring systems based on an inductive storage pulse generator may be used not only to measure the footing resistance of transmission towers; they can also be used for experimental investigation of the effectiveness of lightning protection systems, in particular to obtain the parameters of RLC equivalent circuit of a single grounding device. Two possible topologies of an inductive pulse generator output stage have been considered in the paper. In the first case a step-up transformer is used as energy storage and an IGBT is used as opening switch. In another case an inductor is used as energy storage and MOSFETs are used as opening and closing switches. The experimental current waveforms for both types of generators have been given. They show that an inductor based pulse generator has better characteristics. Therefore it is preferred for this application.
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