Internal Corrosion Damage Mechanism Of High Voltage Transmission Strain Clamp

Strain clamp as an important electric power fittings are widely used in high voltage transmission. Its failure can cause the line to break off and affects the safe and stable operation of power grid. The research of strain clamp damage has become an important direction and hotspot in the research of power transmission system.In this dissertation, the objects of research are old strain clamp and aluminum used for making strain clamp. Scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD), X-ray photoelectron energy spectrometer (XPS), and electrochemical workstation modern analysis methods were used to explore the old strain clamp inner corrosion and influences of alternating current density, temperature, concentration, pH on the corrosion of aluminum used for making strain clamp. The purpose is to determine the influence of internal corrosion mechanism, evolution mode, and the influence law of alternating current density, temperature, concentration and pH on the corrosion. The main research work and results are as follows:The strain clamp internal corrosion concentrated at the port. The corrosion area on the inner clamp surface consists of white powder of AI2O3, AIO(OH) and A100H and a relatively thickness corrosion layer. The black deposited layer consist of carbon black and organic compounds because of the sealing materials’incomplete combustion and gasification. The innermost layer of aluminum surface near the steel core has been damaged by serious corrosion, which causes iron to be overflowed and Fe2C>3 to be formed. Some loose straddle sponge structure and the accumulation of white corrosion products occure on the surface of the galvanized steel core. It’s the typical plane type pitting, the corrosion products are ZnO and AI2O3.The failure mechanism of tension wire clamp is as follows:Defects and aging leads to the electrolyte solution to penetrate into the strain clamp and cause the internal corrosion, which makes the resistance increase and the temperature elevate. High temperature and alternating current can accelerate corrosions. When the corrosion after a long term accumulation reaches to a critical value, the heat can not be dissipated effectively, and lead to arc discharges in the end. Finally, the strain clamp is failure.With AC density increase, the Tafel curve moves to negative directionand reversed at 50A/m2, but icorr increases always. After AC corroded, the Nyquist diagram of AC impedance spectra is gradually changed from single arc to double arc, the Warburg impedance occurs in it, the Bode-Phaze diagram changes from single peak to double peaks. The corrosion tendency of sample is deepened under alternating current. Much pits occurs on the corrosion surfaces, it is alternating between vertical corrosion and parallel corrosion. The corrosion layer formes and sheds continuously. Corrosion products are Al(OH)3 and Al2O3. The corrosion rate rises with AC density increase and accelerates after AC density is over 50 A/m.The decreasing of the pH, the increasing of NaCl concentration and the higher temperature will lead to the following results:Ecorr moves to negative, the corrosion current lcorr increases gradually, linear polarization resistance is reduced, the difficulty of electron transfer reduces, capacitance and surface resistance decreases. Those mean that the corrosion becomes more and more easy. The decrease of pH value will aggravate the pitting corrosion of aluminum, and increase the corrosion rate gradually, and lead the surface morphology to change as follows:pitting are clearer, the number of pitting corrosion cavity are decreased, the surface becomes relatively smooth, crack morphology, more tiny pits and craggy rock weathering morphologies occure. Concentration’s increase leads to the increase of pits’ number on the surface, but the pitting corrosion pits become fuzzy because of the corrosion products’ covering.