Axial and radial electromagnetic-vibration characteristics of converter transformer windings under current harmonics

The winding current harmonic content of converter transformer in operation is rich.However,affected by harmonics,the radial vibration characteristics are quite different from the power transformer,structural loosening and deformation caused by winding vibration are more prominent.Therefore,in view of the influence of current harmonics on axial and radial vibrations,this study builds a 3D winding electromagnetic vibration finite element simulation model,analyses the components and contents of current harmonics,compares the leakage flux and vibration distribution under the fundamental,harmonic and superimposed currents.The correlation relationship between the harmonic components and axial and radial vibration characteristics is obtained,and the vibration measurement test of±800 kV converter transformer in operation is carried out to verify the correctness of the analysis method.The results show that the winding radial vibration amplitude will exceed the axial vibration affected by harmonics.More importantly,under the superposition of the fundamental,5th and 7th harmonic current,the vibration contribution of the converter transformer tank is mainly radial vibration,and the vibration dominant frequency is shifted from 100 Hz under the fundamental current to 400 Hz.

Performance Analysis of Corroded Grounding Devices with an Accurate Corrosion Model

Grounding devices are significant to the operation of the power transmission line and power equipment.The soil and leakage current can easily cause the corrosion of carbon steel grounding devices,resulting in power accidents.Therefore,most carbon steel grounding devices in service are already corroded,and the accurate calculation of grounding parameters for corroded grounding devices is important.However,most existing methods for calculating the grounding parameters of corroded grounding devices usually have the following disadvantages:1)They only consider whether the grounding devices are broken or not,and cannot analyze the grounding parameters of grounding devices with different corrosion degrees;2)They assume that the corroded grounding device is a conductor with a smaller diameter,and ignore the impact of the corrosion product layer,resulting in calculation errors.To solve the above problems,this paper establishes an accurate corrosion model for grounding devices based on the volume expansion coefficient of corrosion products.The grounding parameters calculation method for corroded grounding devices is proposed based on the boundary element method(BEM)and Galerkin’s method.Then the grounding performance of tower grounding grids with different corrosion degrees in different soils(uniform and layered)is analyzed.Finally,some features of grounding parameters of corroded grounding devices are given.This study can accurately calculate the grounding parameters of the corroded grounding devices and has far-reaching engineering significance for the safety of power equipment.

Mode for reducing wind curtailment based on battery transportation

Renewable energy sources, such as wind and solar, face several obstacles, including curtailment, where the generated energy exceeds local demand and production must be reduced because of limited transmission capacity.Simultaneously, consumer demand for large-capacity batteries is expanding given the recent rapid development of electric vehicles(EVs) and plug-in hybrid EVs. A batterycharging mode, in which discharged batteries are transported from battery exchange stations in high-load areas to wind farms, is proposed to alleviate curtailment. In this study, batteries store otherwise curtailed energy and smooth the wind power output simultaneously. The structure of the battery-charging device is discussed, and the concept of a battery-charging container is proposed. The control principle of the battery-charging management unit is presented with a simulation model constructed in the PSCAD/EMTDC environment. A case study is simulated,and the feasibility of the mode is analyzed considering the levelized cost and energy losses. Simulation results show that this mode is a feasible solution to alleviating wind curtailment and providing fresh impetus for developing EV battery exchanges.