| With the construction of China’s power grid and the use of large cross-sectional wires,geomagnetically induced current(GIC)in the power grid are becoming larger and larger,and GIC can cause bias saturation in current transformers with the same principle as transformers in 500kV substations.The bias magnetic saturation will lead to power measurement errors and relay protection misoperation,which will endanger the normal operation of the power system.Hulunbeier power grid and 500kV Haibei substation are located in high latitude,500kV transmission line conductor crosssection is large,and it is affected by geomagnetic storms.This paper combines the actual situation of Hulunbcier power grid and 500kV Haibei station,studies the GIC and its distribution law of 500kV Haibei station ultra-high voltage current transformer,analyzes the impact of geomagnetic storms on ultra-high voltage current transformer,and proposes a management plan.The main research work and results of this paper are as follows.(1)The electrical data and information of two important geological and tectonic units of Erguna Massif and Xing’an Massif as well as the Hailar Basin were collated by inversion,and a stratified and zoned three-dimensional geodetic resistivity model of Hulunbeier area was established.Based on the geomagnetic storm data,the geoelectric field amplitude in Hulunbeier area was calculated by the finite element method under the effect of three geomagnetic storms.Based on the calculated geoelectric field,the GIC model of Hulunbeier power grid was established,and the GIC magnitudes of 500kV transmission lines flowing through Hulunbeier power grid were calculated using the nodal conductivity method.(2)The GIC calculation model of ultra-high voltage current transformer in 500kV substation was proposed.The GIC quantities flowing through each current transformer under three different intensity geomagnetic storms were obtained from the 500kV transmission line GIC calculation,and the GIC distribution law of the 500kV Haibei station ultra-high voltage current transformer was obtained.According to the different applications of current transformers,the ultra-high voltage current transformers in Haibei station were divided into three categories:current transformers for intra-string metering,current transformers for intra-string protection and transformer differential protection current transformers.Theoretical analysis and calculation of its working state,for different applications of current transformers according to the relevant standards of current transformers set different standard limit values.(3)According to the set limit values of current transformers,the risk of GIC bias was evaluated for the 500kV Haibei station EHV current transformers when three geomagnetic storms occurred.The 500kV Haibei station’s ultra-high voltage current transformers with the risk of bias magnetization were identified,and the resistance management method of connecting small resistors in series at the transformer neutral point was proposed to manage the current transformer GIC bias magnetization.The proposed treatment method can not only reduce the risk of bias magnetization of the 500kV Haibei station EHV current transformers,but also reduce the GIC magnitude of the 500kV transmission lines within the Hulunbuir power grid,improving the stability of the Haibei station and the entire Hulunbuir power grid in the face of geomagnetic storm disasters.In addition,the early warning system of geomagnetic storm bias is established to reduce the power loss of the control device during normal operation.Taking Haibei station as an example,the calculation model and algorithm established in this paper are significant for the calculation,assessment and management of geomagnetic storm bias impact.With the construction of China’s 500 kV and above voltage level power grids,the research results of this paper can provide reference and reference for the analysis of biomagnetic impact in other UHV substations. |
