Calculation For Reactive Power Loss Of Single-phase Four Limbs UHV Transformer Due To Geomagnetically Induced Currents With Parameter K

During a geomagnetic disturbance,geomagnetically induced current(GIC)is injected into the grounded neutral transformers.This causes half-cycle saturation of the transformer core,which results in increased transformer reactive power losses(GIC-Q).Mastering transformer GIC-Q is one of the key issues for analyzing the impact of DC bias of transformer resulted by GIC and prev enting the damage of power grid caused by geomagnetic storm.Aiming at single-phase four limbs ultra-high voltage(UHV)transformers which are adopted in the newly constructed 1000 k V UHV power grid,this paper proposes a method with K parameter for calculating the GIC-Q from the engineering disasters prevention perspective.The main contents are as follows:(1)Aiming at the core construction and coil arrangement of the single-phase four limbs UHV transformers including main,regulating and compensating transformers,this paper made a theoretical analysis on formation mechanism,physical mechanism and influence factor of GIC-Q.The results show that the transformers under GIC are in half-wave saturation,and the GIC-Q is increasing extremely.Besides the result indicates that the extent of the increasing of the GIC-Q is related with core construction,voltage classes,dynamic inductance air-gap magnetic resistance and so on.(2)Based on the core and structure parameters,the magnetic circuit and electric circuit coupled model of single-phase four limbs UHVtransformers was set up.The results show that the distortion of exciting currentdeepens under the increasing GIC.Combined with the definition of reactive power,the relation between GIC and GIC-Q was achieved.The relation is linear approximatively.The parameter K can be determined by 2.44.And the error was verified.(3)GIC-Q of different type of transformers was compared.The results show that the rate of increasing GIC-Q of the single-phase four limbs UHV main transformers is higher than the rate of GIC-Q of normal transformers.Under the same GIC,GIC-Q of the single-phase four limbs UHV main transformers is larger than GIC-Q of normal transformers.Therefore,UHV power grid is more sensitive to GIC.The prevention of geomagnetic disaster to UHV power grid is valuable.