Optimization Analysis And Realization Of High Voltage CT Online Power Collection Device

As an important part of power system,high voltage transmission line is responsible for the task of transporting and distributing electric energy.Its normal operation is related to the security and stability of power system.In order to ensure the safety of high voltage transmission line,more and more on-line monitoring device is installed on it.However,due to the particularity of the installation position,the power supply problem of online monitoring device is a technical difficulty.In this paper,several kinds of power supply methods are discussed.Aiming at the problems existing in the application of current transformer power supply.The power output characteristics of CT power supply are analyzed by means of theoretical derivation and simulation.The relationship between output power of CT and filter capacitor voltage is derived in two cases of without considering saturation and considering saturation.Find that the output power of CT increases first and then decreases with the increase of filter capacitor voltage whether the core is saturated or not.There is a maximum power output point,and the maximum power independent of turns.The maximum power is proportional to the square of primary current when maximum power is obtained at core unsaturation stage.When the maximum power is obtained at saturation stage,the maximum power is proportional to the primary current.Through theoretical analysis,the core saturation can be prevented by limiting the maximum filter capacitor voltage.The simulation model is established under the Saber software,and the output power characteristic of CT is simulated.The simulation results are the same as the theoretical analysis.The CT model of different core materials(silicon steel,nano-crystalline,permalloy)is established by MCT in Saber,and the B-H curve of core is modeled by J-A model.The simulation results show that the maximum output power of nano-crystalline material with high permeability is larger when primary current is small,and the maximum output power of silicon steel material with high saturation magnetic induction is larger when primary current is large.The stability of CT output power supply is analyzed,and the conclusion is drawn that the voltage of the filter capacitor is higher than the maximum power point,and it is found that the stable region is the filter capacitor voltage which is higher than the maximum power point.With the change of the load power consumption,the equilibrium point moves on the output power curve,which can reach the maximum power point,but the maximum power point is the critical stable point.With the lowest output 0.5W as the goal,using the silicon steel core,the CT power supply is optimized and designed.The CT model is established,and the simulation results show that the maximum output power of CT increases with the increase of turn number and tends to saturation near the area of starting current due to the influence of rectifier voltage drop.Based on it,the optimization method of selecting turn numbers is given.The influence of DC-DC starting voltage on the power balance is analyzed near the area of starting current,and the method of determining the starting voltage of DC-DC circuit is given based on it.The hardware circuit of CT power supply is designed,which mainly includes the DC-DC start control circuit,which can ensure the power supply works normally near the starting current;The filter capacitor overvoltage protection circuit,which is used to discharge the excess energy of the CT to prevent overvoltage of filter capacitor and prevent saturation of iron core at the same time.The experimental results show that the maximum output power of nano-crystalline and silicon steel CT with the same size is larger under low and high primary current;The maximum output power of CT increases with the increase of the turn numbers near the starting current,which verifies the correctness of simulation results;The DC-DC start control circuit can ensure that the power supply can output normal power near the starting current;The filter capacitor over-voltage protection circuit can ensure that the CT energy can be released reliably when primary current is large,and the filter capacitor voltage stability can be maintained.