| Capacitor voltage transformer(CVT)has been widely used in power system due to its good insulating performance,anti-ferromagnetic resonance and cheap price,and its error will directly affect the accuracy of measurement and the reliability of relay protection.Therefore,to carry out the calibration error of CVT is of great significance to the safety and stability of power network operation.Generally,CVT is based on the off-line calibration method,which has shortcomings such as long calibration cycle,can not get the real-time data errors and so on,while existing online calibration method will bring hidden trouble to the safe operation of power network because of overvoltage,ferromagnetic resonance and other shortcomings.To this end,this paper carried out CVT online calibration research,to solve the shortcomings of the existing calibration methods,proposed to transform the capacitive equipment into a high voltage standard capacitor CVT for online calibration.Firstly,the paper discusses the CVT calibration working principle.And the essence of the CVT calibration is to compare the voltage ratio standard with the calibrated CVT,and the voltage ratio standard is the key of the calibration.The development of CVT calibration at home and abroad has been discussed,the general use of standard voltage transformer and high voltage standard capacitor as a standard device.According to the principle of high voltage standard capacitor online calibrating CVT,transforming LVQB current transformer into a high-voltage standard capacitor and switching low-voltage standard capacitor has been proposed to implement CVT online calibration,and gives a detailed transformation program.One way: make the primary guide rod as a high voltage electrode,and the secondary winding of the shield as a low voltage electrode,the second way: make the primary guide rod as a high voltage electrode,divide the secondary winding shield into external and internal screen and choose internal one as the low voltage electrode,then discuss the circuit configuration of these two works,respectively.In order to verify the feasibility of the new method,and whether it will affect the safety of the power grid,the three dimensional electric field model of the current transformer LVQB is established in this paper,and the insulation performance of it in the normal operation is analyzed.In addition,the floating potential of the secondary winding shielding cover which is caused by the interlock switch fault in the case of using a mutual lock switch to switch low voltage standard capacitance is calculated,and the insulation performance when the maximum suspension potential is reached is analyzed.The effects of pressure,temperature and voltage on the capacitor value of high voltage standard capacitor which is transformed from the current transformer LVQB is discussed,and the capacitor loss is analyzed through the characteristics of dielectric medium. |
