电容电压初值对CVT铁磁谐振影响的仿真研究

电容式电压互感器(CVT)的传统等效电路模型中忽略了电容分压器电容电压初值对等效电路模型的影响,然而在CVT暂态时这一因素的影响不能简单地看成是一个误差问题。基于正确的电容分压器的分压比公式,建立了计及电容电压初值的CVT完整的等值电路模型。基于此电路模型,利用Matlab中的电气系统模块库PSB建立了CVT铁磁谐振暂态过程的仿真模型。仿真结果表明,在二次侧短路又消除短路这种铁磁谐振激发方式下,不同的短路时刻和消除短路时刻对CVT的铁磁谐振过程有影响,甚至出现了持续的振荡过程。在二次电压过零短路同时又在其过峰值时消除短路的情况下,电容电压的初值可以抑制铁磁谐振过电压的持续时间,但电容电压的初值较大时,在系统加压瞬间出现的过电压,可能引起二次侧高速继电保护误动作。

Simulation research on influence of initial capacitor voltage value on CVT ferroresonance

The traditional equivalent circuit of CVT(Capacitor Voltage Transformer) neglects the influence of initial capacitor voltage value of capacitor voltage divider,but it is not neglectable in CVT transient process.Using right voltage division formulas of capacitor voltage divider,a general equivalent circuit of CVT is established,based on which,a simulation model is built up with the power system block-set of Matlab to analyze the ferroresonance process of CVT.Simulation results prove that,under the ferroresonance activation mode of short circuit generation and elimination at secondary side,the generation time and elimination time have influences on CVT ferroresonance process,the enduring ferroresonance oscillation occurs occasionally;under the ferroresonance activation mode of short circuit generated when secondary voltage is zero and eliminated when it is peak,the initial capacitor voltage value of the capacitor voltage divider may depress the duration of ferroresonance overvoltage,but if the value is bigger and system causes overvoltage,malfunction of high speed protection may occur.