电容式电压互感器谐波测量误差分析

Analysis of Harmonic Measurement Error Using Capacitive Voltage Transformer

为研究电容式电压互感器(CVT)因主电路工作在工频谐振造成其频率特性发生畸变而导致谐波测量结果失真问题,在仿真谐振型和速饱和型两种类型CVT的频率特性曲线基础上,通过电能质量扰动装置,进行110 k V两种型号CVT的谐波测量误差试验。试验验证了仿真模型的正确性且杂散电容也是影响CVT频率特性的原因之一。试验结果表明:通过CVT测量谐波幅值和相位存在很大的误差,某些频率下幅值最大可能达到实际值的2倍以上,最小仅为实际值的30%左右,相位也出现在某些频率下120°突变的问题;不同厂家不同型号的CVT之间的误差特性不同,而同厂家同型号CVT的谐波测量误差特性基本一致。最后针对现场大量应用CVT进行谐波测量的问题提出了应用电容式分压器测量、通过接地回路电流测量、采用带谐波测量功能的特种CVT测量以及对测量结果进行修正等改进意见。

To study the distortion of capacitive voltage transformer（CVT） main circuit working at power frequency of its frequency characteristics and harmonics measurement, we simulated the frequency characteristic of CVTs with resonance and saturated reactor damper. Using the power quality producer, we performed the actual device experiments with two types of 110 k V CVT. The experimental results verify the correctness of simulation conclusion, and stray capacitance is also one of the reasons that affect CVT frequency characteristic. Test results show that remarkable errors in amplitude and phase exist in the measurement of harmonic through CVT. The maximum amplitude can reach two times more than the actual value in some frequencies, the minimum is only about 30% of the actual value, and the phase mutation of 120 degrees also appears in some frequencies; CVTs with the same manufacturer and type are basically identical in harmonic measurement error characteristic, conversely CVTs with the different manufacturers and types possess the different error characteristics. Finally, based on the massive application of CVTs, improvement suggestions such as measuring by capacitive voltage divider, measuring through ground loop current, using special CVT, and correcting the measuring results are proposed.