电容式电压互感器电路参数对电网谐波电压测量的影响

Influences of Circuit Parameters of Capacitor Voltage Transformer on Grid Harmonic Voltage Measurements

针对66kV以上等级电网大多采用电容式电压互感器（capacitor voltage transformer，CVT）、其谐波传变特性定量规律不明、不宜进行谐波电压测量的现状，论证谐波条件下的CVT可等效为一线性电路，并以此为基础提出级联分级分析方法。结合实际参数对每级谐波传变特性进行分析，获得CVT电路参数对其谐波传变特性的定量影响规律，即明确利用CVT测量谐波电压的影响因素。仿真结果表明：中间变压器一次侧线圈的等效杂散电容将导致CVT幅频特性在1kHz之后的某频率点发生放大；阻尼器参数影响50Hz以上频段的频率特性变化率；负荷在1～10倍额定负荷范围变化以及中间变压器励磁阻抗在0．1～1倍额定参数范围变化时对CVT频率特性的影响可忽略。所得结论对CVT产品设计及利用其测量谐波电压具有借鉴意义。

The capacitor voltage transformers （CVT） are widely used in China for most of power grids above 66 kV. The rules of harmonic transfer characteristics of CVTs are still unknown so that the measurement of harmonic voltage is hard to operate. This paper demonstrated that CVT can be equivalent to a linear circuit in harmonic conditions, and a kind of cascade classification method was proposed based on that property. The method was useful to get the impact rules between CVT circuit parameters and its harmonic transfer characteristics. The simulation results show that equivalent stray capacitance of the primary side of intermediate transformers can cause some kinds of enlargement of CVTs amplitude-frequency characteristics at a frequency above 1 kHz, damper parameters can affect the rate of frequency characteristics. Besides that, influence of parameter changes such as 1 to 10 times of rated load and 0.1 to 1 times of rated magnetizing impedance of intermediate transformers can be ignored for frequency characteristics of CVTs. Overall, the conclusions are very useful for CVT product design and application in harmonic voltage measurements.