低频条件下标准电压互感器误差特性分析

Analysis of Error Characteristics of Standard Voltage Transformers Under Low Frequency Conditions

为精确分析系统频率对标准电压互感器误差特性的影响,以获得标准电压互感器的低频适用性,首先建立了标准电压互感器的等值电路模型,提出了采用复数磁导率分析铁磁材料低频励磁特性的方法,并搭建了基于锁相原理的测量回路,获得了不同频率下取向硅钢片30P100的复数磁导率;其次,解析得到标准电压互感器空载误差及负载误差函数,并以一台35 kV标准电压互感器为模型,分别通过误差增量反推以及短路法获得一、二次漏阻抗的参数,通过复数磁导率获得低频励磁阻抗参数;最后,通过仿真计算,获得20 Hz及50 Hz下空载误差及负载误差曲线,并与实测结果进行对比验证。研究表明:取向硅钢片的复数磁导率实部与虚部均随着频率的降低而增大,在20~50 Hz频率范围内,标准电压互感器的空载比值差和空载相位差均随着频率的降低而正向偏移;负载比值差受频率影响较小,负载相位差随频率降低而正向偏移,且频率越低,其误差受负荷变化的影响越小。以设计的35 kV标准电压互感器为例,频率改变对标准电压互感器空载比值差的影响量在2×10^(−5)以内,对空载相位差的影响量在0.4′以内,其空载误差在20 Hz和50 Hz下至少可同时满足0.01级误差限值要求。在15 VA负荷时,频率变化对相位差的影响达到3′左右,在20 Hz和50 Hz下仅能同时满足0.5级误差限值要求。该研究获得了标准电压互感器低频误差特性,可为低频柔性交流输电工程用电压互感器试验验证提供支撑。

In order to accurately analyze the impact of system frequency on the error characteristics of standard voltage transformers and obtain the low-frequency applicability of standard voltage transformers,this paper establishes an equivalent circuit model of standard voltage transformers,proposes a method for analyzing the low-frequency excitation characteristics of ferromagnetic materials using complex permeability,and constructs a measurement circuit based on phase-locked principle to obtain the complex permeability of oriented silicon steel sheet 30P100 at different frequencies.Secondly,the no-load error and load error function of standard voltage transformer are obtained analytically.A 35 kV standard voltage transformer is taken as a model,the parameters of primary and secondary leakage impedance are obtained through error increment backstepping and short circuit method,respectively,and the parameters of low-frequency excitation impedance are obtained through complex permeability.Finally,through simulation calculations,the no-load error and load error curves were obtained at 20 Hz and 50 Hz,and compared and verified with the measured results.Research has shown that the real and imaginary parts of the complex permeability of oriented silicon steel sheets increase with the decrease of frequency.In the frequency range of 20 Hz to 50 Hz,the no-load ratio error and no-load phase displacement of standard voltage transformers both shift forward with the decrease of frequency,the load ratio error is less affected by frequency,and the load phase displacement shifts forward as the frequency decreases.The lower the frequency is,the smaller the impact of load changes on their error will be.The designed 35 kV standard voltage transformer is taken as an example,and it is found that the impact of frequency change on the no-load ratio error of the standard voltage transformer is 2×10^(−5),the impact on the no-load phase displacement is within 0.4′,and its no-load error can at least meet the error limit requirements of level 0.01 at both 20 Hz and 50 Hz.At a 15 VA load,the impact of frequency variation on phase displacement reaches about 3′.At 20 Hz and 50 Hz,it can only simultaneously meet the error limit requirement of level 0.5.In conclusion,the low-frequency error characteristics of standard voltage transformers are obtained,providing supports for the experimental verification of voltage transformers used in low-frequency flexible AC transmission engineering.