高压变频工况下调相机启机保护的分析与改进

Analysis and Improvement of Starting Protection for Synchronous Condenser in High-voltage Variable Frequency Condition

计算并分析了调相机采用静止变频器启动的谐波特性,探讨了变频启动系统的变频特性及谐波特性对调相机启机保护的影响。为滤除变频状态下的主要谐波,提高调相机启机保护的计算精度,提出一种改进型的定频采样变数据窗离散傅里叶变换算法。该算法对fs/f0(采样频率/系统频率)为非整数时的固有误差进行补偿,并根据系统频率自适应优化每周期傅里叶变换计算的点数,同时采用拟合函数实时计算正余弦系数表。在此基础上,对调相机启机保护进行了改进,并给出了动作判据。在保护装置上进行了实验验证,结果表明改进后的启机过流保护与启机零序电压保护在不同频率下精度较高,在变频工况下能够准确计算故障中的基波分量。此外,启机差动保护使用峰峰值算法进行差动启动计算,并结合改进型定频采样变数据窗离散傅里叶变换算法进行差流动作判别,能够确保该保护的可靠性与速动性。

The harmonic characteristics of the synchronous condenser using static frequency converter(SFC)starting system are calculated and analyzed, and the influence of frequency conversion characteristics and harmonic characteristics on the starting protection is discussed. In order to filter out the main harmonics in the variable frequency state and increase the calculation accuracy of the synchronous condenser starting protection, an improved fixed frequency sampling variable data window discrete Fourier transform(FFSVDW-DFT)algorithm is proposed. The algorithm compensates for the inherent error when fs/f0(sampling frequency/system frequency)is a non-integer, and optimizes the points number of the Fourier transform algorithm adaptively in each cycle according to the current system frequency. At the same time, the fitted function is adopted to calculate the sine and cosine coefficient table in real time. On this basis, the synchronous condenser starting protection is improved and the action equation is given. The improved starting protection algorithm is experimentally verified on the protection device. The results show that the starting protection using the improved FFSVDW-DFT algorithm has high precision. The fundamental component during the fault could be accurately calculated under the variable frequency condition. In addition, the peak-to-peak algorithm is used for the differential start calculation in the proposed starting protection method by combining with the improved FFSVDW-DFT algorithm for the differential action calculation. Thus, the reliability and rapidity of the protection could be both ensured.