基于小矢量算法的自适应椭圆制动特性变压器差动保护

随着高压、超高压变压器的应用，采用半周或全周数据窗计算方法的传统差动保护，动作时间往往会达到30 ms 以上，已经无法满足快速动作的要求。区外故障时，初始暂态分量、CT饱和以及谐波的影响，使不平衡电流增大，差动保护容易误动。采用小矢量变数据窗的计算方法，同时考虑到区外故障因CT饱和或谐波以及暂态电流等影响使电流波形畸变，自动修复制动电流因波形畸变造成实际电流和估算电流计算的误差，在传统比率制动差动保护的基础上，用椭圆制动特性来描述差动保护。区内故障时，动作时间在10~15 ms左右，同时有效的防止了区外故障时或区外故障切除时保护的误动。仿真和试验证明，采用补偿波形畸变的小矢量算法自适应椭圆制动特性，提高差动保护的可靠性和灵敏性，较之传统比率差动保护具有明显优越性和实用性。

Transformer Adaptive Elliptical Restraint Differential Protection Based on Phaselet Algorithm

With the application of high voltage and ultra-high voltage transformers, the conventional differential protection could not act fast enough while using half or full cycle data window to calculate differential current, which maybe delays above 30 ms. Moreover, protection misopreations often occur with the increase of the imbalance current caused by fault initiation transients, CT saturation, or harmonic contents. Therefore, phaselets variable width window Fourier transform is adopted to calculate differential current and restraint current, which can decrease the variance error between the actual and estimated data values. Based on traditional ratio differential protection, the elliptical restraint characteristic is used to describe differential protection taking in count of the current waveform distortion due to CT saturation, harmonic contents, and initiation transient currents resulting from external faults. In consequence, protection reliability can be improved and action time will be shortened to 10~15 ms. At the same time, protection misoperation can be avoided when an external fault occurs and disappears. Test and simulation shows that protection reliability and sensitivity can be improved greatly if adopting the method suggested which takes advantage of the traditional ratio differential protection.