大容量SVC对变压器差动保护的影响及解决措施

大容量静止无功补偿器(SVC)已在实际工程中获得应用。理论分析和数字仿真表明,在变压器低压侧发生故障时,SVC设备会向故障点注入大量的3次、5次等奇次谐波电流,含量显著且衰减缓慢。现有变压器差动保护为防止在区外故障电流互感器(TA)饱和、励磁涌流及过激磁等情况下产生的差动电流造成保护误动,通常采用谐波制动方法。大容量SVC设备产生的谐波电流可能造成TA饱和判别元件误判,从而引起差动保护动作速度变慢甚至拒动。为此,应避免在低压侧TA饱和判据中采用3次谐波而改用2次谐波。通过实际工程的RTDS试验数据验证了理论分析的有效性。

Impact of Large-capacity SVC on Transformer Differential Protection and the Solutions

The large-capacity static var compensator (SVC) is applied in actual projects. Theoretical analysis and simulation results show that, a large amount of 3, 5 and other odd harmonic currents will be injected into the fault-point from the SVC equipment when faults occur on the low-voltage side of the transformer. What is more, the harmonic current is significant in content and slow in attenuation rate. Traditional transformer differential protection usually adopts harmonic blocking methods to prevent incorrect operation from current transformer saturation at external faults, magnetizing inrush current and over-excitation. Harmonic currents produced by the large-capacity SVC equipment may make the harmonic blocking element make a wrong judgment, leading to slow operation of the differential protection or even failure to operate. To solve this problem, the 2nd harmonic rather than 3rd harmonic should be used in TA saturation criterion. Digital simulation test is performed to verify the validity of theoretical analysis.