DFIG的LVRT措施对输电线路距离保护的影响

Impact of LVRT strategy for DFIG wind power system on wind farm side interconnection line distance protection

双馈感应电机(doubly-fed induction generator,DFIG)特殊的暂态特性影响着输电线路风电场侧距离保护的效果。发生过渡电阻短路时,文章结合DFIG低电压穿越(low voltage ride through,LVRT)措施和控制方式,分析其暂态特性,研究采用转子撬棒和串联制动电阻(series dynamic braking resistor,SDBR)实现LVRT时工频量距离保护的抗过渡电阻能力以及保护误动的可能性。理论分析和仿真结果表明:转子撬棒加强了风电场的弱馈特性,使距离继电器的抗过渡电阻能力变弱;采用SDBR时可通过转子侧变流器(rotor side converter,RSC)调节功率输出,故障电流稳态值相对较大,继电器抗过渡电阻能力较强。此外,由于故障电流普遍较小,容易造成下段线路故障时本段线路保护误动。

The special fault characteristic of doubly-fed induction generator(DFIG) wind power system influences the effect of distance protection on wind farm side interconnection line. This paper researches the fault characteristic of DFIG considering the low voltage ride through(LVRT) strategy and control strategy of converter when there is occurring transition resistance fault, and further researches the impact of rotor crowbar and series dynamic braking resistor(SDBR) on the ability of wind farm side interconnection line distance relays to resist transition resistance and the possibility of protection misoperation. Theoretical analysis and simulation results show that the rotor crowbar increases the weak-infeed property of wind farm and makes the relays resist less transition resistance. When SDBR is used to achieve LVRT, the rotor side converter(RSC) can regulate the power delivery and makes the fault current steady state value relatively larger, and then makes the relays resist larger transition resistance. Besides, because the fault current is little, relays may incorrectly trip when faults occur on next line.