换流站中500kV站用变铁磁谐振过电压的研究

Research on Ferroresonance Overvoltage Occurred in 500 kV Transformer for Power Supply of Converter Station

以某500 kV换流站发生的铁磁谐振现象为例,利用电磁暂态仿真软件PSCAD/EMTDC对换流站的铁磁谐振机制、影响因素及各种消谐措施进行了研究。结果表明:站用变、CVT主电容、断路器断口电容共同构成了谐振回路,断路器的断开操作激发了谐振的发生。断路器在不同时刻断开引起的谐振过电压振荡持续的时间和过电压峰值均有较大的差异;断路器的备用状态对铁磁谐振发生的概率影响较大,当处于热备用状态时,概率约为60%～65%,处于冷备用状态时,概率约为5%～10%;增大励磁特性的拐点以及站用变容量有助于抑制铁磁谐振的发生,但中性点增加电阻对抑制铁磁谐振不起作用,同时铁磁谐振将引起高次的谐波,该谐波与励磁特性的拐点有关。可采用短时投入阻性负荷和降低断路器断口均压电容的办法来抑制换流站铁磁谐振的发生。

Take ferromagnetic resonance occurred in a certain 500 kV converter station for example, the mechanism of the ferromagnetic resonance occurred in converter station, its influencing factors and various resonance suppression measures are researched by electromagnetic transient simulation software PSCAD/EMTDC. Simulation results show that, the transformer for power supply of converter substation, main capacitor of CVT and fracture capacitors of circuit breaker jointly constitute the resonance circuit, and the switching off operation of circuit breaker excites the ferromagnetic resonance. There are obvious differences among durations and peaks of resonance overvoltages caused by switching off circuit breaker at different moments; the standby state of circuit breaker evidently influences the occurrence probability of ferromagnetic resonance： when the circuit breaker is in hot stand-by state the occurrence probability of ferromagnetic resonance is within the range from 60% to 65%, and when the circuit breaker is in cold stand-by state the occurrence probability of ferromagnetic resonance is within the range from 5% to 10%; it is helpful to suppress the occurrence of ferromagnetic resonance by changing the inflexion point on excitation characteristics curve and increasing the capacity of the transformer for power supply of converter station, however adding resistor to the neutral point of the transformer is not helpful in suppressing ferromagnetic resonance. Ferromagnetic resonance leads to high-order harmonics that is related to the inflexion point on excitation characteristics curve. It is feasible to suppress the occurrence of ferromagnetic resonance in the transformer for power supply of converter station by two measures： switching in resistive load inshort-term and decreasing grading capacitors of circuit breaker fractures.