输电线不同类型短路对同步调相机转子损耗及温升的影响

Influence of Different Types of Short Circuit in Transmission Line on the Rotor Loss and Temperature Rise of Synchronous Condenser

同步调相机可为特高压直流换流站提供无功功率,以保持系统电压稳定,防止直流换相失败。交流系统发生短路导致系统电压降低时,调相机会向系统提供大量无功功率。然而,高无功大电流会导致调相机转子损耗和发热增加。为了研究调相机承受系统短路故障的能力,该文将调相机的电磁场、温度场模型与电网模型耦合,计算了输电线路发生单相、两相和三相短路故障时,调相机转子槽楔和铁心的损耗分布,揭示了各部分损耗密度随转子径向深度的变化规律;在此基础上计算了三种短路故障下调相机转子的温度分布,获得了转子最大温升出现的位置;在考虑转子最高容许温度的条件下,揭示了调相机短路持续时间与短路故障类型之间的关系。该研究为提高调相机在系统故障情况下的工作能力提供了理论依据。

Synchronous condenser(SC)can provide the reactive power for the converter station of Ultra High Voltage Direct Current(UHVDC)to keep the stability of the system voltage and prevent DC commutation failure.When the drop of the AC system voltage results from the short circuit of the transmission line,the SC can provide a large amount of reactive power for the power grid.However,the high reactive power and large current of the SC will increase the loss and heat of the SC.By coupling the electromagnetic field and temperature field models of the SC with the model of the power grid,the rotor losses and temperature distributions of the SC are calculated under the single-phase,two-phase,and three-phase short-circuit faults in the transmission line.The ability of the SC to withstand different types of short circuits of the power system is studied.In this paper,the field-circuit coupled time-stepping finite element model of the SC is established and the dynamic processes of the SC under three different short-circuit faults of transmission line are calculated.Then the loss densities of the rotor slot wedges and small teeth under the different short-circuit faults of transmission line are calculated,and the loss densities in different positions of the rotor are compared and analyzed.Finally,the temperature fields of the rotor core and slot wedges are calculated,and the rotor maximum temperature rises are obtained.It is revealed that the relationship between the duration of the SC and the type of short-circuit fault under the consideration of the maximum withstand temperature of the rotor.The results of the loss calculation show that the loss densities of the upper layers of the rotor are larger than that of the middle and lower layers during the short-circuit faults,and the rotor loss densities decrease along with the increase of the radial depth;the loss densities of the slot wedges are higher than that of the small teeth,and the loss density of the large teeth are the maximum.According to the temperature field of the SC under the single-phase,two-phase and three-phase short-circuit faults of the transmission line,the highest temperature rises of the rotor slot wedges are 32.102℃,25.962℃and 17.31℃,respectively;those of the small teeth are 26.039℃,21.331℃and 15.108℃,respectively;and those of the large teeth are 84.03℃,76.3℃and 22.728℃,respectively.The temperature of the rotor large teeth is a key factor that restricts the operating ability of the SC.With the consideration of the maximum permissible temperature of the rotor core,the ability of the SC to withstand different types of short-circuit faults is obtained.The durations of the SC under the single-phase and two-phase short circuit are 3.62s and 3.97s,respectively;the highest temperature of the SC under the three-phase short circuit would not reach the maximum permissible temperature of the rotor core.The conclusions can be drawn as follows:①The maximum loss density of the SC appears on the surface of the rotor large teeth and the loss density of the rotor slot wedges is larger than that of the small teeth.②The rotor loss of the SC is mainly distributed on the rotor surface during the transient process due to the skin effect,the rotor loss under single-phase and two-phase short circuit is larger than that under three-phase short circuit.③The temperature rises of the rotor large teeth are larger than those of the rotor slot wedges and small teeth,the temperature rise of the rotor large tooth is the main factor that restricts the transient operating ability of the SC.④The negative sequence current under the asymmetric short circuit results in the larger rotor loss and temperature rise,therefore,the duration of the SC under asymmetrical short-circuit faults of transmission line is significantly smaller than that under the symmetrical short-circuit fault.