微机消谐装置
Microcomputer harmonic elimination device
微机消谐装置也称二次消谐器，被安装在电压互感器(PT)的开口三角绕组上。正常运行或者发生单相接地故障时装置不动作，而一旦判定电网发生铁磁谐振时，检查井钢模具 隔离墩模具 隔离墩钢模具 流水槽模具 U型槽模具 螺杆启闭机 卷扬式启闭机 铜雕佛像 便会使正反并联在开口三角两端的2只晶闸管交替过零触发导通以限制和阻尼铁磁谐振，当谐振消除后晶闸管自行截止，必要时可以重复动作。装置起动消谐期间，晶闸管全导通，呈低阻态，电阻为几mΩ至几十mΩ。如此小的电阻值足以阻尼高频、基频及分频3种谐振，而且对整个电网有效，即一个系统中只需选择1台互感器安装消谐装置即可。微机消谐装置的主要缺点是难以正确区分基波谐振和单相接地。目前，对基波谐振和单相接地故障判据的主要区别在于零序电压U0的高低。通常，基频谐振定为当U０≥150V时；当30V≤U０＜145V时定为单相接地故障。为了防止在单相接地时由于装置误动使PT长时间过负荷而烧毁的情况发生，通常将该装置基频谐振的判据电压定得比较高。这样，在工频位移电压不是很高的情况下（如空母线合闸）装置将无法动作，就可能使某些励磁特性欠佳、铁心易饱和PT的熔丝熔断。而且这种装置当电网对地电容较大时，它对防止间歇性接地或接地消失瞬间互感器因瞬时饱和涌流而造成熔丝熔断的事故无能为力。此外，在持续时间较长的间歇电弧过电压激发下，流过PT高压绕组的电流将显著增大，仍可能会烧坏PT。由于基频谐振中的频率实际上并不是十分严格的基频，不是完全没有频率突变 。因此，能否在信号处理方法中采用对时频局部化方面极具优势的小波来检测，值得探讨。
Microcomputer harmonic elimination device, also called secondary harmonic elimination device, is installed on the open delta winding of voltage transformer (PT). Once the ferroresonance occurs in the power grid, the two thyristors connected in parallel at the two ends of the open triangle will be switched on alternately to limit and damp the ferroresonance. When the resonance is eliminated, the thyristors can cut off automatically and act repeatedly if necessary. During the start-up of the device, the thyristor is fully on and in a low resistance state, with the resistance ranging from several m Ω to tens of M Ω. Such a small resistance value is enough to damp three kinds of resonance of high frequency, fundamental frequency and fractional frequency, and it is effective for the whole power grid, that is, only one transformer needs to be selected in a system to install a harmonic elimination device. The main disadvantage of microcomputer harmonic elimination device is that it is difficult to distinguish the fundamental resonance from single-phase grounding. At present, the main difference between fundamental resonance and single-phase ground fault criterion is the level of zero sequence voltage U0. Generally, the fundamental frequency resonance is set at U0 ≥ 150V; When 30V ≤ U0 ＜ 145v, it is defined as single-phase grounding fault. In order to prevent Pt from being burnt out due to overload for a long time due to misoperation of the device during single-phase grounding, the criterion voltage of fundamental frequency resonance of the device is usually set higher. In this way, when the power frequency displacement voltage is not very high (such as the closing of the empty bus), the device will not operate, which may cause some Pt fuses with poor excitation characteristics and easily saturated iron core to fuse. Moreover, when the grid capacitance to ground is large, this device can not prevent the fuse fusing accident caused by the instantaneous saturation inrush current when the intermittent grounding or grounding disappears. In addition, the current flowing through the high voltage winding of Pt will increase significantly under the excitation of long lasting intermittent arc overvoltage, and the PT may still be burnt out. Because the frequency in the fundamental frequency resonance is not a very strict fundamental frequency, it is not completely without frequency mutation. Therefore, it is worth discussing whether wavelet, which has the advantage of time-frequency localization, can be used in signal processing.