| Overhead transmission lines icing poses a serious risk to the safety and stabilityof the power system. As one of the most effective and direct deicing methods, DCdeicing technology attracts considerable attention of professionals and researchersaround the world. A wide range of areas in China suffer from severe freezing rainand ice disaster in winter. The new DC deicing technology has been graduallyapplied in power grid in China. But some phenomena such as50Hz protection of theDC deicer abnormal alarm, locking and other issues were encountered when thetransmission lines under deicing are parallel with the operating AC transmissionlines on the same tower. The power frequency electromagnetic interferencegenerated by the adjacent AC transmission lines causes the false operation of the50Hz protection of the DC deicer. With the expansion of power grids and the scarcityof transmission corridor, two circuit or multi-circuit transmission lines on the sametower have become inevitable. So the electromagnetic interference problems of DCdeicer, which caused by the strong electromagnetic coupling between the AC lineswith adjacent and parallel DC deicing lines, can’t be ignored. In addition, becausethe development time of DC deicing technology is not long, the relevantelectromagnetic compatibility research is still weak. Therefore, it is significant tocarry out the basic theoretical study on the electromagnetic interference of DC deicercaused by AC lines and put forward some corresponding anti-interference measures,which will enhance the electromagnetic compatibility of DC deicing system andensure its stable and safe operation.The main contents of the dissertation are as follows:1. The formation mechanism of power frequency induction in DC deicing linesis analyzed theoretically. Based on the electromagnetic transient simulation softwarePSCAD/EMTDC, the model of two-circuit transmission lines on same tower isestablished in which the frequency dependent transmission line model is used. Then,according to the DC deicer’s working principle, the model of DC deicing system isestablished. One circuit of transmission lines are changed into DC deicing state, sothat the simulation model which is used to predict the electromagnetic interferenceof DC deicer is built in this paper.2. The influence factors, such as DC deicing method，the transmission power of parallel AC lines, the parallel length of AC and DC de-icing transmission lines, thedistance between them and transposition are analyzed. Some rules for interferenceattenuation are summarized. Then the influence of the induced current onfundamental frequency protections and the converter transformer of DC de-icingsystem are studied. After that some measures to reduce the induced current arediscussed in this paper.3. By theoretical analyzing, the power frequency equivalent circuits in threecases are established. The three cases respectively are with coupling of parallel linesand operating in normal condition, without coupling of parallel lines but occurringpulse missing fault, with coupling of parallel lines and occurring pulse missing fault.Based on the equivalent circuits, the power frequency component characteristics inthree cases are analyzed. Then the suggestion for optimizing the50Hz protection isput forward. After that the correctness and effectiveness is verified by simulation. |
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