Study On Complex Power Grid Relay Protection Setting Method And Its Engineering Application

Relay protection is the first defense line to ensure the safe and stable running of thepower system. Relay protection can isolate the fault elements selectively and quickly toensure the safety operation of electrical equipment and the stable working of powersystemeffectively. On the contrary, the mal-operation or fail-to-trip of relay protection mayresult in expansion of failures or even lead to large scale blackout, which brings significanteconomic losses. Reasonable setting of relay protection is the important fundament ofplaying relay protection’s part effectively. With the development of power systems, the gridstructure is becoming more and more complex.Especially, the wide application of newtransmission types, represented by parallel transmission lines on same tower, has brought alot of new problems to protection setting. In combination with the foreign practical projectof a hydropower station, this thesis carries out a systematic studyonthe parametercalculation method andshort circuit fault simulation modeling of the parallel transmissionlines on same tower, and the setting calculation method and its engineering problemsof theprotection of the parallel transmission lines on same tower,complex transformer-linecomposition unit as well as high impedance busbar differential protection, etc. The study issignificant to ensuring the safe operation of this power grid as well as promoting theinternational cooperation and communication in the power electrical domain.One of the key issues of relay protection setting calculation method is the parametercalculation method and short circuit fault simulation modeling of the parallel transmissionlines on same tower. Based on the analysis ofbasicparametercalculation method oftransmission lines, a universal calculation method of sequence impedance parameters isadopted in thisthesis. The method can be used for both single transmission line and paralleltransmission lines on same tower, and can improve the calculation accuracy on conditionthat the conductor is without transposition or the tower structure is inconsistent. This thesisintroduces the basic principle and application examples in detail. In addition, for the reasonthat the existing PSASP software cannot directly provide the simulation model of paralleltransmission lines on same tower, the thesis not only analyzes the change characteristics of zero-sequence coupling ofthe whole parallel transmission lines on same tower and part ofparallel transmission lines on same tower, but also proposes the simulation modeling ofparallel transmission lines on same tower in different operating modes, which can meets thesetting calculation requirements of the power grid containing parallel transmission lines onsame tower.There are strong zero-sequence coupling between the two loops of paralleltransmission lines on same tower, which is directly related to the operating mode of theparallel transmission lines. Moreover, the parallel transmission lines on same tower are ofcomplex structure, including whole parallel transmission lines on same tower and part ofparallel transmission lines on same tower, which brings a lot of problems to the settingcalculation ofdistance protection, especially to the setting calculation ofgrounded distanceprotection. The thesis analyzes influences of different operating modes of paralleltransmission lines on same tower on the measuring impedance of distance protection andthe main problems should be noticed in setting calculation. On this basis, combined withthe engineering practice, the setting calculation of grounded distance protection applicableto whole parallel transmission lines on same tower and part of parallel transmission lines onsame tower is proposed in the thesis.In the real power grid, some transformer-line composition unit with specialconstructions has been applied so as to meet the requirements of power demand andinterconnection, which presented new task for protection configuration and settingcalculation.Based on the complex transformer-line-transformer composition unit inengineering practice, the thesis expounds the calculation method of the transformer and theline in thecompositionunit, as well as analyzes the main problems existing in settingcalculation of the composition unit.High impedance busbar differential protection can significantly reduce the unbalancedcurrent flowing into the differential current loop when external fault causes CT saturated,toimprove the ability of anti CT saturation by adding a high resistance in series in differentialcurrent loop. However, because of the differences and implementation techniques betweenhigh impedance busbar differential protection and low impedance digital busbar protection,reasonable setting calculation should be adopted according to its operation characteristics.On the basis of analyzing the fundamental working principle of high impedance busbar differential protection, the thesis gives out the setting calculation method and analyses itsperformance in different operation modes combined with engineering practice.In the end, systematical summary about the research works is given and the furtherwork needed to be further implemented is pointed out.