Research On The Distributed Parameter Circuit Model And Its Application In UHV Transmission Line Protection

The national economy’ rapid development brings out electricity demand growth. Inour country, the primary energy distribution is unbalanced with the productivitydevelopment level. So, it is particularly pressing to build cross-region, cross-basin,large-scale and long-distance electrical grid based on UHV backbone and constructmore strong grid to adapt to the rapid growth of the economy and ensure nationalenergy and economic security, while vigorously developing hydropower and thermalpower. Ultra-High-Voltage (UHV) transmission line has large distributed capacitanceand is always long. It’s difficult to compensate distributed capacitance currenteffectively. Thus, deriving the distributed parameter circuit model which accuratelyconsiders the distributed capacitive current and researching on the distributed parametercircuit model based UHV transient protection algorithm is significant.At first, using “circuit” analysis method, this thesis takes a uniform transmissionline as a cascade of infinite infinitesimal segments to derive a distributed parametercircuit model which can process the transient signal and accurately considers thedistributed parameter characteristic of transmission line. The proposed transmission linemodel can precisely reflect the current and voltage’s variation rule along the line withthe space and time and need not to consider the transmission delay of electromagneticwaves. Theoretically, by phase-model transformation, it can be used in couplingmulti-phase power transmission line with any voltage grade, length, line parameters andoperation mode.Then, this thesis uses ATP software to build transmission line simulation systemand verify the distributed parameter circuit model both in steady state and external faultstate. The simulation results showed that the proposed distributed circuit model isaccurate whenever in a steady state or in a transient one and the accuracy is independentof line length, transition resistance,source angle, and fault type. Then, use actualexternal fault messages to contrast the accuracy between the distributed parametercircuit model and the Bergeron model. The simulation results showed that the proposedmodel is more accurate than the Bergeron model because it accurately considers thedistributed parameter characteristic of transmission line. Meanwhile, this thesisresearched the protection time window of the proposed model and the Bergeron model.Analysis results showed they need equal protection time window. At last, based on the proposed distributed parameter circuit model, a transientbased ultra-high-speed protection algorithm for UHV transmission line is presented.When the line is in a normal or external fault operation state, the current and voltage ofone terminal calculated by the distributed parameter circuit model are almost equal tothe sampled dates; when the line is in an internal fault operation state, the distributedparameter circuit model is broken with the influence of the fault branch and thecalculated current and voltage dates are quite different from the sample ones. So, theModel-Protection takes product of the mean absolute error between the calculationcurrents and sampling currents of one terminal within a very short time after faultoccurring and the mean absolute error between the calculation voltages and samplingvoltages of the same terminal at the same period time as the protection operationcomponent to distinguish internal fault from external fault. Using current and voltagemultiplication joint judgment make the fault features more obvious which improves thesenility of the protection. ATP is used to build a1000kv UHV transmission line modelto simply research the performance of Model-Protection for common breakdown types.Simulation results showed that the proposed Model-Protection algorithm have goodreliability, senility, rapidity and fault phase selection capability.