Study On The Transient Protection Of Trnasmission Line And Bus Based On Fault Initial Angle And Transition Resistance

With the rapid development of the extra high voltage grid, higher requirements on the speed and reliability of relay protection for the transmission lines and busbares are needed. The transient protection, which is based on the high frequency transients generated by the system fault, has a super-high-speed performance, yet its reliability should be improved. This paper thoroughly studied the transient protection technology. Firstly, the mechanism on the generation of fault transients was studied. And then we theoretically analyzed the basic factors that affected the fault transients. The results indicate that the fundamental reason for the low reliability of the transient protection is that the traditional methods have not considered the influences of the fault initial angle and the transition resistance. This paper studied the relationships among the fault characteristic variable, the fault initial angle and the transition resistance. An imputed model of the fault characteristic variable was established. According to the characteristics of the transmission line and busbare system, we proposed several transient protection methods, and analyzed their superiority theoretically. ATP/EMTP simulation verifies the validity of the principle.The related innovative achievements in this thesis are summarized as follows:(1) Two methods were proposed for calculating the fault initial angleThe wave propagation characteristics regarding the mold component of the fault traveling wave in the three-phase transmission lines were studied by using the theoretical analysis. The method of calculating the fault initial angle was derived by utilizing the fault mode component. Phase coefficient characteristics of the three-phase overhead lines were theoretically studied. The method of calculating the fault initial angle was proposed based on the phase coefficients.(2) A normalized-model of transients was established based on the fault initial angle and the transition resistanceThe relationships among the fault characteristic variable, the fault initial angle and the transition resistance were studied, then a normalized-model of transients was established. It effectively eliminates the influences of the fault initial angle and the transition resistance. transient protections for transmission lines and busbar were proposedâ‘ Based on the fault initial angle and the transition resistance, a new non-communication protection for transmission lines was proposedAccording to the difference of the fault transients which were observed at the first end of two lines which were connected with the same busbar, a new non-communication protection for transmission lines was proposed. Two transmission lines of the busbar can be protected by one protection equipment based on the principle. The protected area is twice that from the traditional protection. If each line is equipped with the ralay protection in the form of the traditional configurations, there is no additional investment, and dual protection can be realized.The influences of the initial angle and the transition resistance were eliminated, by the means of fault feature variable being normnized by the fault initial angle and the transition resistance.â‘¡A new transient protection for busbar was proposed based on the fault initial angle, the transition resistanceAccording to the instantaneous amplitude of the fault transient which was observed at the first end of each busbar line, an imputed model on the instantaneous amplitude of the fault transient current was established and a new transient protection for busbar was proposed. It eliminates the influences of the initial angle and the transition resistance, and the reliability was enhanced greatly.â‘¢Based on the fault initial angle and the transition resistance, a new distributed protection for busbar was proposedAccording to the instantaneous amplitudes of the fault transient current and the traveling wave direction which were observed at the outlet end of one line, by the means of fault feature variable being normnized at the condition of the fault feature, fault initial angle and the transition resistance, a new distributed protections for busbar was proposed.The proposed methods can protect one busbar and a transmission line which connected the busbar simultaneously, by only extracting fault transient information from one line, without exchanging the information with other protection units. When one protection unit is faulty or out of operation, it will not affect the normal operation of other protection units. Each protection unit has absolute independence. It meets well with the development trend of the protection devices which are dispersedly installed in switching stations. Compared with the existing distributed busbar(3) Based on the fault initial angle and the transition resistance, new protection, the principle of this method is simpler and has higher reliability.â‘£A directional comparison pilot protection was proposed by the normalization based on the fault initial angle and the transition resistanceAccording to the energy difference of the fault transients between the inside and outside of the busbar which were observed at one end of a line, a new directional comparison pilot protection for transmission lines was proposed. It eliminates the influences of the initial angle and the transition resistance.A directional protection with this principle can simultaneously provide the fault direction for two lines. On average, for n lines only up to n sets of protection devices with this principle can protect all lines. Compared with the conventional directional pilot protection in which two devices must be equipped at both ends of the line, it can save a lot of investment.(4) New smart transient protections based on the fault initial angle, the transition resistance and machine learning algorithms were proposedâ‘ Based on the fault initial angle, the transition resistance and SVM, a smart transient non-communication protection for transmission lines was proposedAccording to the difference of the fault transients which were observed at the first end of two lines which were connected with the same busbar, a smart trasient non-communication protection for transmission lines was proposed. Two transmission lines of the busbar can be protected by one protection equipment based on the principle. The protected area is twice that from the traditional protection. If each line is equipped with the ralay protection in the form of the traditional configurations, there is no additional investment, and dual protection can be realized.The influences of the initial angle and the transition resistance were eliminated, at the condition of the fault feature variable, fault initial angle and the transition resistance being as the SVM input vector.â‘¡Based on the fault initial angle, the transition resistance and SVM, a new distributed protection for busbar was proposedAccording to the instantaneous amplitudes of the fault transient current and the traveling wave direction which were observed at the outlet end of one line, by the means of fault feature variable being normnized or machine learning algorithm at the condition of the fault feature, fault initial angle and the transition resistance being as the support vector machine(SVM) input vector, a new distributed protections for busbar was proposed based on the fault initial angle, the transition resistance.The proposed methods can protect one busbar and a transmission line which connected the busbar simultaneously, by only extracting fault transient information from one line, without exchanging the information with other protection units. When one protection unit is faulty or out of operation, it will not affect the normal operation of other protection units. Each protection unit has absolute independence. It meets well with the development trend of the protection devices which are dispersedly installed in switching stations. Compared with the existing distributed busbar protection, the principle of this method is simpler and has higher reliability.â‘¢A new smart transient protection based on the fault initial angle, the transition resistance and PNN was proposedAccording to the difference between the instantaneous amplitudes of the fault transients which were monitored at two transmission lines of the same busbar, a smart transient protection was constructed by using probabilistic neural network(PNN). With the change of the fault status, it can intelligently adjust the value of protection operation, so it eliminates the influences of the initial angle and the transition resistance. It significantly increases the protection reliability.Thesis innovation can be summarized as follows: two methods were proposed for calculating the fault initial angle; a normalized-model of transients was established based on the fault initial angle and the transition resistance; novel transient protections were proposed based on the initial fault angle and the transition resistance, and the influence of the initial angle and the transition resistance was eliminated, and the reliability was significantly increased. The protected area of some menthods is twice that from the traditional protection.