Research On Novel Primary Protection Technology In Complex And Abnormal Running Condition Of Large Generator-Transformer Unit

It is very important that the large generator-transformer unit is in safe and reliable running conditions for the electric power safety and reliability. The running conditions of the generator-transformer unit usually are complex, and the running conditions'conversion of the pumped-storage hydro-plant is in high frequency especially. It has a strong impact on the performance of the primary protections of the generator-transformer unit. Therefore it is of great significance to improve the performance of the main protection and research the new protection theory continuously. This paper focused on the complex and abnormal running conditions of the large generator-transformer unit and its protection problems. It contained the complex sympathetic inrush theory and characteristics, the differential protection mal-operation reasons caused by the complex sympathetic inrush and its countermeasures, the novel primary protection of generator based on the instantaneous power theory, the weak power-angle stability of the pumped-storage synchronous machine and the novel low power protection.This paper constructed the study model of the complex sympathetic inrush in order to solve the differential protection mal-operation problem caused by the complex sympathetic inrush. The analytic expressions of the flux linkage and current of the transformer were obtained by the LAPLACE-transform and were analyzed in detail. By the theory derivation and the digital simulation, it was pointed out that there were the joint characteristics of both the exponential function and the hyperbolic function under the system power, generator power and load current. Other powers in the transformer secondary windings had influence on the complex sympathetic inrush. Meanwhile the paper revealed the characteristics of the second harmonic current. All the research results provided the theory basis for the novel protection technology study.Based on the theory and characteristics of the complex sympathetic inrush, this paper analyzed the reasons of the transformer differential protection mal-operation caused by the complex sympathetic inrush. The joint digital simulation model of the generator-transformer unit was established. By the simulation study, the characteristics of the differential current, the restraint current and the second harmonic current in the protection were presented. A novel transformer differential protection with the variation ration restraint was proposed. It was unacted on the complex sympathetic inrush and the sensitivity and reliability were good. The mal-operation problem of the classic differential protection was solved by the novel protection effectively.By the digital simulation and the field record data analysis, the mal-operation reason of generator differential protection was concluded. A novel generator differential protection with the enhance restraint function was proposed based on both the second harmonic restraint and the ration restraint function. The mal-operation behavior of the differential protection during the complex sympathetic was blocked by the enhanced restraint function. Meanwhile a special opening criterion concluded from the calculation formula of the differential and restraint current was applied to avoid the refusing action of the protection in the condition of the phase to phase fault. The sensitivity and reliability of the differential protection with the enhanced restraint function were proved by all the test data and results, and the novel generator differential protection with the enhance restraint function had been put into use in the field.With the development of digital power substation technology, the voltage quantity could be used in the primary protection, and the power protection would be applied widely for its simple and reliable features. This paper studied the output instantaneous power of generator when an inner or extent fault took place in generator in the (α,β) coordinate system. The instantaneous power asymmetry degree was defined. A novel generator asymmetry fault protection was proposed, which criterion was made up of the instantaneous power asymmetry degree and its phase characteristic. The sensitivity and reliability of the novel generator asymmetry fault protection was high through the dynamic simulation test. Meanwhile the novel protection connection was simple, and it could be used complementarily with other protections.In order to solve the low power protection mal-operation problem of the pumped-storage synchronous machine when it was in the pumping condition, this paper studied the power swing characteristic and analyzed the mal-operation reasons of the low power protection. A novel multi-zone low power protection was proposed through the digital simulation and the field data analysis. The setting values of the multi-zone low power protection were matching with its delay values, which could adapt to the different stages of power oscillation.All research results were summarized finally and the direction of further research were pointed out.