Study On Electronic Current And Voltage Transformer For Gas Insulated Switchgear

Transformer is one of the most important equipments for electric energy metering and protection in the power system. Its measurement accuracy and reliability have important effects on the security of power system. Currently, the conventional electromagnetic transformer is mainly used to achieve the measurement signals of voltage and current in power system. But it has shortcomings of bulky size, prone to ferroresonance, complex insulation structure, narrow band, small linear range and secondary windings which can not short circuit or open circuit, etc. With the rapid development of integrated automation technology and modern microelectronic technology, the relay protection and second measuring device doesn’t require high-power-driven. The signal of 100V or 5A of the traditional transformer’s secondary output can not be connected with the computer directly. And it is not suited to the developing trend of automation, digitalization and intelligence of the power system. Therefore, the development of the novel transformer replacing traditional transformer becomes the requirement of power system’s further development.The thesis theoretically analyzes the structure and principle of the electronic instrument transformer for Gas Insulated Switchgear. It introduces the insulation design of the capacitive divider in detail, establishes two-dimensional and three-dimensional finite element model of capacitive divider and calculates the high-voltage capacitor, low-voltage capacitor and analyzes electric field distribution with maxwell finite element analysis software. In order to verify the feasibility of insulation design, the electric field distribution and potential distribution of the key position is examined. The impact factor of electronic voltage sensor accuracy is also analyzed and the improvements measures are proposed. Next, the thesis describes the design of the primary bus and the secondary windings of electronic current transformer. Temperature rise of electronic current transformer is simulated using ePhysics3.1 temperature field analysis analyze software to determine whether it meets the requirements of national standard.The error sources of the measuring current transformer (Low Power Current Transformer) and protective current transformer (Rogowski coil) are analyzed in the paper. And then relevant countermeasures are proposed. This thesis also designs a data acquisition system of electronic instrument transformer for GIS which can simultaneously capture 12 second output analog signals of current and voltage. They are converted into digital signals by a high-speed A/D. And the signal which is received by the GPS Receiver is processed. Based on the theoretical analysis and simulation, a prototype of 110kV electronic instrument transformer for GIS has been made. The electronic voltage sensor rated secondary output is 3.25V and its measuring accuracy class is 0.2 and protection accuracy class is 3P.The measuring electronic current sensor’s rated secondary output voltage is 1V and its accuracy class is up to 0.1. The protective electronic current sensor rated secondary output is 150mV and; its accuracy class is 5P. In order to verify the accuracy and stability of electronic instrument transformer, a series of tests have been carried out, such as, temperature coefficient of resistance, the basic accuracy and temperature cycle in the prototype development process. The test results show that the prototype of electronic voltage transformer can satisfy the requirement of GB/T 20840.7-2007, the measuring accuracy class could reach 0.2 and the protective accuracy class is 3P. The prototype of electronic current transformer can satisfy the requirement of GB/T 20840.8-2007, the measuring accuracy class is up to 0.1 and the protective accuracy class is 5P.