Research On The Key Technology Of Optical Current Transformer For Gas Insulated Switchgear

Along with the current widely-spread application of gas insulated switchgear (GIS) in power system, it has become a hot issue to search for an appropriate current transformer (CT) suitable for GIS to replace the regular CT. As an excellent product of new current transformer, OCT that has been under research since mid-20th century has the best future for application. As the research went deeper and the technology advanced, our country has made great breakthroughs in this field in the past two decades, with OCT being put into commercial use. Magnetic concentrator ring OCT has more advantages than other types of OCTs in combining features of GIS. Its being put into use has, however, been affected due to the problems of measurement accuracy and long-term running stability.This paper tries to, by solving the existing problems of magnetic concentrator ring OCT, make magnetic concentrator ring transformer take full use of its own advantages to promote its use. In order to fulfill this purpose, it first researches on the possible factors affecting its measuring quality of magnetic concentrator ring OCT, such as overall structure, air gap openings, air gap face and incision, all based on the analysis of sensing principle of magnetic concentrator ring. Then it comes up with single air gap two fissure magnetic concentrator rings OCT (external-hoop OCT).The changes in the set of magnetic structure of external-hoop OCT will definitely lead to a redistribution of magnetic field around the current to de measured and the magnetic field in the air gap of magnetic concentrator ring will also change accordingly, which will furthermore affect the measuring quality of external-hoop OCT. This paper takes the analyzing method of magnetic circuit combined with Ansoft simulation software to analyze influences on the magnetic field inside the air gap from magnetic concentrator ring's size, two fissure structure, length of air gap, ferromagnetic material, flux leakage and other factors and to search for the factors affecting relative errors of the external-hoop OCT's air gap line integral. On this basis, it will move on to search for the law of influences on relative errors of the external-hoop OCT's air gap line integral from changes of these factors. The common variation law of the two can be figured out by contrasting between the permeability character of ferromagnetic material and the relative error character of air gap line integral.This paper also analyzes whether the law concerning about influences on output characteristics of external-hoop OCT from a variety of factors is universal. The program to optimize external-hoop OCT will be worked out based on the universal law. The Ansoft software will be used to conduct measurement simulation of both DC and AC. The optimization program will be tested whether it is able to improve measurement accuracy. external-hoop OCT designed this time lives up to the measurement accuracy standard of 0.2S for current transformer.This paper builds a simulation model for assisted analysis by the use of Ansoft software and at the same time it carries out a test on the actual model of external-hoop magnetic concentrator ring, helping to create a better future for the use of external-hoop OCT.