The Research For Optical Current Transformer Applied In Substation

Now,the current transformer we generally used in power grid is still electromagnetic current transformer(ECT).However,the disadvantages of the traditional electromagnetic current transformer are emerging gradually with the power grid is more and more huge and complex.When short fault occurs in power system,high amplitude of short circuit current will make the current transformer generate magnetic saturation.Then,the output of the secondary current will have serious distortion,protection will be failure.Finally,power s ystem will occur a serious accident.And,traditional electromagnetic current transformer have a poor performance about transient measurement.In order to ensure the accuracy of the relay protection,the present protection we used is that we extract the po wer frequency component as the characteristic from the fault current.This leads to the time delay when electromagnetic current transformer measure current.It cannot satisfy the quick-action of relay protection.Due to the traditional electromagnetic current transformer has a series of problems,we start looking for a new type of current transformer to replace the traditional electromagnetic current transformer,so that can improve the reliability and quick-action of relay protection.As a new type of current transformer,the optical current transformer(OCT)based on Faraday effect has the performance of no magnetic saturation,high insulation and economical efficiency,furthermore,it is able to reflect the primary current directly.It compared with ECT has a significant advantage.In recent years,OCT has received wide attention of researchers at home and abroad,and gradually form a relatively mature technology.At present,OCT has been put into operation in the several domestic substations successfully,and achieved good effect.This paper,we put forward a high precision grade and good stability of OCT,by studying the principle,signal conversion method and the ways of improving the measurement accuracy and stability of OCT.Because OCT is different from ECT about measuring principle,it can reflect the full waveform of the primary current more accurately,and current waveform measured by OCT can be calculated directly.So,the algorithm that OCT is applied to the differential protection is different from traditional protection algorithm.This paper will put forward an algorithm for bus differential protection based on optical current transformer,and simulate the actual bus differential protection by using RTDS,and then,verify the feasibility of the new protection algorithm.This paper contrast the traditional differential protection algorithm with the optical differential protection algorithm under the laboratory environment.Simulate the fault current by RTDS and set up the actual protection system so that we can verify the feasibility of the optical differential protection algorithm and analyze the advantages and disadvantages by contrast with the traditional differential protection algorithm.Finally,we can achieve the optical current transformer applied in substation.