Study on the transient characteristic measurement system of current transformer

Abstract

Nowadays, thirteen ultra-high voltage direct current (UHVDC) transmission projects have commissioned in China, including Jinping-Sunan, Fulong-Fengxian, Yibin-Jinhua project, and so forth. Meanwhile, another two UHVDC transmission projects are under construction. The highest UHVDC voltage level is ±1100kV. The HVDC transmission is superior in high capacity and long transmission distance, and its control response put forward higher requirements for the transient characteristics of DC current transformer. At present, there is no test method and equipment for testing the transient characteristics of the DC current transformer. Therefore, mastering the transient response characteristics of operating DC current transformer remains to be a challenge. In this paper, a transient test system of DC current transformer is developed, which includes a step current output unit, a high precision acquisition unit and a calibrator algorithm. The system was used to test the rising time, maximum overshoot and transient delay of the DC current transformers installed on the pole line and valve outlet. This study can clarify the influence factors of the transient characteristics of DC transformer on the control and protection system of UHVDC, and can define the principle of selecting the transformer parameters to meet the requirements of the control and protection system of UHVDC. The results of this study have great significance to improve the performance of UHVDC control and protection system.

Online measurement of birefringence of sensing fibers in the AFOCT system

“…Under typical online usage, the deviation in the measured current value of the DC transmission lines should be below 0.1% during the operation, otherwise the AFOCT system must give an alarm. In other words, the amplitude noise in the AFOCT system would be only acceptable, when it leads to 0.1% error of the measured current value, as well as the Faraday phase shift F according to Equation (7). For the nonideal case δ SF = 0.065 and T SF = 0.6, our model gives B π/2 = 0.5580 and B π = 0.9939 as F = 0.03 rad.…”

“…Usually, the birefringence measurement of the sensing fiber needs to first uninstall the sensing fiber from the AFOCT system, followed by an offline optical experiment to measure its birefringence. 7 This method is not only cumbersome to operate, easy to cause damage to the sensing fiber, but also has a certain measurement error between the offline and online sensing fiber. Therefore, it is highly desired a method that can online measure the birefringence of the sensing fiber.…”

“…To achieve the accurate measurement of the current value in transmission lines, it is very necessary to determine the birefringence of the sensing fiber of AFOCT. Usually, the birefringence measurement of the sensing fiber needs to first uninstall the sensing fiber from the AFOCT system, followed by an offline optical experiment to measure its birefringence 7 . This method is not only cumbersome to operate, easy to cause damage to the sensing fiber, but also has a certain measurement error between the offline and online sensing fiber.…”