Papers by Keyword: Current Transformer

Abstract: This research focused on the effect of harmonic to the performance of current transformer (CT) operates under harmonic conditions. Due to the increasing of harmonic in power system, the CT did not perform well. The CT may saturates due to the presence of voltage and current harmonics. In this project, a laboratory test was conducted to investigate and analyze the influence of harmonics to the CT performance. This CT has been test with different Total Harmonic Distortion Current (THD_i) at primary side and constant primary current. The experiment result shows the secondary current CT errors will increases when THD_i increases.

Abstract: This paper aims to analyzing and probing the influences of power system harmonics on a differential relay used for distribution transformer protection. The increased use of nonlinear devices in industry, commercial and residential areas can lead to a significant increase the level of harmonic distortion in the power system. This harmonic has the significant effects to the differential protection systems components such as current transformer (CT) and relay. The CT tends to saturate due to the presence of current harmonics in power system, so it will produce magnitude secondary current error and make the differential relay to miss operations. The harmonic distortion effects on the differential protection have been investigated through laboratory test. To determine the CT errors when operates under harmonic condition, the CT has been test with certain level of THD_i. The result of this testing was found that with increasing of the THDi, the magnitude of secondary current error increased and differential relay will operate at no fault conditions.

Abstract: On the basis of the resistance model of high voltage electric power metering system, we make a study on the saturation of the measuring CT when the load is heavy. Through experiments on measuring current transformers, we chose high-quality power frequency magnetic core of the least saturation. On the secondary side of the measuring CT, circuit debugging was carried on and through experiments, optimal circuit parameters were determined to optimize the detection circuit which reduced the resistance of the secondary side of the measuring CT to the utmost to decrease the magnetic flux in the magnetic core to weaken saturation. Through FIR filter we extract detection signal from the fault signal to diagnose the fault. The practical test show the extracted detection signal can accurately judge the fault.

Abstract: This paper combines methods such as decision-making theory and method, the risk early warning theory and mathematical statistics theory [1,2]. With case analysis, some risk assessment and risk early warning is studied systematically on the automatic low voltage current transformer verification system. First of all, on the basis of risk identification, a indicator evaluation system for the verification system is established. Combined with the structure of the low voltage current transformer verification system, the indicator system is built on both the overall system and various key units of the system. Then risk assessment of the system is conducted. The risk assessment includes state analysis on each indicator, setting up the indicator state probability model, setting the indicator weight; also a confidence level is analyzed. Thirdly, risk early warning is made. The risk early warning threshold is taken as the basis of the early warning, which guarantees the safety and steady operation of the system. Finally, some example verification is done upon the automatic low voltage current transformer verification system, which provides reference on risk assessment and early warning for some enterprises and institutions.