259 / 2022-03-14 22:25:01

Influence of Frequency Fluctuation on Protection of AC Area of Flexible HVDC Transmission

frequency fluctuation, disturbance signal , abnormal protection,protection method

Purpose/Aim

The existing AC area protection of flexible HVDC transmission is mainly configured and set based on the fault characteristics of traditional AC system, without considering the influence of flexible HVDC system. Besides, the influence of frequency fluctuation on electrical parameters is not considered and the influence of the disturbance signal on the protection system may also lead to the abnormal operation of the protection system. The relationship between the magnitude of error and the amplitude of frequency fluctuation needs to be studied, and the influence of frequency fluctuation on different protections needs to be researched.

Experimental/Modeling methods

The influence of frequency fluctuation on common Fourier Algorithm under different factors is deduced theoretically. The simulation model of flexible HVDC transmission is established to study the action characteristics different protections in AC area under frequency fluctuation and disturbance signal.

Results/Discussion

The derivation shows that there are errors in the voltage, current amplitude, phase angle and impedance calculated by Fourier Algorithm, which means the frequency fluctuation will bring deviation to these parameters’ measurement. Considering the influence of frequency fluctuation on the protection, by simultaneously monitoring multiple electrical parameters in the AC area of the flexible HVDC transmission system, the logic judgment device comprehensively judges the changes of differential current, AC-voltage and frequency to determine the operation state of the system, and improves the reliability by delaying remeasurement and rejudgment.

Conclusions

The frequency fluctuation will bring deviation to the AC current amplitude measurement, which may cause the misoperation of the protection system. By the detection of frequency, the influence of frequency deviation on current measurement is eliminated and by delaying remeasurement and rejudgment, the influence of disturbance signal is eliminated. It can provide relevant theoretical support for relay protection devices in AC area for flexible HVDC transmission project, which is conducive to the actual construction of the project.