DESIGN OF TWELVE PULSE RECTIFIER USED IN HVDC SYSTEM

Electrical & Electronics Engineering

National Conference on "Recent Advances in Materials Science & its Applications" & "Recent Trends in Electrical, Electronics, Computing and Information Technology"

The prototype model of a twelve pulse bridge rectifier circuit with a power rating of 2KW, transmission voltage level of 200V and current rating of 5A is developed for a bipolar HVDC transmission system. A twelve pulse bridge rectifier circuit is the cascade connection of two six pulse bridges connected in series on the DC side. The phase displacement of 30 degrees is given to the lower six pulse rectifier bridge with reference to the upper six pulse rectifier bridge. This phase displacement is obtained by proper designing of three phase converter transformer with the 500VA, 415V/50V, 3A Star/Star, Star/ Delta rating. The transformer secondary winding is connected in star and in delta to obtain a phase shift of 30 degrees. The simulation models of both six pulse and twelve pulse bridge rectifiers are simulated using MATLAB platform. The FFT analysis is performed on both the models and the comparison results proves that with the increase in the pulse number the total harmonic distortion (THD) content is reduced from 35.66% for six pulse rectifier to 12.46% for twelve pulse rectifier. Due to this reason twelve pulse bridge rectifiers are preferred in HVDC transmission systems. The experimental results of twelve pulse rectifier were tabulated and observed that with increase in the firing angle (α) the DC output voltage decreases for both R and RL loads. The waveforms were recorded using digital oscilloscope for different firing angles and by adding LC filter the ripples are further reduced and smooth waveform is observed.

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