18-Pulse transformer device for flexible connection of asynchronous power systems

Abstract

Transmission of active power between power systems with the same nominal frequencies, linked via phase-rotating transformer is examined. The device is based on hexagonal scheme, and due to new proposal, provides symmetrical 18-phase output system of voltages, wherein the various phases of it are connected to different phases of three-phase receiving system by means of semiconductor switching elements, composed in two groups to reduce a quantity of switching keys. For reducing oscillations of transmitted active power, caused by 20° step switching of the phase angle between the voltages of the connected systems PWM modulation method is used, thus providing a smoother angle switching. It was shown, that increasing the number of phases sufficiently reduces the level of harmonic distortion of currents and voltages on the buses of receiving power system, so at some conditions the requirements, imposed on higher harmonics content in high voltage electrical networks could be met without the use of additional filters.