Qatar University

Qatar Foundation for Education, Science and Community Development

Ayman S Abdel-Khalik

Ahmed Massoud

Shehab Ahmed

Ahmed Elserougi

The method of converting high voltage AC lines into bipolar high voltage DC systems makes use of the three transmission lines (referred to as the positive pole, the negative pole, and the modulating pole) in an existing high voltage AC system as transmission lines in a bipolar high voltage DC system. When current from the power source is up to the thermal current limit of the transmission lines, the transmission lines operate in two-wire mode, where current is delivered in the positive pole and returned in the negative pole, the modulating pole being open. When power source current exceeds the thermal current limit, operation is in three-wire mode, alternating for predetermined periods between parallel configuration of the positive pole and the modulating pole to divide current for delivery to the load, and parallel configuration of the negative pole and the modulating pole, dividing the return current.

Three wire DC transmission circuit with modulated pole

The direct current (DC) side fault isolator for high voltage direct current (HVDC) converters () includes a first set of double thyristor switches () connected across the line-to-line voltage terminals between first and second phases of alternating current (AC) terminals of a HVDC converter (), and a second set of double thyristor switches () connected across the line-to-line voltage between the second phase and a third phase of the AC terminals of the HVDC converter (). In use, the first and second sets of double thyristor switches () separate the HVDC converter () from an external power grid () during direct current (DC) side faults by turning on these thyristors ().

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Houston, TX, United States of America

Ayman S Abdel-Khalik