Ultra high voltage (UHV) transmission systems offer the ability to transport electricity over long distances with minimal power loss using either alternating current (AC) or direct (DC) current.
While DC transmission provides less energy loss when travelling over greater distances, AC transmission can allow for branches within the transmission lines and thus connect to several different cities.
The former Soviet Union launched the first commercial UHV transmission line connected the nearly 500 kilometres between the towns of Ekibastuz and Kokchetav in Kazakhstan in September 1985 with a voltage of 1 150 kV.
Other countries have since adopted this technology. A pilot project was put into place in India in 2012 using AC transmissions which has since been expanded while another UHV system using DC transmission is near completion. A 2 500 km UHV system has been built in Brazil using DC transmission that connects the energy from the northern part of the country to the population centres in the south. In China, the largest number of UHV transmission lines have been built using both DC and AC transmission.
As the demand for electricity increases worldwide, power transmission lines will need to provide greater capacity. The use of renewable energy, generally from sites located far distances from cities such as offshore wind farms or photovoltaic installations in deserts, will require high transmission capacity over long distances. For these reasons, the need for UHV transmission systems will increase in the future.
Standardizing UHV AC systems
Standardization of UHV AC systems is underway. In 2013, the IEC set up a technical committee, TC 122, which provides standards for UHV AC transmission systems exceeding 800 kV. TC 122 provides system level specifications used for the design, construction and operation of sites rather than the equipment standards.
According to the Secretary of TC 122, Eiichi Zaima, “the integration of technical knowledge from all stakeholders is the key to develop well-balanced international standards in TC 122”.
Liaisons with CIGRE
The IEC has been working closely with CIGRE, a global members organization that develops and shares technical expertise in power systems. The two organizations have cooperated on UHV standardization since their joint international symposium on UHV transmission which took place in Beijing in 2007.
TC 122 work programme
Since 2014, TC 122 has published three technical specifications and one technical report. The technical report, IEC TR 63042-100, provides an overview of the guidelines and standards for UHV AC transmission systems with the aim of ensuring the reliability, availability, and environmental aspects of the systems.
The published technical specifications provide inform the requirements for UHV AC transmission systems related to their voltage regulation and insulation design (IEC TS 63042-101), substation design (IEC TS 63042-201) and on-site acceptance tests (IEC TS 63042-301).
Current areas of work include general systems design, transmission line design, commissioning and guidelines for the measurement of UHV AC transmission line power frequency parameters.
As Zaima notes, “with electricity demand increasing, UHV transmission technology is becoming increasingly essential for the future supply of power”.
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