OPERATION & MAINTENANCE OF POWER PLANTS
Once in operation, maintenance
costs are lower as there is no need for oil monitoring or checks on tanks and radiators. In addition, because they have no bushings, there is no risk of bushing failure, a common failure mode for oil-filled transformers. Lastly, although catastrophic failures or spills are very rare, their cost is built into insurance. With the potential for reducing budgets
in several areas, it is worth considering dry- type transformers on a case-by-case basis to see whether there is a TCO advantage. Taking account of all the lifetime costs, dry-type transformers can be the most economical choice as well as the safest, with potential savings in the region of 11 to 18%.
SAFETY IN “WORLD’S LARGEST” APPLICATIONS Dry-type transformers are traditionally used most when safety for people, property and the environment are the top priority. For example, the world’s tallest building, Dubai’s Burj Khalifa, relies on a distribution substation on the 155th floor that was equipped by ABB. Te substation provides power for everything from elevators to lighting and HVAC (heating, ventilation and air conditioning) systems. Te substation technology includes 72 dry-type transformers that were specially designed for the tower with a flexible enclosure to fit in a compact space. Te world’s largest iron ore mine, Vale’s Carajás mine in Brazil, also relies
on a fleet of ABB’s dry-type transformers. It is equipped with 135 ABB cast coil transformers to step power down to supply power for equipment such as excavators, stackers, reclaimers and conveyors. ABB delivered the transformers as part of a contract for electrical and automation systems to enable a major expansion of the facility.
RATED UP TO 72KV FOR SUB- TRANSMISSION Tere has been steady development in dry-type transformer technology in recent years. Tis has opened up potential for new applications. Dry-type transformers are now available at higher voltages than ever before – units are now available with ratings of up to 72kV. Tis makes dry-type transformers suitable for sub-transmission applications for utilities, heavy industry, offshore oil and gas facilities, and managing power at infrastructure such as airports and stadiums. One utility operator in north America
has replaced an oil-filled 27MVA transformer unit with a 30MVA 69kV HiDry transformer. By switching to dry- type unit, the operator eliminated the need for a fire suppression system and removed risk of oil leakage into a nearby waterway. Tese are completely free from insulating oil, including the on-load tap changer (OLTC), which is used to vary the voltage output.
THE NEW TRANSFORMER D
epending on the system, switching of fast-acting breakers, such as vacuum or
gas-insulated breakers, can produce fast transient over-voltages inside transformer windings that, over time, may lead to failures. These failures result in unexpected system downtime and unrepairable equipment; both incredibly costly to network managers. ABB’s latest product, the Transient Voltage Resistant Transformer
TVRT FOR SWITCHING RESISTANCE In addition, ABB has introduced a new range of dry-type transformers that are designed specifically for applications that experience frequent switching (once per month or more often). Te Transient Voltage Resistant
Transformer (TVRT) has potential applications in heavy industry, data centres, traction infrastructure or to supply power for multi-pulse rectifiers. It also has potential to connect solar photovoltaic installations, which can experience sudden drops and peaks in output as clouds pass.
SEALED FOR SUBMERSIBLE APPLICATIONS
Another potential application for dry-type transformers is that they can be supplied in hermetically sealed tanks for harsh environments, for example urban networks that may be vulnerable to flooding, offshore platforms, mines and chemical processing plants that might have a corrosive environment. One such transformer beneath the
streets of Manhattan in New York has survived hurricanes Sandy and Irina and continued to function in spite of being submerged under 20ft of water. Te tank is over-pressured with nitrogen and equipped with sensors to detect any loss of pressure that might indicate tank corrosion.
Pablo Castano-Mariscal is with ABB
www.abb.com
(TVRT), eliminates this potential failure mode during network switching operations. By using integrated winding varistors, the TVRT is protected from switching transients and works in any electrical network without the need of additional system analysis for design. The technology is simple.
Varistors are placed strategically along the windings in proprietary arrangements to limit transient over-voltages from both breaker
reignitions and amplified voltages from harmonic resonance. Combined with advanced winding design, the technology controls peak voltages indeterminant of the connected system characteristics. Compared to some available existing RC snubber circuit solutions, the TVRT eliminates the risk and maintenance that comes with oil-filled capacitors and does not affect the overall size of the installation. l
www.engineerlive.com 19
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