Modern power transformers for underground substations
Today’s trend is for higher density populations in cities and urban areas. This increases the energy supply demand, together with a reduction in available space for the energy infrastructure.
A suitable and increasingly popular solution to address this is to use power transformers within underground substations.
Extensive research and development by Hitachi ABB Power Grids over decades into the special needs and demands of such power transformers has delivered two complementary proven technology solutions that offer non-flammable or minimal fire risk outcomes depending upon the requirement and scope. Both solutions are suitable for environmentally sensitive applications.
A suitable and increasingly popular solution for high population densities in the urban areas is the use of power transformers within the underground substation
Hitachi ABB Power Grids has production technology integrated solutions, with current service experience ranging to 420 kV and 400 MVA, using ester filled transformers. They can be optionally combined with a TXpandTM flexible, rupture resistant tank solution delivering a truly minimal fire risk solution.
The alternative, non-flammable solution, subject to the dimensional, mass requirements, and cooling configuration requirements of the substation for the range to 145 kV, 63 MVA is to apply dry type, HiDry power transformers.
Special demands for power transformers in underground substations
Beyond the normal energy transfer, safety, longevity requirements, underground power transformers must meet additional demands compared to the traditional outdoor substation including:
· Greatly improved fire safety management both within the underground substation and above ground level
· Significantly reduced risk of a breach of the transformer system tank in the unlikely event of an internal fault
· Increased environmental consideration for the control and consequence of loss of cooling / insulation media
· Suitable cooling equipment configurations for heat dissipation of transformer losses from below ground while in proximity to the local population
· Compact arrangements underground to minimize the size and cost of the underground substation transformer room.
In order to recognize the manner with which these multiple demands are met, some background understanding of the ester fluid characteristics and behavior is appropriate.