Extra High Voltage Substation Back Up Storage Source


  • Substations use dc supply systems to sustain control functions during periods of loss of the ac power system.
  • Many extra high voltage (EHV) substations have a single battery and charger system to supply dc power.
  • The eastern U.S. blackouts of 2003 and other system events have revived interest in redundancy within the power system.
  • The battery and charger can be a significant single point of failure that is expensive to mitigate.
  • Maintenance requirements of lead acid batteries have also driven further interest in alternatives.


  • Calculate the reliability of the present dc storage system in EHV substations.
  • Compare the present battery system with other storage systems based on reliability and cost.
  • Recommend the most economical and reliable redundant system.


  • Reliability of present dc system is high, but could increase if a redundant battery or a redundant battery system were put in parallel with present system.
  • Due to low initial cost and proven lifetime and reliability, lead acid batteries are still best alternative for the time being.
  • Ultracapacitor and fuel cell hybrid systems (with batteries) are close to being viable alternatives. In order to become viable, costs need to decrease in the future and these alternatives need to see more field testing.



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