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synchronous generation and system fault current limitations

When a fault or short-circuit occurs in an electric power system, all synchronous generators contribute current directly to that fault until protective equipment acts to either isolate the fault or trip (switch off) the generators. The Consolidated Edison system has been designed to operate successfully for the isolation of these faults at the highest levels of current that can be anticipated for the electric power system. If the fault current exceeds the ability of the equipment to protect the system, the result could be a catastrophic failure of the protective equipment as well as significant portions of the electric system infrastructure.

The fault current contribution of any distributed generation that uses synchronous generators must be considered prior to the acceptance and approval of the customer’s application. In some areas, the margin between the ratings of the protective equipment and the calculated fault current may be too narrow, precluding the installation of additional synchronous generation. In these cases, additional mitigating measures must be taken. There are several options that may be available for customers, depending on their choice of DG configuration:

  • Reduction of total aggregate synchronous generation at the site to an acceptable level.
  • Use alternative generation strategies, such as induction or DC inverted generators.
  • Use an “AC-to-AC DC Link” product, in which the electric conversion equipment would also minimize the generator’s fault current contribution.
  • Use a “Fast Fuse” or “Power Fuse”, which acts to rapidly trip the customer’s generator within an acceptable time limit.
There may be additional options available, depending on your choice of DG equipment and the electric system infrastructure near your proposed site. These options can be explored and evaluated through discussions with the DG experts at Con Edison.

View Synchronous Generation Placement Availability In The Con Edison Service Area

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