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System HILP Event Demand Disconnection (SHEDD)

Funding mechanismNetwork Innovation Allowance (NIA)
DurationApr 2020 - Apr 2022
Estimated expenditure400K
Research areaNetwork improvements and system operability, New technologies and commercial evolution
  • August 2021

    The team have been reviewing and documenting findings from workshops carried out within the industry to feed into final outcomes of the project, including th…


The objectives of the project is to design and test a new LFDD scheme to maximise its future performance as the network continues to decarbonisation, Distribution Generation (DG) integration increases, and system inertia continues to decrease.


Low Frequency Demand Disconnection (LFDD) is designed to limit the fall in frequency for extreme events beyond those defined as ‘secured’ events in the SQSS and Operating Code OC6 (Demand Control) of the Grid Code.

Under exceptional circumstances where the frequency deviates for more than 60 seconds (e.g. loss of more than one large generator) there may be certain circumstances where the normal contracted frequency response may not be sufficient to maintain the system frequency between the statutory limits where the total loss of generation exceeds the amount secured for and a deficit of generation arises. In order to reduce the generation deficit (or excess in demand) to maintain stability, Distribution Network Operators (DNOs) have low frequency relays to disconnect demand (LFDD).

The current LFDD schemes do not take into account the move to decarbonize through growth of distributed generation and decreasing system inertia. This reduces the effectiveness of LFDD schemes which could potentially put the whole system at risk; while if the response results in sub-optimal economic disconnection of customers, the economic impact (and so cost to consumers) of High Impact Low Probability events will be higher than necessary.


The following deliverables will be explored:

  • Review the year-round performance of the LFDD scheme as the uptake of Low Carbon Technologies (LCTs) increase to identify opportunities to improve its technical and commercial performance in the short and medium term.
  • Consider a range of options for redesign of the current LFDD scheme to maximise its performance in the short term and for a new “smart” alternative to the LFDD scheme in the medium term.
  • Assess those options for redesign, including testing within “war game” simulations to demonstrate performance under simulated HILP events.
  • Identify the optimal solution for both short and medium term improvements to the LFDD scheme, and develop a plan for the way in which it could be rolled out, completed by the necessary technical specifications.