Assessment of Risk Against Regulator Requirements for Duration of Long Supply Interruptions Mohd Ikhwan Muhammad Ridzuan Dr Sasa Djokic The University of Edinburgh, UK

Introduction Distribution network operators (DNOs) have to make sure the frequency and duration of interruptions experienced by their customer are within specified or agreed limits and targets DNOs may be rewarded, penalized or liable for compensation based on their actually achieved reliability performance An important aspect of the related analysis is assessment of RISK that DNOs face (based on relevant characteristics and operation strategies of their networks and other influential factors)

Input Data & Parameters: Fault Rates & Repair Time

Input Data & Parameters: Daily Variation of Interruption Probability

Continuity of Supply Requirements: UK Security and Quality of Supply

Continuity of Supply Requirements: UK Guaranteed Standard of Performance

Continuity of Supply Requirements: Italian Supply Quality Standard

Continuity of Supply Requirements: Italian Guaranteed Standard of Performance

Test Network Typical UK urban distribution network MV: Meshed (but operated radially in normal conditions), with an alternative supply point (unrestricted support) LV: Radial (3-phase & 1-phase service connections)

Risk Assessment Procedures Analytical Approaches: Based on mathematical models, which typically limit outputs to one set of results, e.g. mean values of reliability indices, corresponding to the specified input mean data. Offer only a general “snapshot” characterisation of the analysed system, as they will always provide the same set of output results for the same set of input data, parameters and models. Probabilistic (Monte Carlo) Approaches: Allow to model a wide range of variations of practically all input parameters and data in one or few simulation/calculation set-ups, without the need to repeat calculation after a change in input data. Outputs are reliability indices, which are typically presented as probability distributions with the corresponding mean values.

Risk Assessment Procedures WHY COMBINE PROBABILISTIC & ANALYTICAL RELIABILITY ASSESSMENT? Probabilistic Approaches give probability distributions of customer interruptions (which customers will be interrupted and how frequently) and probability distributions of interruption durations Analytical Approaches could incorporate Regulator Requirements, if actual limits are used as input data For example, if we assume that every faulted component has repair time of exactly 18 hours, with the same duration applied for transfer to alternative supply and time required for network reconfiguration, the worst possible network reliability performance for which there will still be no penalty incurred due to supply interruptions longer than 18 hours will be calculated Afterwards, analytically calculated reliability indices are used as “benchmark limits” for directly assessing risks of penalty

Considered Scenario 12 Considered Scenarios (Existing Networks & Future “Smart Grids”): Existing Network Configurations & Functionalities (SC-1A/B): In accordance with Security of Supply Requirements (MV network have switching functionalities for transferring to alternative supply and for reconfiguration; otherwise large number of customers will be exposed to excessively long supply interruptions)

Considered Scenario 13 Considered Scenarios (Existing Networks & Future “Smart Grids”): “Smart Grid” Scenarios (SC-6A/B): Represent functionalities available in future networks -- in this case automatic remote-controlled switching implemented in MV network (LV network is still protected only by the fuses)

Considered Scenario 14 Considered Scenarios (Existing Networks & Future “Smart Grids”): Various Regulator Requirements (SC 2A/2B to SC-5A/5B): Used ONLY for analytical assessment and formulation of corresponding limits and thresholds against which risks of penalties will be assessed after probabilistic results are obtained

Results: Analytical Assessment 15 MV Network OnlyMV Network & LV Equivalent

Results: System Assessment Significant increase of CAIDI value is indicated for Scenario SC-6A/6B, when “smart grid“ automatic switching is applied… (?!)  CAIDI (MV Network) CAIDI (MV Network & LV Equivalent)

Results: System Assessment SAIFI (MV Network) SAIFI (MV Network & LV Equivalent) All faults previously cleared after 15min or 3 hours are in SC-1A/1B resulting in short interruptions (due to <3min automatic switching). Corresponding supply interruptions are no longer contributing to the average interruption duration (resulting in a higher risk of penalty… still, number of faults reduced in SC-6A/6B

Results: Customer Assessment SAIFI (SC-1A)CAIDI (SC-1A)

Results: Customer Assessment SAIFI (SC-1B)CAIDI (SC-1B)

Results: Customer Assessment SAIFI (SC-6A)CAIDI (SC-6A)

Results: Customer Assessment SAIFI (SC-6B)CAIDI (SC-6B)

Risk Results SC-1A (%)SC-6A (%)SC-1B (%)SC-6B (%) Limit SC-2A/2B (GSP-UK) Limit SC-3A/3B (GSP-Italy) SC-1A (%) SC-6A (%) SC-1B (%) SC-6B (%) SC-1A (%) SC-6A (%) SC-1B (%) SC-6B (%) Customer Limit SC- 2A/2B (GSP- UK) Limit SC- 3A/3B (GSP- Italy) System Risk’s Customer Risk’s

THANKS!Questions? Mohd Ikhwan Muhammad Ridzuan Dr Sasa Djokic The University of Edinburgh, UK