This paper provides a mapping and sample of recently developed risk assessment techniques that are available for the distribution system operator. Three estimates on the value of more detailed risk analysis are desccribed. I.e. component reliability importance indices can be used to divversify the maintenance efforts, gaining better expected system performance at no cost. Furthermore, components that are assumed to be relatively harmless (based on average values) are identified as critical for longer interruptions. Finally it is shown that losses in a transformer are critical in the decision on transformer lifetime.

One major objective of maintenance management activities in electrical distribution systems is to find the right level of investments. Within an MSc thesis project at KTH, the probabilistic reliability software RACalc has been developed to support the decision making in the distribution system maintenance planning and risk analysis. This paper desccribes the algorithms in RACalc and shows on present status on RADPOW, an additional reliability tool developed within the research group. Calculations with RACalc is in this paper exemplified with a case study on an existing Swedish distribution system, were the program is used to determine the components’ importance to the system reliability indices. The result show that if the failure rate can be decreased by 10% on the 21% most important components, the overall system reliability improvement is more than 7%.

In the planning of the electrical transmission system it is of greatest concern to quantify the security margin for unwanted conditions in the system. This paper proposes an approach based on quantifying the risk of insufficient transmission capacity in bottlenecks in the system. Stresses in these critical transfer sections (CTS) provide a potential risk to corrective actions, or worst, load curtailments. The proposed method provides a general screening of component outages in order to find potential risk events for the CTS. Furthermore, the severity of each risk event is quantified based on the likelihood of the event and the consequence on the section's transmission capacity. The components' contribution to the risk of insufficient capacity in the CTS is then based on these risk events' severity. The method investigates several forecasted load levels during the year and consequently gives an input to a scheme for a risk based transmission system planning. The method is demonstrated on the reliability test system RBTS.

This paper presents a method to quantify and rank transmission system components by their importance for system reliability under different load scenarios. Each component is ranked by three separate importance indexes based on its expected outage rate and impact on: 1) system security margin; 2) load supply; and 3) generation units. By studying these three interests individually, a more complete view of the risks to system reliability can be assessed. The method is demonstrated on a detailed power system model (7000 components) of a significant part of the Great Britain transmission system at 400 and 275 kV. The results show how sensitive the component indexes are to the load scenario. The method provides an input for decision-making when planning maintenance and new investment and can be used as a complement to deterministic criteria.

In the long-term and operational planning of the power transmission system (PTS), one challenge is to identify components critical to system reliability. In this paper, the importance of each component for system reliability and vulnerability are quantified for two scenarios in a model of the Great Britain (GB) PTS. The scenarios are: (1) technical failures based on statistical data and (2) sabotage where the attacker has the ability to immobilize two contiguous components. In a novel method approach, the total importance of each component is based on three separate indices that include the system impact on (i) security margin, (ii) load, and (iii) generation. The final result of the GB system screening, including nearly 7000 components and 50 million outage events, is a ranking list indicating the 30 most critical components for each of the two scenarios. The results show that a component ranking that only includes risks of technical failures cannot be used to describe critical sabotage threats. Based on the results, the system operator can perform further and more detailed analysis on a few components and then make the necessary investments to improve the system reliability for equipment failures and strengthen the system vulnerability against sabotage.