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How do you cope with the “double risk trend” in reliability? (Part 1)

This is the first in a series of blogs focused on how to cope with “the double risk” trend in reliability, and how smart transmission and distribution grids can mitigate this risk.

Our present day society has become highly dependent on reliable electric energy supply, due to the ever increasing networking and electronic information exchange developments. Together with the shift in the fuel mix—substitution of other energy sources to electricity and the increase of variable renewables, this dependency will further increase and creates a double risk trend. We are heading towards unprecedented changes in the power system caused by the unstoppable electrification and transition to a sustainable energy supply. The double risk trend urges governments and transmission system operators to take measures to improve the availability of the system through standards and codes. Good progress is being made by NERC in the US, while in Europe ENTSO-E is pushing these developments forward. Standards and codes have a positive effect in driving industry towards controlling important risks in bulk power transmission systems and increase reliability—for example, mandatory vegetation management that reduces the risk of cascading (due to tree grow-in), ensuring interoperability of equipment from different vendors, seamless grid integration of variable renewables, and adequate protective control settings that contribute to the prevention of disasters, such as the August 2003 blackout in the US. Although the progress is encouraging, is it enough? In my next blog I will elaborate on a few factors that highly contribute to this double risk trend, and how they will shape the future of the electric power system.

Figure 1: Public grid investment per delivered kWh

Figure 1:  Necessary public grid investment per delivered kWh to the customer

For more than a century, the availability of the electricity grid has been around 99.9 percent—”three nines” in industry jargon—and this figure differs from country to country. This corresponds to an average power outage of roughly nine hours a year for a low-voltage connected customer. In a modern economy with microprocessor-based industrial controls and information technology networks at least 99.9999 percent reliability—”six nines”—is needed, equivalent to no more than three seconds of outages a year. Such a high overall reliability figure cannot be achieved with a public electricity grid without excessive investments. Figure 1 indicates the necessary public grid investment per delivered kWh to the customer to achieve a given availability, with the assumption of abundant generation.

When we talk about the reliability of the grid we actually mean its availability or “up time,” often measured in a percentage of the year. Reliability is a time-dependent probability function, and availability is the average reliability over time. Adequacy, or the ability to deliver the requested power, is a third metric and is associated with grid capacity. Not surprisingly, a grid with a high availability can have insufficient adequacy.


How do you cope with the “double risk trend” in reliability? (Part 2)
How do you cope with the “double risk trend” in reliability? (Part 3)

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