IEEE Power & Energy Magazine - January/February 2015 - 68

Sumo includes live power grid data (measurements and
topology from supervisory control and data acquisition, or
SCaDa), live weather data, and real-time reliability analyses. for short-term forecast application, it includes power

Weakest Link (Span)

grid data based on load flow forecasts, reliability analyses
based on these forecasts, and detailed weather forecasts.
Sumo combines different subsystems into a meaningful and helpful tool for operating the power grid. It includes
such functions as measurements, reliability analyses, forecasts, and Dtr (see figure 7). Calculations are based on current and forecast weather (from t0 to t0 + 3 hours). Currently
there are 17 web services implemented. they are providing
approximately 115 methods to the clients (subsystems). the
system's internal state is held in a relational SQL database.
Gridding of Weather Data and Weather Forecasting

figure 10. A practical example of a weakest link determining the line rating.

Symbol

Meaning
Thunderstorm-
Lightning Activity
High Wind Speeds
(Gale or Storm)

for the purpose of allowing fine-grained weather data input
into the Dtr calculations, weather data are gridded onto a
500 × 500-m grid (see figure 8). Live weather measurements
are gridded using a microscale weather model and terrain elevation data along with a midscale meteorological model, as
depicted in figure 8. this is done to effectively approximate
weather data on the parts of the power line corridors lacking
weather measurements. this then serves as an input to Dtr.
weather forecasts are based on results from a commercially obtainable, larger midscale weather model and live
weather measurements acquired from the weather station
network of the Slovenian tSo, elektro-Slovenija (eLeS).
they are calculated periodically for six horizons in the future
(15, 30, 45, 60, 120, and 180 minutes). the forecasts are then
also gridded onto the 500 × 500-m grid.

High Air Temperatures

Load Forecasts and Reliability Analyses
Low Air Temperatures
Extreme Rainfall

figure 11. Exceptional weather event warnings.

35%

33%

51%

50%

Load forecasts for n and n-1 scenarios and n-1 reliability
analyses are calculated periodically. they are based on:
✔✔ live measurements of active and reactive power nodal
injections across eLeS's power grid (SCaDa)
✔✔ live measurements of nodal voltages across eLeS's
power grid (SCaDa)
✔✔ live topology data (SCaDa)
✔✔ live measurements from eLeS's perimeter and internal network, with active and reactive power flows
✔✔ topology forecasts from the internal planning process
✔✔ DaCfs from entSo-e
✔✔ hourly production, demand, and transit forecasts from
the Slovenian power exchange operator
✔✔ load forecasts synchronized to the six weather forecast horizons.
DTRs

21%

23%

29%

32%

figure 12. Thunderstorm and lightning activity event
notification.
68

ieee power & energy magazine

for a given power flow, the Dtr upper limit is set by the
weakest link in its path from a source to a destination node.
In the case of calculating DtLr, the power line is split
into sections. generally speaking, each section has its own
weather data, its own conductor physical properties, and
its own geographical orientation. So a thermal rating needs
to be calculated for each section. for the power line as a
whole, the minimum obtained thermal rating is declared as
the power line's thermal rating (see figure 9).
january/february 2015

Table of Contents for the Digital Edition of IEEE Power & Energy Magazine - January/February 2015