Transmission Network Performance Report 2005 - National Grid

Transmission ReliabilityFY20051.5 Number of Disturbances• The following figure compares transmission outages distributed throughthe year for both FY2004 and FY2005. The blue line shows the outagesfor FY2004 and the red line shows the outages for FY2005. Thesenumbers represent the total number of disturbances, which were eithermomentary or sustained in nature.Figure 1-1: Cumulative Number of Outages by Month7006005004003002001000Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb MarFY2004 FY2005 5 YR AVG• The number of disturbances in FY2005 was higher than for FY2004.Although this represents a slight decrease in reliability performance overlast year, FY2005 performance was mostly consistent with the 5 yearAverage. This performance must be considered taking into account thatthe lightning season in FY2004 was significantly better than the 5 yearaverage while that in FY2005 was significantly worse.• The highest rate of incidence of outages occurred during warm weatherconditions with 58% of all outages occurring between May and August.Compared to FY2004, there was an increase of over 200% in lightninginitiated outages in FY2005 (an increase of 33% over the 5 YearAverage).• The following figure indicates the weekly profile of events in FY2005 inboth New England and New York. The green bars indicate the NewEngland events while the blue bars indicate New York events. Calloutsare used against weeks that had abnormally large number of outagesand identify the major causes for the performance. In FY2005 Lightningstorms were responsible for all the major event weeks.6 National Grid Performance Report