Level 5b TLR’s have been rising exponentially over the past five years, with over 85 occurring in 2008 as compared with only five in 2002. More than 50% of level three Energy Emergency Alerts called in 2007 and 2008 were due to TLR 5a or 5b declarations, when firm load interruption was imminent or in progress. While TLR’s are more an indicator of congestion on popular paths, they do indicate that the grid is being pushed harder than it was in the past – which does raise reliability concerns. We will be working with you to investigate this issue further in 2009.
The TLR (Transmission Loading Relief) Procedure is an Eastern Interconnection-wide process that allows reliability coordinators to mitigate potential or actual operating security limit violations while respecting transmission service reservation priorities. Over-scheduling transactions on Firm Point-to-Point Transmission Service paths is an indication of increased congestion. Trends towards increasing number of TLR Level 5 or higher may provide an early warning signal that ability of the system to reliably supply electricity during times of peak period is declining. For detailed TLR procedure, please refer to NERC reliability standard IRO-006-3 ¯ Reliability Coordination ¯ Transmission Loading Relief.
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