Federal Energy Regulators Seek Answers Tied To Dynamic Line Ratings

The Federal Energy Regulatory Commission (FERC) has launched an inquiry that seeks to answer a wide range of questions related to the use of dynamic line ratings (DLRs) on electric transmission lines.

Transmission line ratings represent the maximum transfer capability of each transmission line. These ratings can change based on weather conditions. The use of DLRs allows the capacity of a line to be updated regularly based on a wide range of weather and line-specific factors affecting the operation of electric transmission lines.

FERC’s Notice of Inquiry (NOI), which was issued on Feb. 17, builds on Order No. 881, which FERC approved in December of last year.

Order No. 881 directs transmission providers to use ambient-adjusted ratings (AARs) as the basis for evaluating near-term transmission service as well as for the determination of the necessity of certain curtailment, interruption or redispatch of near-term transmission service. AARs set transfer capability for transmission lines taking into account the effects of forecasted ambient air temperatures and the presence of solar heating.

Order No. 881 found that line ratings based on conservative assumptions about worst-case, long-term air temperature and other weather conditions can lead to underutilization of the transmission grid. Therefore, requiring all transmission providers to use AARs will better utilize the grid and help lower costs for consumers, FERC concluded.

Order No. 881 also acknowledged that transmission line ratings could be based on factors beyond forecasted ambient air temperatures and the presence of solar heating.

Applying these factors to reflect other weather conditions like wind, cloud cover, solar heating intensity and precipitation, as well as transmission line conditions such as tension or sag, could lead to greater accuracy and enable greater power flows, FERC said.

In addition, the Commission explained that the use of dynamic line ratings can detect situations where flows should be reduced for safe and reliable operation and to avoid unnecessary wear on transmission equipment.

FERC concluded in Order No. 881, however, that the record was insufficient to assess the relative benefits, costs and challenges of dynamic line rating implementation. In issuing the NOI, FERC is attempting to gather additional information on these issues.

The NOI seeks to further explore:

  • Whether the lack of DLR requirements renders current wholesale rates unjust and unreasonable;
  • Potential criteria for DLR requirements;
  • The benefits, costs and challenges of implementing DLRs;
  • The nature of potential DLR requirements; and
  • Timeframes for implementing potential DLR requirements.

Initial comments in response to the NOI are due 60 days after publication in the Federal Register, with reply comments due 30 days later.

The NOI is available here.