#9 dynamic line ratings: What are ERCOT’s existing practices with thermal line ratings?
The ERCOT Energy Management System (EMS) utilizes a State Estimator application to determine system status using a real-time snapshot of the system. It uses this snapshot to develop a powerflow basecase and run a Powerflow study. The results of the study are used to run the Real-time Contingency Analysis (RTCA) application to identify congestion on the ERCOT System every 5 minutes.
The basecase includes the current generation plan, transmission and generation outages, system load and dynamic line ratings (if provided by TO’s). RTCA displays all current constraints and the post-contingent overloaded element based on the line ratings provided by the TO’s. It also shows the pre and post contingency loading on the overloaded element based on the study results. The ERCOT Operator then takes action to reduce MW flows on the post contingent overloaded element to below the emergency rating and thus solve the congestion. These actions are done in accordance with ERCOT Operating Guide 3.1.6 that identifies the line ratings methodology and congestion techniques used by ERCOT. 
Guide 3.1.6
3.1.6 Responsibility For Equipment Ratings
TDSPs are responsible for determining the rating of their facilities.
Technical limits established for the operation of transmission equipment shall be applied consistently in TTC calculations, engineering studies, real-time security analyses, and operator actions.
TDSP’s shall provide ERCOT with three (3) nominal Transmission Facility Ratings:
· Continuous Rating: Represents the continuous MVA rating of a Transmission Facility (including substation terminal equipment in series with a conductor or transformer) at the applicable ambient temperature. The Transmission Facility can operate at this rating indefinitely without damage, or violation of National Electrical Safety Code (NESC) clearances.
· Emergency Rating: Represents the two (2) hour MVA rating of a Transmission Facility (including substation terminal equipment in series with a conductor or transformer) at the applicable ambient temperature. The Transmission Facility can operate at this rating for two (2) hours without violation of NESC clearances or equipment failure.
· Fifteen Minute Rating: Represents the fifteen (15) minute MVA rating of a Transmission Facility (including substation terminal equipment in series with a conductor or transformer) at the applicable ambient temperature and with a step increase from a prior loading of ninety percent (90%) of the Continuous Rating. The Transmission Facility can operate at this rating for fifteen (15) minutes, assuming its pre-contingency loading was ninety percent (90%) of the Continuous Rating limit at the applicable ambient temperature, without violation of NESC clearances or equipment failure. This rating takes advantage of the time delay associated with heating of a conductor or transformer following a sudden increase in current.
In operating the Transmission Grid, ERCOT shall use these ratings as follows:
· ERCOT shall limit pre-contingency flows to enforce the Continuous Rating. 
· If a valid Remedial Action Plan is unavailable to unload the Transmission Facility post contingency or the pre-contingency loading is greater than ninety percent (90%) of the Continuous Rating, ERCOT shall enforce pre-contingency System Operating Limit(s) to control the post contingency loading of the facility to levels below the Emergency Rating. The enforcement shall be implemented in a manner such that the post contingency loading will be at, or below, Continuous Rating within two (2) hours.
· If a Remedial Action Plan is documented at ERCOT to relieve the loading on the Transmission Facility within fifteen (15) minutes; ERCOT shall enforce pre-contingency System Operating Limit(s) to control the post contingency loading of the facility to levels below the Fifteen Minute Rating. The enforcement shall be implemented in a manner such that the post contingency loading will be at, or below, Emergency Rating within fifteen (15) minutes.
· ERCOT shall use best efforts to restore all Transmission Facilities to within Continuous Ratings as soon as practicable, based on Good Utility Practice.
In addition, from the Delta Design Notes for the ERCOT Dynamic Rating Project:
OVERVIEW:
Transmission facilities (primarily lines/conductor and autotransformers) are typically rated assuming a high ambient temperature (summer peak), low amounts of convection cooling, and conservative values for each. While this conservative rating is appropriate for summer weather patterns in ERCOT, it suggests that additional transmission capacity is often available if the actual ambient temperature or convection is known. Due to the difficulty in monitoring and obtaining wind speed data in relation to a specific transmission facility, the rating of the transmission facilities is based on ambient temperature data; however, some Transmission Providers may wish to provide “dynamic” ratings, which are based on more than temperature changes. Hence, the concept of dynamically rating transmission elements is based on at least ambient temperature to reflect the actual conditions rather than the worst expected conditions.
REAL TIME:
ERCOT will accept temperature adjusted transmission facility ratings for real time via one of the following two mechanisms:
•	Ratings may be delivered via ICCP from Transmission Service Provider. These ratings can be either in AMP or in MVA. ERCOT shall utilize these real-time ratings in its SCADA alarming, real-time security analysis and congestion management process. 
•	Transmission Service Provider can send the ratings by weather zone temperature which can be used to determine ratings based on a look up table between lines vs. temperatures. 
The TSP sends the ratings to ERCOT SCADA system via ICCP block1. ERCOT will define the ICCP points for the transmission facilities.
The TSP can choose to provide real time ratings either in AMP or MVA or via weather zone temperature by transmission facility type.
FUTURE STUDY PERIODS:
The ratings for the studies can be determined from ERCOT weather forecast and dynamic ratings look up table.
A file is generated every hour one file for a day for the next 7 days. Each file will have ratings (Normal, emergency and 15 Min) for transmission facility by hour for the entire day