Real-Time Ratings for Transmission Systems

Use actual system conditions in place of worst-case conditions to increase thermal and stability limits.
The objective of this research initiative is to apply sensing, monitoring and reporting technologies to gather real-time system information. This would allow system operators to get more capacity from the system by basing operating limits on actual conditions, rather than on worst-case assumptions. It would also allow transmission system engineers to re-evaluate the static ratings currently applied to transmission lines, upgrading line ratings where possible.

Benefits:

• Higher capacity from existing lines and equipment: improved asset utilization
• Savings from deferred capital investment in costly new lines and upgrades
• Avoided congestion costs due to constrained transmission corridors
• Increased system reliability that results from better access to resource options in emergencies
• Reduced costs to ratepayers as a result of greater access to remotely located lower cost sources of power

Research Program Plan (pdf)
A comprehensive overview of the objectives, goals and strategies of this Research Initiative.

Technical Advisory Committee

The members of the Technical Advisory Committee represent California utilities, the California Independent System Operator, the CEC PIER Program and the CIEE. Their goals are to assist in setting research priorities, providing technical guidance and oversight to research efforts, and supporting the transfer of technical results into achievable business benefits for the California transmission system.

Real-Time Ratings Program Overview presented at the first TAC meeting (pdf)

Proposed agenda for the Third Technical Advisory Committee Meeting on September 16, 2004

Completed Projects

Dynamic Circuit Thermal Line Rating (pdf)
In this project San Diego Gas & Electric (SDG&E) investigated the feasibility of providing real-time transmission line ratings to system operators by monitoring actual conductor tension and environmental factors. Unlike previous systems that stored data for later analysis, the monitoring system developed for this project provided real-time ratings directly to the system operator. The results were evaluated to determine if the real-time ratings would allow more efficient and economic dispatch of an economy generation source that was constrained by the static line limits.

Sagging Line Mitigator (pdf)
The objective of the SLiM project was to create a simple, affordable, and compact device that can be easily installed on a span to resolve sag problems or to permit up-rating of a transmission line. The guiding design principle was that the SLiM device should be a passive device and act by reducing effective line length under the same conditions that cause the line to sag. That is, the same temperature change that leads to thermal expansion and sag in a transmission line conductor activates the motion of the SLiM device. Upon heating, the device retracts and shortens the effective conductor length. Upon cooling, the device lengthens and releases tension on the conductor. This report details the design and laboratory testing of a first prototype device.

Implementing Real Time Ratings for Path 15
California's Path 15, comprising several high-voltage transmission lines, is the main transmission interface between northern and southern California. At certain condition times of the year, the flow on this Path is limited by the thermal rating of the lines. The objective of this project is to investigate the feasibility of implementing real-time thermal monitoring data into the remedial action schemes of Path 15, thereby enabling higher overall Path flows and alleviating transmission congestion.

Development of a Real-Time Monitoring/Dynamic Rating System for Overhead Lines
This project developed a video-based system for monitoring transmission line ground clearances/sags on a real-time basis. The associated software models the clearances/sags in all spans to provide a real-time rating for the line. The goal for the line rating software design was to enable the system to be used by transmission system operators, including utilities and the Independent System Operator (ISO) for three purposes: 1) real-time monitoring/dynamic rating of lines, 2) studies to evaluate the performance of existing lines and to re-rate their capacity, and 3) monitoring the status of clearances/sags in "safety critical" areas.

Ongoing Projects

PG&E-CAISO Real-Time Data Integration Project
This project will evaluate the feasibility and cost-effectiveness of using a customized data server to process and transmit the data from multiple real-time transmission system monitors to a utility energy management system (EMS), as opposed to the standard method of transmitting the monitors' data through utility communication systems to the energy management system (EMS) and performing data processing there. This project will also develop utility and CAISO operator displays based on the data.

Project Summary (pdf)

Status Report (pdf)

Real-Time Transmission Line Ratings for a Multi-Utility Area
The goal of this project is to demonstrate the feasibility of using real-time transmission line ratings in a large, multi-utility area under normal system conditions for two simultaneous purposes: mitigation of voltage constraints in the area, and development of forecasting methods to facilitate more efficient generator dispatch.

Back to TRP