REAL-TIME MONITORING AND DYNAMIC THERMAL RATING OF POWER TRANSMISSION-CIRCUITS

ANSI standards for power equipment, and a vast store of technical lite rature, describe various methods by which thermal ratings may be adjus ted if actual weather conditions are known or if the ''overload'' is t o be applied for a limited period of time. These methods have been giv en various names including dynamic thermal rating, on-line rating, and dynamic ratings to describe the process of adjusting thermal ratings of power equipment for actual weather conditions and actual electrical load patterns. This paper discusses in detail a recent project undert aken by the Electric Power Research Institute (RP 3022-7) as part of i ts research on Flexible AC Transmission. This project avoids dependenc e on temperature measurement, instead, calculating critical equipment component temperatures based solely on real-time weather and electrica l current. Inexpensive, commercially available weather stations, digit al data loggers, and IBM-compatible PC computers are combined with sop histicated thermal algorithms to yield a portable, flexible, instrumen tation method which can rate several transmission circuits simultaneou sly, including underground cable, overhead lines, power transformers, current transformers, switches, bus, line traps, and circuit breakers. Useable increases of 5% to 15% in the thermal capacity of transmissio n equipment circuits result.