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The North American Electric Reliability Corporation (NERC) FAC-008-5 requires Transmission and Generation (T&D) operators to complete and maintain facility ratings for their Bulk Electric System (BES) for components carrying 100 Kilovolts (kv) or more of electricity . This includes major components found in substations and switch yards such as wave traps, transformers, and insulators, as well as the conductors inside and outside of substations throughout the BES. NERC states that the methodology used to establish the ratings of the equipment on the BES shall be consistent with one of the following; Ratings provided by equipment manufacturers or obtained from equipment manufacturer specifications such as nameplate rating, one or more industry standards developed through an open process such as Institute of Electrical and Electronic Engineers (IEEE) or International Council on Large Electric Systems (CIGRE), or a practice that has been verified by testing, performance history or engineering analysis .
For large components, nameplate data can be acquired visually and the elements needed for the facility rating easily obtained. However, the manufacturer’s specifications for conductors relies heavily on good record keeping, as nameplates are not affixed to the conductors themselves. In the absence of good records, T&D operators have employed caliper measurements to find the overall diameter of the conductor and the diameter of individual strands. This data is then matched with manufacturer’s equipment tables to narrow the possibilities of the conductor type. With the conductor type identified, or narrowed to a range of possibilities, conductor ratings can be included into the facility ratings for the BES.
Terrestrial Close Range Photogrammetry (TCRP) replaces the need for calipers. TCRP is the process of measuring conductor and strand diameter using digital photography. This method can be employed from distances up to 400 feet from the conductor. Additionally, a count of the strands on the outer layer is attained. With these three data points, conductor type is more accurately established, without the need for any physical contact with the conductors themselves, increasing safety and speed and decreasing the cost of obtaining data when compared to more traditional methods.