Most lines only require a single set of rating values that apply irregardless of the direction that energy is flowing. However, for some lines, Transmission Providers may require separate “directional” ratings that differ depending on the direction energy is flowing.

This decision documents strategy for representing directional ratings in TROLIE.


TROLIE will contain no specific schema elements to represent directional ratings. For lines that require directional ratings, TROLIE servers must expose unique resource identifiers representing each direction.

A Rating Direction as a Resource

While a rating direction against a particular piece of equipment doesn’t map directly back to the physical model, it is a natural fit for TROLIE implementations to consider each direction as a separate anchor against which TROLIE servers can attach ratings. Each direction could have its obligation tracked for providing ratings data separately, as it is possible that values for each direction could be provided independently. In addition, it is safe to assume that many systems will represent the ratings over time as a time series, both to meet FERC’s 5-year history requirement and for other study purposes. It is convenient to simply represent the ratings as a single time series per resource, vs a time series per resource per direction.

An alternative would be to mark each series with explicit directions in the model, including a special value for “both” when directional ratings don’t apply. We feel this would add extra complexity to the model to accommodate the minority of devices on the system, and is the wrong tradeoff.

Directional-Resource Naming

While directional ratings are supported by many systems involved in grid operations (EMS, Markets, modeling etc), there is currently no consistent approach to how they are represented. IEC CIM also has no provision for directional ratings in the transmission model as of version 17. So, there is no existing standard to gravitate to.

Much like the rules on naming, TROLIE will need to be flexible in order to accommodate the inertia of established software systems, models and methodologies. Therefore, TROLIE is not opinionated on how these names are structured. Some possible examples are simply listed in the examples section to provide guidance, as referenced below.


TROLIE server implementations are responsible for translating resources into rating directions, and exposing identifiers that represent each direction. Some possible examples are provided here for guidance.