Digital Substation or Digital Secondary System—What's the Difference?
What Does “Digital Substation” Mean?
A substation is one of the elements of an electric power system. It is composed of high-voltage apparatus designed and sized for the substation operating voltage (called the primary system) and low-voltage equipment (referred to as a secondary system).
Given this definition, what does the term “digital substation” mean? For some, it simply means using fiber-optic cables to communicate between the relays in the control house and the instrument transformers, breakers, and merging units in the station yard. For others, it is synonymous with industry protocols defined by the IEC 61850 collection of standards.
Substation primary equipment is not digital; there are no digital breakers, no digital transformers, and no digital surge arresters. Therefore, it is not possible to have a completely “digital” substation.
The digital substation concept promises to digitize a portion of the substation secondary system by eliminating the majority of analog secondary circuits between the instrument transformers and protective relays.
Why SEL Uses the Term “Digital Secondary Systems”
SEL’s mission is to make electric power safer, more reliable, and more economical. We stay true to this mission by helping customers around the world protect, control, and monitor substation primary equipment using digital devices and communications protocols in substations.
With this in mind, we use the term “digital secondary systems” to more accurately define what portions of the substation can be digitized. As you browse the SEL website, you will see this new term used in our literature related to SEL Time-Domain Link (TiDL) and Sampled Values technologies.