‘Digital’ substation: Safer, reliable and economical

A substation is one of the elements of an electric power system, 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, the term “digital substation” 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.

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 digitise a portion of the substation secondary system by eliminating the majority of analog secondary circuits between the instrument transformers and protective relays.

SEL’s use of 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’s 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 digitised. 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.

Robust solutions for digital secondary systems
Modernise your substation by choosing from two SEL digital secondary system solutions that advance how you protect and control the primary equipment in your substation.
• Apply SEL Time-Domain Link (TiDL) technology, which uses a secure point-to-point fiber connection to eliminate complex Ethernet network design
• Use an SEL Sampled Values (SV) solution with IEC 61850-9-2

These solutions improve safety by moving high-energy signals out of the control house and reduce the costs associated with running copper wiring for protective relaying. Placing SEL relays in the yard near the primary equipment is another way to achieve these benefits.

SEL TiDL technology: A simple, fast, and secure solution

SEL relays in the substation yard: Providing the fastest protection speed
Customers from all over the world have placed SEL relays in outdoor cabinets in the substation yard to achieve copper reduction benefits similar to a digital secondary system. This is possible because SEL relays are built to reliably operate in harsh environments while providing unmatched protection. The relays transmit digital data, such as SCADA information, back to the control house via fiber-optic cables.

Article by:
Schweitzer Engineering Laboratories