Date Code 20200326
SEL Application Guide 2020-04
Use SEL-300 and SEL-400 Series Relays to
Set Up POTT and DCB Schemes
Jared Candelaria, Hardesh Khatri, and Avinash Maddela
I
NTRODUCTION
The first SEL-300 series relay, the SEL-321-1 Phase and Ground Distance Relay, was introduced
in 1993 and has been used to provide pilot protection on transmission lines ever since. Now, more
than 20 years later, SEL-300 series relays are still widely used. However, as utilities upgrade their
systems, SEL-300 series relays are being replaced by relays with additional functionality, such as
SEL-400 series relays. It is not uncommon for these upgrades to occur on a tie line, where each
end of the line is owned by a different utility. Occasionally, one utility will upgrade its terminal to
match a new standard relaying package, while the other utility will choose to keep their existing
protection. Dissimilar relays on either end of the line do not maintain conventional pilot protec-
tion; however, it is possible to maintain pilot protection. SEL does not recommend connecting dis-
similar relays for pilot protection.
This application guide details how to program SEL-300 and SEL-400 series relays to maintain
pilot protection coordination by using either a permissive overreaching transfer trip (POTT) or a
directional comparison blocking (DCB) scheme. The SEL-400 series relay covered in this applica-
tion guide is the SEL-421-5 Protection, Automation, and Control System. The SEL-300 series
relays covered in this application guide include the SEL-311C-1 Transmission Protection System,
the SEL-311L Line Current Differential Protection and Automation System, and the SEL-321-1
Phase and Ground Distance Relay.
For the examples in this guide, we use the SEL-421-5 to represent all the SEL-400 series relays.
For the SEL-300 series relays, we consider two cases, one with the SEL-311C-1 representing all
variations of the SEL-311 relays and the other with the SEL-321-1. The reason for considering the
SEL-321-1 relay separately than the other SEL-300 series relays is that the internal logic of the
SEL-321-1 is different compared to the other SEL-300 series relays. This guide shows two pilot
protection scheme examples, one between the SEL-421-5 and SEL-311C-1 relays, and the other
between the SEL-421-5 and SEL-321-1 relays.
We assume the reader of this guide has a basic understanding of pilot protection, so this application
guide does not go into detail on the schemes. For an in-depth discussion of POTT and DCB
schemes, refer to [1] and [2].
NOTE:
POTT and DCB schemes are not available on the SEL-311A Phase and Ground Distance Relay and the
SEL-311B Distance Relay With Recloser.
S
AMPLE
S
YSTEM
shows a typical two-terminal system. Relay 1 is an SEL-421-5 and Relay 2 can be an
SEL-311C-1 or an SEL-321-1. The two relays communicate through a fiber-optic connection to
implement a POTT or DCB scheme.
Application Guide
Volume I
AG2020-04
