# Bus protection isolator-replica interface

Canonical URL: https://eloragrid.ai/symbols/bus-protection-isolator-replica-interface
Publisher: Elora Grid
Updated: 2026-11-03
Lookup label: BPII
Drawing use: Schematic
Reference families: Manufacturer

Representation: Functional block
Installation focus: substations
Input: Disconnector replica states
Output: Current-to-zone assignment

Relates measured disconnector positions to the current assignment used by the bus protection.

## In plain English

### What this block does

Relates measured disconnector positions to the current assignment used by the bus protection.

### A simple example

In a substation feeder bay, local current and voltage measurements may combine with a remote-end signal before the protection issues the assigned trip request. Backup actions use their own defined initiations and supervision. For this reference, the drawing identifies “Disconnector replica states” at the input and “Current-to-zone assignment” at the output. Invalid position information requires defined handling.

### What the drawings help you do

Start at the named input: Disconnector replica states. Identify its source device or document and the state represented on the drawing. Follow the named output: Current-to-zone assignment. Cross-reference its destination and separate the command from confirmation that the equipment responded.

### Terms

- Input: Disconnector replica states
- Output: Current-to-zone assignment
- Application reference: An explanation of a named drawing function or circuit relationship; the project documents define the equipment and its connections.

Concept diagram: Disconnector replica states → BPII → Current-to-zone assignment
A reading guide. The entry's original illustration and input/output facts describe this application.

- [SEL-411L line differential protection overview](https://selinc.com/products/411l/)


## What it represents

Relates measured disconnector positions to the current assignment used by the bus protection. A protection scheme combines measurements, decision elements and communication or trip outputs to protect a defined part of the network. A function number names a job; the scheme interface shows how that job connects to other equipment.
In a substation feeder bay, local current and voltage measurements may combine with a remote-end signal before the protection issues the assigned trip request. Backup actions use their own defined initiations and supervision. For this reference, the drawing identifies “Disconnector replica states” at the input and “Current-to-zone assignment” at the output. Invalid position information requires defined handling.
Keep each protected zone, initiating quantity, blocking signal and trip destination distinct. Settings, communication performance and coordination require the approved protection study and selected relay documentation. The functional block is an independent explanation of this named application. Equipment-specific ratings, terminal connections and operating conditions must be established in the project documentation.

## How to read it

- Start at the named input: Disconnector replica states. Identify its source device or document and the state represented on the drawing.
- Follow the named output: Current-to-zone assignment. Cross-reference its destination and separate the command from confirmation that the equipment responded.
- Invalid position information requires defined handling.
- Keep each protected zone, initiating quantity, blocking signal and trip destination distinct. Settings, communication performance and coordination require the approved protection study and selected relay documentation.

## Information to show or reference

- Label the source and connection reference for disconnector replica states.
- Identify the destination and defined state of current-to-zone assignment.
- Record the equipment or control-document revision supporting this functional block.
- Check this application limit in the project design: Invalid position information requires defined handling.

## Important distinction

Invalid position information requires defined handling. This reference describes the named application; it does not establish a new IEC graphical symbol, an ANSI device-function number or an exact manufacturer connection diagram.

## Facts

- Representation: Functional block
- Installation focus: Substations
- Input / boundary: Disconnector replica states
- Output / connection: Current-to-zone assignment
- Lookup label: BPII is a library lookup label, not a standard device designation.

## Public references

- [SEL-411L line differential protection overview](https://selinc.com/products/411l/) — Schweitzer Engineering Laboratories. Public technical context for substation protection scheme interfaces. Line protection, breaker failure, communications and protection coordination. The application text and educational graphic are independently authored; the publisher does not certify this representation.

## Graphic scope

Independent original educational concept illustration by Elora Grid. Not a certified standards graphic or manufacturer footprint. Unitless; not to scale. Original artwork licence: https://creativecommons.org/licenses/by/4.0/. Publisher material is linked only.