# VT secondary fuse supervision interface

Canonical URL: https://eloragrid.ai/symbols/vt-secondary-fuse-supervision-interface
Publisher: Elora Grid
Updated: 2026-11-03
Lookup label: VSFSI
Drawing use: Schematic
Reference families: Manufacturer

Representation: Functional block
Installation focus: substations
Input: Voltage fuse supervision
Output: VT-circuit health indication

Reports the assigned voltage-circuit fuse condition to the protection or alarm system.

## In plain English

### What this block does

Reports the assigned voltage-circuit fuse condition to the protection or alarm system.

### A simple example

In a substation bay, one voltage circuit can feed protection while a separately identified winding supplies metering. A voltage-selection circuit must make clear which bus or line measurement is being used. For this reference, the drawing identifies “Voltage fuse supervision” at the input and “VT-circuit health indication” at the output. Fuse loss must be distinguished from primary undervoltage.

### What the drawings help you do

Start at the named input: Voltage fuse supervision. Identify its source device or document and the state represented on the drawing. Follow the named output: VT-circuit health indication. Cross-reference its destination and separate the command from confirmation that the equipment responded.

### Terms

- Input: Voltage fuse supervision
- Output: VT-circuit health indication
- Application reference: An explanation of a named drawing function or circuit relationship; the project documents define the equipment and its connections.

Concept diagram: Voltage fuse supervision → VSFSI → VT-circuit health indication
A reading guide. The entry's original illustration and input/output facts describe this application.

- [Indoor current and voltage transformers](https://www.abb.com/gb/en/areas/electrification/medium-voltage/grid-components/core-components/indoor-instrument-transformers)


## What it represents

Reports the assigned voltage-circuit fuse condition to the protection or alarm system. A voltage-transformer secondary arrangement connects a defined primary voltage measurement to protection, metering or control inputs. Winding identity, fuse protection and the voltage reference must remain visible across the drawing.
In a substation bay, one voltage circuit can feed protection while a separately identified winding supplies metering. A voltage-selection circuit must make clear which bus or line measurement is being used. For this reference, the drawing identifies “Voltage fuse supervision” at the input and “VT-circuit health indication” at the output. Fuse loss must be distinguished from primary undervoltage.
Show the primary measurement point, secondary connection, protective devices and relay reference. A missing measurement can resemble a real system disturbance unless the voltage-circuit health is supervised appropriately. 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: Voltage fuse supervision. Identify its source device or document and the state represented on the drawing.
- Follow the named output: VT-circuit health indication. Cross-reference its destination and separate the command from confirmation that the equipment responded.
- Fuse loss must be distinguished from primary undervoltage.
- Show the primary measurement point, secondary connection, protective devices and relay reference. A missing measurement can resemble a real system disturbance unless the voltage-circuit health is supervised appropriately.

## Information to show or reference

- Label the source and connection reference for voltage fuse supervision.
- Identify the destination and defined state of vt-circuit health indication.
- Record the equipment or control-document revision supporting this functional block.
- Check this application limit in the project design: Fuse loss must be distinguished from primary undervoltage.

## Important distinction

Fuse loss must be distinguished from primary undervoltage. 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: Voltage fuse supervision
- Output / connection: VT-circuit health indication
- Lookup label: VSFSI is a library lookup label, not a standard device designation.

## Public references

- [Indoor current and voltage transformers](https://www.abb.com/gb/en/areas/electrification/medium-voltage/grid-components/core-components/indoor-instrument-transformers) — ABB. Public technical context for voltage-transformer secondary arrangements. Current and voltage measurement transformers and their secondary interfaces. 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.