# VT secondary star-point identification

Canonical URL: https://eloragrid.ai/symbols/vt-secondary-star-point-identification
Publisher: Elora Grid
Updated: 2026-11-03
Lookup label: VSSI
Drawing use: Schematic
Reference families: Manufacturer

Representation: Functional block
Installation focus: substations
Input: Phase voltage windings
Output: Secondary neutral reference

Shows the common neutral of the documented phase-voltage secondary arrangement.

## In plain English

### What this block does

Shows the common neutral of the documented phase-voltage secondary arrangement.

### 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 “Phase voltage windings” at the input and “Secondary neutral reference” at the output. The neutral connection must not be assumed.

### What the drawings help you do

Start at the named input: Phase voltage windings. Identify its source device or document and the state represented on the drawing. Follow the named output: Secondary neutral reference. Cross-reference its destination and separate the command from confirmation that the equipment responded.

### Terms

- Input: Phase voltage windings
- Output: Secondary neutral reference
- Application reference: An explanation of a named drawing function or circuit relationship; the project documents define the equipment and its connections.

Concept diagram: Phase voltage windings → VSSI → Secondary neutral reference
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

Shows the common neutral of the documented phase-voltage secondary arrangement. 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 “Phase voltage windings” at the input and “Secondary neutral reference” at the output. The neutral connection must not be assumed.
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: Phase voltage windings. Identify its source device or document and the state represented on the drawing.
- Follow the named output: Secondary neutral reference. Cross-reference its destination and separate the command from confirmation that the equipment responded.
- The neutral connection must not be assumed.
- 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 phase voltage windings.
- Identify the destination and defined state of secondary neutral reference.
- Record the equipment or control-document revision supporting this functional block.
- Check this application limit in the project design: The neutral connection must not be assumed.

## Important distinction

The neutral connection must not be assumed. 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: Phase voltage windings
- Output / connection: Secondary neutral reference
- Lookup label: VSSI 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.