# VT measurement ratio scaling block

Canonical URL: https://eloragrid.ai/symbols/vt-measurement-ratio-scaling-block
Publisher: Elora Grid
Updated: 2026-11-03
Lookup label: VMRSB
Drawing use: Schematic
Reference families: Manufacturer

Representation: Functional block
Installation focus: substations
Input: Measured voltage and ratio
Output: Primary-basis voltage quantity

Scales the secondary measurement to the assigned primary-voltage basis.

## In plain English

### What this block does

Scales the secondary measurement to the assigned primary-voltage basis.

### 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 “Measured voltage and ratio” at the input and “Primary-basis voltage quantity” at the output. Scaling does not correct a wiring error.

### What the drawings help you do

Start at the named input: Measured voltage and ratio. Identify its source device or document and the state represented on the drawing. Follow the named output: Primary-basis voltage quantity. Cross-reference its destination and separate the command from confirmation that the equipment responded.

### Terms

- Input: Measured voltage and ratio
- Output: Primary-basis voltage quantity
- Application reference: An explanation of a named drawing function or circuit relationship; the project documents define the equipment and its connections.

Concept diagram: Measured voltage and ratio → VMRSB → Primary-basis voltage quantity
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

Scales the secondary measurement to the assigned primary-voltage basis. 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 “Measured voltage and ratio” at the input and “Primary-basis voltage quantity” at the output. Scaling does not correct a wiring error.
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: Measured voltage and ratio. Identify its source device or document and the state represented on the drawing.
- Follow the named output: Primary-basis voltage quantity. Cross-reference its destination and separate the command from confirmation that the equipment responded.
- Scaling does not correct a wiring error.
- 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 measured voltage and ratio.
- Identify the destination and defined state of primary-basis voltage quantity.
- Record the equipment or control-document revision supporting this functional block.
- Check this application limit in the project design: Scaling does not correct a wiring error.

## Important distinction

Scaling does not correct a wiring error. 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: Measured voltage and ratio
- Output / connection: Primary-basis voltage quantity
- Lookup label: VMRSB 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.