# Dedicated transformer-protection CT core interface

Canonical URL: https://eloragrid.ai/symbols/dedicated-transformer-protection-ct-core-interface
Publisher: Elora Grid
Updated: 2026-11-03
Lookup label: DTCCI
Drawing use: Schematic
Reference families: Manufacturer

Representation: Functional block
Installation focus: substations
Input: Transformer winding CT
Output: Differential relay input

Identifies the CT circuit assigned to a particular transformer protection winding input.

## In plain English

### What this block does

Identifies the CT circuit assigned to a particular transformer protection winding input.

### A simple example

In a substation protection panel, separate CT cores can supply metering and protection circuits with different duties. A test boundary must preserve the secondary arrangement required by the selected CT and test device. For this reference, the drawing identifies “Transformer winding CT” at the input and “Differential relay input” at the output. Winding identity and polarity must remain explicit.

### What the drawings help you do

Start at the named input: Transformer winding CT. Identify its source device or document and the state represented on the drawing. Follow the named output: Differential relay input. Cross-reference its destination and separate the command from confirmation that the equipment responded.

### Terms

- Input: Transformer winding CT
- Output: Differential relay input
- Application reference: An explanation of a named drawing function or circuit relationship; the project documents define the equipment and its connections.

Concept diagram: Transformer winding CT → DTCCI → Differential relay input
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

Identifies the CT circuit assigned to a particular transformer protection winding input. A current-transformer secondary arrangement carries a measuring current from a defined primary location to metering or protection inputs. Core identity, polarity and the connected circuit determine the measurement's meaning.
In a substation protection panel, separate CT cores can supply metering and protection circuits with different duties. A test boundary must preserve the secondary arrangement required by the selected CT and test device. For this reference, the drawing identifies “Transformer winding CT” at the input and “Differential relay input” at the output. Winding identity and polarity must remain explicit.
Trace every secondary connection and the assigned earthing point against the actual connection diagram. These illustrations explain circuit roles and never prescribe a live CT switching or disconnection procedure. 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: Transformer winding CT. Identify its source device or document and the state represented on the drawing.
- Follow the named output: Differential relay input. Cross-reference its destination and separate the command from confirmation that the equipment responded.
- Winding identity and polarity must remain explicit.
- Trace every secondary connection and the assigned earthing point against the actual connection diagram. These illustrations explain circuit roles and never prescribe a live CT switching or disconnection procedure.

## Information to show or reference

- Label the source and connection reference for transformer winding ct.
- Identify the destination and defined state of differential relay input.
- Record the equipment or control-document revision supporting this functional block.
- Check this application limit in the project design: Winding identity and polarity must remain explicit.

## Important distinction

Winding identity and polarity must remain explicit. 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: Transformer winding CT
- Output / connection: Differential relay input
- Lookup label: DTCCI 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 current-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.