# Control-transformer secondary distribution interface

Canonical URL: https://eloragrid.ai/symbols/control-transformer-secondary-distribution-interface
Publisher: Elora Grid
Updated: 2026-11-03
Lookup label: CSDI
Drawing use: Schematic
Reference families: Manufacturer

Representation: Functional block
Installation focus: switchgear
Input: Transformer secondary
Output: AC control distribution

Identifies how the selected transformer secondary feeds the documented control branches.

## In plain English

### What this block does

Identifies how the selected transformer secondary feeds the documented control branches.

### A simple example

In a switchgear lineup, separate protected branches may feed trip coils, closing coils and protection electronics. Their alarm contacts help the station controller identify which operating capability is unavailable. For this reference, the drawing identifies “Transformer secondary” at the input and “AC control distribution” at the output. Secondary earthing must follow the actual design.

### What the drawings help you do

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

### Terms

- Input: Transformer secondary
- Output: AC control distribution
- Application reference: An explanation of a named drawing function or circuit relationship; the project documents define the equipment and its connections.

Concept diagram: Transformer secondary → CSDI → AC control distribution
A reading guide. The entry's original illustration and input/output facts describe this application.

- [SEL-RPM redundant power module](https://selinc.com/products/RPM/)


## What it represents

Identifies how the selected transformer secondary feeds the documented control branches. Control power supplies the command, protection and indication equipment associated with a switchgear assembly. The drawing must distinguish the source, each distribution branch and the functions lost if that branch fails.
In a switchgear lineup, separate protected branches may feed trip coils, closing coils and protection electronics. Their alarm contacts help the station controller identify which operating capability is unavailable. For this reference, the drawing identifies “Transformer secondary” at the input and “AC control distribution” at the output. Secondary earthing must follow the actual design.
Follow the actual positive, negative or neutral returns and the protective device on each branch. A healthy voltage indication does not establish that every downstream path can deliver its required operating current. 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 secondary. Identify its source device or document and the state represented on the drawing.
- Follow the named output: AC control distribution. Cross-reference its destination and separate the command from confirmation that the equipment responded.
- Secondary earthing must follow the actual design.
- Follow the actual positive, negative or neutral returns and the protective device on each branch. A healthy voltage indication does not establish that every downstream path can deliver its required operating current.

## Information to show or reference

- Label the source and connection reference for transformer secondary.
- Identify the destination and defined state of ac control distribution.
- Record the equipment or control-document revision supporting this functional block.
- Check this application limit in the project design: Secondary earthing must follow the actual design.

## Important distinction

Secondary earthing must follow the actual design. 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: Switchgear
- Input / boundary: Transformer secondary
- Output / connection: AC control distribution
- Lookup label: CSDI is a library lookup label, not a standard device designation.

## Public references

- [SEL-RPM redundant power module](https://selinc.com/products/RPM/) — SEL. Public technical context for switchgear control-power supervision. Independent AC and DC sources for station auxiliary power. 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.