# Winding temperature indicator

Canonical URL: https://eloragrid.ai/symbols/winding-temperature-indicator
Publisher: Elora Grid
Updated: 2026-10-28
Lookup label: WTI
Drawing use: Schematic, SLD
Reference families: IEC, Manufacturer

Transformer indicator that adds a CT-heated thermal image to top-oil temperature to estimate winding hot-spot temperature.

## In plain English

### What does Winding temperature indicator mean?

A winding temperature indicator estimates transformer winding hot-spot temperature, which cannot easily be measured directly. A sensor in the top-oil pocket is heated by a small element fed from a CT on the load current, so the reading rises with both oil temperature and load, and its contacts control fans and give alarm and trip.

### A simple example

The schematic should show the CT feeding the heater, the calibration resistor and each contact stage. The symbol does not show the thermal gradient setting, which must be adjusted to the transformer heat-run data for the reading to be meaningful.

### What the drawings help you do

Trace the CT circuit feeding the thermal image heater. Identify contact stages for cooling, alarm and trip. A WTI estimates winding hot-spot with a thermal image; an oil temperature indicator reads oil temperature only.

### This particular reference

Transformer indicator that adds a CT-heated thermal image to top-oil temperature to estimate winding hot-spot temperature. A WTI estimates winding hot-spot with a thermal image; an oil temperature indicator reads oil temperature only.

### Terms

- Winding: A coil of conductor inside an electrical machine or transformer.
- Normally open / normally closed: The contact state in the normal condition defined for the drawing.
- Signal: Electrical information passed between devices, rather than necessarily the main power supply.

Concept diagram: Identify the device and form → Read the connections and state → Check the equipment reference
A guide to reading this reference. The original symbol illustration and its drawing notes appear below; these boxes are not a wiring diagram.

- [ETR-4000 and ETR-5000 transformer protection function tables](https://www.eaton.com/us/en-us/catalog/electrical-circuit-protection/transformer-relays.html)
- [IEC graphical symbols for diagrams](https://tc3.iec.ch/tc-activity/graphical-symbols-for-diagrams/)


## What it represents

A winding temperature indicator estimates transformer winding hot-spot temperature, which cannot easily be measured directly. A sensor in the top-oil pocket is heated by a small element fed from a CT on the load current, so the reading rises with both oil temperature and load, and its contacts control fans and give alarm and trip.
The schematic should show the CT feeding the heater, the calibration resistor and each contact stage. The symbol does not show the thermal gradient setting, which must be adjusted to the transformer heat-run data for the reading to be meaningful.

## How to read it

- Trace the CT circuit feeding the thermal image heater.
- Identify contact stages for cooling, alarm and trip.

## Information to show or reference

- Show heater CT
- List contact stages
- Reference gradient setting

## Important distinction

A WTI estimates winding hot-spot with a thermal image; an oil temperature indicator reads oil temperature only.

## Facts

- Inputs: Top-oil temperature plus CT-fed heater
- Outputs: Cooling, alarm and trip contacts
- Preview: Functional illustration of the device role; not a product footprint or certified standard graphic

## Public references

- [ETR-4000 and ETR-5000 transformer protection function tables](https://www.eaton.com/us/en-us/catalog/electrical-circuit-protection/transformer-relays.html) — Eaton. Public transformer protection context including thermal functions.
- [IEC graphical symbols for diagrams](https://tc3.iec.ch/tc-activity/graphical-symbols-for-diagrams/) — IEC. IEC context for graphical symbols used in diagrams; no IEC graphic is reproduced.

## 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.