# Transformer main-tank oil-level alarm

Canonical URL: https://eloragrid.ai/symbols/transformer-main-tank-oil-level-alarm
Publisher: Elora Grid
Updated: 2026-11-03
Lookup label: TMOA
Drawing use: Schematic
Reference families: Manufacturer

Representation: Functional block
Installation focus: substations
Input: Main oil-level contact
Output: Main-tank level alarm

Reports the documented low or abnormal oil-level condition in the main tank system.

## In plain English

### What this block does

Reports the documented low or abnormal oil-level condition in the main tank system.

### A simple example

In a substation transformer bay, a protection panel receives winding-current measurements and equipment alarm contacts. An operator can then distinguish an electrical protection operation from a cooling-system or physical-condition alarm. For this reference, the drawing identifies “Main oil-level contact” at the input and “Main-tank level alarm” at the output. Oil level varies with operating conditions.

### What the drawings help you do

Start at the named input: Main oil-level contact. Identify its source device or document and the state represented on the drawing. Follow the named output: Main-tank level alarm. Cross-reference its destination and separate the command from confirmation that the equipment responded.

### Terms

- Input: Main oil-level contact
- Output: Main-tank level alarm
- Application reference: An explanation of a named drawing function or circuit relationship; the project documents define the equipment and its connections.

Concept diagram: Main oil-level contact → TMOA → Main-tank level alarm
A reading guide. The entry's original illustration and input/output facts describe this application.

- [SEL-487E transformer protection relay](https://selinc.com/products/487E/)


## What it represents

Reports the documented low or abnormal oil-level condition in the main tank system. Transformer monitoring interfaces connect physical sensors and protection calculations to the station's alarms and trip logic. Temperature, oil, gas, pressure and electrical measurements indicate different conditions and require separate interpretation.
In a substation transformer bay, a protection panel receives winding-current measurements and equipment alarm contacts. An operator can then distinguish an electrical protection operation from a cooling-system or physical-condition alarm. For this reference, the drawing identifies “Main oil-level contact” at the input and “Main-tank level alarm” at the output. Oil level varies with operating conditions.
Identify the sensor or calculation, its monitored zone and its assigned response. Alarm and trip thresholds, sensor fitting and protection settings belong to the selected transformer documentation and the approved protection design. 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: Main oil-level contact. Identify its source device or document and the state represented on the drawing.
- Follow the named output: Main-tank level alarm. Cross-reference its destination and separate the command from confirmation that the equipment responded.
- Oil level varies with operating conditions.
- Identify the sensor or calculation, its monitored zone and its assigned response. Alarm and trip thresholds, sensor fitting and protection settings belong to the selected transformer documentation and the approved protection design.

## Information to show or reference

- Label the source and connection reference for main oil-level contact.
- Identify the destination and defined state of main-tank level alarm.
- Record the equipment or control-document revision supporting this functional block.
- Check this application limit in the project design: Oil level varies with operating conditions.

## Important distinction

Oil level varies with operating conditions. 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: Main oil-level contact
- Output / connection: Main-tank level alarm
- Lookup label: TMOA is a library lookup label, not a standard device designation.

## Public references

- [SEL-487E transformer protection relay](https://selinc.com/products/487E/) — SEL. Public technical context for transformer protection and monitoring interfaces. Transformer protection, monitoring and measurement 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.