---
title: "Transformer conservator, explosion vent and breather"
subject: "Power Plant Equipment"
chapter: 4
key: "semester_7/power_plant_equipment:transformer-conservator-vent-breather"
source: https://www.bctengineer.com/q/semester_7/power_plant_equipment/transformer-conservator-vent-breather
site: BCT Engineering
---

# Transformer conservator, explosion vent and breather

Power Plant Equipment · Chapter 4: Substation Equipments

- Asked in: 2081 Baisakh, 4 marks
- Video: [Transformer Full Details | Transformer Oil | Breather | Explosion Vent | Conservator Tank](https://www.youtube.com/watch?v=4zWVxQtDNr4) — Niket Shah Plus
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_7/power_plant_equipment/transformer-conservator-vent-breather
- Whole chapter: https://www.bctengineer.com/md/semester_7/power_plant_equipment/chapter-4

## Question

Explain the function following parts of a power transformer. i) Conservator tank ii) Explosion vent iii) Breather

## Short answer

Conservator tank accommodates oil expansion/contraction, keeps main tank full and minimizes oil-air contact. Explosion vent releases sudden pressure during internal faults to prevent tank rupture. Breather contains silica gel that dries air entering conservator, and an oil cup traps dust, maintaining oil dielectric strength.

## Answer

#### i) Conservator tank

A small cylindrical tank mounted above the main tank and connected to it by a pipe (with the Buchholz relay in between).

- Oil expands and contracts with load and temperature; the conservator takes up this change, so the **main tank always stays completely full** of oil.
- Only the small oil surface in the conservator touches air, which reduces oxidation and moisture absorption.
- Its oil level indicator shows the oil level.

#### ii) Explosion vent

A bent pipe on top of the main tank, closed by a thin diaphragm (bakelite/glass), or a modern spring-loaded **pressure relief valve**.

- During a severe internal fault, arcing decomposes oil into gas and pressure rises suddenly.
- The diaphragm bursts and releases the pressure, preventing the tank from bursting or exploding.

#### iii) Breather

A small container filled with **silica gel**, with an oil seal cup, fitted on the conservator air pipe.

- When the oil contracts, air is drawn into the conservator through the breather.
- Silica gel absorbs moisture (blue colour turns pink when saturated); the oil cup traps dust.
- This keeps the oil dry and maintains its dielectric strength.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. What is the main purpose of the conservator?
   A. Take up oil expansion/contraction so the main tank stays full and only a small surface meets air
   B. Release pressure in a fault
   C. Dry the air
   D. Cool the winding
   Answer: A. It lets oil volume change without leaving air in the main tank. (Key point: Conservator)

2. What does the explosion vent do in a severe internal fault?
   A. It removes moisture from the oil
   B. The diaphragm bursts and releases pressure, preventing the tank from bursting
   C. It signals the Buchholz relay
   D. It tops up the oil
   Answer: B. Arcing decomposes oil into gas; the vent relieves the sudden pressure. (Key point: Explosion vent)

3. What does the silica gel in the breather do, and what does pink colour mean?
   A. It absorbs oil; pink means it is fresh
   B. It cools the air; pink means overheating
   C. It absorbs moisture from incoming air; pink means it is saturated
   D. It filters dust only; pink means clean
   Answer: C. Blue gel turns pink when saturated and must be replaced to keep the oil dry. (Key point: Breather)

## Related in Power Plant Equipment

- [Parts of a power transformer](https://www.bctengineer.com/question.md?key=semester_7%2Fpower_plant_equipment%3Apower-transformer-parts) — Power Plant Equipment, chapter 4, asked 2×
- [Function of surge tank in hydro plant](https://www.bctengineer.com/question.md?key=semester_7%2Fpower_plant_equipment%3Asurge-tank-function) — Power Plant Equipment, chapter 1
- [Excitation system with stabilizing transformer: transfer function](https://www.bctengineer.com/question.md?key=semester_7%2Fpower_plant_equipment%3Aexcitation-stabilizing-transformer-model) — Power Plant Equipment, chapter 3, asked 13×
- [Function of reactor in power system](https://www.bctengineer.com/question.md?key=semester_7%2Fpower_plant_equipment%3Areactor-function) — Power Plant Equipment, chapter 4, asked 3×

## Related in other subjects

- [Valid lossless function; Foster II and Cauer II](https://www.bctengineer.com/question.md?key=semester_5%2Ffilter_design%3Alossless-three-functions-foster-cauer-ii) — Filter Design, chapter 4, asked 2×
- [Forebay function and surge tank types](https://www.bctengineer.com/question.md?key=semester_6%2Fhydro_power%3Aforebay-function-surge-tank-types) — Hydro Power, chapter 5
- [Design: 500 kVA 66/11 kV power transformer](https://www.bctengineer.com/question.md?key=semester_5%2Felectric_machine_design%3Adesign-500kva-66-11kv) — Electric Machine Design, chapter 3, asked 6×
- [Design: 4000 kVA 66/11 kV power transformer](https://www.bctengineer.com/question.md?key=semester_5%2Felectric_machine_design%3Adesign-4000kva-66-11kv) — Electric Machine Design, chapter 3, asked 5×