Full analysis of the working principle of gas relay: the “first line of defense” for internal faults in oil immersed transformers

1.Industry background and application hotspots

In oil immersed transformer protection systems,gas relay (Buchholz relays) are widely recognized as the most sensitive and earliest activated internal fault protection devices.
With the continuous promotion of new energy, energy storage, and power grid upgrades, the safety and reliability of medium and high voltage oil immersed transformers are increasingly valued, and gas relays are at the core of this trend. In overseas markets (Europe, Middle East, Africa, South America), gas relays are often listed as mandatory components and explicitly written into IEC, IEEE, and technical specifications of national power companies.

2.What is a gas relay

Gas relay is a mechanical protective relay specifically used to detect internal abnormalities in oil immersed transformers, usually installed on the connecting pipeline between the transformer body oil tank and the oil storage tank (oil pillow).
Its core functions include:

Detecting gas accumulation caused by internal faults
Detect abnormal oil flow (severe internal malfunction)

3.Operating principle of gas relay (analysis of core technology)

3.1 Minor Internal Malfunction – Gas Accumulation Principle

When the following problems occur inside the transformer:

• Partial discharge of winding
• Iron core overheating
• Insulation aging
• Micro arc discharge in oil

Transformer oil will decompose and produce gases (such as H ₂, CH ₄, C ₂ H ₂, etc.). Gas rises along the oil circuit and accumulates in the relay chamber, causing a decrease in oil level and triggering:

Upper float action

Output alarm signal (Alarm)

This stage usually does not trip, providing an early intervention window for operation and maintenance personnel.

3.2 Serious Internal Malfunction – Oil Flow Impact Principle

When the following faults occur:

Interturn short circuit of winding
phase-to-phase short circuit
Iron core grounding
Severe insulation breakdown

Intense oil flow will occur inside the transformer, impacting the baffle or oil flow blades inside the relay, thereby triggering:

Lower float or oil flow baffle action
Output trip signal (Trip)
Immediately cut off the power of the transformer

4.Typical structural composition of gas relay

Standard gas relays typically include:

• Sealed shell (cast aluminum or stainless steel)
• Upper float (alarm contact)
• Lower float or oil flow baffle (trip contact)
• micro switch
• bleed valve
• Test button
• terminal block

The high-end models also support gas sampling interfaces for DGA (dissolved gas analysis).

5.Technical comparison between gas relay and other protection methods

Gas relay is the only device that can issue an alarm in the early stages of a fault.

6.Key technical points for selection and installation

Must be installed horizontally
The installation position should be close to the transformer body
The slope of the pipeline is generally maintained at 1-3% (towards the oil storage tank)
The relay must be completely filled with oil and free of bubbles
Regularly conduct functional testing and deflation checks

7.International Market Trends and Export Focus

In export projects, customers usually focus on:

• Compliant with IEC 60076/IEC 60255 standards
• Protection level (IP55/IP65)
• contact rating
• Does it support third-party testing reports

With the continuous improvement of power grid safety levels, gas relays have been upgraded from “optional configurations” to “mandatory safety components”. For oil immersed transformers, they are not only accessories, but also key protection nodes that determine whether accidents will escalate.

Luoyang Datang Energy Technology Co., Ltd. is a high-tech enterprise integrating R&D, manufacturing and supply of power equipment such as transformers, new energy components, distribution cabinets and inverters. With technological innovation as the core, we focus on creating high-reliability and high-performance power solutions to serve global customers. With a strict quality control system and international standard certification, we continue to output excellent products and enable customers to build safe and stable power systems.