TX
Power transformer
Equipment transferring electrical power between winding circuits.
SLD / Schematic
Symbols · BR
Buchholz relay
Gas-and-oil actuated relay in the pipe to the conservator, giving alarm on gas build-up and trip on oil surge.
In plain English
What does Buchholz relay mean?
A Buchholz relay is fitted in the pipe between an oil-filled transformer tank and its conservator. Slow gas accumulation from minor internal faults operates an alarm float, while a rapid surge of oil from a serious internal fault operates a trip element, so the schematic shows two separate contacts.
A simple example
On single-line diagrams it may appear only as a label on the transformer, while the control schematic shows its alarm and trip contacts wired to alarm indication and the transformer trip relay. The symbol does not show the gas sampling procedure or the test arrangement used during maintenance.
What the drawings help you do
Identify separate alarm and trip contacts. Follow the trip contact to the transformer lockout or trip relay. A Buchholz relay detects gas and oil movement; a sudden pressure relay responds to rapid tank pressure rise.
This particular reference
Gas-and-oil actuated relay in the pipe to the conservator, giving alarm on gas build-up and trip on oil surge. A Buchholz relay detects gas and oil movement; a sudden pressure relay responds to rapid tank pressure rise.
- 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.
- Coil
- A wound conductor that can produce a magnetic field when energised.
Read the source: ETR-4000 and ETR-5000 transformer protection function tables · IEC graphical symbols for diagrams
Schematic / SLD · BR
What it represents
A Buchholz relay is fitted in the pipe between an oil-filled transformer tank and its conservator. Slow gas accumulation from minor internal faults operates an alarm float, while a rapid surge of oil from a serious internal fault operates a trip element, so the schematic shows two separate contacts.
On single-line diagrams it may appear only as a label on the transformer, while the control schematic shows its alarm and trip contacts wired to annunciation and the transformer trip relay. The symbol does not show the gas sampling procedure or the test arrangement used during maintenance.
How to read it
- Identify separate alarm and trip contacts.
- Follow the trip contact to the transformer lockout or trip relay.
Information to show or reference
- Show alarm contact
- Show trip contact
- Reference transformer trip relay
A distinction that matters
A Buchholz relay detects gas and oil movement; a sudden pressure relay responds to rapid tank pressure rise.
Sources you can follow
These public references support the explanation and provide further detail. Their graphics and downloadable files remain with their publishers.
ETR-4000 and ETR-5000 transformer protection function tables
Public transformer protection context in which mechanical transformer protections are wired.
IEC graphical symbols for diagrams
IEC context for graphical symbols used in diagrams; no IEC graphic is reproduced.
About this graphic
This illustration was authored independently by Elora Grid to explain the concept. It is not reproduced from a customer drawing, an official standard graphic or a manufacturer CAD file. Its correspondence to an exact IEC or IEEE symbol identifier has not been certified.
SVG and DXF downloads contain this original artwork. DXF uses unscaled drawing units; a GA envelope supplies no product dimensions, clearances or fabrication information. Original artwork is available under CC BY 4.0. Third-party references retain their own terms.
Explore related references
Put the reference into a drawing workflow.
Elora Grid helps electrical teams work with drawings, specifications and equipment information. Explore the drafting workflow or join the early-access waitlist.