Hot Topics
Plant Ex-Stock
Fault Reports
What's On
About Us


Buchholz Relays

A Buchholz relay is a gas and oil operated device installed in the pipework between the top of the transformer main tank and the conservator.  A second relay is sometimes used for the tapchanger selector chamber.  The function of the relay is to detect an abnormal condition within the tank and send an alarm or trip signal.  Under normal conditions the relay is completely full of oil.  Operation occurs when floats are displaced by an accumulation of gas, or a flap is moved by a surge of oil.  Almost all large oil-filled transformers are equipped with a Buchholz relay, first developed by Max Buchholz in 1921.

General Arrangement

Front View

Rear View  (Cover Removed)

A - Gas Collection Chamber

B - Upper Float
C - Lower Float
D - Oil Surge Detector

Conditions Detected
A Buchholz relay will detect:

bulletGas produced within the transformer
bulletAn oil surge from the tank to the conservator
bulletA complete loss of oil from the conservator (very low oil level)

Fault conditions within a transformer produce gases such as carbon monoxide, hydrogen and a range of hydrocarbons (Tutorial T3).  A small fault produces a small volume of gas that is deliberately trapped in the gas collection chamber (A) built into the relay.  Typically, as the oil is displaced a float (B) falls and a switch operates - normally to send an alarm.  A large fault produces a large volume of gas which drives a surge of oil towards the conservator.  This surge moves a flap (D) in the relay to operate a switch and send a trip signal.  A severe reduction in the oil level will also result in a float falling.  Where two floats are available these are normally arranged in two stages, alarm (B) followed by trip (C).

Gas and Oil Flows
Buchholz relays are equipped with a number of gas and oil inputs and outputs, including test and sampling facilities

Gas sampling - a graduated sight glass provides an indication of the volume of gas that has accumulated, typically 100-400cm3.  After an alarm or trip signal has been received this must be collected and analysed before the transformer is returned to service.  Gas collection can be done at the relay, or at ground level if suitable arrangements exist.  Clearly the latter is a safer and more convenient option.

Functional Tests - a test petcock enables dry air to be admitted into the relay to check correct operation.  A trickle of air is equivalent to a gradual accumulation of gas.  A blast simulates an oil surge.  These tests are sometimes referred to as 'blowing the Buchholz'.  On completion it is important that the relay is bled to remove the air that has been introduced.

Draining - a valve in the bottom of the relay enables an oil sample to be taken or the relay to be drained.  As with gas sampling, this facility can be brought down to ground level for enhanced operator safety and convenience.

A range of accessories and services are available to assist with the safe and correct operation of Buchholz relays including:

Watch culture has a long history, slowly, watches for people, especially for men, with the significance of beyond the watch itself.From the point of view of clothing, watches can play a role in the relatively monotonous men's clothing. The watch rolex replica cost is generally more expensive, so watch slowly become a relatively luxurious goods, so a watch only has a considerable value of man, for he is the identity status symbol. However, the value of the watch fake rolex watches itself is expensive, is only a symbol of the material (of course, the material is a prerequisite, very important), behind the watch, there is a deeper cultural meaning. For a man, having a high quality watch, is a symbol of their own responsibility to shoulder and remind you to have a happy family, reminds you of rolex replica the one you love also love your wife, that you should be focus on their careers, remind you should have a big heart, special significance remind you of the time of treasure watches for men, in the limited time inside, make you endless happiness, remind you of others as a symbol of responsibility.
bulletGround level oil and gas sampling kits
bulletGas sampling devices - automatic
bulletGas sampling devices - manual
bulletOn-site gas testers - simple air/fault gas analysis
bulletOn-site gas testers - complex fault gas composition
bulletRelay test kits


For further information visit our Catalogue of products and services or contact us


Tutorial Index