Buchholz Protection for Transformers

The Buchholz protection, protects the transformer again every abnormal phenomenon produce inside the tank. It bases in the fact that the irregularities in the transformer functioning cause heating in the winding and in consequence the production of gases from the oil, the quantity and speed of its production increases at the time the damage spreads. 

The gases that are produce inside the tank go up through the tube in which the relay is installed and they get trap in it.

Disposition of the relay is shown in the scheme 2. The relay box is filed with oil and it contains the floats a1 and a2. When ever little gas bubbles are produce, this elevate from the transformers tank to the oil tank and get trap in the relay, in it the level of oil drops progressively. The top float inclines and when the amount of gases is sufficient, it causes contacts c1 to close and activated the alarm circuit.

In the cases that no measure is taken given the alarm or given the failure the amount of gases is high, the second float drops closing a2 causing the main transformer circuit breaker to open. If a electrical arc is produce inside the transformer, a violent flow of gases will go to the oil tank and c2 to will close suddenly preventing important damage to the transformer.        

Over the top of the relay is a faucet b1, that allows gasses to scape. another faucet b2, allows to prove that the floats and contacts are in good shape.

The relay detects shorcircuits between windings, core and core - windings, phase interruption, excessive overload, oil leak etc. The great advantage of this relay is its high sensibility to warn deterioration or incipient faults, when the most sensibly protection systems wont be that effective.

The characteristic of the gases trp in the Buchholz relay can give an idea of the type of defect and where it produced. The most simple verification is the combustibility test of the gas.  In case of electric arc the oil decomposes producing acetylene that is flammable.

The color of the gases can give an idea of the nature of the defect.

• White: Paper destruction.
• Yellow: Wood destruction.
• Black or Grey: Oil decomposition.
• Red: Winding isolation damage.  

      A peephole allows to see the gases, the color have to be seen minutes apart from the moment of the event.