Power Transformer Bucholz operation 1

[govender1]

We have recently repaired(rewound)a 1 MVA,22kV to 6.6Kv,3 phase power transformer. After energising it, it came out on bucholz three times within a space of a month.A DGA test proved that everything is normal.

What could be wrong or what am I missing?

Govender1

 

[vijaythai]

A bucholz relay operation,when DGA shows normal results may be due to the following causes.
1)Release of air trapped inside the transformer.
2)Sudden drop in atmospheric tmperature or sudden drop in
tmperture with a choked breather.
3) Vibration of b'relay.
After operation,if thereis gas found in b'relay points to a faulty circuit.

 

[jghrist]

An Investigation of Sudden Pressure Relay Failures, presented at the 57th Annual Georgia Tech Protective Relay Conference, May 1998 by Hong-Ming Shuh and Scott L. Short of the Tennessee Valley Authority investigated several false operations of sudden pressure relays. The relays were Qualitrol type 900. They found that the relays can be damaged if the isolation valve is closed for a long period of time and the relays are subject to temperature rise from any source such as exposure to the sun while the valve is closed. The isolation valve should only be closed temporarily when there is a requirement fot maintenance or test. It is advisable that the bleed valve on the relay be opened to prevent pressure buildup from the trapped oil in the sensing bellows area.

 

[jbartos]

Suggestion: There are different manufacturers of Buchholz relays. Some Buchholz relays are better than others.
Reference:
A. R. van C. Warrington "Protective Relays Their Theory and Practice," Volume I, Chapman & Hall Ltd., 1971,
Section: 10.3.1. Buchholz Relays on page 382 addresses subtleties of Buchholz relays. There might be pinhole leaks in the relay.