Bucholtz trip

[khadisa]

We have a 90MVA, 330/132/13.8KV Y/Y/D transformer.The transformer was used to replace an old one that got burnt while maintaining the old relays and wiring. It is grounded though an earthing transformer via the tertiary winding. Recently the transformer started tripping on bucholtz.Once the relay is reset the transformer can be closed without anything been done on the transformer. Sometimes it will trip while not loaded or even completely isolated. what could be the cause of this, please?

 

[ScottyUK]

Presumably the relay is being tripped by gas accumulating in the relay? A gassing fault evolving large volumes of gas in a short period of time is is indicative of a fairly serious problem in the transformer tank: analysis of the gas if you can collect it, or DGA on the oil if not, would give you some idea what type of fault it is in terms of temperature and perhaps material involved. This is the first step you must do. I am surprised you do not carry out DGA on a routine basis so you can trend the behaviour of the transformer, especially if it has just entered service. You will need to do an internal inspection to identify the location of the fault, but the DGA results should identify what kind of fault you are looking for.

When you say the transformer is tripping even when isolated, it is probable that gas bubbles evolved by the internal fault are slowly collecting in the relay and building up to the trip level.


----------------------------------

Your body may be a temple. Mine is an amusement park...

 

[ARC12]

Vibration? I have seen two instances of this.

One was a 75 MVA arc furnace transformer that tripped occasionally when a large overhead crane ( located in the same building ) rolled by.

The second was a large auto-transformer located near railroad tracks that tripped on several ocassions when a locomotive rolled by.

 

[bradh01]

The bucholtz relay can trip due to sudden oil flow between the transformer tank and conservator tank, or due to gas accumulation. Typically the gas can be purged (for analysis) to clear the relay. Check to make sure these trip contacts are in the correct state. We have seen these bucholtz relays go bad, but it is rare.

The bucholtz contacts typically go to a "seal in" relay, and the seal in relay contact is in the trip circuit. This seal in unit could also be bad.