Transformer trouble

[7533]

I am working on a reffinery in the Netherlands, so excuse me if i don't use the right english/american terms.

Last week one of our feeding transformers fell out without any indication of the cause of it.
We checked the Buchholz relay, the pressure switch on the tapchanger system, the overload relays, the overcurrent relays, the rotor of the tapchanger and we took an oil sample. In spite of all these checkups we still didn't find any cause of the problem.

Is there anybody who have had transformerproblems without any indication?

 

[dpc]

What does "fell out" mean? If you mean the circuit breaker protecting it tripped, there should be some indication of what relay caused the breaker to trip.

It would help if we knew the transformer size, voltage, etc.

You may have to disconnect the transformer and do insulation resistance tests and other transformer tests.

 

[unclebob]

Have you look for burned animal/bird near the transformer?
Sometimes, they seem to be attracted by the bushings...
This is great for testing differential protection.

 

[rcw retired EE]

Which protective relay or protection device tripped the transformer off line?

Some differential relays can misoperate on inrush currents when a nearby transformer is energized.

Some transformers trip when a fault out on the power system causes the local voltage to rise as the transformer momentarily supplies fault current. The spurious voltage can momentarily pick up the coil of a seal-in tripping relay if the circuit is not desinged correctly.

Wihtout more information, it is difficult to tell.

 

[powerjunx]

7533, its hard to tell such inquiry. A sound and good protection scheme will determine the cause.

If the latter case you cited, " fell out without
indications ", i suggest you to further submit more information.

 

[gentech84]

When was the transformer last tested? Do you have the results? Had you noticed a steady temperature increase? Have you noticed high neutral currents possible associated with high THD?

 

[09041982]

If your load is Inverter driven motors, there seems to be harmonics.

Also you have to check your differential relay settings.