Transformer Temperature Trip

I wouldn't know without measuring the current on each phase, Uncle. You could do that.

Shorted winding on L1 inside the transformer itself perhaps.

Your unlikely to find it with a standard meter but a specialised meter that can detect shorted windings should be able to. I don't know what their proper name is, but you can hire them.

I believe it is called a TTR meter? (Transformer turns ratio). We got a temp pad mount xformer once that was giving funny voltage reading. Turned out to be a 385V instead of 480V nameplate was wrong. They used one to find out what it was.

sethuamanj:

Core saturation and harmonics can do such a wonderful job of transforming transformer into an oven. How much temperature did you notice?

is it due to unbalance loading?

Highly probable.

As already suggested. Measure the loading on each phase and then conclude or delve deeper.

THERE COULD BE MORE THAN ONE REASONS FOR THE PROBLEM.

FIRST THE UNBALANCED LOAD, FOR WHICH YOU NEED MEASURING LOAD CURRENT AND ANALYSE.

SECOND IT COULD BE COIL SHORT CIRCUITING.. YOU MAY HAVE TO MEASURE TURNS RATIO IN COILS AND NOTE ABNORMALITY. THIS CAN EVEN BE MEASURED BY OUTPUT VOLTAGES IN ALL THE PHASES.

THIRD COULD BE HARMONICS IN INPUT SUPPLY.

AND FOURTH I AM NOT SURE SOME ONE TALKED OF MAGNETIC SATUARTION OF CORE. MAY BE IT RESULTS FROM ALL THE THREE ABOVE...

SOME FUNNY THINGS LIKE LOOSE CONTACTS AT THE TERMINATION COULD SOMETIMES MAY BE THE CAUSE. CHECK THEM TOO.

Sssssshhhhhhhhhhhhhhhhhhhhhhhh!

hello sir,

First thanks for your response.. As you suspect coil short circuit. Is they is any chance for getting coil short circuit when transformer working normally for more than 6 months continuously.

Just a guess.

Most of the possible causes of high temperature have been suggested.

However, does the L1 temperature sensing device output in fact conform to the actual temperature at its probe?

Give more details from name plate like vector group,voltage,current & type of temperature trip & what other protective relays are installed.

hello,

It is 5MVA 22kv/11kv Dry-Type transformer, vector group = dyn11, temp relay is a china made with PT100 sensor. thanks for ur response.

Check the relay or replace with another & see. You didn't mention nameplate current.

How about a telephone call to the transformer manufacturer's Technical Helpline?

What does it say on the equipment's maintenance records?

Mr, Iyengar has correctly predicted the cause.

To repeat it may be due to one of these reasons

1) an inter turn short , which may not be detected by differential protection depending upon where short circuit accured in the winding.

2) May be due to magnetic circuit fault (I.e., imperfection or damage on insulation of core) resulting in local eddy current circulation.

Both of these diffect can be identified by conducting a magnetic balance test.

You may have a loose, or high resistance xfmr connection that is causing the temperature rise.

Scanning the connections and windings during operation with a camera or other non-contact thermal scanning device should help identify where the issue is originating.

Very unlikely high windingtemp due to winding / load faults to be picked up by just one temp sensor whereas the temp rise had not spread to the neighbouring windings through the core.Probably the thermocouples or senseing units are questionable .

Now that various suggestions have come qand many agree that all the probable causes are listed out there, Better start from doubting the sensor reading. Once ensure that the readinbg is actual and ok then proceed to rest seeing easier one first unless you are more than sure that it is noit the fault by your local and situationjal decisions.

Transformer heating is a result of higher impedance, which is due to higher DC loads connected to xmer.