Transformer Turn Ratio (TTR) Testing

Hi Siswanto,

Great post! Very informative - pictures very helpful.

GA from me!

Mike

Great answer Siswanto. Thanks for the info.

plz let me know one thing as well that what should be the applied voltage level for this test?

respect to Siswanto !

could you, pls explain why winding resistance test is to be done too - generally both of them - TTR and W resistance are to comfirm health of winding insulation ?

and btw one more question -

Power factor - Dissipation factor - watt loss test- Doble test - are all of them just diffirent names of the same ? am I right?

BR

AndreY

Dear Friends

andreY:

vinukumar

Thank you for your questions and feedback. I appreciate to all of you…

To Andrey. Its good question, why winding resistance test is also done,

Yes you right, both of test are basically used to diagnostics transformer, and both of these measurement are used to detect winding problems such as, short inter turn, bad connections, loose contacts etc..

Measurement of Winding DC Resistance should be compared to factory measurement, agreement within 5% to factory measurement is consider satisfactory.

Winding DC Resistance to be converted to the reference temperature used at the factory measurement (usually 75⁰C)

Note. Its important the final measurement of Winding DC Resistance is when the meter is stable (winding resistance cant not be measured instantaneously), its normally need long time to get stable due to the charging time in the winding.

Winding DC Resistance is supplements test and its useful when DGA shows generation of heat gases ( C2H6, C2H4, CH4, C2H2), as we know that when XFMER produce gases over the limit value is generate by thermal fault round 300⁰C up to 700⁰C. these thermal fault can resulting over heating on the winding and even they are not short insulation found.

So Winding Resistance is useful also to calculation of I²R component conductor losses, to analysis of XFMER we should test as much as we can do , its helping us easier to make a conclusion.

Due to the resistance very sensitively to temperature change, during measuring, winding temperature must be recorded, unfortunately almost of winding temperature sensors are usually using RTD's, and the sensors can not installed close the copper, so the temperature measurement is not precise ( app 15⁰C less than hot spot temperature). Its very difficult to get exactly information temperature winding, inaccurate measurement during test can occur, thus the Winding DC Resistance mostly used as highlight what happening with the XFMER winding. That why the other test such as TTR should be performed also.

Andrey quote:

Power factor - Dissipation factor - watt loss test- Doble test - are all of them just diffirent names of the same ? am I right?

Yes its just the name, but for the doble test should be included the capacitance test, when you test Power factor or dissipation power factor, you can also directly measure the capacitance and excitation

To vinukumar,

Please let us know detail tests to be performed on Transformers before and after commissioning or guide us to good study material with practical illustrations.

How to install the meter and how to do when we inspect the TTR test, its very simple, voltage source (use variable voltage / slide regulator single phase), install the outgoing slide regulator to HV side XFMER (phase H1, H2), set the voltage (normally 230V) , measure by volt meter-1 and hold, and then read the induction voltage at LV side x1-x2 by voltmeter-2, do to other phases remaining and tapping, calculate the maximum deviation from each test tapping to name plate , the good quality for new transformer normally within 0.1% max 0.5%.

Damaged XFMER Winding, 40 MVA, 150 kV / 20 kV

Damaged on the OLTC, MR V / I / 250

Good Luck

Regards

Sis

Great post. Greatly appreciated.

Hi Siswanto

Excellent answer and illustrations. Please let us know detail tests to be performed on Transformers before and after commissioning or guide us to good study material with practical illustrations.

Regards

Vinukumar

let us know detail tests to be performed on Transformers before and after commissioning or guide

Dear : vinukumar

INSPECTIONS ITEMS

Can you tell me where I can find the .5% deviation spec? What the testing standard is? IEEE, ANSI

Is there a IEEE or IEC for "The ratio obtained from the field test should agree with the factory within 0.5%. New transformers of good quality normally compare to the nameplate within 0.1%" wich states that for NEW TRANSFORMERS TTR should be 0.1%?

Please let me know. Thank you.

Is there a IEEE or IEC which states that for New transformers of good quality normally compare to the nameplate within 0.1%?

Please let me know.