TRANSFORMER TURN RATIO (TTR)

1-TTR test detects shorts between turns of the same coil, which indicates insulation failure between the turns.

2- Transformer ratio test is conducted to ensure that the turn’s ratio tally with the name plate details

3- Tap changer connections are done correctly.

Measurements are made by applying a known low voltage across one winding and measuring the induced voltage on the corresponding winding. Low voltage is normally applied across a high voltage winding so that the induced voltage is lower, reducing hazards while performing the test.

Q: Which voltage level is applied for this test?

Voltmeter method on TTR Test

Transformer ratio test is conducted to ensure that the turns ratio tally with the name plate details and also that tap changer connections are done correctly. Ratio test is done using a transformer turns ratio tester or with voltmeters. With the turns ratio tester, the turns ratio is directly read on the tester for each tap and for each phase of the winding.

The turns ratio can also be tested by applying a single phase ac voltage on the HV side and measuring the voltage on the low voltage side at all tap positions

Two ac voltmeters are used, one connected to the high-voltage winding and the other connected to the low voltage winding. The high-voltage winding is excited to a voltage not exceeding the rating of the voltmeter, in approximately 10%,

in practically (approximately 230V)

Both voltmeters are read simultaneously. A meaningful ratio measurement may be made using only a few volts of excitation. The transformer should be excited from the

highest voltage winding in order to avoid possibly unsafe high voltages. Care should be taken during the application of voltage and during the measurement. It is important that simultaneous readings of both voltmeters be made.

Q: TTR and W resistance are to confirm health of winding insulation ?

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.

Q: Power factor - Dissipation factor - watt loss test- Doble test - are all of them just different 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.

Q: How to install the meter and how to do when we inspect the TTR test?

Ans: 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%.