Winding obstruction trial of transformer is likewise finished as type test, routine test and field test.
At the production line, it decides the accompanying:
- Computation of I2R misfortunes in a transformer.
- Computation of twisting temperature toward the finish of transformer temperature climb test.
- As a rule for surveying possible misfortunes in the field.
This is finished nearby to check for free associations, broken transmitter wires, high contact obstruction in tap transformers, high voltage leads and blames because of bushings.
Strategy for Estimating Transformer Winding Opposition For star-associated auto transformers the obstruction of the HV side is estimated between the HV terminal and the IV terminal, then between the IV terminal and the impartial.
For delta-associated windings, the winding opposition will be estimated between sets of line terminals. As the obstruction of individual windings in a delta association can’t be estimated independently, the opposition per winding will be determined by the accompanying equation:
Obstruction per winding = 1.5 × estimated esteem
The resistance is measured at ambient temperature and then converted to resistance at 75oC for all practical purposes of comparison with specified design values, previous results and diagnostics.
Winding resistance at standard temperature of 75oC
Rt = Twisting opposition at temperature t.
t = Winding temperature.
For the most part, transformer windings are immersed in protection fluid and covered with paper protection, making it difficult to quantify the actual winding temperature in the de-stimulating transformer when estimating the transformer winding impedance. In this case an approximation is made to calculate the temperature of rotation, as:
Winding temperature = normal temperature of protective oil
Normal oil safety temperature should be reached 3 to 8 hours after de-energizing the transformer and when the difference between top and base oil temperature is less than 5oC.
Impedance can be estimated with a basic voltmeter-ammeter technique, a Kelvin extension meter or a programmed winding opposition estimation unit (ohmmeter, ideally a 25 amps pack).
ALERT FOR VOLTMETER AMMETER TECHNIQUE: Current shall not exceed 15% of rated winding current. Too many qualities can cause error by heating the winding and subsequently changing its temperature and resistance.
Note: An estimate of the winding resistance of the transformer shall be completed at each tap.