Technology Literature

What is Main Items of Transformer Factory Acceptance Testing

1. Winding DC Resistance testing:

Measure the winding resistance of all winding and all partial connections. The difference between the winding resistance of each phase of the transformer should be less than 2%. That is: [R(max) - R(min)] / R(avr) < 2%. When the low-voltage winding is a delta connection, the DC resistance of each phase should be provided for the semifinished product. The difference between the phases should be less than 2% of the average value. The difference between the DC values obtained from the side of the line should be less than 1% of the average value.

2. Turns ratio testing(TTR), junction group and polarity verification

Transformer turns ratio testing should be made at all coils and all tap positions. The turns ratio vol deviation of the transformer does not exceed ±0.5% at all tap positions. The connection group is correct.

The polarity of the transformer should be "reduce polarity".

3. Short-circuit impedance and load loss testing

The impedance tolerance cannot be greater than the specified value.

The load loss measurement should be made at the rated voltage tap position. The loss measurement is corrected using a correction factor. The correction factor is determined based on the accuracy of the calibrated meter. For measuring load losses with very low power factor (0.03 or less), the phase angle error of all instrument transformers should be corrected. All impedance and load loss values should be converted to the reference temperature (75 °C).

4. No-load loss and no-load current testing (including harmonic testing of no-load current)

The testing should be carried out at 50%, 60%, 70%, 80%, 90%, 100%, 105% and 110% of the rated voltage respectively. No-load loss and no-load current measurement.

Measurement of initial no-load loss and no-load current: Before all insulation tests, the no-load loss and no-load current are measured at 10%, 50%, 60%, 70%, 80% of the rated voltage, and then In the range of 90% to 115% of the rated voltage, it is measured step by step with 5% as the primary voltage. The no-load loss and no-load current should be measured on the low-voltage winding. The no-load and no-load current values shall be measured and corrected in accordance with relevant standards.

After all the insulation tests are completed, the loss measurement at the rated voltage will be taken as the actual measured value with the last measured no-load loss value.

5. The temperature rising(Heat run) testing.

Transformers with the same specifications only require the first transformer to perform the temperature rise test. However, if the temperature rise of the first transformer exceeds the specified temperature rise limit, all other transformers should be subjected to a temperature rise test. If the total loss of any transformer exceeds the total loss of the transformer in the first temperature rise test, the transformer still needs to be tested for temperature rise (except the calculation results can prove that the temperature rise of this transformer winding still does not exceed the specified value) Case.

Calculate the temperature rise of the transformer at the same time when the three sides are fully loaded to meet the requirements for guaranteed performance.

When the demand side needs it, cooperate with the demand side to implement the hottest fiber temperature measurement test of the winding.

6. Transformer oil testing.

The insulating oil test includes physical, chemical, and electrical performance tests and provides a factory test report. The breakdown voltage strength(BDV) test was carried out with a 2.5 mm ball gap, and the breakdown voltage should not be lower than 50 KV; the breakdown voltage strength test was performed using a plate electrode, and the breakdown voltage should not be lower than 40 kV. Measure the dielectric loss factor of the oil, the dielectric loss factor should be less than 0.5% (at 90 °C), and the moisture content should be less than 15 mg / l. After the transformer oil is injected into the transformer tank, after completing all the specified factory routine test items, the micro-water analysis and chromatographic analysis in the oil shall be carried out. The acetylene content shall be 0, and the analysis results shall be provided to the operating unit. The oil in the on-load tap-changer oil tank should also be subjected to simplified tests and micro-water tests. The oil pressure is greater than 40kV/2.5 mm and the moisture content should be less than 15 mg/l.

The test items are required for transformer manufacture (with corresponding tester types):

Test Object

Testing Item

Tester Type


Insulation Resistance of Winding



DC Leakage Testing in 1min



Winding Resistance Testing



Winding Deformation Testing



Heat run Testing



Turns Ratio Testing



Tap Changer Dynamic Testing



Short Circuit Impedance Testing



No-load Power Factor Testing



Dan Delta Testing



Oil Breakdown Voltage (BDV)Testing



Oil Tan Delta Testing



Degaussing analyzer



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