DL/T 911-2016Frequency response analysis on winding deformation of power transformers (English PDF)

5.1 Basic requirements for detection instruments

For the basic requirements of transformer winding deformation tester, please refer to

Appendix A.

5.2 Sweep frequency detection range

The sweep frequency detection range shall include the frequency band of 1kHz ~

1000kHz.

5.4 Sweep frequency accuracy

The frequency accuracy of the sine wave signal output by the signal source shall not exceed 0.01%.

5.5 Scanning frequency interval

The scanning frequency interval should be 1kHz.

5.6 Impedance matching method

The output impedance RS of the sine wave signal output source US of the detection instrument shall be 50ohm; the input impedance of the two signal detection terminals U1 and U2 shall not be lower than 1Mohm; a 50ohm matching resistor R shall be installed between the signal response terminal and the common terminal (see Figure 1).

5.7 Detection accuracy

The detection instrument shall have a dynamic detection range of -100dB ~ 20dB; the absolute error of detection within the range of -80dB ~ 20dB shall be less than 1dB.

5.10 Data query function

The search function can be used to query the historical data of the same model, the same manufacturer and the transformer.

6.1 Detection condition requirements

6.1.1 Detection shall not be carried out in thunderstorms, rain, snow and other weather.

The detection shall strictly implement the requirements of the power safety work regulations; it shall strictly implement the organizational and technical measures to ensure safety. The test personnel shall be trained and have the ability to conduct on-site tests.

6.1.3 Before testing, all leads connected to the end of the transformer bushing shall be removed; the removed leads shall be as far away from the tested transformer bushing as possible.

6.2 Wiring requirements

6.2.1 All wiring shall be stable and reliable. Special wiring clamps shall be used to reduce contact resistance.

6.2.2 The same wiring method shall be used for the same transformer or the same model.

The test cable and ground lead on the excitation end and the response end can be led down along the porcelain sleeve of the bushing. The ground wire cannot be entangled and shall be electrically connected to the metal box of the transformer nearby, to maintain good high-frequency grounding performance.

6.3 Wiring method

6.3.1 According to the connection structure of the transformer winding, select the

excitation end (input end) and response end (measurement end) of the winding to be tested according to Figure 2; the ends of other windings are suspended.

7.1 Analysis and judgment principle

The frequency response analysis method is used to judge the deformation of transformer windings. The frequency response data curves of three-phase windings of the same voltage level are mainly compared longitudinally, laterally, comprehensively; the changes in the amplitude-frequency characteristics of the transformer windings are judged by the correlation coefficient.

7.2 Longitudinal comparison method

The longitudinal comparison method refers to comparing the amplitude-frequency response characteristics of the same transformer, the same winding, the same tap position, the different periods;

7.3 Lateral comparison method

The lateral comparison method refers to comparing the amplitude-frequency response characteristics of three-phase windings of the same voltage level of the transformer. If necessary, the amplitude-frequency response characteristics of the same model transformer manufactured by the same manufacturer at the same time are used to judge whether the transformer winding is deformed. This method does not require the original amplitude-frequency response characteristics of the transformer;

7.4 Comprehensive analysis method

The comprehensive analysis method mainly compares the three-phase frequency response fingerprints of the transformer laterally and longitudinally; makes a judgment based on the differences in the three-phase frequency response fingerprints.

See Appendix F for an example of using the comprehensive comparison method to judge the deformation of the transformer winding.

7.5 Analysis process

7.6 Winding deformation analysis

7.6.1 The typical amplitude-frequency response characteristic curve of transformer

winding usually contains multiple obvious peaks and troughs. The changes in the distribution position and number of peaks or troughs are important bases for analyzing transformer winding deformation. See Appendix I for the typical amplitude-frequency response characteristic curve of transformer winding deformation.

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