What is Sweep Frequency Response Analysis Test ?

What is Sweep Frequency Response Analysis Test ?

SFRA Test Definition

SFRA test of transformer is a method used to assess the condition of transformer windings by analyzing their frequency response to electrical inputs.

Purpose of SFRA testing

• Assessing the mechanical integrity of windings: Detecting whether the windings are displacements, deforms or short circuits.

• Monitoring the health of the transformer:Changes in the condition of the transformer windings can be tracked by comparing historical data.

• Anticipate potential failures: Detect possible failures early so that preventive measures can be taken.

Principles of SFRA testing

• Excitation signal:A wide-band sweep signal (usually from a few hundred Hertz to several megahertz) is applied to the transformer winding.

• Response signal: The output signal of the winding is measured and its amplitude and phase response is recorded.

• Data analysis: The state of the winding is analyzed by comparing the frequency response curves of the winding at different frequencies.

Test procedure

Preparation stage:

• Disconnect the power supply to the transformer and ensure that it is fully discharged.

• Connect the SFRA tester to the primary or secondary side of the transformer.

Excitation signal application:

• A wide band sweep signal is applied to the winding using the tester.

• Signals usually start at low frequencies and gradually increase to high frequencies.

Collection of response signal:

• The tester will automatically record the output signal of the winding and obtain its amplitude and phase information.

• Each winding is usually tested separately and at a different voltage tap position.

Data analysis:

• The collected data is compared to raw or historical data.

• Changes in the frequency response curve are analyzed to identify signs of winding deformation or displacement.

Data analysis index

• Amplitude change:If the amplitude changes significantly at a particular frequency, it may indicate the presence of winding deformation or displacement.

• Phase change:A sudden change in phase may also indicate a change in the winding structure.

• Spectrogram: Anomalies can be identified by comparing spectrograms between different tests.

Matters needing attention

• Test environment: Ensure that the test environment is dry and free of interference to obtain accurate test results.

• Reference data: Benchmarking data is required for effective comparison.

• Safety:All safety regulations should be observed during testing, especially when high voltage equipment is involved.

Example Data Sheet for SFRA Test Result

Conclusion

SFRA testing is a very effective tool that can help maintenance engineers assess the health of transformer windings, detect potential problems in time, and take appropriate measures to prevent major failures.