220kV Capacitive Voltage Transformer Tan Delta Test Report

I. On-site Test Main Information

This report documents a 220kV capacitive voltage transformer (CVT) tan delta test conducted at a traction substation using the HXOT 700B tan delta tester.

1. Basic Information

Figure: HXOT 700B tan delta tester

II. Test Method

2.1 Preparation

The crew completed safety measures including voltage checking, discharging, and grounding, and made test preparations.

Figure: Safety measures on site

2.2 Test Wiring

1. Check the nameplate of the CVT under test, open the secondary terminal box, and verify the terminal numbers and names.

Figure: Inspecting CVT secondary terminal box

2. The capacitance and tan delta of the upper-section high-voltage capacitor are measured with the positive connection method.

Figure: Positive connection diagram

3. The lower-section high-voltage capacitor and the medium-voltage capacitor are installed in the same bushing with no intermediate lead available, so the self-excitation method is used to measure their capacitance and tan delta. The wiring method can refer to the diagram posted inside the secondary terminal box, as shown below.

Figure: Self-excitation wiring method

2.3 Test Process

After wiring is completed, configure the corresponding test method, test voltage, and frequency. Then long-press Confirm to start output.

Figure: Test process

2.4 Test Results

After the test, C1 capacitance was 12.5nF with tan delta of 0.069%; C2 capacitance was 48.89nF with tan delta of 0.078% — both qualified.

Figure: C1 test result of lower-section high-voltage capacitor

Figure: C2 test result of medium-voltage capacitor

III. Test Summary

Tan delta measurement is a fundamental insulation test method that can effectively reveal overall moisture deterioration, aging, and local defects in electrical equipment insulation. It is widely used in electrical manufacturing, installation, commissioning, and preventive testing. Tan delta measurement of transformers, instrument transformers, reactors, capacitors, bushings, and arresters is the most basic method for evaluating their insulation performance.

During the test, attention should be paid to whether the test object satisfies the positive-connection condition: the low-voltage measurement end or secondary end must be insulated from ground. If this condition cannot be met, the reverse-connection method should be used. Between the two methods, the positive-connection method is preferred.