What does the maintenance of current transformers involve?

Fault Prevention and Handling of Current Transformers
1 Handling of Oil Leakage in Current Transformers

Oil - immersed current transformers are most prone to oil leakage. Common oil - leakage parts mainly include the secondary outlet box, the upper and lower sealing surfaces of the porcelain sleeve, the oil tank, the base, the oil conservator, and the metal expander.

Methods for handling oil leakage: For oil leakage at the secondary outlet box, if the small porcelain sleeve or terminal board is cracked, replace the small porcelain sleeve or terminal board. For oil leakage at the upper and lower sealing surfaces of the porcelain sleeve, if the sealing washer is damaged, replace the sealing washer, and apply sealant on the sealing surface when replacing the sealing washer. If the oil leakage is caused by poor assembly of the sealing washer, such as misalignment or folding of the sealing washer, replace the sealing washer and re - assemble.

If the oil leakage is caused by the flange sealing surface not meeting the requirements or foreign objects being caught, handle the sealing surface. If the weld of the corrugated sheet of the metal expander cracks or is permanently deformed, replace it with a new metal expander. If sand holes cause oil seepage in the cast - aluminum oil conservator, use a hammer and a punch to plug the sand holes.

For oil leakage at the welds of welded parts such as the oil tank, base, and oil conservator, if the leakage is not serious, use leak - blocking glue for temporary treatment; if the leakage is serious, carry out live - oil welding repair. However, after welding repair, take a sample of the transformer oil for transformer oil chromatographic analysis. If harmful gases are generated, transformer oil degassing treatment is also required. If it is necessary to drain the transformer oil for repair, transport the current transformer back to the maintenance workshop for repair work. The transformer oil should not be contaminated, and the body of the current transformer should not get damp.

2 Oil Change of Current Transformers

When the quality of the insulating oil of the current transformer deteriorates and affects the insulation performance of the transformer itself, all the insulating oil can be drained, and new oil that has been properly treated and qualified can be re - injected according to the oil - changing process.

3 Handling of Excessive Water Content in SF₆ Gas - Insulated Current Transformers

For SF₆ gas - insulated current transformers in operation, if the water content in the SF₆ gas exceeds the standard, dewater the SF₆ gas. Use an SF₆ gas recovery and treatment device to recover the SF₆ gas, and after treating it to be qualified, re - fill it into the current transformer. Let it stand for 1 day and then re - measure the water content in the SF₆ gas. If it is still unqualified, check the treatment process and recover and treat again until it is qualified.

4 Other Common Faults of Current Transformers

When the dielectric loss factor of the current transformer increases, increase the number of dielectric loss factor measurement tests, closely monitor the development and change of the dielectric loss factor, and conduct a transformer oil chromatographic analysis test. When acetylene is found to be generated, quickly find out the cause or take the current transformer out of service.

When the content of single hydrogen in the transformer oil chromatographic analysis of the current transformer exceeds the standard, closely monitor its growth trend. If multiple measurements are carried out and the measurement results are relatively stable, a fault may not necessarily occur, and degassing treatment can be carried out. If the content of single hydrogen grows rapidly, it should be taken seriously.

5 Fault Prevention Measures

Corresponding fault prevention measures can be formulated according to the common faults of current transformers:

For U - shaped structure capacitive current transformers, to ensure the correct operation of the bus differential protection, the secondary winding for bus differential protection should be set on the side close to the bus. This avoids the misoperation of the bus differential protection and the expansion of the accident impact range when the main insulation breakdown accident occurs at the bottom of the U - shape.

When the grid capacity increases and the system short - circuit current increases, re - check whether the dynamic and thermal stable current values of the current transformers in operation can still meet the requirements. If they cannot meet the requirements, replace the current transformers with those whose dynamic and thermal stable currents meet the requirements in a timely manner.

Regularly or irregularly carry out live - line monitoring work such as infrared temperature measurement. Detect the hidden dangers of current transformers in advance before accidents occur, classify and handle them according to the monitoring data, and try to avoid accidents.