Research on Abnormal Partial Discharge Test of High Voltage Transformer on Site
1、 Overview of Partial Discharge Test
（1） Introduction to Partial Discharge
Partial discharge refers to the phenomenon where electrical equipment generates a large field strength under the action of an external voltage, resulting in discharge in the insulation area of the electrical equipment, but no discharge channel is formed in the discharge area of the electrical equipment.
Partial discharge phenomenon mainly occurs in High-Voltage Electrical Equipment, such as in high-voltage transformers, which can easily cause damage to the insulation parts of high-voltage electrical equipment.
Therefore, partial discharge tests must be conducted on high-voltage transformers before they leave the factory or are put into use. There are two main reasons for partial discharge in high-voltage transformers:
One is that the insulation performance or other performance indicators of the high-voltage transformer itself are not qualified; Secondly, there may be issues with the material or production process of the high-voltage transformer.
（2） The hazards of partial discharge
The hazards of partial discharge mainly manifest in the following aspects: firstly, partial discharge can cause electrical equipment to overheat, thereby causing damage to electrical equipment;
Secondly, partial discharge can produce a series of adverse phenomena and reactions, such as chemical reactions, electrical pulses, electromagnetic radiation, etc. These adverse phenomena and reactions will cause serious harm to the surrounding environment and the life and health of the people;
The third is that discharge can easily cause the insulation layer of the transformer to be broken down, greatly reducing the insulation performance of the transformer and ultimately leading to accidents.
（3） The significance of partial discharge test
Conducting on-site partial discharge tests on high-voltage transformers can accurately detect the insulation performance and other performance indicators of the transformer, while also effectively reflecting the design level and production process control level of the transformer.
Partial discharge test is an important part of high-voltage transformer testing, which has the advantages of easy operation, high accuracy, and good flexibility. It is widely used in transformer detection. Therefore, conducting partial discharge test on high-voltage transformers is of great significance
2、Research on Abnormal Partial Discharge Test of High Voltage Transformer on Site
Based on work requirements, the author will analyze and study the abnormal situation of partial discharge tests on high-voltage transformers in the field based on their actual situation and practical experience.
On November 8th, a high-voltage transformer was just assembled and ready to leave the factory. According to relevant requirements, a partial discharge test was conducted on the high-voltage transformer on site. Through experiments, it was found that the high-voltage transformer had an abnormal phenomenon of excessive discharge capacity.
There are two main reasons for this abnormal phenomenon:
- first, there are bubbles in the insulation of the transformer;
- Secondly, there are bubbles in the oil of the transformer.
After learning this, the transformer should be carefully inspected and cleaned before the next partial discharge test, and bubbles should be eliminated through a temperature rise test.
On November 11th, after the transformer underwent a temperature rise test, a partial discharge test should be conducted again after the temperature of the equipment parts cooled down. The test results were found to be the same as three days ago.
So the experimenters speculated that there might be a problem with the transformer bushing, so they carefully inspected the bushing and two-phase high-voltage bushing in the transformer and found that gas was escaping. Therefore, they decided to let it sit for a period of time until the gas was fully released.
On November 15th, the third partial discharge test was conducted on the transformer, and it was found that the discharge amount of the first phase of the transformer was too small. Therefore, the test personnel conducted an extraction test on the oil in the transformer, and the results showed that it was a normal situation.
On November 22nd, a partial discharge test was conducted on the first phase of the transformer, and an abnormal situation was discovered through the test: at the beginning of the test, the partial discharge amount of the first phase of the transformer was very unstable, but gradually stabilized after 6 to 10 minutes.
The partial discharge of the first phase of the transformer is still within the range specified in the technical agreement. Then, on November 24th and November 26th, partial discharge tests were conducted on the first phase of the transformer, and oil samples were taken from the transformer for analysis.
Through the analysis of the results obtained from the above experiments, it is shown that the insulation performance of transformers continues to decline and deteriorate through multiple partial discharge tests.
The cause of abnormal discharge in transformers is not only the presence of bubbles in the oil, but also the insulation performance of the transformer. In addition, analyzing the load transfer capacity of the transformer can correctly identify the location of abnormal discharge in the transformer.
3、 Problems and Solutions in Partial Discharge Testing of High Voltage Transformers
（1） Defects in Transformer Structure and Solutions
When there are defects in the transformer structure, the electric field distribution in the insulation medium will be uneven, and the discharge amount will exhibit unstable phenomena during partial discharge tests.
The solutions to the defects in the transformer structure include: strict and careful inspection of the transformer structure before conducting partial discharge tests to ensure its rationality, and induction withstand voltage, lightning impulse and other tests on the transformer. Only after the transformer passes these tests can partial discharge tests be carried out.
（2） Effects of corona discharge and solutions
Under high voltage conditions, transformers are prone to corona discharge, which can cause abnormal discharge in some poorly grounded parts of the high-voltage transformer under the action of an electric field, thereby seriously affecting the discharge detection results of partial discharge tests.
Solution to corona discharge noise: Carefully inspect the high-voltage transformer to ensure complete grounding and shield the high-voltage bushing to prevent corona discharge caused by high voltage.
4. Conclusion
In summary, this article analyzes and discusses the overview of partial discharge tests, the study of abnormal discharge tests in high-voltage transformers on site, and the problems and solutions in partial discharge tests of high-voltage transformers.
It is of great significance, not only to ensure the quality of high-voltage transformers and ensure the normal operation of the power system, but also to promote the sustainable development of China's power industry.