Analysis on High Voltage Test Technology of Power Transformer
In recent years, with the continuous improvement of my country's economic and technological level and the rapid development of social development, my country's power input and power demand have also continued to increase. As the most commonly used electrical equipment in the power system, power transformers are one of the main equipment in substations and power plants, and are essential for power generation, power supply and electricity consumption. High voltage test on power transformer is an important means to ensure the safe operation of transformers. Taking the working principle of power transformers as the starting point, we will study and explore the test conditions, test methods and test contents of high-voltage test technology for power transformers, analyze its feasibility, and put forward reasonable suggestions on how to conduct high-voltage tests on power transformers safely and effectively.
Because there is a certain risk in the high-voltage test of power transformers, it is necessary to comprehensively consider all factors involved in the test process before conducting the test. It is necessary to consider the safety and rationality of the test and ensure the smooth completion of the test. It is necessary to have a comprehensive and detailed understanding and understanding of the test conditions, test methods, test content and even test safety of the high voltage test of power transformers, and conduct effective research and analysis on the relevant data of power transformers, make scientific and reasonable judgments, and strive for the best Conduct high-voltage tests on power transformers in a safe and effective environment.
1. Test conditions for high voltage test of power transformer
In the process of high-voltage test on power transformers, in order to improve the standardization of the high-voltage test process and the accuracy of the high-voltage test results as much as possible, it is necessary to make a certain degree of reference to the different rated conditions used in the high-voltage test, and to The ICBC conditions included in the conditions are extracted to the maximum, reasonable and effective. Otherwise, it is difficult to ensure the standardization and rationalization of the high-voltage test of power transformers.
1. Effectively control the temperature and humidity of the high pressure test
When testing indoors, the environment should be strictly and effectively controlled according to the relevant data requirements of the high-voltage test of the power transformer. The temperature of the high-voltage test of the power transformer should not be too high, the highest should not exceed 40℃, and the same should not be very low. Below -20°C. It can be seen that the temperature roughly hovers between -20°C and 40°C, which is the best temperature range for high-voltage test of power transformers. If the temperature of the power transformer is hovering between 25°C and 30°C during the high voltage test, the relative humidity of the surrounding air should be effectively controlled, and the relative humidity should be kept below 85%. Only when the temperature range and relative humidity of the high voltage test meet the indicators of the power transformer high voltage test can the test efficiency be improved and the most accurate conclusions can be drawn.
For outdoor tests, it is more difficult to control the temperature and humidity. Generally speaking, you should wait for the climatic conditions to meet the test requirements before performing the test.
2. Ensure the insulation of power transformers
When conducting high-voltage tests on power transformers outdoors, it is necessary to effectively guarantee the insulation of power transformers. First, the suitability of the test environment temperature and humidity should be ensured, and the dirt, chemical dust and related dust that affect the insulation performance of power transformers should be ensured. Gas and other factors are controlled reasonably and effectively to avoid damage to the insulation performance of power transformers, which will affect the test results.
3. Strictly control the rated capacity and voltage to maintain sufficient heat dissipation
When conducting high-voltage tests on power transformers, in addition to considering the test environment and the insulation of the power transformer, the most important thing is to strictly control the rated capacity and voltage of the transformer, and to maintain sufficient heat dissipation to avoid the risk of The voltage exceeds the standard, causing damage to the power transformer.
2. Test method for high voltage test of power transformer
In order to ensure the standardization and accuracy of the test results, scientific, reasonable and effective test methods must be adopted when conducting high voltage tests on power transformers. The basic process of power transformer high voltage test mainly includes the following contents:
1. Routine test
Perform wiring in accordance with the wiring principle of the relevant test equipment. After the wiring is completed, the relevant responsible person will conduct a comprehensive and detailed inspection to ensure the safety and accuracy of the wiring.
Next, turn on the power, carry out the test operation in accordance with the operating method of the relevant test equipment, and record the test data.
After the test is completed, turn off the test instrument and cut off the test power supply.
2. AC withstand voltage test
First, the wiring should be carried out in accordance with the relevant wiring schematic diagram. After the wiring is completed, the relevant responsible person will conduct a comprehensive and detailed inspection to ensure the safety and accuracy of the wiring.
Secondly, check the specification of the voltage regulator in the control box to ensure that it is adjusted to the "zero" position, and check whether the power transformer and the control box have good contact with the wiring.
Once again, when the power transformer is turned on and the green indicator light is on, the tester presses the start button and waits for the boost after the red indicator light is on.
In the process of boosting, the tester must rotate the regulator in the control box strictly in a clockwise direction at a constant speed to ensure that the boosting process proceeds slowly. In the process of boosting, pay close attention to the changes of related instruments and the operation of the regulator.
Finally, when the high voltage test of the power transformer is completed, the tester must quickly adjust the voltage to the "zero" position, and immediately cut off the power after pressing the stop button. Finally, don't forget to untie the lead of the power transformer and the control box to remove everything Security risks.
3. Test content of high voltage test of power transformer
The test content of the power transformer high voltage test mainly includes: measuring the insulation resistance, DC resistance, transformation ratio, leakage current, testing the dielectric loss factor and AC withstand voltage test. In order to ensure the authenticity and reliability of the high-voltage test of power transformers, the test content must be carefully selected in strict accordance with relevant regulations.
1. Measure insulation resistance
The purpose of measuring the insulation resistance is to check the degree of overheating and aging of the insulation of power transformers, the overall degree of moisture and contamination, which is the simplest and most convenient test in the high voltage test. If the temperature is too high, the absorption of damp insulation will change irregularly when the temperature is above 35℃, and the absorption of dry insulation will decrease after reaching the limit, which will seriously affect the effect of high-voltage test. Therefore, the ambient temperature and humidity must be appropriate Under the circumstances of carrying out the test.
2. DC resistance measurement
The purpose of measuring the DC resistance of transformer windings is to reflect the short-circuit between windings, the broken strands of the windings, the contact state of the tap switch, the difference in wire resistance, and the poor contact of the joints. It is also to judge whether the DC resistance of each phase winding is balanced, and the voltage regulator switch The effective means of whether the gear is correct is an important inspection item in the transformer test.
3. Measurement of transformation ratio
The measurement methods of power transformer transformation ratio mainly include transformation ratio bridge method, double voltmeter method and so on. The purpose of measuring the transformation ratio is to check whether the voltage ratio of each tap of the winding is within the technically allowable range, check the correctness of the number of winding turns, and determine whether the lead of each tap of the winding and the tap switch are connected correctly. In addition, in the transformer transformation ratio test, the test of the wiring group can also be performed simultaneously. Having the same wiring group is a prerequisite for parallel operation of the transformer, so the judgment of the power transformer wiring group is also necessary in the high-voltage test. One of the commonly used methods include phase method, AC voltmeter, DC induction, group table and other methods.
4. Leakage current measurement
The measurement of leakage current is to check whether the power transformer itself has quality problems. By adopting the test method of adding DC high voltage, if the leakage current of the power transformer in the high voltage state is lower than the leakage current of the power transformer in the low voltage state, the high voltage of the power transformer The insulation resistance is lower than the low-voltage insulation resistance, indicating that the leakage-proof function of the power transformer has quality defects and cannot meet the high-voltage test requirements. It also shows that the power transformer itself has quality problems and cannot participate in the high-voltage test.
5. Dielectric loss factor test
Measuring the dielectric loss tangent value tanδ of the transformer is mainly used to check the overall dampness of the transformer, the deterioration of the glaze, the sludge attached to the windings and the serious local defects, etc. It is a more effective means to judge the insulation status of the transformer below 31.5MVA. Measuring the dielectric loss tangent value of the transformer is to measure the bushing together, but in order to improve the accuracy of the measurement and the sensitivity of detecting the defect, if necessary, a decomposition test can be carried out to identify the location of the defect.
6. AC withstand voltage test
The AC withstand voltage test on power transformers is the most effective method to identify the insulation strength, especially for local defects of the main insulation, such as damp, cracks, loose windings, and surface pollution of the main insulation. Check whether the insulation strength of the power transformer is defective, so as to avoid unnecessary safety accidents caused by the aging of the insulation performance of the power transformer.
4. Safety technical measures for high voltage test of power transformer
1. Strictly follow relevant laws and regulations and do a good job of protection
Before conducting high-voltage test of power transformers, we must make full preparations, strictly abide by relevant national laws and regulations, conduct high-voltage tests under the premise of not violating the legal scope of the country, and do comprehensive protection work to prevent accidents.
At the periphery of the high-voltage test site, high-voltage leads and high-voltage test equipment, the safety nets must be pulled in strict accordance with the relevant provisions of the "Electric Safety Work Regulations", and the warning signs of "high-voltage danger, please do not approach" should be set up. If necessary, special personnel can be hired Guards, it is strictly forbidden for non-staff to approach or enter, to eliminate all potential safety hazards.
2. Appoint test personnel with strong knowledge and rich experience
According to the relevant regulations of the high voltage test of power transformers, there must be two or even more than two personnel involved in the high voltage test. One of the testers with strong knowledge and rich experience shall be selected as the person in charge to conduct reasonable and orderly conduct on other test personnel. The work arrangement allows each tester to clarify his own work content, familiarize himself with his own work process, and at the same time strengthen his own safety awareness and legal awareness.
In the high-voltage test, the tester with less experience is generally selected as the operator, because the work is relatively simple and the technology content is low. After the operator completes the wiring work, the person in charge is responsible for a comprehensive inspection of the wiring to check whether the wiring is connected properly , Whether the safety measures are correct, all personnel should be evacuated after inspection to ensure the safety of test personnel.
3. Provide appropriate electric power education to staff
In the high voltage test of power transformer, in order to ensure the personal safety of the staff, it is necessary to strengthen technical training and learn safety knowledge for the staff. When training employees, they need to focus on strengthening their technical level and educating employees on professional knowledge. They need to be proficient in the principles of high-voltage testing, familiar with the test process, and analyze the data in combination with the test situation, and then make corresponding responses. Judgment. The safety awareness of employees also needs to be strengthened. The transformer test work is more meticulous, and certain preparations need to be made during the actual test. Before work, you should carefully formulate a work plan, select test equipment reasonably, check the connection status of the tested equipment, and ensure that the test is carried out in an orderly manner.
In summary, the high-voltage test of power transformers is a cumbersome, complex, and high-tech test project. Therefore, during the high-voltage test process, the test conditions, test methods and test contents of the high-voltage test of power transformers must be carefully selected and done well. All-round protection preparations, selection of high-quality test personnel, I believe that under the joint efforts of these comprehensive factors, the high-voltage test of power transformers will be completed safely and smoothly, obtain the most accurate test data, and scientifically judge the comprehensive performance of the power transformer .