Why should the impact test be done before the transformer is put into operation

Shock testing is not a power system term. It is generally a test method to determine the safety, reliability and effectiveness of military and civilian equipment when they are subjected to external force impact or action. The impact test in electrical engineering generally includes operation impact test, lightning strike impact test and steep wave front impact test, the purpose of which is to test the insulation strength of electrical equipment.

The impact test of the power system is divided into three types

1. The pulse test method is stipulated, and the sine wave is used for the test. For example, the sine wave vibration testing machine is widely used in national defense, aerospace, aviation, communication and other industries, and is suitable for finding early faults, simulating actual working condition assessment and structural strength test.

2. Shock spectrum test method. Such as the impact test bench, it can controllably simulate the size and duration of the impact force, etc., and is used to accurately test the adaptability of the product to the environment. It is also often used to test whether the product packaging can protect the product and avoid The product was damaged during shipping handling.

3. Specify the test method of the testing machine. For example, the gravel impact tester is specially designed for the anti-gravel impact test of automotive materials and surface coatings.

According to the temperature, the impact test is divided into: normal temperature impact test, the test is carried out at room temperature, generally within the range of 23 ± 5 degrees Celsius; Take it out to complete the impact test.

In the power grid system, in addition to some necessary tests and protection and secondary tests according to the handover test standards, the transformers newly put into operation usually have to do no-load full-voltage closing impact tests before they are officially put into operation. There are two purposes for the transformer to conduct the impact closing test.

1. In the case of no charge, when the no-load transformer is opened, an operating overvoltage may occur. When the neutral point of the power system is not grounded or grounded through the arc suppression coil, the overvoltage amplitude can reach 4~4.5 times the phase voltage ; When the neutral point is directly grounded, it can reach 3 times the phase voltage. Therefore, in order to check whether the insulation strength of the transformer can withstand the full voltage or operating overvoltage, an impact test is required.

2. In the case of electrification, when the no-load transformer is put into use, an excitation inrush current will be generated, and its value can reach 6 to 8 times the rated current. Because the excitation inrush current generates a large electromotive force, in order to evaluate the mechanical strength of the transformer, the excitation Whether the initial stage of inrush current attenuation can cause malfunction of the relay protection device requires an impact test.

Usually, a newly installed transformer is generally required to be closed five times without load to comprehensively detect the insulation, mechanical strength and differential protection action of the transformer. Because the closing angle is different at each closing time, the corresponding excitation inrush current is also different, sometimes large and sometimes small. After the first impact, it must continue to run for more than 10 minutes, and after the subsequent impact, wait for more than 5 minutes before the next impact. A full impact test typically takes 1 hour.

HZ2423 Transformer Winding Deformation Frequency Response Tester