Precautions for Testing Transformers

The test transformer is the equipment for AC withstand voltage testing, and AC withstand voltage testing is one of the main methods for testing the ability of electrical appliances, electrical equipment, electrical devices, electrical circuits, and electrical safety equipment to withstand overvoltage. It plays an important role in power engineering, and the operation of AC withstand voltage test should ensure safety. Therefore, it is necessary to maintain a rigorous attitude and pay attention to the following matters:

1、 Insulation of test transformer

Before starting the AC withstand voltage test using a test transformer, sufficient preparations should be made. Currently, dry-type test transformers, oil immersed test transformers, and gas filled test transformers are generally used. For these three types of transformers, it is necessary to check whether the oil immersed test transformer leaks oil, whether the insulation gas pressure in the gas filled test transformer is normal, and whether the appearance is damaged. If possible, a digital megohmmeter can be used to measure the insulation of the test transformer.

Oil immersed test transformer

Oil immersed test transformer

2、 Protective resistance of test transformer

When conducting voltage withstand tests, resistors should be selected reasonably to avoid the impact of overvoltage on the performance of the test transformer or test transformer operation box. The selection of protective resistors should adhere to the principle of reasonableness to achieve effective protection of the equipment.

In the withstand voltage test, if the tested object is flashover or breakdown, its capacitance will suddenly decrease and strong electromagnetic oscillation will be generated inside the power testing equipment. In this regard, the testing personnel should connect protective resistors in series in the circuit to effectively control overcurrent.

In addition, if the equipment surface flashover is caused by factors such as air humidity and dirty equipment surface, the withstand voltage test result is considered unqualified. The test transformer should be cleaned accordingly and retested to ensure the accuracy of the test results.

Precautions for the operation box of the test transformer

Test transformer operation box

Test transformer operation box

3、 Overvoltage setting of test transformer operation box

Due to the destructive nature of the withstand voltage test, the applied voltage is often several times the rated voltage of the transformer. Excessive voltage can damage the insulation medium, leading to phenomena such as enlargement and heating. Therefore, during the withstand voltage test, the characteristics of the insulation medium and the actual operation of the power frequency withstand voltage test equipment should be fully combined to reasonably determine the test voltage, avoiding harm to the safety of the test personnel and equipment.

4、 Wiring of the test transformer operation box

In the AC withstand voltage test, after connecting the test wiring, it needs to be inspected by other personnel and confirmed that there is no loss. At the same time, it is necessary to increase the observation of the measuring device for the power frequency test transformer. When the protection action is turned on, the reasons should be analyzed, and adverse factors affecting the transformer test results should be eliminated in a timely manner to ensure that the withstand voltage test is carried out in an orderly manner.

5、 Determine the zero position of the test transformer operation box

Before applying pressure, it is necessary to ensure that the voltage regulator of the test transformer operating box is in zero position and cannot switch on at more than one-third of the specified test voltage. By controlling the voltage value reasonably, it is possible to avoid the equipment's withstand time process when approaching the specified voltage value, providing convenience for the testing personnel to observe the testing process.

6、 Power supply for the operation box of the test transformer

In the AC withstand voltage test, it is particularly important to note not to cut off the power supply when the voltage value is high, in order to avoid transient situations that may cause breakdown of the high-voltage test transformer, damage to the measuring instrument, etc.

Note that if the test transformer experiences discharge or other phenomena during the experiment, the power supply should be cut off in a timely manner. Due to the overvoltage generated by discharge, similar to wave cutting shock, continuous action will inevitably damage the longitudinal insulation of the test transformer, causing breakdown between turns, layers, etc.

7、 Check the heating condition of the test transformer

When the high-voltage test transformer is made of organic insulation material, personnel should immediately touch it after completing the test. If there is local heating, it proves that the insulation performance of the equipment is poor. Corresponding treatment should be carried out before conducting a secondary test to determine whether the equipment performance meets industrial production requirements.

During the process of testing multiple transformers, timely marking should be made for transformers that have broken down to provide assistance for subsequent work.