Some of the main factors that affect the power frequency withstand voltage test are as follows:
1. First of all, we need to choose the appropriate capacity of the test equipment. If the capacity of the test equipment is insufficient or too large, the field test will be affected.
2. The impact of altitude on test requirements: with the increase of altitude, the spatial density decreases, the average free travel of electrons in the electric field increases, and the electrons can collect more kinetic energy between the two collisions (compared with the normal density), which is more likely to cause ionization, so the discharge voltage of the air medium decreases.
3. In order to prevent overvoltage during the test: if the voltage is not gradually increased from zero in the power frequency voltage withstand test, but the soil frame voltage on the primary winding of the test transformer appears on the test product, it is due to the excited surge overvoltage. If the power supply is suddenly cut off during the test, overvoltage will be caused due to self-induced potential for small volume test samples. Either of the above conditions can lead to mispuncture of the test item. Therefore, when carrying out power frequency voltage withstand test, the test operation rules should be strictly observed.
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4. The impact of increased capacity on the test value: in the AC power frequency voltage withstand test, the product under test is usually a capacitive load, and the high voltage winding of the transformer under test is connected with the capacitor under test. In this way, the capacitive current flowing through the capacitive load causes a voltage drop in the winding impedance of the test transformer, and the voltage on the secondary side of the test transformer is reduced, which is significantly greater than the calculated secondary side voltage. Conversion rate. This phenomenon is called the “capacity increase effect”, it can be seen that the original ratio is not applicable, the increase process is proportional to the short-circuit impedance of the transformer, and the general increase range is about 4%. Thirty percent.
5. Impact of pressure waveform distortion on test results: Because there are many nonlinear loads in the power unit, harmonic circuit components increase, and the problem of grid voltage waveform distortion becomes more and more serious. In order to protect the correct test results, its peak value must be measured to eliminate measurement errors due to voltage splash distortion.
In the actual power frequency voltage withstand test, the following points should also be noted:
1. The test transformer and control box should be reliably grounded;
2. During the test process, the voltage boost speed cannot be too fast, and the full voltage is not allowed to be turned on or off suddenly;
3. Clean and dry the test items to avoid damage to the test items and errors caused by the test;
4. During the test process, if the test product is short circuited or broken down, the overcurrent relay in the control box will work. At this point, zero out the regulator and cut off the power supply before removing the test product.
5. When high-voltage AC/DC testing is carried out, two or more people must be involved, and the division of labor should be clearly defined, and each other’s methods should be clearly defined. There is a special person to supervise the site safety and observe the test status of the product under test;
6. During the boost or withstand voltage test, if any of abnormal conditions are found, the voltage should be reduced immediately, and the power supply should be cut off to stop the test, and the test should be carried out in the case of causing the cause.
Post time: Dec-07-2023