Test Principle Of Withstand Voltage Tester

When the transformer was first produced, it had not been tested for a long time in a harsh environment. When the rated voltage and frequency power supply was applied externally for testing, the voltage between the winding turns, layers and segments was not enough to reach the breakdown voltage at the dielectric defects, which made it difficult to cause discharge and breakdown at these insulation defects. The no-load current and no-load power consumption of this transformer with insulation fault hidden dangers were not much different from those of similar transformers with good insulation performance, so it was difficult to find these hidden dangers;
The induction withstand voltage test applies a voltage of more than 2 times the rated voltage to the transformer, which can establish a higher and more concentrated field strength at the longitudinal insulation defects, and the voltage between the winding turns, layers and segments reaches and exceeds the breakdown voltage at the dielectric defects; the induction withstand voltage test applies a frequency of more than 2 times the rated frequency to the transformer, and the higher frequency can greatly reduce the breakdown voltage of the solid dielectric, making the insulation defects easier to be broken down; the action time of the external voltage specified in the induction withstand voltage test can also ensure the breakdown of the insulation defects; therefore, the induction withstand voltage test can reliably detect the quality of the longitudinal insulation performance of the transformer.
The reason why the frequency of the power supply applied to the transformer in the induction withstand voltage test is above 2 times the rated frequency is that: the characteristic curve of the transformer's excitation current i――the main magnetic flux amplitude Фm is generally designed to be close to the curved saturation part at the rated frequency and rated voltage (as shown in Figure 1), and because the main magnetic flux Фm is determined by the external voltage U when the power frequency remains unchanged:
U= E=4.44WfФm Фm
U――external power supply voltage, V △Фm
E――induced electromotive force of the energized winding, V
f――external power supply frequency, Hz
W――number of turns of the energized winding, n
Therefore, applying a voltage △i i above 2 times the rated voltage to the transformer will inevitably lead to severe saturation of the core, and the main magnetic flux Фm will increase △Фm, Figure 1
As can be seen from Figure 1, the excitation current i will increase sharply, causing the transformer to heat and burn; in order to make the transformer core still unsaturated when the voltage is applied more than 2 times, the frequency of the power supply needs to be increased to more than 2 times the frequency.
In the inductive withstand voltage test, a power supply with a voltage of more than 2 times and a frequency of more than 2 times is applied to the primary side of the transformer. The main magnetic flux of the transformer will induce induced electromotive force E1 and E2 on the primary and secondary sides at the same time, and they are more than 2 times of their rated working state respectively. Therefore, the inductive withstand voltage test can test the longitudinal insulation performance of the main and secondary windings at the same time. Of course, we can also test from the secondary side of the transformer as needed, but the applied voltage should be more than 2 times the no-load voltage of the transformer under the rated working state, and the frequency should also be more than 2 times the rated frequency.
System composition principle of Aino transformer dedicated inductive withstand voltage tester
The transformer dedicated inductive withstand voltage tester launched by Aino Company uses Intel's 80c196kc single-chip microcomputer chip as the control and calculation core of the system. It is composed of measurement circuit, control switching circuit, power module and user interface circuit. Its key technology is variable frequency voltage regulation and precision measurement.