Basic principles and selection of withstand voltage tester

The withstand voltage tester is also called the electrical insulation strength tester or the dielectric strength tester. A specified AC or DC high voltage is applied between the live part and the non-live part (usually the outer shell) of an electrical appliance to check the withstand voltage of the electrical insulation material. During long-term operation, electrical appliances must not only withstand the rated working voltage, but also withstand the short-term overvoltage higher than the rated working voltage caused during operation (the overvoltage value may be several times higher than the rated working voltage value). Under the action of these voltages, the internal structure of the electrical insulation material will change. When the overvoltage intensity reaches a certain value, the insulation of the material will be broken, the electrical appliance will not be able to operate normally, and the operator may be electrocuted, endangering personal safety.

1. Structure and composition of withstand voltage tester
(1) Step-up part It
consists of voltage regulating transformer, step-up transformer and step-up power supply
on and off switch. 220V voltage is added to the voltage regulating transformer by on and off switch. The output of the voltage regulating transformer is connected to the step-up transformer. Users can control the output voltage of the step-up transformer by adjusting the voltage regulator.
(2) Control part
It consists of current sampling, time circuit and alarm circuit. When the control part receives the start signal, the instrument immediately connects the power supply of the step-up part. When the current of the measured circuit exceeds the set value and the sound and light alarm is issued, the power supply of the step-up circuit is immediately cut off. When the reset or time-out signal is received, the power supply of the step-up circuit is cut off.

(3) Display circuit
The display shows the output voltage value of the step-up transformer. It shows the current value of the current sampling part and the time value of the time circuit, which is generally a countdown.

(4) The above is the structure of the traditional withstand voltage tester. With the rapid development of electronic technology and single chip, computer technology; program-controlled withstand voltage tester has also developed rapidly in recent years. The difference between program-controlled withstand voltage tester and traditional withstand voltage tester is mainly the boost part. The high voltage boost of program-controlled withstand voltage tester is not regulated by the voltage regulator through the mains, but by a single chip computer to generate a 50Hz or 60Hz sine wave signal and then amplify and boost it through the power amplifier circuit. The output voltage value is also controlled by the single chip computer. The principles of other parts are not much different from those of traditional withstand voltage tester.

2. Selection of withstand voltage tester
The two most important indicators for selecting a withstand voltage tester are the maximum output voltage value and the maximum alarm current value, which must be greater than the voltage value and alarm current value you need. Generally, the high voltage value and the alarm judgment current value are specified in the standard of the tested product. If the applied voltage is higher and the alarm judgment current is larger, the power of the withstand voltage tester step-up transformer is larger. Generally, the power of the withstand voltage tester step-up transformer is 0.2kVA, 0.5kVA, 1kVA, 2kVA, 3kVA, etc. The highest voltage can reach tens of thousands of volts. The maximum alarm current is 500mA-1000mA, etc. Therefore, you must pay attention to these two indicators when selecting a withstand voltage tester. If the power is too large, it will cause waste. If the power is too small, the withstand voltage test cannot correctly judge whether it is qualified or not. We believe that the power method of selecting a withstand voltage tester specified in IEC414 or (GB6738-86) is more scientific. "First, adjust the output voltage of the withstand voltage tester to 50% of the specified value, and then connect the test product. When the observed voltage drop is less than 10% of the voltage value, the power of the withstand voltage tester is considered to be sufficient." That is, if the voltage value of the withstand voltage test of a certain product is 3000 volts, first adjust the output voltage of the withstand voltage tester to 1500 volts and then connect the test product. If the output voltage drop of the withstand voltage tester is not greater than 150 volts at this time, then the power of the withstand voltage tester is sufficient. There is a distributed capacitance between the charged part of the test product and the outer shell. The capacitor has a CX capacitive reactance, and when an AC voltage is applied to both ends of this CX capacitor, a current will be drawn. The

magnitude of this current is proportional to the capacity of the CX capacitor and the applied voltage value. When this current is greater than or exceeds the maximum output current of the withstand voltage tester, this withstand voltage tester cannot correctly judge whether the test is qualified or not.