Basic principle selection of the hottest insulatio

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Basic principle of insulation resistance tester, selection of

I. voltage withstand tester

voltage withstand tester is also called electrical insulation strength tester or dielectric strength tester. A test in which a specified AC or DC high voltage is applied between the live part and the non live part (usually the shell) of the electrical appliance to check the withstand voltage capacity of the insulating material of the electrical appliance. In the long-term operation, the electrical appliance should not only bear the effect of rated working voltage, but also bear the overvoltage effect caused by the short-term higher than the rated working voltage in the operation process. 7. Sample diameter: 10 400mm (the overvoltage value may be several times higher than the rated working voltage value). Under the action of these voltages, the internal structure of electrical insulating materials will change. When the overvoltage intensity reaches a certain value, the insulation of the material will break down, and the electrical appliance will not operate normally, and the operator may get an electric shock, endangering personal safety. 1. Structure and composition of voltage withstand tester

(1) the booster part

consists of voltage regulating transformer, booster transformer and power on and off switch of booster part

The voltage of

220v is connected, and the cut-off switch is added to the voltage regulating transformer. The output of the voltage regulating transformer is connected to the step-up transformer. Users only need to adjust the voltage regulator to control the output voltage of the step-up transformer

(2) the control part is composed of current sampling, time circuit and alarm circuit. When the control part receives the start signal, the instrument immediately turns on the step-up part of the electric stepless speed regulation 0.1 (5) 00 mm/min stepless speed regulation transmission system: Taiwan gapless T-shaped screw, Taiwan Abba fine ball screw optional installation: computer source. When the measured circuit current exceeds the set value and an audible and visual alarm is sent, the power supply of the boost circuit shall be cut off immediately. Cut off the power supply of the booster circuit after receiving the reset or time signal

(3) display circuit

the display shows the output voltage value of the step-up transformer. The current value of the current sampling part and the time value of the time circuit are generally countdown

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

2. Selection of withstand voltage tester

the most important two indicators for selecting withstand voltage tester are that the maximum output voltage value and maximum alarm current value must be greater than the voltage value and alarm current value you need. Generally, the applied high voltage value and alarm judgment current value are specified in the standard of tested products. If the applied voltage is higher and the alarm judgment current is larger, the power of the voltage withstand meter step-up transformer is larger. Generally, the power of the voltage withstand meter 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, we must pay attention to these two indicators when selecting the voltage withstand meter. 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. According to iec414 or (GB), we think it is more scientific to choose the power method of voltage withstand instrument. "First adjust the output voltage of the withstand voltage meter to 50% of the specified value, and then connect the tested object. When the observed voltage drop is less than 10% of the voltage value, the power of the withstand voltage meter is considered to be sufficient." That is, if the voltage value of the withstand voltage test of a product is 3000 V, first adjust the output voltage of the withstand voltage tester to 1500 V and then connect the tested object. If the output voltage of the withstand voltage tester drops at this time, it should not be tightened in time; If it is greater than 150 volts, the power of the voltage withstand meter is sufficient. There is distributed capacitance between the live part of the tested object and the shell. There is a CX capacitive reactance in the capacitor. When an AC voltage is applied to both ends of the CX capacitor, it will lead to a current. Flange ball valve

the current is directly proportional to the capacity of Cx capacitor and the applied voltage. When the current is large enough or exceeds the maximum output current of the voltage withstand meter, the voltage withstand meter cannot correctly judge whether the test is qualified or not

II. Insulation resistance tester

the insulation performance of electrical products is one of the important signs to evaluate their insulation, which is reflected by the insulation resistance

we measure the insulation resistance of products, which refers to the insulation resistance between live parts and exposed non live metal parts (shells). According to different products, apply a DC high voltage, such as 100V, 250V, 500V, 1000V, etc., and specify a minimum insulation resistance value. Some standards stipulate that the insulation resistance shall not be less than 1m Ω per kV voltage. At present, in the product standards of household appliances, only the thermal insulation resistance is usually specified, and the insulation resistance value under normal conditions is not specified. The insulation resistance value under normal conditions is formulated by the enterprise standard. If the normal insulation resistance value is low, it indicates that there may be some hidden danger or damage in the insulation structure. If the insulation resistance of the motor winding to the shell is low, it may be caused by the damage of the equalizer slot insulation of the winding during wire embedding. When using electrical appliances, due to sudden power on or power cut-off or other reasons, the circuit generates overvoltage, and breakdown occurs at the damaged insulation, causing personal safety or threat

1. Structure and composition of insulation resistance meter

insulation resistance meter is also known as megger, megger and megger. The insulation resistance meter is mainly composed of three parts. The first is the DC high voltage generator, which is used to generate a DC high voltage. The second is the measurement circuit. The third is display

(1) DC high voltage generator

to measure the insulation resistance, a high voltage must be applied at the measuring end. This high voltage value is specified as 50V, 100V, 250V, 500V, 1000V, 2500V, 5000v in the national standard of insulation resistance meter...

there are generally three methods to generate DC high voltage. The first type is hand-operated generator. At present, about 80% of the megger produced in China adopts this method (the source of the name of the megger). The second is to boost the voltage through the mains transformer and obtain DC high voltage through rectification. The method adopted by general mains megger. The third method is to use transistor oscillation type or special pulse width modulation circuit to generate DC high voltage. Generally, battery type and mains type insulation ohmmeters adopt the method

(2) measurement circuit

in the megger (megger) mentioned above, the measurement circuit and the display part are combined into one. It is completed by a current ratio meter head, which is composed of two coils with an included angle of 60 ° (about). One coil is parallel at both ends of the voltage, and the other coil is connected in series in the measuring circuit. The deflection angle of the pointer of the meter depends on the current ratio in the two coils. Different deflection angles represent different resistance values. The smaller the measured resistance value is, the greater the coil current in the measuring circuit is, and the greater the deflection angle of the pointer is. Another method is to use linear ammeter as measurement and display. In the head of the current ratio meter used previously, because the magnetic field in the coil is non-uniform, when the pointer is at infinity

, the current coil is just at the place with the strongest magnetic flux density, so although the measured resistance is large, there is little current flowing through the current coil, and the deflection angle of the coil will be large at this time. When the measured resistance is small or 0, the current flowing through the current coil is large, and the coil has been deflected to a place with low magnetic flux density, and the resulting deflection angle will not be large. In this way, nonlinear correction is achieved. Generally, the resistance value of the megger head needs to span several orders of magnitude. However, when the linear current meter is directly connected in series into the measuring circuit, it is not enough. The scales at high resistance are all crowded together and cannot be distinguished. In order to achieve nonlinear correction, nonlinear elements must be added to the measuring circuit. So as to achieve the shunting effect when the resistance value is small. When the resistance is high, there is no shunt, so that the resistance value can reach several orders of magnitude. With the development of electronic technology and computer technology, digital display meter gradually replaces pointer meter

the digital measurement technology of insulation resistance has also been developed, among which the voltage ratio meter circuit is one of the better measurement circuits, and the voltage ratio meter circuit is composed of voltage bridge circuit and measurement bridge circuit. The output signals of these two bridges are directly converted into digital value display through a/d conversion and then processed by single chip microcomputer

2. Selection of insulation resistance meter

the selection of insulation resistance meter is mainly to measure the voltage value, and the other is the range to be measured, whether it can meet the needs. If the measurement is very frequent, it is best to choose the alarm setting function

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