I. Analysis of the setting and misjudgment of the upper limit current
The working principle of the insulation voltage tester is to determine the leakage current generated by the high voltage test object. Here, the leakage current test voltage is several or even several times the leakage current of the measured object under the rated voltage, which is denoted as. The current set on the insulation voltage tester is the trip current of the instrument, denoted as. The condition of the general withstand voltage test of the insulation voltage tester increases with the increase of the test voltage. When the test voltage rises to the upper limit of the set voltage and maintains for 60 seconds, the insulation of the measured object is not broken during this process. That is, the insulation resistance tester test instrument will prompt the test to pass; otherwise, if the insulation of the test object is penetrated, the current flowing through the measured object and the instrument at this time, the insulation voltage tester will issue a current alarm, indicating that the test is not qualified. Insulation voltage tester trip current is only a reference value rather than a limit value, and the setting is to determine whether the insulation is broken down, only as a pointer, the test voltage setting is the limit pointer (this we have in front of several Has been described in the e-newsletter.) The setting directly affects the determination result of the withstand voltage test. If the setting is too small, the qualified product may be misjudged as a defective product; the other is that the setting will be too large, and the defective product will be erroneously judged as a qualified product.
In addition to normal testing, the following situations can occur:
Hi-Lim/Max-Fail, Short, and Breakdown.
When the upper limit alarm occurs, the leakage current exceeds the trip current value (does not meet the factory-set upper limit current limit), or it is beyond the range of the insulation withstand voltage tester, but in this case, the measured object does not have to be high-voltage breakdown. It can only indicate that the leakage current exceeds the reference value, and further quality appraisal of the product is needed to determine whether the product has serious safety problems; when the instrument indicates a short circuit, it means far beyond the measurement range of the insulation withstand voltage tester, the measured object enclosure and The L and N lines are short-circuited and there are serious safety problems. It is necessary to verify whether the connection between the insulation withstanding tester and the measured object is short-circuited, and then make a re-measurement of the product; when the breakdown voltage appears, At this time, the insulation has failed and the product has been subjected to high pressure breakdown. The insulation material and quality of the product must be redefined.
Second, the setting of the lower limit current
Insulation withstand voltage testers on the production line are used very frequently, especially test lines, test fixtures, etc. are often in active state, easily causing the internal core wire to break open, and generally not easy to find. As long as there is an open circuit at any point in the loop, the high voltage output from the insulation voltage tester cannot be truly added to the measured object. All of these reasons will cause the set high pressure to not be added to the measured object when the compressive strength test is performed. Naturally, the current flowing through the measured object is almost zero because it does not exceed the upper limit of the dielectric withstand voltage tester. Set the value, then the instrument will give a test qualified notice that the insulation is qualified. However, the test data in this case is not true. If the test object at this time happens to be defective in insulation performance, serious misjudgment will result.
Third, how to avoid the occurrence of miscarriage of justice
In the withstand voltage test, we all believe that the smaller the leakage current, the better. Therefore, many operators do not set the lower limit current (general factory value is set to zero). If the above situation occurs, there is a misjudgment. It is possible that a reasonable setting of a lower limit at this time can solve this situation. When the pressure tester is not connected to the measured object, empty test is performed. At this time, there is a small imaginary current. We only need to set the lower limit current to be slightly higher than the value of the null test current. When the test circuit appears open circuit (if the operator fails to connect the measured object or the test line is short cracked), because the leakage current value is lower than the lower limit setting, the insulation voltage tester will prompt an alarm. Then we need to check whether the test line or open circuit appears on the connection, so as to ensure the effectiveness of product testing. In the insulation resistance test, the same problem also exists. For general products, it is always considered that the higher the insulation resistance of the product is, the more satisfactory the requirements are. However, if the phenomenon of open circuit between the insulation withstanding tester and the measured object also occurs, the same misjudgment phenomenon will occur. At this time, we can avoid this by setting the upper limit of the insulation resistance.
Fourth, how to determine the situation prompted by the instrument alarm
A fully functional insulation withstand voltage tester is required to provide sufficient information for the operator. When the instrument is alerted, it can quickly provide some information to the operator in order to improve the production efficiency. Below we have a wealth of project experience in the provision of customer-related test services Huayi, how to provide information through the instrument, the operator can fully understand whether the test object is not caused by improper operation.
V. Conclusion
Many advanced insulation withstand voltage testers on the market today provide a variety of functions to avoid false positives in tests. Operators must also provide comprehensive, systematic, and standardized operational training. This reduces false positives and improves Product testing efficiency and product quality have important implications.
Pressure test equipment operating procedures
First, run inspection test
1. Connect one end of a 0.7 MΩ standard resistor to the ground of the voltage tester.
2. Turn on the power and set the withstand voltage test instrument and alarm leakage current to 5mA.
3, open the withstand voltage tester, with the test stick hit the other end of the standard resistance, adjust the voltage in the instrument to send an alarm within the 3410V to 3590V, then determine the instrument is in normal working condition, if the instrument is not in the range of 3410V to 3590V alarm, the instrument Not working properly.
4. When the function of the equipment is found to be invalid during the operation inspection and the inspection result fails to meet the specified requirements, the operator shall retest the product that has been tested since the previous inspection and pass the pressure resistance tester to the maintenance.
Second, familiar with the pressure tester's various performance and operating requirements, should be fixed by the post operation, non-personnel personnel is strictly prohibited operation.
Third, the operation steps:
The operator's seat and foot must be covered with a rubber insulation pad. Only when the test lamp is extinguished, no high-voltage output can be used to connect or disassemble the tested model.
1. Calibrate the instrument before testing. (Method: Leakage current of 5mA, use 700KΩ ceramic resistance between the ground clamp and the high-pressure test probe until the instrument alarm prevail.
2. Connect the tested model to confirm that the voltmeter is specified as “0â€. When the test lamp is off, clamp the instrument ground clamp to the heat sink of the tested machine and press the power switch of the tested model.
3. Set the withstand voltage tester test conditions: A, voltage: 3500V; B, leakage current: 5mA; C, test time timing: 4 seconds when the production line.
4. Place the test stick probe against any AC input metal insert on the power cord head.
5. Press the start button to observe the test result. In the set time, the ultra-leakage lamp does not light, and the measured model is qualified.
6. If the tested model exceeds the set leakage current value, the instrument will automatically cut off the output voltage. At the same time, the alarm will be triggered and the ultra-leakage lamp will be on. If the tested model is unqualified, the alarm sound can be cleared by pressing the reset button. When retesting, press the start button again.
Fourth, the use of matters needing attention:
1. Under the operator's feet, insulate the rubber pad and wear insulated gloves to prevent the danger of life caused by high voltage electric shock;
2. The instrument must be grounded reliably;
3. When connecting the tested object, it must ensure that the high voltage output is "0" and in the "reset" state;
4. During the test, the ground of the instrument and the tested body must be connected reliably and it is forbidden to open the circuit.
5. Do not short-circuit the output ground wire and the AC power cable to avoid high voltage in the housing and cause danger.
6. Avoid high voltage output terminals and ground short circuit as much as possible to prevent accidents;
7. Test light, ultra-leakage light, once damaged, must be replaced immediately to prevent misjudgment;
8. When troubleshooting, you must cut off the power;
9. When the instrument is adjusted to no-load high pressure, the leakage current indication header has initial current, which is normal and does not affect the test accuracy.
10. The pressure tester should avoid direct sunlight and do not use or store it in high temperature, humid and dusty environment.
5. Pay attention to the maintenance of the voltage tester. The operator must disconnect the power of the instrument when leaving the job.
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