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Share a few test methods for ultra-low frequency AC withstand voltage devices

2018-04-25 00:00:40

Ultra-low frequency insulation withstand voltage test is actually an alternative to power frequency withstand voltage test. In the power frequency voltage test of large and medium-sized machines, motors, power cables and other test products, because their insulation layer presents a large capacitance, so a large capacity of the test transformer or resonant transformer is needed. Such huge equipment, not only bulky, high cost, but also very inconvenient to use. In order to solve this contradiction, the method of reducing the test frequency and thereby reducing the test power supply capacity is widely used in the world. The new generation of "VFL series 0.1Hz ultra-low frequency high voltage generator" adopts the latest power electronic components and microcomputer technology, further reducing the size and weight of the equipment, fool operation, more stable performance, and overcoming the shortcomings of the first generation of mechanical booster with short service life, high failure rate and large volume. Below, explain the two test methods of this instrument in detail!


1, a special high voltage connection cable 2, a special low voltage connection cable 3, a power line 4, 2 power supply insurance 5, a discharge rod


The instrument consists of two parts: a controller and a booster.


Power cable withstand voltage test method: disconnect all the electrical equipment connected to the cable to be tested, use a megohm meter to test the insulation parameters of each phase of the cable, and pass the test before carrying out the ultra-low frequency withstand voltage test. Test wiring: Connect the test equipment to the test cable with the attached special connection wire as shown in the figure. Close the power supply after carefully checking that the wiring is correct, set the test frequency, time and voltage again, as well as the overcurrent protection value and overvoltage protection value on the high voltage side, and then start the boost test.


In the process of boost and withstand voltage, if it is found that the output waveform is abnormally distorted, the current is abnormally increased, the voltage is unstable, and the phenomenon of odor, smoke, abnormal sound or flash burning occurs in the test cable, the boost voltage should be stopped immediately, and the cause should be identified after shutdown. If these phenomena are caused by the weak insulation part of the test cable, it is considered that the voltage test is unqualified. If it is determined that the test cable is caused by air humidity or surface dirt, the test cable should be cleaned and dried before the test.


Related content learned from experience


In the process of voltage resistance, if there is no abnormal sound, odor, smoke and data display instability, it can be considered that the insulation has withstood the test of the test. In order to better understand the insulation situation, the surface state of the insulation should be monitored as fully as possible, especially for air cooled units. Experience indicates that appearance monitoring can detect abnormal insulation phenomena of synchronous motor that cannot be reflected by the instrument, such as surface corona, discharge, etc.

Matters needing attention

When the instrument is usually not used, it should be stored in an ambient temperature of -20 ° C ~ 60 ° C, relative humidity of no more than 85%, ventilation, and no corrosive gases. Storage should not be close to the floor and walls.


In humid areas or humid seasons, if the instrument is not used for a long time, it is required to turn on the power once a month (about two hours) to make the moisture distribution and protect the components.


When the instrument is used outdoors, avoid or reduce direct exposure to sunlight as much as possible. When the instrument is used outdoors, avoid or reduce direct exposure to sunlight as much as possible.