DC high voltage generator caused by the output voltage of 120KV, the output current of 5mA, the operating frequency of 40kHz and other characteristics and is widely used in electric power test for power cable detection test and lightning arrester leakage current test; DC high-voltage generator adopts the intermediate frequency voltage doubling circuit, the new DC high-voltage generator using PWM pulse width modulation technology and high-power IGBT devices, according to the theory of electromagnetic compatibility, using special shielding, isolation and grounding measures, so that the DC high-voltage test to achieve high quality. The new DC high voltage generator applies PWM pulse width modulation technology and high power IGBT device, according to the electromagnetic compatibility theory, adopts special shielding, isolation and grounding measures, so that the DC high voltage test realizes high-quality, portable and can withstand the rated voltage discharge without damage; DC high voltage generator has a variety of protection functions, such as: low-voltage over-current, low-voltage over-voltage, high-voltage over-current, high-voltage over-voltage, zero-position protection, no-grounding protection, and so on.
Two, the application of the test of power cables
1, measurement of insulation resistance
Should be carried out on each phase, respectively, the other two phases of the conductor, the metal shield at both ends of the cable or the metal sheath and armored layer access, for the test, as long as it is noted that the cable is a capacitive device, capacitive equipment to do the insulation resistance and absorption ratio of the situation should be noted. For example: full discharge before and after the test. First fire after lap, first disconnected after the blackout shaking the meter and so on.
2, DC withstand voltage and leakage current test
Oil paper insulated cables only do DC withstand voltage, do not do AC withstand voltage, because the AC Ig increase may lead to thermal breakdown; hot state, the electric field distribution is not uniform, easy to damage the cable. It should be noted that: the cable core connected to the negative polarity, the cable moisture, moisture with a positive charge, if the core connected to the negative polarity, moisture will be concentrated to the core, the moisture in the insulation increases, the leakage current increases, easy to find defects, if the core is positive polarity, the moisture to the lead packet infiltration, the moisture in the insulation decreases, the leakage current decreases, it is not easy to find defects.
3, rubber-plastic cable test
Rubber-plastic cable refers to PVC, cross-linked polyethylene, ethylene-propylene rubber-insulated cables, which is characterized by large capacity, high voltage level lightweight structure, easy to bend, and is now gradually replacing the oil-paper insulated cables. Crosslinked polyethylene cable and the familiar oil-impregnated paper tundish cable difference in addition to the main insulation between the phases is crosslinked polyethylene plastic, there are two layers of semiconductor gel coatings, in the outer surface of the core wire coated with a had semiconductor gel, to overcome the corona and free discharge, so that there is a good transition between the core wire and the insulating layer, in the outer surface of the interphase insulation, the second layer of semiconductor gel coated in the copper tape shielding, the copper tape shielding layer is just a layer of 0.1mm thick thin copper tape, composed of interphase shielding layer.
1) determine whether the rubber-plastic cable into the water method
In the cable before operation, redo the terminal or joints, lining layer broken into the water: with a two-armed bridge to measure the same temperature in the copper shield and conductor of the DC resistance; when the ratio of the former and the latter with the operation of the former than an increase in the shielding layer of the DC resistance increases, the copper shielding layer may be corroded; when the ratio of the former and operation of the DC resistance is reduced, the accessories in the When the ratio decreases compared with that before the commissioning, it indicates that the contact resistance of the alternating current connection in the accessories may increase.
2) voltage test
DC high voltage generator voltage test is divided into DC voltage test and AC voltage test, rubber and plastic cables, especially cross-linked polyethylene cables have been rapid development, due to the use of high-pressure crosslinked polyethylene cables using DC withstand voltage exists there is an obvious disadvantage, it is not appropriate to use DC voltage test, for the following two reasons: a, the DC test voltage process of cross-linked Polyethylene cable and the nearby formation of space charge, the insulation has an accumulative effect, accelerating the aging of insulation, shortening the service life; b, DC voltage insulation electric field distribution and the actual operating voltage is different, the former according to the resistivity distribution and the latter according to the distribution of dielectric constant.
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