The DC high-voltage generator under the UHV power company can help many power workers conduct various power tests more conveniently.
1. Measure insulation resistance
The metal shielding or metal sheath and armor layer of the cable should be carried out on each phase and connected to the metal shielding and armor layer of the cable. For this test, as long as the cable is a capacitive device, the capacitive device is insulated. Attention should be paid to the resistance and absorption. For example, complete discharge before and after testing. After a round of fire, disconnect first.
2. DC withstand voltage and leakage current test
Insulated cables are only designed for DC withstand voltage and not for AC withstand voltage, as AC IG can cause thermal radiation; Uneven distribution of heat and electric field can easily damage cables. It should be noted that the cable core wire has a negative polarity, and after the cable is sorted, the moisture carries a positive charge. If the iron core is the negative electrode, the concentration of moisture will increase the amount of moisture inside the insulation, leading to an increase in leakage current and making it easier to detect defects. If the iron core is of positive polarity and moisture enters the lead sheath, the moisture in the insulation decreases, and the leakage current decreases, making it difficult to detect defects.
3. Rubber cable testing
Rubber and plastic cables refer to PVC, cross-linked polyethylene, and ethylene rubber insulated cables, which have the characteristics of large capacity, high voltage, and easy bending, and have gradually replaced oil paper insulated cables. Cross linked polyethylene cable is different from the familiar oil immersed paper release cable. The main insulation is cross-linked polyethylene plastic, and there are two layers of semiconductor rubber coating. The outer surface of the core is coated with semiconductor rubber metal wire. Overcoming corona and free discharge, there is a good transition between the core wire and the insulation layer. The outer surface of the middle insulation is coated with a second layer of semiconductor adhesive, and the copper strip shielding layer is only 0.1mm thick. Thin copper strips form phase shielding.
1) Determine the method of water ingress for rubber cables
Before cable transportation, after repairing the terminal or joint, if the inner lining is damaged after entering the line: measure the DC resistance of the copper shield and conductor at the same temperature using a double line bridge; When the positive resistance increases, the direct current resistance of the shield increases, which may corrode the copper shielding layer; When the ratio decreases, the contact resistance of the replacement electrical contact in the attachment increases. possible.
2) Stress testing
The DC high-voltage generator withstand voltage test is divided into DC withstand voltage test and AC withstand voltage test. Currently, rubber and plastic cables, especially cross-linked polyethylene cables, are developing rapidly. Due to the disadvantage of high-voltage cross-linked polyethylene cables having DC resistance, they are not suitable for DC voltage test. There are two points: a. Cross linked polyethylene cables and nearby cross-linked polyethylene cables and nearby DC test voltage accumulate insulation effect, accelerate insulation, and shorten service life; B、 The distribution of insulation electric field under DC voltage is different from the actual working voltage. The former is distributed according to resistivity, while the latter is distributed according to dielectric constant.
