2024-11-08
35KV cable outer sheath fault detection
1.On-site situation
(1) Cable grade: YJV1/400-26/35kV single-core cable
Cable length: 1000m 1320m 520m 600m 800m
(2) Cable ends: There are seven circuits (three of which are double-stranded) and 30 cables in total. One end of the cable is in the 301 main transformer room, and the other end is connected to each transformer terminal (synthetic No. 1, water system No. 1, step-up transformer No. 1, 2, 3, vaporization No. 1, purification No. 2)
(3) Cable path: The cable path is clear and all are laid on bridges.
(4) Cable joint position: There is no joint in the middle and no cross-connection box.
(5) Cable insulation resistance: 30 cables, 16 outer sheaths are zero to ground when tested by multimeter.
2. Testing equipment
3.Testing Process
(1) Insulation test: Use the 0.5kV gear of the electronic megohmmeter to measure 30 armored lead wires respectively. The resistance of 16 test wires to the ground is zero, and the resistance of the multimeter test wires is also zero. This means that there are 16 cable faults.
(2) Path finding: The on-site path is clear;
(3) Rough fault detection: Use the burn-through bridge test. Some fault tests are accurate, while some have large errors (related to multi-point grounding). Using the 502 host test, there are 4 fault points 40-60 meters away from the 301 main transformer room, 2 fault points 200 meters away from the 301 main transformer room, 3 fault points 290 meters away from the 301 main transformer room, 3 fault points 215-224 meters away from the 301 main transformer room, and one fault point 360 meters away from the 301 main transformer room. The rest of the fault points are at the end of the cable.
(4) High voltage detection: Use 515-8 pressure test to find the fault point at the approximate location of the rough measurement
(5)Withstand voltage test
After the fault point was handled, 523 was used for withstand voltage (5000V), and the withstand voltage passed. Insulation test: 500V test, the insulation was above 0.5M/500 meters, which passed.
4.Summary
1. The cable fault tester has reference value for rough measurement in the outer sheath test of multiple parallel cables.
2. High voltage flash may cause sparks between the gaps in the cover plate, so you need to pay more attention during the test.
3. The 35kV cable outer sheath insulation test uses a 500V voltage level, and the test is qualified if 500M is greater than 0.5M. If necessary, you can do a withstand voltage test of DC5000V for one minute.
4. When applying pressure, pay attention to the zero-sequence transformer wiring. It is best if the signal line can be short-circuited and grounded.
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