Preparation of cable and oil cup terminal
3.1 From the outside to the inside, the cross-linked cables are outer sheath, steel tape armor, copper tape shield, outer semiconductor shield, insulation layer, inner semiconductor shield and conductor stranded wire. Before conducting partial discharge and withstand voltage test, the outer sheath, armored steel strip and copper strip shielding layer shall be stripped first, and then the outer semiconductor shielding layer shall be stripped with special tools.
3.2 For 10kV cross-linked cables, the exploitation length of the outer semiconductor shield is generally 150-200mm, and for 33kV cross-linked cables, the exploitation length is generally 450-500mm. The stripping length of the copper strip shielding layer should be 100mm longer than the exploited outer semiconductor shielding layer (not too long). The steel strip left outside the end of the oil cup should be cut flat and should not be scattered around the oil cup. It is better to fix it with steel strip to avoid tip discharge. The root of the cut surface exploited by the outer semiconductor shielding layer should be as smooth as possible, and there should be no semiconductor tip, and there should be no residual semiconductor traces on the insulating surface to avoid discharge.
3.3 The test insulating oil in the oil cup shall be filtered and dried, and the breakdown field strength shall be above 40kV, otherwise the accuracy of the test results will be affected. Freon (F113) and silicone oil can also be used as insulating media.
3.4 Both ends of the test cable shall be placed in the oil cup terminal, with many copper pins at the bottom. The oil cup that leads the high voltage to the cable is called the near end oil cup, and the corresponding oil cup is called the far end oil cup. When installing the near-end oil cup, it is necessary to push the elastic copper needle upward to ensure good contact between the copper needle and the cable conductor core; When installing the remote oil cup, just insert the sample cable into the oil cup. Note that transformer oil (or other insulating medium) should completely cover the root of the cut surface of the outer semiconductor shielding layer to avoid root discharge.
3.5 For 35kV cross-linked cables, the system is also equipped with a set of stress cone device to improve the root electric field. During installation, after exploiting the outer semiconductor shielding layer, the fixed cable rack should extend about 35mm beyond the root of the section of the outer shielding layer, and then lead the grounding lead of the stress cone to the outside of the oil cup and connect it with the cable grounding.
3.6 Clean the surface of the oil cup, connect the high-voltage lead with quick connector to the near end oil cup, and then conduct the cable test (see Figure 1)
The use method of the three-core oil cup is similar to the above. When the three-core experiment of the 10kv finished cable is carried out at the same time, the cable exploitation length is the same as the above figure. It is only necessary to nail the small steel nails into the near-end three-core conductor, and then connect the three-core conductor with 1.5~2.5 square copper wire, and then put the three-core cable into the oil cup and hang it on the bottom hook. The far end is directly immersed in the oil cup.
When the three-core test is conducted for the 35kv finished cable, the exploitation length is as per the 35kv experiment standard above. During exploitation, the cable conductor shall expose the insulator as much as possible by 5mm. If sufficient contact is considered, small steel nails shall be nailed into the three-phase conductor and connected with bare copper wire, so as to ensure full contact between its end and the oil cup, and ensure that the girth is flat Ф The stress cone of 76 is sleeved at the girth of three-phase cable and fully grounded. You can use it with confidence. Special attention should be paid to the high requirements for insulating oil in the 35kV cable laboratory. For example, the oil should be dried at 70 for 30 minutes in wet weather. The oil cup should also be clean, and the residual aluminum and copper powder inside should be cleaned regularly.
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