The role of shielding on medium-pressure cross-linked polyethylene is very important. It can improve the uniformity of electric field distribution.
According to the standard understanding, the shielding is divided into non-metallic shielding (conductor shielding, insulating shielding), and metal shielding (copper strip, copper wire). ).
The medium-voltage cross-linked cable now uses a compacted circular conductor structure to improve the electric field on the conductor surface.
On the other hand, I understand that it acts as a water-blocking function.
However, even with this pressing method, there are tiny gaps between the conductor filaments, which will inevitably cause uniformity of the electric field distribution, and the fine burrs generated when the conductors are twisted will cause an increase in partial discharge, which is an serious.
Conductor shielding helps to improve this aspect of the defect and close contact with the insulation.
The role of the insulating shield is also to reduce the air gap between the insulation and the copper strip and to uniformly insulate the surface electric field.
The volume resistivity of the insulating shield exceeds the standard requirement and is likely to cause an increase in the amount of discharge, so it is important to check the volume resistivity of the raw material.
The function of the copper strip shield is to act as a channel for leakage current when a short circuit occurs, and the capacitor current and the lightning protection function during operation.
When the finished product is subjected to the withstand voltage test, the insulation shield should also be stripped for a period of time.
The 8.7/10 kV cable generally has a small end breakdown.
Why is the 26/35 kV cable end breakdown rate high?
Moreover, the breakdown point is 2---3mm under the semi-conductive port.
The analysis is
1. As the voltage increases, the electric field strength gradually increases.
2. The shielding stripping length is not enough and the semi-conductive port is not smooth.
3. The stress cone is not installed properly. These aspects are the main cause of the end breakdown. The treatment method is that the length of the insulation shielding peeling is increased.
According to the experience, it is not less than 70cm.
The screw of the stress cone is installed on the semi-conductive opening 2mm. The smooth processing can be smoothed by the glass, but the insulation cannot be damaged.
Domestic indoor outdoor terminal accessories are now mainly based on cold shrinking, and the technology basically has no problem.
The key is the handling of shielding. If the handling is not good, it is easy to cause a terminal breakdown.
The key is the processing of the external shielding port.
According to the relevant data, the attachment breakdown caused by improper control of the semi-conductive port is higher than other reasons, because the electric field is concentrated and the semi-conductive port is here.
The treatment should be smooth, such as 35 kV cross-linked cable, most of which now use a non-peelable outer shield.
Only by stripping the semi-conducting by means of the stripping knife, the closing may not be very smooth, and the thin glass may be used to scrape the slope of the semi-conducting arc once, which is favorable for the uniformity of the electric field.
The application or improvement of shielding technology on cross-linked cables will continue to improve with the development of the information society.
Only by constantly exploring and discovering, will we find more problems and continue to verify through practice to improve products. quality.
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