In recent years, with the gradual deepening of urban network transformation in domestic cities and the rapid progress of cable production and construction technology, the failure rate of power cable lines has been greatly reduced compared with the past, but compared with developed countries, there is still a certain gap.
According to the responsible party, the causes of cable line faults can be roughly divided into manufacturing quality problems, line system design problems, construction quality problems, and external damage.
In addition to the non-technical reason of force failure, field construction quality should be the most difficult to control among many reasons.
The cause of cable line fault can be divided into cable body problem and cable accessory problem according to the location.
Among them, cable accessories fault accounts for a very high proportion.
As a cable construction practitioner, I have heard and seen many cable accessories faults, due to the installation quality problems, resulting in the accessories into the tide or leakage, and then caused by a very high proportion of the fault.
This kind of problems caused by poor sealing in the installation of cable accessories are common in cable construction.
Necessity of multiple seals for high voltage cable accessories
At present, in the cable lines of 110KV and above voltage grade, as the cross-linked cables occupy the absolute dominant position at home and abroad, the cable accessory technology mainly focuses on the cross-linked cables.
Due to the different insulation materials used for various cables, different sheath, and different operating conditions of cable accessories and the surrounding environment, the requirements for sealing are naturally different.
The main purpose of the seal for the end head is to prevent leakage of insulating oil.
Because transformer terminals, GIS terminals or dry terminals with oil pressure compensation devices account for a small proportion in the power grid, the terminals without oil pressure monitoring and compensation devices are used in a large number, and it is difficult to confirm the amount of remaining oil once the oil leakage occurs.
The decrease of the oil content in the terminal will lead to the change of electric field distribution, resulting in the change of internal insulation creep distance, and finally lead to the breakdown of the attachment.
For the terminal of insulation oil leakage, it is difficult to solve the problem of insulation oil leakage with the current plugging technology, except for necessary monitoring and waiting for power failure to replenish oil or reinstallation
Sealing to the middle joint is mainly a waterproof problem.
Due to the high underground water level in Tianjin, water often accumulates in the connector well even in the non-rainy season, and the cable connector is generally immersed in water all the year round. Therefore, it is very important to ensure the sealing and waterproof performance of the intermediate connector.
Poor sealing effect, because once the joint internal moisture into the joint, under the action of the electrophoretic force, water will enter the cable insulation layer, and longer duration of operation, the cable insulation middle water branches and eventually lead to run cable breakdown, so bad cable joint seal will seriously affect the service life of the cable line.
Sealing the ground system is mainly the waterproof problem of the ground box.
Because once the box seal is not good water, leading to multi-point grounding, it will cause the metal sheath induced current is too large, reduce the load flow, affect the operation.
In view of the importance of sealing to cable accessories and the geographical characteristics of Tianjin area, it is necessary to further strengthen the strength of multiple sealing in the construction of high voltage cable accessories.