The ADSS optical fiber cable, which is tensioned at work, is in a powerful electromagnetic field existence around the space around the wire. The optical cable coupling between the wire and the capacitance between the wires and the earth makes it in a space potential. Under the action of the space potential, a damp or dirty (inevitable) optical cable surface has generated a ground leakage current with the ground. The heat evaporates the surface water of the optical cable. The surface leakage current. When the potential at both ends of the dry belt is high enough, the discharge is generated to form an arc (called the "dry band arc"). The basic condition of electrostatic corrosion is to have a certain leakage current and a high enough space potential.
Dilament leakage current:
According to data on the West Coast of Hantersstor, Scotland: The arc does not occur when the ground leakage current is less than 0.3mA. Therefore, 0.3mA is recognized as the threshold value of the arc; when the ground leakage current exceeds the threshold of about 0.5mA, the arc will be generated; as the ground leakage current exceeds 1mA, the electrical or lonely will be serious; At about 5mA), the arc activity will stop, that is, the large current does not generate an arc. The test results also show that the degree of electrostatic corrosion is related to the tension of the optical cable.
The standard for the ADSS cable to withstand space potential:
According to the corresponding standards and specifications, the spatial potential that ADSS cable outer condoms can bear are divided into two levels.
Class A: PE Guard ≤12kV;
Class B: AT cover ≥12kV; the upper limit of the B -Class sheath has not been provided in the relevant standards and specifications. The general method is 20-25KV.
Activity length:
The ground leakage current is driven by space potential. At a certain gear of the transmission line, assuming that the distance between the optical cable and the wire is unchanged (consistent) and the distance from the earth is unchanged (in fact impossible, just assumption), the end distance of each point of the surface of the optical cable and the ground end of the ground is changing It is very large. Although the induction voltage in the center of the gear is very high, the charging constant is very large, the charging current is extremely small, and the surface of the optical cable has no leakage current; as the end of the golden gear that is close to the tower, the inductive voltage tends to zero the same time ground leakage The current becomes larger, and the ground leakage current on the ground is the maximum value. If the arc condition is met, the electrical corrosion will occur. The distance from a certain point from the ground leakage current to the end of the golden gear is called "activity length", that is, the most likely dangerous area of electrostatic corrosion. Therefore, there are two activity lengths in a stall.
The influence of dual -circuit phase:
The space potential on the optical cable suspension point is affected by the arrangement of the three -phase wire phase, and the changes in the single circuit phase have almost no effect. In the dual-circuit system, in terms of the installation of ADSS, the ABC-ABC phase is the smallest, and the other phase of the phase has expanded to varying degrees, especially the "space" of the ABC-CBA phase as the maximum. For a suspension point: Double -line lines are more complicated when they run back due to the power outage on one side. The space potential may become smaller or larger. In addition to the influence of other influences, when the suspension point of a certain optical cable is certain, the space potential will also be affected by the diameter of the wire and the ground wire, the division of the wire, the wind of gold and the wind cable.
Control of electrostatic corrosion:
As far as you are currently known, all electric erosion failures occur in the "activity length" area. Therefore, the scope of control is also concentrated in the activity length range.
Static control:
Under static conditions, the AT cover ADSS cable working in the 220kV system, the space potential of the hanging point should be controlled at no more than 20kV (the double -back and multi -back co -stands should be lower); For the PE protective ADSS cable, the space potential of the hanging point should be controlled at the space potential design of the 8KV. Static hanging point should be considered:
(1) System voltage and phase arrangement (dual circuit and multiple circuits are important).
(2), the tower shape (including the tower head and the call).
(3) The length of the insulator strings (changes in the length according to the pollution level).
(4) Direct diameter and division of the guide/ground wire.
(5) The safety limit of the wire and the ground and the ground.
(6) Control of tension/arc perpendicular/span (under the conditions of windlessness, ice -free, and at the annual average temperature conditions, the ES ES with a load of not greater than the optical cable is 25%RTS; under the design meteorological conditions, its load is not greater than greater than that The MAT of the optical cable is 40%RTS).
(7) Corresponding to the jump line (tensor tower) and grounding (such as cement rod line) to study and consider its influence.
Dynamic control:
In dynamic conditions, the AT cover ADSS cable working in the 220kV system, the space potential of the hanging point should be controlled at less than 25kV; Control at least more than 12kv. Dynamic conditions should be considered at least:
(1) The system voltage is the nominal voltage. In some cases, there will be a error of +/- (10-15)%, and the positive tolerance will be taken;
(2), golden string (mainly hanging skewers) and the wind of optical cables;
(3) The possibility of replacement of the original phase;
(4) The possibility of running the single circuit of the dual -circuit system;
(5) The actual situation of pollution in the region;
(6) Newly intertwined lines and things that may have;
(7), the municipal construction and development plan along the line (maybe the ground may be raised);
(8) Other situations affecting the optical cable.
The electrostatic corrosion of the ADSS cable sheet that is tension during operation is caused by the ground leakage current and dry band arcs of 0.5-5mA by the space potential (or electric field strength) of the capacitor coupling. If measures are taken to control the ground leakage current below 0.3mA, and the shape will not be continuously arc, the electrom corrosion of the sheet will not occur in principle. At present, the most realistic and effective method is to control the tension and space potential of the optical cable. The static space potential design of the AT or PE protective ADSS optical cable should not be greater than 20kV or 8KV, respectively. Under the worst dynamic conditions, it should not be more than 25kV or 12kV, respectively. The optical cable can run safely. The static space potential is 20KV (mostly 220kV system) or 8kV (mostly 110kV system) system in the system. One of the effective measures for corrosion. At the same time, the vibration damage of the ADSS cable and other anti -vibration methods (such as applicable anti -vibration hammer) are carried out.
It cannot simply determine the installation position of the optical cable (often referred to as the "hanging point") at the distance of the system voltage level and/or the departure wire. The space potential of the hanging point should be calculated based on the specific situation of each tower type. Although there have been many ADSS cable electrostatic corrosion failures in recent years, a large number of practice has proved that the ADSS cable can continue to be promoted in the 110kV system; Can continue to be promoted. Under the premise of ensuring the quality of ADSS cables, the electrom corrosion of the ADSS optical cable can be controlled by standardizing the design, construction and operation conditions of the ADSS cable. It is recommended to formulate and implement corresponding specifications/regulations.
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