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High Voltage Cable Structure
Three cables come under this type of cable; they are as follows-
(a) H-type
(b) S.L. Type
(c) H.S.L. Type
For low voltage and medium voltage, belted (stripped) cables can be used because the dielectric stress is limited to this voltage, but as the voltage increases, the dielectric stress increases, resulting in high and very high voltages. The design of the cables has to be changed at high voltage. Triphase cables produce both radial and tangential stresses (a core belted cable produces only radial stresses). The tangential stress acts along the insulator, while the radial stress acts perpendicular to the insulator.
Generally, the tangent stress radius is about 1/10 as compared to the radial force. As a result, the current is different from O. Along with this, the electrical resistance and dielectric of the paper would have been much higher in the Yank direction than in its tangent direction. As a result, the tangential stress causes a capacitance current (different from the capacitive erosion current. These currents produce power and local heating effects in the cable. A fault can develop at any moment. After that, the tangential stress causes a belted-out current). Voids and vacuum space are created in the insulator of the cable. These ionize the gap and damage the insulation of the bill. Therefore, the belted cable is not suitable for high voltage.
The above problems are eliminated by allowing erosion currents to flow through the ground wire into the ground with the help of earthing in screened cables. Below are the different types of H.T. Cables Mentioned. Types of High Voltage Cables :-
(a) H-type cable
Figure 1 shows an H-type cable. It is named after the H-type of its inventor, M.Hochstadter. In this type of cable, no belt insulation type is used but. Each code of cable is wrapped with paper to the desired thickness. Over this paper, a layer of metalized, perforated paper is applied to facilitate the process of impregnation and voids. is not likely.
The expansion and contraction coefficient of this porous metalized paper is also similar to that of the dielectric. After this, a cloth tape made of copper wires is wrapped jointly on all three coils, and over it, the lead sheath is provided directly without providing the belt insulating. The pre-described method, such as braiding or bedding, anchoring, and serving folds, is provided on top of the loading sheath. All metal casings and lead sheaths are placed at ground potential with the help of ground wire so that erosion current does not flow through the insulator and the insulator has only radial stresses.
Thus the dielectric loss is reduced, and the heat dissipation surface increases due to the metalized cover. As a result, the current carrying capacity of the cable increases, and the size of the H-type cable is smaller for the same current carrying capacity. This type of cable is suitable for voltage up to 66 kV.
- Read more: Classification of Overhead Transmission Line
(b) S.L. Type Cables
S.L. The structure of (Separately Lead Sheathed) cable is shown in Figure 2. In this type of cable, each core is first insulated with impregnated paper, and then a separate lead sheath is mounted on each of them so that each cable appears separately. Then the three cores are joined together with filler material, and armoring and serving on the cable is done like other cables.
These types of cables have the following characteristics
(i) There is no lead corpus on all three ends of the cable, which makes bedding of the cable possible.
(ii) The core to core fault is very less in this type of cable as the cores are well insulated from each other.
(iii) It has an electric stress radius.
(iv) The metal sheath helps in heat distribution in the loaded cables, thereby increasing the current carrying capacity of the cables.
(v) The electric stress affects only the paper dielectric, which is quite uniform, and as a result, the voids are not present in the electric field.
(vi) This type of cable can be used up to 66KV voltage.
(c) H.S.L. Type Cable
H.S.L. The cable-type is shown in Figure 3, which is H type, and S.L. Types of cables are combined. Each code is blocked with paper, and then a metalized paper fund is placed on top of it and then a lead cell. After that, filler material is applied by including all three whips. After this, braiding, armoring, and serving are done like other cables.
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