Transmission Line Basics and Accessories

Transmission line basics

(a)The composition of the transmission line

The transmission pathway is composed of power lines, substation and distribution equipment.

Transmission lines from the structure can be divided into two types of overhead lines and cable lines.

The main components of overhead transmission and distribution lines are: conductors, lightning lines (referred to as lightning lines), fixtures, insulators, towers, ties and foundations, grounding devices, etc.

(b)The role of each component and classification

(1), conductor

Conductor is fixed in the tower to convey the current with the metal line, due to the wire running in the atmosphere all year round, often under tension, and by the wind, ice, rain, snow and temperature changes, as well as the impact of chemical impurities contained in the air erosion. Therefore, the wire material should have good electrical conductivity, but also must have sufficient mechanical strength and corrosion performance. Currently in the transmission line design, overhead conductors and lightning lines are usually made of aluminum, aluminum alloy, copper and steel materials, they have a high conductivity, good heat resistance, high mechanical strength, vibration resistance, corrosion resistance, light weight and other characteristics.

Nowadays, transmission lines mostly use steel wire with high mechanical strength in the center, surrounded by steel-core aluminum stranded wire with high electrical conductivity, as shown in Figure 0-2. Steel-core aluminum strand is slightly smaller than copper conductivity, but has high mechanical strength, light weight, cheap and other characteristics, especially for high-voltage transmission lines. Steel-core aluminum stranded wire can make the file distance enlarged because of its high tensile strength and small arc sag.

Steel-core aluminum strand is divided into normal type (LGJ), reinforced type (LGJJ) and light type (LGJQ) according to its different aluminum and steel cross-sectional ratios. In the high-voltage transmission lines, the normal type is used more. In the ultra-high voltage lines use more light type. In areas of high mechanical strength, such as large crossings, heavy ice areas, etc., the use of reinforced more.

(2), lightning protection line

Lightning line role is to prevent lightning directly on the wire, and the lightning current into the earth. Lightning line hanging on the top of the tower, and in each base tower are connected to the grounding line and grounding body, when the thundercloud discharge lightning strikes the line, because the lightning line is located above the wire, the first lightning hit the lightning line, and with the lightning flow through the grounding body into the earth, thereby reducing the chances of lightning striking the wire, play a lightning protection role. 35kV lines are generally only in, out of the power plant or substation at both ends of the lightning line, the 110kV and above lines are generally along the whole line. 110kV and above lines are generally set up along the whole line lightning line, lightning line commonly used galvanized steel stranded wire.

(3), the line metallurgy

Usually the transmission line using metal parts in general called fixtures, it has a wide range of types. The following is a brief introduction to several types of fixtures.

1、Connecting fitting

Connecting fixture is used to connect the hanging insulator to form insulator string, such as ball head hanging ring, bowl head hanging plate (as shown).

2、Connecting fixture

Connecting the gold is used to connect the wire or lightning line, mainly for the wire various crimping methods (clamp pressure, hydraulic, burst pressure, etc.) used to connect the tube and repair the tube, and trench line clamps, pre-stranded wire, etc..

The connection method of the wire is mainly clamped and crimped, when the wire cross-section is less than or equal to 240 mm2, the use of clamped pipe connection, when the wire cross-section is greater than or equal to 300 mm2, the use of pressure tube connection, such as hydraulic or burst pressure method connection, lightning line are connected using the crimping method.

3、Fixed fixture

Fixed gold is used to fix the wire on the insulator string, or the lightning line fixed in the gold string, such as dangling wire clips, tension-resistant wire clips. In addition, in order to prevent and reduce the impact of corona on ultra-high-voltage lines, also used XGF type anti-corona dangling wire clip.

4、Protection fixture

It includes the wire and lightning line anti-vibration gold and insulation gold. Anti-vibration gold has: anti-vibration hammer, guard line, damping line, repair strips, aluminum wrapped belt, etc. Insulation metal has: spacing bar, even pressure ring, shielding ring, heavy hammer, etc.

1) Spacer bar. Used in the split wire, the role is to prevent the whip between the wire, suppress the breeze vibration, suppress the sub-grade distance shock.

2) Even voltage ring. Used to even out the voltage distribution on the insulator ring, in order to make the insulator each piece to bear the voltage is basically uniform.

3) Shielding ring. Used to reduce the strength of the corona on the fixture ring called shielding ring.

4) Heavy hammer. Can inhibit the overhanging insulator string or jumper insulator string swing too large, straight line tower on the wire and lightning cable is pulled up.

5) Anti-vibration hammer. Can reduce the amplitude of vibration, thereby reducing the vibration of the wire.

5、Drawing wire fixture

Mainly used for pulling wire tower pulling wire tightening, adjusting and connecting, can be divided into tightening, adjusting and connecting three types. As shown in the figure for the adjustable UT-type wire clip, the use of the clip can adjust the tension of the wire; adjustable U-shaped screws, can adjust the tension of the wire; wedge can be fixed with the body of the wire clip wire.