What Is a Power Transmission Line?

The power transmission line is realized by boosting the power generated by the generator with a transformer and then connecting it to the power transmission line through control equipment such as a circuit breaker. Structural form, transmission lines are divided into overhead transmission lines and cable lines.

Widely used in three phases

The basic process of power transmission is to create conditions

The protection of transmission lines is divided into primary protection and backup protection.

(1) Lightning strike.

Commonly used professional terms for transmission lines are: pole tower height, pole tower nominal height, suspension point height, line distance, root opening, overhead ground wire protection angle, tower burial depth, jumper wire, initial extension of wire, pitch, split wire , Arc droop, limit distance, horizontal distance, vertical distance, representative distance, wire transposition, guide (ground) line vibration, pole tower. ^[4]

Transmission line path selection

Path selection and survey are the key to the entire line design. The rationality of the scheme plays an important role in the economic, technical indicators and construction and operating conditions of the line. In order to shorten the path length reasonably, reduce the investment on the line, and ensure the safety and reliability of the line, it is convenient to operate. Sometimes a line needs to travel back and forth for 3 to 5 trips to determine the best solution. A comprehensive test of patience and responsibility.

During the project selection phase, the designer should conduct a full capital search and research on the above-ground, underground, under-construction, and planned engineering facilities according to the actual situation of each project. Short, few corners, few crossings, and better terrain conditions. Comprehensively consider the cost of compensation and civil work, and avoid trees, houses and cash crop planting areas as much as possible.

In the survey work, both the economic rationality of pole positions and the possibility of establishing key pole positions (such as corners, intersections, and special locations where pole towers must be established, etc.) are taken into account. In particular, special measurements must be repeated to compare and make pole towers Position as far as possible to avoid difficult traffic areas, to create better construction conditions for the assembly of towers and tight lines.

Selection of transmission towers

Different tower types are different in terms of cost, land occupation, construction, transportation, and operation safety. The cost of the tower project accounts for about 30% to 40% of the entire project. The reasonable choice of the tower type is the key.

For new construction projects, if only investment is allowed, only 1 or 2 linear cement rods are generally used.

Transmission tower

The angle steel tower is selected, the material preparation is simple and clear, the construction operation is convenient, and the safety level of the line is improved. For the lines with the same tower multiple times and constructed along the planned road, the towers generally use steel pipe towers with a small footprint. However, if the steel towers are used for large corner towers due to structural reasons, the deflection of the pole top is likely to be deformed, and the foundation construction costs will also be It is double the angle steel tower. The straight tower uses steel pipe tower and the corner tower uses angle steel tower. The scheme is more reasonable and can meet the requirements of environment, investment and safety.

In view of the hidden danger caused by insufficient distance to ground after more than ten years of operation of many old lines, the appropriate selection of higher pole towers and the reduction of the horizontal distance in the design of new lines can increase the distance between the conductor and the ground. In the line elevation project, a wine glass (Y-shaped) steel pipe tower with a small footprint and easy installation is designed. The construction period can be shortened from 3 to 5 days of a traditional pole tower to 1 day, which can reduce the power outage time.

Basic design of transmission lines

The tower foundation is an important part of the transmission line structure, and its cost, construction period and labor consumption account for a large proportion in the entire line project. The construction period accounts for about half of the entire construction period, the transportation volume accounts for about 60% of the entire project, and the cost accounts for about 20% to 35% of the entire project. The quality of the foundation selection, design, and construction directly affects the construction of the line project.

According to the actual geological conditions of the project, it is more important to optimize the design of each foundation section by section and foundation. Especially for bearing towers that have a large impact on cost, it is refined from four legs to two pulls and two pressures or three pulls and one pressure. It is economically reasonable.

Transmission Line Concluding Remarks

Looking at the power transmission construction projects in recent years, each project has its own characteristics. In the design, it is impossible to guarantee the design quality and meet the needs of the development of the power grid if it is removed from the actual project. Only in accordance with the actual situation, adapting to local conditions, through optimization schemes, scientific and technological research, and continuous exploration and innovation, can we meet the requirements of building a strong power grid and create a new situation in engineering design that is "advanced technology, safe and reasonable".

Transmission line construction

In the past construction of 66kV and above transmission lines, it is often encountered that individual conductors are worn due to various reasons during construction and need to be handled, causing inconvenience to construction.

1 Wire wear during loading and unloading and transportation

The wire is prone to wear and tear and preventive measures during loading and unloading and transportation:

1.1 The wire spool is deformed, the spool board is lost, and the outer protective layer of the spool is dropped.

Measures to be taken: Visual inspection is required before loading, unloading and transportation.

1.2 The bobbin rolls, flips, and collides with the surroundings in the transport vehicle.

Measures to be taken: Anchorage measures such as studs are installed under the spool during transportation to ensure that the spool cannot be rolled and turned at will, and that the spool must be placed in an upright position and cannot be horizontally inverted.

1.3 Improper method of hoisting wires during loading and unloading.

Take measures: Use a crane to hoist the wire spool, load it lightly, and do not collide, and the length of the sling should be appropriate to prevent the axle from being squeezed and deformed by the sling. Pay attention to whether the spool side plate is damaged and deal with it in time to prevent the wire from being damaged.

2 Wire wear during pay-off

The wire is prone to wear during the tension release process and anti-wear measures:

2.1 The friction between the wire and the bobbin.

Take measures: During the laying process, send someone to take care of the spool car at any time. If there is friction, stop at any time and change the direction of the spool car or take measures such as cushioning.

2.2 When the wire is changed, the snake leather cover and the wire are damaged.

Take measures: Check the quality of the snake holster before use to see if there are any hard objects that can scratch the wire, and handle it gently when using it.

2.3 During the wire laying process, friction with the span in the putting-out gear.

Measures to be taken: Before the construction of the tension line, the tension of the wire must be calculated to ensure that the span and the distance between the span and the span are not guaranteed. If the calculation cannot guarantee the friction, measures such as lifting the lower wire should be taken.

2.4 The wire rubs against the traction rope and the guide rope.

Measures to be taken: Avoid the friction of display wires, guide ropes and traction ropes, and arrange the display sequence. Make sure that the wire spreading, the guide rope and the traction rope spreading are kept in contact with each other, and a special person will be sent to monitor the pay-off process at each tower during the pay-out process.

2.5 The traction plate is turned over and so on.

Measures to be taken: If the height difference between the two sides of the tension tower is large, the double block should be suspended at different heights. In order to ensure that the float is always under stress, it should be noted that the meaning, positioning, and length of the steel rope sleeve connection are calculated based on the height difference, gear pitch, tension and angle of rotation before construction. If the tension tower rises, you can hang one or two pulleys upside down according to the corner size on the ground. The tension of the wire during the construction of tension and tension shall be adjusted smoothly to prevent impact, and the situation of each gear shall be strictly monitored during the tension. Find money to check the quality of the rotary connector in detail, and the degree of rotation flexibility.

2.6 lift operation, friction between the traction rope and the wire, mutual wear of the wire, release of the pressure wire rope, the wire wears the wire during the lift and other processes.

Measures to be taken: According to the orientation of the wires after being lifted off, lift the distant wires first and lift off in order to prevent poor collision between the traction ropes or the wires. When releasing to Xi'an pressure rope, apply a soft rope and prevent the wire and the rope from rubbing against each other. When crimping before lift-off, you should cross the ground according to the various positions along the line to minimize the remaining length of the wire and keep the wire safe to the ground after lifting Headroom.

2.7 Wear between the ground anchor part of the conductor and the tools.

Measures to be taken: Wear-resistant measures should be used between the conductor and the tools. For example, during the anchoring process, the anchor steel anchor, the anchor steel rope, and the cable clamper should be glued, and the wire sleeve should be covered with rubber.

2.8 The wires are worn in contact with the ground.

Measures to be taken: The ground shall be laid with protective strips such as colored strips, straw mats, and tarpaulins before the wires fall to protect the wires from direct contact with the ground. A support shall be placed below to leave the ground and specially protected.

3 Wire wear during attachment installation

3.1 Wire lifting tools and wires are worn.

Measures to be taken: Use the hanging rope and hook which have been glued, and the contact length between the hook and the wire is greater than 50mm.

3.2 The wire is worn during the installation of the spacer rod. During the installation of the spacer rod, the car should be installed with a protection hose. The speed should not be too fast. It should be advanced at a steady and uniform speed. The brakes should be used at the speed during the downhill process. Line hose. ^[5]