OPGW power cable

Taxonomy:OPGW power cable
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Date of release:2019/06/22
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introduce

OPGW power cable

The optical fiber composite overhead ground wire (OPGW) is a ground wire that integrates the communication optical cable and the lightning protection line of the overhead transmission line. It must meet the technical requirements of optical fiber communication, and at the same time meet the characteristic requirements necessary for the ground wire, including machinery. Strength and electrical performance. Because this kind of ground wire is built into the stranded wire, it is installed on the ground top frame of the high-voltage overhead transmission line. It has the advantages of safety, reliability, no electromagnetic induction and maintenance-free. Therefore, it has been abroad since the late 1970s. Gradually applied in overhead transmission lines, and the use of more and more, according to incomplete statistics, the world has laid OPGW cable up to 100,000 kilometers. Since the 1990s in China, the use of OPGW fiber optic cable has also been increasing. At present, more than 10,000 kilometers of lines are in operation.

The OPGW cable project involves two majors: line and communication. The different aspects of the work are different. The angle of consideration is different. Therefore, it is necessary to discuss some principles in the bidding and design process. At the same time, due to the large difference in the structure of OPGW optical cables produced by various manufacturers, the adopted standards are also inconsistent. Therefore, it is necessary to fully understand the characteristics of OPGW optical cables of various structures in the project bidding, so as to select suitable products.

First, OPGW cable standard

(1) Main characteristic parameters of OPGW cable

The main characteristic parameters of the OPGW cable are almost always related to the line distance of the line tower, the sag characteristics, the wind load and the ice load, the suspension point of the OPGW cable, and the allowable tension. It can be summarized as follows:

(1) the number of optical fibers;

(2) fiber type and optical characteristics;

(3) The total outer diameter (mm) of the OPGW cable;

(4) Calculated conductor cross-sectional area (mm2);

(5) Calculated linear mass (kg/km);

(6) rated breaking force (RTS) (KN);

(7) modulus of elasticity (MPa);

(8) Linear expansion coefficient (1/°C *E-6);

(9) Linear DC resistance (ohm/km);

(10) Maximum allowable operating temperature range (°C);

(11) Short-circuit current capacity (I2t) (KA2·S);

(12) Maximum allowable tensile force (MAT) (KN).

The OPGW cable with excellent performance should meet the above requirements. At the same time, in order to have a comprehensive understanding of the characteristics of the OPGW cable used, and to check whether it meets the requirements required by the project, various characteristics experiments should be carried out.

(2) Performance test of OPGW cable:

At present, there are two standards for OPGW optical cable in the world, one is the IEC 1396 standard of the International Electrotechnical Commission, the electrical, mechanical and physical performance requirements and experimental methods of optical fiber composite overhead ground wire; the other is the American Institute of Electrical and Electronics Engineers. IEEE 1138 Standard "Fiber Composite Overhead Ground Wire for Power Lines". The two standards have their own characteristics. For the convenience of comparison, the performance requirements of the two standards for the OPGW cable are listed below:

It can be seen from the table that the IEC related standard is very complete. In addition to the general requirements for the cabling of the OPGW cable, the IEC 1396 standard refers to a large number of relevant standards, such as the implementation of IEC 793 for fiber parameters, and does not provide specific data, so operability Not strong, but the description of OPGW cable structure requirements is more flexible; and IEEE 1138 standard provides special detailed regulations for OPGW fiber optic cable components, cable structure and experiment, as well as OPGW cable tension, site acceptance experiment, installation, Packaging and other requirements have been very detailed, so it is more operability, but its structural requirements for OPGW cable are more inclined to the structure of the optical unit in the center of the cable, and its experimental content is also less than a lightning test.

Therefore, in the OPGW cable tendering and design process, the OPGW cable standard implementation should be based on the IEEE 1138 standard, supplemented by the IEC 1396 standard, that is, the optical cable type experimental content adds lightning strike experiment based on the content specified in IEEE 1138; the optical fiber type experimental content is IEEE 1138 specifies content execution; cable factory inspection content is selected in routine experimental content.

Second, the structural characteristics of OPGW cable

The structure of the OPGW includes a fiber unit structure and a ground unit.

(1) Optical fiber unit and its structure

In normal operation and installation, a reasonable fiber unit structure should minimize the stress and attenuation of the cable core. Therefore, the design of the fiber unit structure needs to consider the necessary mechanical protection structure to prevent the core of the cable from being squeezed, the appropriate core length to reduce the core force, and take measures to achieve moisture and heat resistance.

From the fiber-optic unit structure, the degree of tightness of the cable core arrangement can be divided into a buffer tight structure and a loose-sleeve structure.

Cushion tight structure

The basic theoretical basis: the bundle of fiber optic cable cores can only be pulled off when the elongation is 2%, but the maximum elongation of the bare ground wire in actual operation is only a few thousandths of an order, so the cable core allows The elongation is far greater than the actual elongation of the ground wire, and the optical attenuation of the core can meet the engineering requirements. The most typical tight-fitting structure is an aluminum frame with a plurality of straight grooves or spiral grooves in the longitudinal direction, and the grooves are placed for the fiber unit. The typical structure is shown in Fig. 1.

Structural features: OPGW diameter is relatively small, thus reducing the wind load and ice load applied to the line tower; providing protection to the fiber to increase the resistance to bending; due to the metal separation positioning groove, it has high resistance to extrusion. Therefore, the OPGW has strong resistance to external loads and is suitable for engineering with harsh conditions.

2. Loose structure

Basic theoretical basis: the core of the optical cable placed in the protection tube of different materials is processed by the adjustment of the density of the filler, or the different structural forms to treat the excess length of the optical fiber; at the same time, the actual length of the core in the OPGW is greater than the ground force in the force situation. The length of the lower part, so that the core can be free from force or force.

The loose-sleeve structure OPGW is further divided into a central fiber-optic type, a layered and loose-sleeve skeleton structure.

Central fiber-optic loose-sleeve structure features: There are many ways to protect the core of the optical cable, but the cable diameter is large and the disk length is short.

Layer twisted loose-sleeve structure features: the shape is close to the ordinary ground wire, easy to be accepted by the operation department (currently more used in Guangdong Province), while the length of the disk is longer, which is beneficial to reduce fiber joint loss, but the manufacturing process and core The quality requirements are relatively high, and the means of fiber protection are slightly less. Loose truss structure features: The lateral pressure resistance is comparable to that of the tight-fitting structure, but it can only accommodate up to 48 fibers due to structural constraints, and cannot be used in projects with more fibers (less currently used in engineering).

The above comprehensive comparison of various structural forms of the buffer tight structure and the loose-sleeve structure, it should be said that the two structures have their own advantages and disadvantages, and their comprehensive performance (including mechanical strength, electrical properties and optical properties) can meet the standard requirements and meet the requirements of experiments. The use requirements should be considered reasonable. However, the different aspects of the engineering conditions should be different. For example, the engineering conditions are bad, the external load is large, and the road transportation conditions are poor. First, safety issues should be considered. Therefore, the OPGW's resistance to external force is often emphasized. When the engineering conditions are good, If the length of the line is large, a structure with a small light attenuation (such as a layered loose-sleeve structure) should be used.

(2) Ground unit (outer stranded conductor)

The grounding unit (outer stranded conductor) is mainly composed of aluminum-clad steel wire (AS wire) and aluminum alloy wire. Its main functions are:

1. OPGW is an overhead ground wire, which needs to have bearing components, and the outer stranded conductor acts as a bearing force, so that the fiber optic cable core in the OPGW will not or rarely bear external force.

2. It has a certain metal cross section. When the OPGW line is short-circuited or struck by lightning, a strong current will cause the conductor to heat up, and the proper metal cross-section will ensure that the OPGW temperature rise is within the allowable range, so that it will not be damaged by heat. optical fiber.

3. The outer stranded conductor can provide an additional layer of protection to the light unit to protect the light unit from mechanical and external forces and other adverse conditions.

3. Requirements and conditions for the application of OPGW optical cable on overhead transmission lines

(1) Application requirements

OPGW is a channel for power fiber-optic communication, and at the same time acts as a lightning protection line in overhead transmission lines. Therefore, it is required to meet the following requirements in application:

1. First consider the number, type, application wavelength and light attenuation of the optical unit, and consider the transmission capacity required by the system, the transmission wavelength of the optical transceiver and the system interface. These requirements directly affect the cable component, the design of the core and the state of the core in the OPGW.

2. As a lightning protection line, it must also meet the electrical, mechanical and physical performance requirements of the ground wire. That is, in terms of electrical performance, the short-circuit current capacity and lightning protection requirements of the system should be met. As the grounding line application, OPGW is often supplemented by another shunting ground line. Therefore, according to the requirements of the system, the single-phase short-circuit current of the substation should be calculated, and the short-circuit fault time and the shunting ratio of the two grounding lines to the short-circuit current should be determined. Determine the minimum short-circuit current heat capacity to determine the minimum conductive metal cross-sectional area of the OPGW, DC resistance and its diameter; and to meet the total tensile force, elastic modulus, thermal expansion coefficient and linear weight in terms of mechanical and physical properties.

(2) Fittings and accessories used by OPGW

According to the structural characteristics of the OPGW, when the line is erected, it must use its special fittings and accessories, including tensile clamps, suspension clamps, anti-vibration hammers, connecting plates, fastening clamps, down-conducting clamps, and sag adjustment. Board, jumper clip, U-shaped hook ring and junction box.

(3) OPGW installation design

The installation design of the OPGW should be considered in conjunction with the wire stress, sag and insulation clearance, and its load should not exceed the range of use allowed by the existing tower and foundation. Therefore, the characteristic curve of the OPGW should be calculated according to the main technical parameters of the selected OPGW, and the junction box, various fittings, attachment layout, outline drawing and installation drawing of the various types of fittings and accessories should be designed.

Initial elongation treatment

For the initial elongation of OPGW, the cooling method can be used, that is, the ratio of aluminum to steel of the OPGW is checked, and the initial elongation is treated with reference to the cooling value of the adjacent wire or the ground wire.

2. Anti-vibration measures design

Among the fittings used by OPGW, the tension clamp is pre-twisted, the suspension clamp is equipped with pre-twisted wire and rubber gasket. These two fittings have certain anti-vibration ability. In order to further strengthen the anti-vibration capability, it is considered to install an anti-vibration hammer, which is generally calculated according to the gear distance:

When the span is ≤300M, install an anti-vibration hammer;

When the span is >300M, install two anti-vibration hammers.

3. OPGW construction erection should pay attention to the problem

The construction of OPGW is different from ordinary steel strands. Care should be taken to prevent permanent damage to avoid the impact of fiber performance in the future. It should be considered: OPGW torsion, microbending, local radial pressure outside the clamp and contamination of the fiber. . Therefore, the following effective measures should be taken during the construction phase to solve:

(1) Prevent OPGW from twisting

Install a counterweight and anti-torsion device on the running plate and the tightening clamp;

Use special double groove pulleys;

Tension anti-wire machine with double winch;

(2) Prevent and reduce the microbend and stress of OPGW

No acute angles are allowed (control the minimum bending radius of 500mm);

The diameter of the OPGW cable disc should be no less than 1500mm;

The diameter of the pulley should be more than 25 times the diameter of the OPGW, generally not less than 500mm; the inside of the pulley should have a nylon or rubber gasket to prevent scratching the surface of the OPGW;

Suitable traction line and payout fittings;

Specify the maximum disk length of the OPGW to be 6000M to prevent the number of pulleys from passing;

The line angle of the continuous discharge line is limited to ≤30°. In the tensile section of a discharge line, the OPGW after the corner should be in a "C" shape;

(3) Control of the take-up tension:

Hydraulic tensioning machine with traction device and traction machine;

Limit the speed of the line to be ≤ 0.5 m / s;

(4) Prevent fiber contamination

At the OPGW construction and erection, attention should be paid to the end of the package;

In addition, before the OPGW arrives at the site, before the erection, after the erection is completed for the fiber connection and the construction of the whole line is completed, the optical fiber attenuation acceptance test of the OPGW should be carried out in time.