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Knowledge of OPGW Optical Cable

DATE:2022-11-03   VISITS:162

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Introduction about OPGW

OPGW optical cable, also known as optical fiber composite overhead ground wire. The optical fiber is placed in the ground wire of the overhead high-voltage transmission line and installed on the top of the transmission line tower to form an optical fiber communication network on the transmission line.

Optical fiber uses the difference in the refractive index of the core and cladding materials to transmit light energy in the optical fiber, which has become a major revolution in the history of communications. Optical fiber cables are light in weight and small in size, and have been adopted by power systems to transmit dispatching telephones, telecontrol signals, relay protection, TV images and other information between substations and central dispatching stations. In order to improve the stability and reliability of fiber optic cables, a structure in which the fiber optic cable is combined with the phase conductor of the transmission line, the overhead ground wire and the power cable has been developed abroad.

OPGW is suitable for lines with high voltage exceeding 110kv, with a large span (generally more than 250M); easy to maintain, easy to solve the problem of line crossing, and its mechanical characteristics can meet the large crossing of the line; the outer layer of OPGW is metal armor, which is suitable for high Piezoelectric corrosion and degradation have no effect; OPGW must be powered off during construction, and the power loss is relatively large, so OPGW should be used in new high-voltage lines above 110kv; the fiber material is glass fiber, which is fragile and fragile.

The OPGW optical cable is wrapped with metal wires, which makes the optical cable more reliable, stable and firm. Because the overhead ground wire and the optical cable are combined into one, compared with other types of optical cables, it not only shortens the construction period but also saves the construction cost. In addition, if the OPGW made of aluminum clad steel wire or aluminum alloy wire is used, it is equivalent to erecting a good conductor overhead ground wire, which can reduce the potential supply current of the transmission line, reduce the power frequency overvoltage, and improve the power line to the communication line. It has many benefits such as interference and dangerous effects.

Because the optical fiber has the characteristics of anti-electromagnetic interference and light weight, it can be installed on the top of the transmission line tower without considering the optimal hanging position and electromagnetic corrosion. Therefore, OPGW has significant features such as high reliability, superior mechanical properties, and low cost. This technique is especially suitable and economical for new installations or replacement of existing ground wires.

Common OPGW structure,There are three main categories: aluminum tube type, aluminum frame type and (stainless) steel tube type.

During the construction process, the OPGW should be prevented from being pulled, scratched, sprained, crushed and broken, and the optical cable should be pulled smoothly without being squeezed.

Model of OPGW

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Common types of optical cables: G.651, G.652, G.653, G.654, G.655 and G.656 are divided into two categories

(1) Class G.651 is a multimode fiber, and IEC and GB/T are further subdivided into four subclasses A1a, A1b, A1c and A1d according to their core diameter, cladding diameter, and numerical aperture parameters.

(2) The G.652 category is a conventional single-mode fiber, which is currently divided into four subcategories: G.652A, G.652B, G.652C and G.652D. IEC and GB/T name G.652C as B1.3 , and the rest are named B1.1.

(3) G.653 fiber is a dispersion-shifted single-mode fiber. IEC and GB/T classify G.653 fiber as B2-type fiber. G.653 fiber is suitable for point-to-point long-distance, high-speed single-channel systems.

OPGW installation design

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The installation design of OPGW should consider the coordination with wire stress, sag and insulation gap, and its load should not exceed the allowable range of existing towers and foundations. Therefore, the characteristic curve should be calculated according to the main technical parameters of the selected OPGW, and the layout, outline and installation drawings of the junction box, various hardware and accessories should be designed in combination with the actual engineering.

1. Treatment of initial elongation

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

2. Design of anti-vibration measures

Among the fittings used by OPGW, the tension clamp is of pre-twisted wire type, and the suspension wire clamp is equipped with pre-twisted wire and rubber gasket. These two types of fittings have certain anti-vibration capabilities. In order to further strengthen the anti-vibration capability, it is possible to consider installing an anti-vibration hammer, which is generally calculated according to the span:

When the span is less than or equal to 300M, install an anti-vibration hammer;

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

What Need to be Paid Attention to in OPGW Construction and Erection?

The construction and erection of OPGW is different from ordinary steel strands. Care should be taken to prevent permanent damage to avoid affecting the performance of the optical fiber in the future, and should focus on: OPGW torsion, micro-bending, local radial pressure outside the clip and pollution to the optical fiber . Therefore, in the construction stage, the following effective measures should be taken to solve it:

(1) Prevent and reduce the microbending and stress of OPGW

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

The diameter of OPGW cable reel should not be 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 inner side of the pulley should have a nylon or rubber lining to prevent scratching the surface of the OPGW;

Appropriate pulling wire and pay-off fittings;

The maximum coil length of the specified OPGW is 6000M to prevent the number of times over the pulley;

The line rotation angle of the continuous pay-off is limited to ≤30°. In a tension section of the pay-off, the OPGW direction after the corner should be in a "C" shape;

(2) Control of pay-off tension:

Hydraulic tension pay-off and tractor with tension release device;

Limit pay-off speed ≤ 0.5 m/s;

(3) Prevent OPGW from twisting

Install counterweight and anti-twist device on the board and the tightening clamp;

Adopt special double-groove pulley;

Tension line machine with double winch;

(4) Prevent fiber pollution

In the construction and erection of OPGW, attention should be paid to encapsulating the ends;

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

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Application of OPGW

OPGW optical cable is mainly used on 500KV, 220KV, 110KV voltage level lines, and is mostly used on new lines due to line power failure, safety and other factors.

The Applicable Features of OPGW:

(1) OPGW must be powered off during construction, and the power outage loss is relatively large, so OPGW should be used in new high-voltage lines above 110kv;

(2) Lines with high voltage exceeding 110kv have a large span (generally more than 250M);

(3) The outer layer of OPGW is metal armor, which has no effect on high-voltage electrical corrosion and degradation;

(4) It is easy to maintain, easy to solve the problem of line crossing, and its mechanical characteristics can meet the large crossing of the line;

(5) In the performance indicators of OPGW, the larger the short-circuit current, the more armored conductors are required, and the tensile strength is correspondingly reduced. However, under the condition of a certain tensile strength, to increase the short-circuit current capacity, only increase The metal cross-sectional area increases, resulting in an increase in the cable diameter and cable weight, which poses a safety issue to the strength of the line tower.



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