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Factory acceptance testing for communication optical cables refers to the process where, before the optical cables are supplied, the construction unit organizes relevant engineering units to conduct sampling inspections on the functions and performance of the supplied optical cables at the manufacturer's facility. If necessary, on-site supervision can be arranged. The main contents of the acceptance include inspections of the cable's structural dimensions, optical performance, mechanical performance, fitting compatibility, and environmental performance indicators. These tests ensure that the cables meet required standards, highlighting the advantages of fiber optic cable such as high bandwidth, low signal loss over long distances, and immunity to electromagnetic interference, as well as the benefits of fiber optic cable including enhanced reliability in power line communication systems and reduced maintenance needs in harsh environments. A thorough examination of the fiber optic cable components-such as the optical fibers, strength members, protective sheathing, and any integrated metallic elements-is essential to verify overall integrity and performance. The factory acceptance testing team should submit an acceptance report, and products that fail the acceptance shall not leave the factory. The contents, methods, and judgment criteria for factory acceptance of different types of optical cables shall be executed in accordance with relevant national standards and industry standards.We will focus on the acceptance criteria for the mechanical properties (such as tensile strength, stress-strain characteristics, and pulley passage performance) and environmental properties (such as dripping and water penetration performance) of optical fiber composite overhead ground wire (OPGW) cables.

OPGW Tensile and Stress-Strain Test

Test Purpose

The tensile and stress-strain test is used to determine the optical characteristics (changes in optical attenuation rate) and several mechanical characteristics, including stress limits, of the optical unit under tensile load. This test is particularly important for evaluating the maximum fiber optic cable length and how far a fiber optic cable can be run in practical applications without exceeding safe strain limits. The tensile and stress-strain test shall be conducted in accordance with GB/T 1179-2017 and DL/T 832-2016.

Test Apparatus

The tensile and stress-strain test apparatus consists of a horizontal tensile testing machine (as shown in Figure 1-1) and an optical fiber comprehensive tester composed of an optical fiber dispersion tester and an optical time-domain reflectometer (OTDR) (as shown in Figure 1-2). When performing optical fiber attenuation measurements, the light source and power meter should be installed at both ends of the tested optical fiber respectively. The two ends of the tested sample should be fixed with engineering matching fittings before applying force to ensure that the optical unit does not displace relative to the optical cable.

Figure 1-1：Horizontal Tensile Testing Machine

Figure 1-2：Fiber Optic Comprehensive Tester

Test Method

During the test, the fiber optic cable distance for the sample shall not be less than 100m to accurately simulate real-world fiber optic cable distance chart scenarios. Install the optical cable sample on the tensile testing machine, fusion splice the optical fibers into a single loop, and measure the loss in the 1550nm wavelength band when different loads are applied to the optical fiber. The optical fiber should be relaxed to the initial load before and after applying the load. During measurement, monitor the cable load, optical fiber loss, optical fiber strain, and cable strain at a sampling frequency of 1Hz. The operating steps are as follows:

1. Apply the initial load to 2% of the rated tensile strength (RTS) to straighten the optical cable, then remove the load and install the strain gauge under no tension;
2. Increase the load to 30% RTS, hold for 30min, take readings at 5min, 10min, 15min, and 30min, then unload to the initial load;
3. Reapply the load to 50% RTS, hold for 1h, take readings at 5min, 10min, 15min, 30min, 45min, and 60min, then unload to the initial load;
4. Reapply the load to 70% RTS, hold for 1h, take readings at 5min, 10min, 15min, 30min, 45min, and 60min, then unload to the initial load;
5. Reapply the load to 85% RTS, hold for 1h, take readings at 5min, 10min, 15min, 30min, 45min, and 60min, then unload to the initial load;
6. Reapply the load until the optical cable breaks, reading the tensile force and elongation at the previous time intervals while uniformly increasing until reaching 85% RTS. This final step helps determine the maximum pulling force of fiber optic cable and practical limits for pulling fiber optic cable during installation.

• During the test, a uniform loading rate should be maintained, preferably reaching 30% RTS in 1–2min.
• The test measures changes in optical fiber loss, optical fiber strain, and strain limit data, as shown in Figure 1-3.

Figure 1-3：Optical Cable Stress-Strain Test Curve Diagram

In Figure 1-3, curve 1 represents cable strain, curve 2 represents optical fiber strain, curve 3 represents optical fiber loss characteristics, and point A is the critical point where the optical fiber begins to strain after the cable is subjected to a certain stress; at this point, the cable strain is equivalent to the excess length of the optical fiber.

Test Requirements

1. When the cable stress reaches the annual average operating tension (everyday stress, EDS) of 18%–25% RTS, the optical fiber should have no strain and no additional loss.
2. When reaching the maximum allowable tension (MAT) of 40% RTS, the optical fiber strain should be below 0.05% (layer-stranded type) or 0.1% (central tube type), with no additional loss; under MAT load, if the optical fiber loss rate experiences a permanent or temporary increase greater than the specified value, the test is considered failed.
3. When reaching the ultimate operating strength (UOS) of 60% RTS, the optical fiber strain should be below 0.35% (layer-stranded type) or 0.5% (central tube type), and the additional optical fiber loss should recover to normal after the tension is released. If the ultimate stress of the optical fiber is less than UOS, the test is considered failed. These thresholds relate closely to the max length for fiber optic cable under operational loads.
4. If any component of the OPGW cable [AS (aluminum-clad steel) wires, AA (aluminum alloy) wires, and optical fiber unit] breaks before reaching 95% RTS stress, the test is considered failed.

• Relative slippage between the cable, optical fiber, and optical unit during the test is considered a failure.