A weather-resistant, anti-aging, and anti-PID DC power cable specifically designed for photovoltaic power plants

Abstract

This invention discloses a weather-resistant, anti-aging, and anti-PID DC power cable specifically designed for photovoltaic power plants. The cable core comprises multiple insulated cores twisted together, with a metal overall shielding layer and an outer sheath sequentially covering the core. The insulated cores include tin-plated copper conductors and a cross-linked polyolefin insulation layer. At least one bare copper drain wire is disposed within the core, extending longitudinally and directly contacting the inner surface of the metal overall shielding layer. This invention achieves a synergistic effect through the ion-capturing effect of the hydrotalcite in the insulation layer and the low-resistance charge dissipation effect of the drain wire. This suppresses ion migration at its source while promptly dispersing accumulated charge, significantly improving the cable's anti-PID performance. Combined with a composite shielding structure and radiation cross-linking process, the cable exhibits excellent long-term weather resistance and anti-aging performance, making it suitable for long-term operation on the DC side of outdoor photovoltaic power plants.

Description

Technical Field

[0001] This invention relates to the field of photovoltaic power transmission cable technology, specifically to a weather-resistant, anti-aging, and anti-PID DC power cable for use on the DC side of a photovoltaic power station and its manufacturing method. Background Technology

[0002] With the continuous expansion of photovoltaic power plant installed capacity, the long-term operational reliability of photovoltaic cables has become a key factor affecting the power generation efficiency and service life of the power plant. Under the high voltage DC operating environment of photovoltaic systems, potential-induced degradation (PID) effect will occur inside the modules and cables: under the action of DC high voltage field, the anions and cations inside the insulation material undergo directional migration and accumulate at the insulation interface to form space charge, which leads to a decrease in insulation resistance and deterioration of insulation performance. In severe cases, it can cause insulation breakdown and shorten the service life of the cable.

[0003] Existing solutions for improving anti-PID cables can be mainly divided into two categories: one is the material modification path, which involves adding ion trapping agents (such as hydrotalcite) to the insulation layer to fix migrating ions and suppress ion migration from the source; the other is the structural optimization path, which involves adding shielding or drainage structures to discharge charges and reduce the accumulation of interface charges.

[0004] However, there are technical obstacles to combining the two approaches mentioned above: the material modification approach relies on the layered crystal structure of hydrotalcite to "capture" and "fix" ions, which is a passive defense strategy; those skilled in the art generally believe that the captured ions are already in an electrically neutral equilibrium state within the insulating system and will not migrate to the interface, thus eliminating the need for additional charge discharge paths. The structural optimization approach, on the other hand, aims to "guide" and "discharge" interface charges through a diversion structure, which is an active diversion strategy and does not fundamentally block the causes of ion migration. For a long time, the field has lacked both the technical motivation to combine the two approaches and has generally held the technical bias that "once ions are captured, there is no need for further diversion and discharge," resulting in existing solutions failing to simultaneously achieve ion source suppression and timely charge discharge. The overall performance against PID needs improvement, and the long-term weather resistance and anti-aging performance cannot meet the 25-year service life requirements of outdoor photovoltaic power stations. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a weather-resistant, anti-aging, and anti-PID DC power cable for photovoltaic power plants. Through the synergistic effect of material modification and structural optimization, it simultaneously achieves ion migration suppression and low charge resistance discharge, significantly improving the cable's anti-PID performance and long-term weather aging resistance.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A weather-resistant, anti-aging, and anti-PID DC power cable for photovoltaic power plants includes a cable core formed by stranding multiple insulated cores. The cable core is covered by a metal overall shielding layer and an outer sheath in sequence. The insulated core includes a tinned copper conductor and a cross-linked polyolefin insulation layer extruded outside the tinned copper conductor. At least one bare copper lead wire is provided inside the cable core. The bare copper lead wire extends continuously along the longitudinal direction of the cable core and is in direct contact with the inner surface of the metal overall shielding layer.

[0007] Furthermore, the contact resistance per unit length between the bare copper lead wire and the total metal shielding layer is no greater than 5mΩ / m, forming a low-impedance charge discharge path.

[0008] Furthermore, the cross-sectional area of ​​the bare copper lead wire is not less than 1 / 10 of the nominal cross-sectional area of ​​the tin-plated copper conductor, and not less than 2.5 mm², to ensure current carrying and discharge capacity.

[0009] Furthermore, the total metal shielding layer is a composite shielding structure, consisting of an inner soft copper strip wrapping layer and an outer tin-plated copper wire braided layer, which combines high shielding coverage with excellent mechanical bending performance.

[0010] Furthermore, the raw materials of the cross-linked polyolefin insulation layer include hydrotalcite-based anion absorbers; preferably, the raw materials of the cross-linked polyolefin insulation layer also include metal ion passivators.

[0011] Furthermore, the raw materials of the cross-linked polyolefin insulation layer, by weight, include the following components: 100 parts of base resin, 2-5 parts of hydrotalcite anion absorber, and 0.5-2 parts of metal ion passivator.

[0012] The present invention also provides a method for manufacturing the above-mentioned cable, including conductor preparation, insulation extrusion, cabling and laying of lead wires, composite shielding wrapping, sheath extrusion, and irradiation crosslinking steps.

[0013] The beneficial effects of this invention are as follows: This invention achieves excellent anti-PID performance through a synergistic mechanism of material ion capture and structural charge dissipation: On the one hand, the hydrotalcite-like anion absorber in the cross-linked polyolefin insulation layer has a layered crystal structure, which can capture and fix anions and metal cations in the insulation system, suppressing ion migration under high-voltage electric fields from the source; on the other hand, the bare copper guide wires set in the cable core are in direct contact with the overall metal shielding layer, forming a low-impedance discharge path, which can promptly conduct away the induced charge accumulated on the insulation surface, avoiding space charge accumulation. The synergistic effect of these two factors significantly improves the anti-PID performance compared to single material modification or single structural optimization schemes; compared with the comparative example of Example 1 and a single scheme, the insulation resistivity retention rate after PID testing increased by more than 40%, and the insulation resistance can be maintained stably for a long time.

[0014] This invention employs a composite shielding structure consisting of soft copper strip wrapping and tinned copper wire braiding, combined with directional bare copper drain lines. This allows the contact resistance per unit length to be controlled within 5mΩ / m, resulting in low discharge path impedance and high reliability. It avoids the defects of poor contact and large impedance fluctuations that are common with traditional gap-placed drain lines.

[0015] The insulation layer formula of this invention adopts an open component design, which is compatible with conventional processing aids based on the core functional components, and is suitable for existing cable production equipment. No new special process equipment is required, and mass production is highly feasible. With the combination of radiation crosslinking process and weather-resistant outer sheath, the cable can meet the long-term operation requirements of -40℃ to 125℃, and has excellent resistance to ultraviolet rays, damp heat, and aging. It is suitable for the full life cycle use needs of outdoor photovoltaic power stations. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the cross-sectional structure of the photovoltaic power station-specific weather-resistant, anti-aging, and anti-PID DC power cable described in this invention.

[0017] In the diagram: 1-Tin-plated copper conductor, 2-Cross-linked polyolefin insulation layer, 3-Bare copper lead wire, 4-Soft copper strip wrapping layer, 5-Tin-plated copper wire braided layer, 6-Outer sheath. Detailed Implementation

[0018] The present invention will be further described in detail below with reference to specific embodiments, but the scope of protection of the present invention is not limited to the content described.

[0019] I. Test Method Description The performance parameter testing methods involved in this invention are as follows: 1. Unit length contact resistance test: A DC low resistance tester (test accuracy 0.1μΩ) is used. A 1m long sample of finished cable is cut off, and the test electrodes are connected to the end of the bare copper lead wire and the end of the metal shielding layer respectively. A DC test current of 1A is applied, and the DC resistance value after stabilization is read. This is the unit length contact resistance, and the unit is mΩ / m. Data is recorded every 10s during the test, and the data is recorded continuously for 5 minutes to obtain the time domain waveform of the contact resistance.

[0020] 2. PID resistance test: According to the IEC62770 standard, the cable sample is placed in an environment of 85℃ and 85%RH, and after applying a DC voltage of 1500V for 1000h, the retention rate of insulation volume resistivity is tested. The higher the retention rate, the better the PID resistance.

[0021] 3. Thermal aging performance test: In accordance with GB / T2951.12 standard, the insulation layer sample was placed in a thermal aging chamber at 135℃ for 168 hours, and the change rate of tensile strength and the change rate of elongation at break were tested.

[0022] II. Preparation of Examples and Comparative Examples The main cable structure of each embodiment is the same as that of the comparative example: it includes two insulated cores with a nominal conductor cross-sectional area of ​​4 mm², and a metal shielding layer and an outer sheath are sequentially arranged outside the cores; the base resin of the insulation layer is a blend of 100 parts by weight of ethylene-vinyl acetate copolymer (EVA) and linear low-density polyethylene (LLDPE).

[0023] The core parameter settings for each embodiment are as follows: Example 1: A bare copper lead wire with a cross-sectional area of ​​0.5 mm² (1 / 8 of the conductor cross-sectional area) is set up; the total metal shielding layer is a composite structure of soft copper tape wrapping + tinned copper wire braiding; the insulation layer is added with 3 parts by weight of magnesium aluminum type hydrotalcite (average particle size 1 μm) and 1 part by weight of metal ion passivating agent MD1024; when cabling, the lead wire is laid out through a directional conductor, and the copper tape wrapping tension is controlled at 10N.

[0024] Example 2: A bare copper lead wire with a cross-sectional area of ​​2.5 mm² is set up; the rest of the structure and formula are the same as in Example 1.

[0025] Example 3: Two bare copper lead wires are set up and symmetrically arranged on the outer edge of the cable core; the rest of the structure and formula are the same as in Example 2.

[0026] Example 4: 2 parts by weight of magnesium-aluminum type hydrotalcite and 0.5 parts by weight of metal ion passivating agent MD1024 were added to the insulating layer; the remaining structure and process were the same as in Example 2.

[0027] Comparative Example 1: No bare copper lead wires were provided, and the insulation layer formula was the same as in Example 1.

[0028] Comparative Example 2: Bare copper lead wires were provided, and no hydrotalcite or metal ion passivating agent was added to the insulation layer. The rest of the structure was the same as in Example 1.

[0029] Comparative Example 3: The guide wire is placed in the gap of the cabling, without directional layout and tension control, and the rest is the same as Example 1.

[0030] Comparative Example 4: A bare copper lead wire and a hydrotalcite insulation layer were set up. No tension was applied during the copper strip wrapping process, and the lead wire and the shielding layer were in a loose contact state; the rest of the formula and main structure were the same as in Example 1.

[0031] III. Performance Test Results Contact resistance per unit length (mΩ / m) 3.2 2.1 1.5 2.3 - 3.5 8.7 15.7 Insulation resistivity retention rate (%) after PID test 89.2 91.5 93.1 87.6 62.4 58.7 76.3 63.1 Change rate of tensile strength of insulation layer under thermal aging (%) +5.2 +3.8 +4.1 +4.5 +4.7 +2.9 +5.0 +4.9 Change rate of elongation at break due to thermal aging of insulation layer (%) -8.3 -7.5 -7.1 -7.8 -9.2 -10.5 -8.8 -9.0 Regarding the positive change rate of tensile strength due to heat aging: This invention uses an irradiated cross-linked polyolefin insulation system. In the early stage of heat aging, the residual cross-linking sensitizer in the sample will continue to undergo cross-linking reaction under thermal conditions, resulting in a slight increase in the degree of cross-linking. Therefore, the tensile strength shows a slight increase, which is a normal phenomenon of the cross-linking system and not an abnormal data point. As the aging time increases, the tensile strength will gradually decrease. The change rate of tensile strength of this formulation system can still be controlled within -10% after 1000 hours of heat aging, which meets the standard requirements.

[0032] The test results show that: 1. The contact resistance per unit length in Examples 1-4 is ≤5mΩ / m, and the insulation resistivity retention rate after PID testing is higher than 87%, significantly better than the comparative examples. This demonstrates the significant synergistic effect of "hydrotalcite ion capture + low-impedance discharge of the drainage line," with anti-PID performance far superior to a single improvement scheme. Taking Example 1 as an example, its insulation resistivity retention rate (89.2%) is 43% higher than that of Comparative Example 1 (62.4%) which only involves material modification, and 52% higher than that of Comparative Example 2 (58.7%) which only involves structural optimization. The improvement is significantly higher than the simple superposition of the two schemes.

[0033] 2. Comparative Example 4 has both hydrotalcite and drainage wire structures, but due to its excessively high contact impedance (15.7 mΩ / m), its anti-PID performance is only close to that of Comparative Example 1, and far lower than that of Example 1. This proves that low-impedance contact is a necessary prerequisite for achieving synergistic effects: only when the drainage wire and the shielding layer form a stable low-impedance path can they cooperate with the ion trapping effect of the material to jointly improve the anti-PID effect; if the contact is poor or the discharge path fails, even if both types of structures are present, synergistic gains cannot be generated.

[0034] 3. In Comparative Example 3, the lead wire was only placed in the gap of the cabling without directional bonding control, and the contact resistance reached 8.7mΩ / m. The anti-PID effect was significantly reduced, proving that the low-impedance contact achieved by the present invention through directional layout and tension control is the key to ensuring performance.

[0035] 4. All samples met the requirements of photovoltaic cable standards for thermal aging performance and demonstrated excellent long-term anti-aging properties.

[0036] IV. Manufacturing Process Details The cable manufacturing method of the present invention is as follows: 1. Conductor preparation: Tin-plated copper conductors are made by bundling and re-stranding multiple strands of tin-plated soft copper wire. The conductor surface is smooth and free of burrs and oxidation defects.

[0037] 2. Insulation extrusion: Cross-linked polyolefin insulation material is uniformly extruded over the tin-plated copper conductor using an extruder. The extrusion temperature is controlled at 120~140℃, and the insulation layer thickness deviation is controlled within ±0.1mm.

[0038] 3. Cable forming and guide wire laying: Multiple insulated wire cores are stranded together by a cable forming machine, with the stranding pitch ratio controlled at 12 to 16 times; during the cable forming process, a directional conductor is set at the cable core inlet end to accurately introduce the bare copper guide wire into the outer edge of the cable core, so that it is laid continuously along the longitudinal direction of the cable core to avoid deviation and twisting.

[0039] 4. Overall shielding wrapping: First, wrap the soft copper strip with an overlapping method, with an overlap rate of not less than 15%. Apply a preset tension of 8~12N during the wrapping process to ensure that the inner surface of the soft copper strip is tightly attached to the bare copper lead wire. Then, use a braiding machine to braid tin-plated copper wire on the outside of the soft copper strip with a braiding density of not less than 80% to form a composite overall shielding layer.

[0040] 5. Sheath extrusion: An irradiated cross-linked low-smoke halogen-free polyolefin sheath material is extruded over the metal shielding layer using an extruder. The sheath thickness meets the requirements of GB / T33767 standard.

[0041] 6. Irradiation crosslinking: The finished cable is crosslinked by irradiation using an electron accelerator, with the irradiation dose controlled at 120~180kGy to ensure that the degree of crosslinking between the insulation layer and the sheath layer meets the requirements.

Claims

1. A weather-resistant, anti-aging, and anti-PID DC power cable for photovoltaic power plants, comprising a cable core formed by stranding multiple insulated cores, wherein the cable core is sequentially covered with a metal overall shielding layer and an outer sheath, and the insulated core comprises a tinned copper conductor and a cross-linked polyolefin insulation layer extruded over the tinned copper conductor, characterized in that, The cable core is provided with at least one bare copper lead wire, which extends continuously along the longitudinal direction of the cable core and is in direct contact with the inner surface of the metal shielding layer.

2. The photovoltaic power station-specific weather-resistant, anti-aging, and anti-PID DC power cable according to claim 1, characterized in that, The contact resistance per unit length between the bare copper lead wire and the total metal shielding layer is no greater than 5mΩ / m.

3. The photovoltaic power station-specific weather-resistant, anti-aging, and anti-PID DC power cable according to claim 2, characterized in that, The cross-sectional area of ​​the bare copper lead wire shall not be less than 1 / 10 of the nominal cross-sectional area of ​​the tin-plated copper conductor, and shall not be less than 2.5 mm².

4. The photovoltaic power station-specific weather-resistant, anti-aging, and anti-PID DC power cable according to claim 3, characterized in that, The overall metal shielding layer is a composite shielding structure, consisting of an inner soft copper strip wrapping layer and an outer tin-plated copper wire braided layer.

5. The photovoltaic power station-specific weather-resistant, anti-aging, and anti-PID DC power cable according to claim 4, characterized in that, The raw materials for the cross-linked polyolefin insulation layer include hydrotalcite-based anion absorbers.

6. The photovoltaic power station-specific weather-resistant, anti-aging, and anti-PID DC power cable according to claim 5, characterized in that, The raw materials for the cross-linked polyolefin insulation layer also include metal ion passivating agents.

7. The photovoltaic power station-specific weather-resistant, anti-aging, and anti-PID DC power cable according to claim 6, characterized in that, The raw materials of the cross-linked polyolefin insulation layer, by weight, include the following components: 100 parts of base resin, 2-5 parts of hydrotalcite anion absorber, and 0.5-2 parts of metal ion passivator.

8. The photovoltaic power station-specific weather-resistant, anti-aging, and anti-PID DC power cable according to claim 7, characterized in that, The hydrotalcite-type anion absorber is magnesium-aluminum hydrotalcite with an average particle size of 0.5~2μm; the metal ion passivator is N,N'-bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyl]hydrazine, commercially known as MD1024.

9. The photovoltaic power station-specific weather-resistant, anti-aging, and anti-PID DC power cable according to claim 8, characterized in that, The raw materials for the cross-linked polyolefin insulation layer also include one or more of the following: antioxidants, ultraviolet absorbers, cross-linking sensitizers, and lubricants. The outer sheath is an irradiated cross-linked low-smoke halogen-free polyolefin sheath layer.

10. A method for manufacturing a weather-resistant, anti-aging, and anti-PID DC power cable for photovoltaic power plants as described in any one of claims 1 to 9, characterized in that, Includes the following steps: (1) Conductor preparation: Tin-plated copper conductors are made by stranding tin-plated copper wire bundles; (2) Insulation extrusion: Cross-linked polyolefin insulation material is extruded over the tin-plated copper conductor to form an insulated wire core; (3) Cable making and guide wire laying: multiple insulated wire cores are twisted into a cable. During the cable making process, bare copper guide wires are introduced into the outer edge of the cable core through a directional conductor, so that the guide wires are laid continuously along the longitudinal direction of the cable core. (4) Overall shielding wrapping: A soft copper strip is wrapped around the outside of the cable core to form an inner shield. During the wrapping process, a preset tension of 8~12N is applied to make the inner surface of the soft copper strip tightly adhere to the bare copper lead wire; then, tin-plated copper wire is braided around the soft copper strip to form an outer shield, thus obtaining the overall metal shielding layer. (5) Sheath extrusion: Low-smoke halogen-free polyolefin sheath material is extruded over the metal total shielding layer to form an outer sheath; (6) Irradiation crosslinking: Electron beam irradiation crosslinking is performed on the finished cable to obtain the finished cable.

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