Distributed Fiber Optic Temperature Measurement Technology High Voltage Cable Temperature Measurement Solution

Distributed Fiber Optic Temperature Measurement Technology High Voltage Cable Temperature Measurement Solution

Distributed fiber optic temperature measurement technology is the development direction of intelligent temperature measurement for high-voltage and ultra-high voltage cables in the future. The distributed fiber optic monitoring system for cables is a detection system distributed along the entire cable transmission system. By utilizing the fiber optic distributed monitoring system, real-time online monitoring of the temperature of the operating cables is carried out, tracking the process of cable temperature changes and accurately locating hot spots. It can also analyze the safety of transmission lines based on the surrounding environment. The 220 kV high-voltage intelligent temperature measurement cable is a high-voltage fiber optic composite temperature measurement cable independently designed by our company. The unique built-in fiber optic structure design in the cable enables it to have distributed fiber optic temperature measurement capabilities, which can monitor temperature changes during line operation in real time. An analysis was conducted on the defects in the process of placing fiber optic cables, and a fiber optic S-shaped swinging device was designed.

The structural characteristics of fiber optic cables embedded in cables

Through multiple experiments and repeated comparisons, the 220 kV high-voltage intelligent temperature measurement cable independently designed by our company adopts a unique structure with built-in optical fibers. The optical fibers are placed in an S-shape between the wrinkled aluminum sheath and the top of the insulation core (using buffer tape gaskets as protective layers to prevent pressure damage to the optical fibers during production or high-temperature burns caused by extrusion of the aluminum sheath). The S-shaped placement structure design of the built-in optical fibers in the cable avoids the following drawbacks: a. There are two ways for the optical fibers to be embedded inside the cable: parallel to the longitudinal straight line of the cable and winding. When the cable is powered on and running, the temperature of the conductor and insulation will increase. Due to the significant difference between the linear expansion coefficient of the optical fiber and the linear expansion coefficient of the conductor and insulation material, if the optical fiber is placed parallel to the longitudinal line of the cable, the optical fiber fixed on the inner surface of the aluminum sheath of the cable or the outer surface of the insulation core may experience tensile stress due to the inability to elongate synchronously with the heated cable, resulting in increased additional attenuation of the optical fiber and affecting the accuracy of the optical fiber temperature measurement. At the same time, due to the large diameter of high-voltage cables, the outer length of the cable will be stretched when it is bent. If the optical fiber placed parallel to the longitudinal straight line of the cable is exactly on the outer side of the bend, it is highly likely to be pulled apart. b. When the optical fiber is wrapped in a spiral shape on the outer surface of the cable insulation core buffer strip, the cable will bend or twist when it is wound on the finished cable or installed on the lower coil, causing the optical fiber to also bend or twist accordingly. If the cable is twisted in the same direction as the wrapping direction, the optical fiber will be tightened and stretched. If the cable is twisted in the opposite direction, the optical fiber will relax. Even after the cable is bent or twisted back, there will still be wrinkles and distortions in the optical fiber, leading to increased additional attenuation of the optical fiber and affecting the accuracy of optical fiber temperature measurement. c. When the optical fiber is wound in a spiral shape on the outer surface of the insulation wire core, the insulation wire core expands due to heat, causing stress on the optical fiber tightly wound on the insulation wire core. Cables are produced at room temperature. When fully charged and running at full load, the conductor temperature sometimes reaches 90 ℃. When the temperature rises from room temperature to 90 ℃, the insulation thickness will expand by about 1.5 mm, that is, the outer diameter of the insulation will expand by about 3 mm. The optical fiber tightly wrapped around the insulation core will not be able to absorb this expansion volume, resulting in increased additional attenuation of the optical fiber and affecting the accuracy of the optical fiber temperature measurement [3].

The S-shaped placement structure design of the cable with built-in optical fibers has the following advantages: Most high-voltage cross-linked polyethylene insulated power cables in China use aluminum sheaths with a corrugated surface and certain flexibility (i.e. wrinkled aluminum sheaths), and there is a certain gap between the aluminum sheaths and the buffer tape on the surface of the cable insulation core. When the optical fiber is placed in an S-shape between the wrinkled aluminum sheath and the gap at the top of the insulation core, it can reduce the tension on the finished cable when it is wound up or installed and laid down, which can cause bending or twisting of the cable and affect the optical fiber. Due to the heavy weight of large-sized high-voltage cables, the insulation core of extruded or argon arc welded cables is prone to sinking below the inner sleeve of the aluminum sheath. The protruding parts on the inner side of the cable insulation core and the wrinkled aluminum sheath are prone to mutual compression. The S-shaped placement of optical fibers on the surface of the insulation core avoids the shortcomings of the spiral winding method, which makes the optical fibers susceptible to compression damage.

The process flow for placing optical fibers inside the original 220 kV high-voltage intelligent temperature measurement cable is as follows: a. At the front end of the buffer tape wrapping, two operators place the optical fibers in an S-shaped or serpentine shape along the cable length direction on the cable insulation core, with an S-shaped pitch of 400-500 mm and an S-shaped amplitude of 30-40 mm; b. Use semi conductive tape (50 mm (length) x 10 mm (width)) perpendicular to the cable direction to stick the optical fiber onto the cable insulation core; c. Two layers of semi conductive buffer water blocking tape with a width of 160 mm and a thickness of 2.0 mm are used to cover the fiber optic that has been glued with the tape for protection. Both sides of the semi conductive buffer water blocking tape are glued with tape every 500-600 mm at the S-shaped peak of the fiber optic. When the semi conductive buffer water blocking tape has a joint, the upper and lower layers of the tape are glued together [4]; d. Do not add optical fibers within a range of 0.5 meters between the front and rear ends of the cable to prevent damage to the optical fibers during the production of the ends; The inner diameter of the cable reel should be greater than 20D (D is the cable diameter) to prevent the bending radius of the cable from being too small and damaging the optical fiber; e. After entering the wrinkled aluminum sheath process and the outer sheath process, it is the same as the production process of ordinary high-voltage cables, but it is necessary to avoid the cable from being subjected to strong or excessive instantaneous tensile force during the production process, maintain the constant tension of the cable during the winding process, and ensure that the inner diameter of the finished cable’s winding reel is greater than 20D.

Although the performance test results of the 220 kV high-voltage intelligent temperature measurement cable produced using this process flow are qualified, there are still problems: using manual methods to manually arrange the optical fiber into an S-shape, stick it firmly with tape, and then wrap it with wrapping tape, resulting in low production efficiency, high labor intensity of operators, irregular S-shape of the optical fiber, and unsatisfactory results. At the same time, due to the certain forward speed of cable production, relying on manual placement of the optical fiber on the insulation surface of the cable during cable movement, there are safety hazards, which can easily cause safety production accidents.

Design of Fiber Optic S-shaped Swinging Device Built into the Cable

Design of Fiber Optic S-shaped Swinging Device

A fiber optic S-shaped swinging device (i.e. fiber optic swinging device) was designed to address the shortcomings of the manual built-in fiber optic technology in the original 220 kV high-voltage intelligent temperature measurement cable. The device mainly consists of friction wheels, gear transmission mechanisms, eccentric wheels, swinging arms, enz.

This device belongs to an unpowered swinging device. The outer circumference of the cable is designed with a friction wheel that is tightly attached to the cable and rotates with the cable’s movement. The rotation axis of the friction wheel is perpendicular to the direction of cable movement; Design a swing arm on the outer circumference side of the cable; The front end of the swing arm is connected to a swing arm driving mechanism that drives the swing arm to swing. There is a gear transmission mechanism between the friction wheel and the swing arm driving mechanism, which uses the movement of the cable to drive the friction wheel. Through the transmission of the gear transmission mechanism and eccentric wheel, the swing arm of the device can swing to a certain extent, ensuring that the optical fiber does not bear large pulling force; The optical fiber passes through the mold hole at the rear end of the swing arm and adheres firmly and stably in an S-shape to the outer shielding surface of the cable insulation; Four tape guide rods are wrapped around the cable and distributed at the four corners of a square. The tape guide rods are parallel to the cable, and the buffer tape is wrapped around the cable after passing through the tape guide rods. The optical fiber is wrapped, fixed, and protected; The outer circumference of the cable is connected to a hollow tube, which is installed on the hollow tube liner seat and can be adjusted 360 ° to ensure that the optical fiber can be placed on any side of the cable.

The transmission mechanism of the device includes: the front end of the swing arm is equipped with a swing arm fulcrum, the swing arm driving mechanism is an eccentric wheel, the eccentric wheel is connected to the rear side of the swing arm fulcrum, the rear end of the swing arm is equipped with a double mold seat, and mold holes are set on the double mold seat; The shaft of the friction wheel is installed on the bearing seat 1, which is equipped with a rolling bearing to cooperate with the friction wheel shaft. The bearing seat 1 is equipped with a locking seat, which is equipped with a locking screw. The gear transmission mechanism includes a gear 1 fixed to the friction wheel shaft. Gear 1 meshes with gear 2 for transmission. Gear 3 is fixed to the shaft of gear 2, which meshes with gear 4. The shaft of gear 4 is installed on the bearing seat 2, which is equipped with a rolling bearing to cooperate with the shaft of gear 4. Gear 5 is fixed to the shaft of gear 4, which meshes with gear 6. The shaft of gear 6 is installed on the bearing seat 3, and the eccentric wheel is fixed to the shaft of gear 6. On the axis. When the cable moves forward, the tape guide rotates counterclockwise, and the tape passes through the tape guide and wraps around the cable. At the same time, the friction wheel tightly pressed on the surface of the cable generates sufficient friction, driving gear 1 and transmitting it in multiple stages to gear 2, gear 3, gear 4, gear 5, and gear 6. Gear 6 then drives the eccentric wheel to rotate. The rotation of the eccentric wheel causes the swing arm on the eccentric wheel to swing around its pivot point. The fiber optic cable passes through the mold hole installed on the swing arm, and as the cable moves and the swing arm swings, it naturally forms an S-shaped shape, which is then wrapped and fixed by the wrapping tape.

Verification of the Use Effect of Fiber Optic S-shaped Swinging Device

The structure of the S-shaped fiber optic swing device is compact and compact, without the need for additional power or modification of the original 220 kV high-voltage intelligent temperature measurement cable’s built-in fiber placement process. This can greatly reduce the labor intensity of operators, greatly improve production efficiency, and the S-shaped shape formed by the built-in fiber optic is neat and tidy, with very ideal results. In order to verify the actual use effect of the fiber optic S-shaped swing device, two OPHC-YJLW03 127/220 kV 1 × 2 500 mm2-CTG-12B1 220 kV high-voltage intelligent temperature measurement cables with lengths of 530 m and 490 m were made using it, and the main performance of the finished cable was tested. The performance of the two 220 kV high-voltage intelligent temperature measurement cables met the relevant national standards. These two 220 kV high-voltage intelligent temperature measurement cables underwent full performance type tests, and the test data met the design requirements.

A built-in fiber optic S-shaped swing device for 220 kV high-voltage intelligent temperature measurement cables has been designed. The production results show that the designed fiber optic S-shaped swing device has high production efficiency, stable process structure, and excellent product performance. The 220 kV high-voltage intelligent temperature measurement cable product has been used by multiple units such as State Grid and Southern Power Grid, and has received good feedback from users. In the future, high-voltage cables will develop towards intelligence and integration, and it can be expected that high-voltage intelligent temperature measurement cables will have broad market development prospects.