Design of Automatic Disconnection Device for Non-power Outage Operation of High-voltage Line

A set of remote electric control disconnection device for high-voltage line with strong adaptability, easy operation, and high safety has been designed to address the problems of multiple spans, wide coverage, and difficulty in coordinating power failure with construction crossing operation. The design process aimed to reduce the weight and improve the reliability of the mechanical structure, and conducted computation and simulation of the traction force and safety load of the electrified tight cable. Based on the designed live disconnection device, experiments were conducted for different spans and cable diameters, while meeting the scope of infrastructure crossing sections. The experiments proved that the designed disconnection device has good effects in practical applications, and can select any point in the straight span to break the cable, in order to achieve safe and convenient uninterrupted operations in power recovery service.


Introduction
Non-power outage operations refer to on-site operations carried out by power workers while the power equipment and supply remain working, mainly used for the maintenance of power lines such as overhead lines and cables [1] .The high-voltage line disconnection tool is an indispensable auxiliary device during the non-power outage maintenance process of high-voltage transmission lines.Its main function is to tighten the cables, so as to ensure the safe and smooth implementation of subsequent work processes [2,3]   .At present, some existing devices are bulky and expensive, as well as require manual cable tensioning and load transfer, resulting in low efficiency [4,5] .Therefore, this article designs an electric disconnection device with remote control function and light weight, which may reduce the application costs and improve work efficiency.The main work of the paper is as follows: (1) A new type of disconnection device with light weight has been designed inspired by the advanced lightweight technology in automobiles [6] .Simulation analysis and verification of the traction force and equipment safety load of the developed device have been carried out.Compared with the existing similar equipment, 2kg weight reduction has been achieved, improving the equipment's work efficiency and saving costs.
(2) In order to verify the reliability and practical effect of the equipment, a set of straight span nonpower outage safe operation methods have been carried out based on the designed disconnection device [7] , along with the experimental verification.On the basis of meeting the scope of infrastructure crossing sections, any point in the straight span can be selected to disconnect the cable to expose the cable stylet conductor, which leads to an obvious operation and recovery range.

Design objectives and requirements
According to the basic requirements for live work on high-voltage lines, and in accordance with the Electric Power Safety Work Regulations, the following design principles should be followed: (1) The selection of tools and instruments follows a lightweight design, while meeting the mechanical strength requirements, minimizing the weight of the disconnecting device, reducing battery energy consumption.
(2) The tools and instruments have strong versatility and are easy to assemble.They can quickly build up straight aerial segments for different spans and cable diameters, forming an obvious operation range; and after recovery, the safe and stable operation of the line will not be affected.

Mechanical structure of the disconnection device
The designed live automatic disconnection device mainly consists of insulation tension traction and tension breaking switches, used for cutting live overhead distribution lines.Through mechanical loads, parallel currents can be created to avoid interference in related operations, which in turn achieve the non-power outage operation in power maintenance service.Its important mechanical components include flexible cable insulation support rods, insulation suspension rods, insulation shields, end clamps, electric drive mechanisms, etc.The structural schematic diagram is shown in Figure 1.

Electrical driving system
The electrical driving system of this device mainly consists of a motor, a reducer, and a remote microcontroller.The model selection of motors and reducers mainly involves the key parameters such as power, torque, speed, reduction ratio, volume, and weight.Moreover, according to the lead analysis of the designed lead screw, mechanical efficiency, motor reduction ratio, rated tension and other parameters, the torque required by the motor under the rated tension can be calculated based on the following formulas, where P denotes power, U denotes rated voltage, I denotes rated current, n denotes revolution speed, i denotes reduction ration and  denotes torque; the subscript m and s denote the motor and the lead screw, respectively.

Working principles
The working principle of the disconnection device is that the remote micro-controller can start/control the motor and generate power, which is transmitted to the lead screw through the reducer, driving the lead screw to convert rotational motion into linear motion.The screw is connected to the motor, reducer, bearing, right end fixture, and insulation shell as a whole for the right part movement; The left end fixture is connected to the insulating rod as a whole for the left part movement.The left and right parts are connected by a sliding bracket and a sliding groove, as shown in Figure 2. When the disconnecting device is stretched, it moves backwards.

Simulation analysis and optimization
In order for the developed device to adapt to different types of overhead cables, it is necessary to verify the mechanical properties of cables in different type, which is updated and optimized from the initial version of the disconnection device.The design procedure is shown in Figure 3.At the same time, inspired the lightweight technology of automobiles [8] , the weight of the disconnection device can be significantly reduced, which in turn the energy consumption of the battery can be reduced, and the operation time can be improved without degrading performance.Based on the initial version of the device, the load capacity of its key components and electrical drive tension structure is simulated and verified, and its safety parameter range is determined to provide theoretical guidance for the lightweight design of the equipment.

Verification of traction force on cables
It will inevitably generate excessive traction force on the cables during the process of tightening the cables with electricity during the application of the disconnection device.The length of tightening is called the excessive traction length [9] .In order to ensure the safety of the tightening of live cables during the operation process, that is, to consider the risk of cable breakage as the basis for judgment, the following two conditions must be met: (1) There is no risk of cable breakage during the live tightening process, that is, controlling the excessive traction force of the cable not to exceed the allowable stress of the cable; (2) After tightening the cable, the tensile force of the "connector" installed after disconnecting the cable in the middle range will not exceed the breaking force of the "connector".
This article conducts parameter configuration and ANSYS on typical line types such as JKLYJ-10/50, JKLYJ-10/240, JKLYJ-1/185, and JL-240, exploring the allowable range of breaking force.The results are shown in Table 1

Mechanical simulation of lead screw
The screw part of the disconnection device is a slender flexible shaft with threads, steps, grooves, etc. on the surface, which can convert rotational motion into linear motion.As shown in Figure 4, the lead screw will be subjected to axial tension at both ends when the tightener is extended during operation.2. When the material of the lead screw is 40Cr, the maximum equivalent stress obtained through simulation is 652.84MPa, and the axial breaking force is 63964.15N;When the material of the lead screw is 718H, the maximum equivalent stress obtained by simulation is 820.75MPa, and the axial breaking force is 80415.69N.Compared with the parameters in Table 2, it can be seen that the weight of the lead screw is basically the same when using 718H and 40CR materials, but the axial breaking force is relatively large for 718H materials.Thus, the selection of 718H material for the lead screw is better, and the axial breaking force of the lead screw is 80415.69N.63964.1580415.69Taking 718H as the material for the lead screw, with a radius of 6mm as the initial value for lightweight optimization, the maximum stress should not exceed 980MPa.After iterative calculation, when the theoretical optimal solution radius that meets the optimization setting is equal to 2.1mm, the maximum stress of 887.7MPa is lower than the yield stress of 980MPa.Table 3 shows the weight comparison of the lightweight iteration process for the screw part.For the simulations before and after lightweight, the maximum displacement is located at the end face of the lead screw on the motor side, and the maximum stress is located at the overlap between the lead screw and the bearing seat, which is consistent with the practical situation.The results are shown in Figure 5.

Mechanical simulation of gear
Ensuring that the gear transmission does not fail is an important prerequisite for ensuring the normal operation of the equipment.By calculating the speed of the driving wheel and the torque of the driven wheel, the gear thickness (or hollowing out) is modified to reduce weight while the speed is constant.Simulation analysis is conducted on the gear to obtain the minimum weight of the transmission mechanism within a reasonable range.The gear pairs have been simulated and analysed by ANSYS, and the smoothness of meshing and the dynamic characteristics have been evaluated based on transient dynamics.Taking 40Cr material as the initial variable, the parameter settings are shown in Table 4. Taking a thickness of 12mm as the initial value for optimization, the maximum displacement calculated at this stage is 0.004mm with the maximum stress 98MPa, indicating a high safety factor.Set thickness as the design variable and enter the optimization module, with the goal such that the constraint of stress not exceeding the yield strength of the material.In this way, the optimal thickness is derived as 4mm by simulation, along with the maximum stress is 245MPa, as shown in Figure 6.Considering the axial stiffness, overload and tooth surface assembly requirements, the thickness of 4mm is taken for subsequent topology optimization of lightweight hollowing out.The topology results are also shown in Figure 6, where the blue area can be removed without degrading the device performance.Consequently, the comparison of the lightweight iteration process for the gear part is shown in Table 5, finally resulting in 48% weight reduction.0.046241 0.054585 0.100826 -48% Based on the above analysis and design, the completed lightweight scheme can significantly reduce the weight of the tool, improve the efficiency of actual operation and transportation convenience, while ensuring its application reliability and stability.At the same time, considering the processing technology and load margin of actual tool components, reasonable selection was made within the parameter range of theoretical analysis, and the design and manufacturing of the actual cutting tool prototype were ultimately completed.Field experiments were conducted, and reliable results were obtained.

Field experiment
Based on the designed disconnection device, a safe non-power outage operation method for straight span crossing on high-voltage line can be formed [10] .Firstly, the bypass operation method is used to build the bypass system, and then the designed disconnection equipment is used to achieve the operation process using the bridging method.An on-site experiment was conducted based on the above method as shown in Figure 7.  6 indicate that, with a weight reduction of 2kg, the expansion and contraction speed of the device increased by 20mm/min.Although the maximum tensile force decreased by 0.5kN, the measured indicators meet the usage requirements and can effectively carry out bypass operations without power outage in the distribution network.

Conclusion
In this paper, a set of remote electric control disconnection device for high-voltage line has been designed to address the problems of power failure with construction crossing operation.The design process was initiated by the analysis of the mechanical structure and the electrical driving system, then the important components of screw and gear were optimized for reliability and lightweight, which improved the feasibility and adaptability in application.Finally, the on-site experiments proved that the designed disconnection device has good effects in practical applications, and can select any point in the straight span to break the cable, which achieved safe and convenient uninterrupted operations in power recovery service.

1 .
Left moving part as a whole; 2. Slip sheet and chute; 3. Right moving part as a whole Figure 2. Moving Parts in Back Directions of the Device

Figure 3 .
Figure 3. Mechanical Design Procedure of the Breaking Equipment

Figure 4 .
Figure 4. Structure of the Screw Part of the Equipment Explicit dynamic simulation was performed on the lead screw for the axial tension it bears.Taking 40Cr and 718H materials as initial variables as examples, the results obtained are displayed in Table2.When the material of the lead screw is 40Cr, the maximum equivalent stress obtained through simulation is 652.84MPa, and the axial breaking force is 63964.15N;When the material of the lead screw is 718H, the maximum equivalent stress obtained by simulation is 820.75MPa, and the axial breaking force is 80415.69N.Compared with the parameters in Table2, it can be seen that the weight of the lead screw is basically the same when using 718H and 40CR materials, but the axial breaking force is relatively large for 718H materials.Thus, the selection of 718H material for the lead screw is better, and the axial breaking force of the lead screw is 80415.69N.Table 2. Simulation Results of the Screw Part in 40Cr and 718H Material Type 40Cr 718H Material density(Kg/m3) 7850 7800 Elastic modulus(MPa) 211000 205000 Poisson's ratio 0.277 0.3 Tensile strength(MPa) 980 1100 Yield strength(MPa) 785 980 Tangential strength(MPa) 80800 90000 Area of applied tension in simulation (mm²) 97.9783 97.9783

Figure 5 .
Figure 5. Maximum Displacement and Stress after Lightweight

Figure 6 .
Figure 6.Stress Distribution with Thickness of 4mm and the Topological Structure

Figure 7 .
Figure 7. Experiment Scene Loading experiments were conducted on the device under different tensile forces and the experimental results indicate that the tool can ensure normal operation even at a maximum design load of 7kN.The experimental results in Table6indicate that, with a weight reduction of 2kg, the expansion and contraction speed of the device increased by 20mm/min.Although the maximum tensile force decreased by 0.5kN, the measured indicators meet the usage requirements and can effectively carry out bypass operations without power outage in the distribution network.Table 6.Comparisons of Design and Experiment Parameters Operation Parameters Design Parameters Measured parameters Total mass 10kg 8kg Maximum tightening range 380mm 380mm Load expansion speed 150mm/min 170mm/min Stretch length 1800mm 1800mm Insulation length 480-860mm 480-860mm Maximum traction force 7kN 6.5kN

Table 1 .
. Simulation Result of Different Types of Cable

Table 2 .
Simulation Results of the Screw Part in 40Cr and 718H

Table 4 .
Parameters of Transient Dynamics Simulation in 40Cr

Table 5 .
Lightweight Result of the Gear Thickness Driving gear mass (kg)

Table 6 .
Comparisons of Design and Experiment Parameters