A metal sheath grounding structure for multiple parallel 27.5kV cables

Abstract

The utility model discloses a multi-parallel 27.5kV cable metal sheath grounding structure, which belongs to the field of power distribution grounding protection technology, including a busbar, an input side loop, an output side loop and a current detection device; the busbar is connected with multiple input side loops and one output side loop; the shielding layer and armor layer of each cable metal conductor at one end of the same-phase power supply cable are respectively connected to different input side loops; the shielding layer and armor layer of multiple cable metal conductors at the other end of the same-phase power supply cable are respectively connected in parallel to different sheath protectors; the sheath protector and the output side loop are respectively connected to different grounding devices; the input side loop and the output side loop are both equipped with current monitoring devices for collecting currents of each loop. The structure improves the reliability of cable operation, can collect and monitor the current of the cable metal sheath and the grounding branch in real time, and timely discover problems such as excessive current in each loop.

Description

Technical Field

[0001] The utility model belongs to the technical field of power distribution grounding protection, and specifically relates to a multi-parallel 27.5kV cable metal sheath grounding structure. Background Art

[0002] Different from the three-phase AC power supply mode of the electric power system, the electrified railway traction power supply system adopts industrial frequency single-phase AC power supply. The cables fed to the grid from the traction substation are mostly 27.5kV single-core and multiple cables are connected in parallel. The metal sheath of the 27.5kV cable in the traction power supply circuit mainly adopts single-end grounding mode, that is, one end is directly grounded and the other end is grounded through a sheath protector. For long lines, they will be divided into appropriate multiple units, and each unit adopts single-end grounding mode. The 27.5kV cable metal sheath is composed of a cable metal shielding layer and a metal armor layer. In the actual on-site wiring process, the metal sheath connection methods for multiple parallel cables mainly include the centralized grounding scheme of the cable metal sheath end and the separate grounding scheme of the cable metal sheath end. The centralized grounding scheme of the cable metal sheath end is as follows: Figure 1 As shown in (a), the grounding schemes for the ends of the cable metal sheath are as follows: Figure 1 As shown in (b) in the figure. Since the metal shielding layer and armor layer of the cable are directly grounded at one end and connected in parallel at the other end, circulating current is inevitable. Therefore, it is necessary to conduct quantitative research and analysis on the connection method of the cable metal sheath to prevent excessive circulating current from causing problems and hidden dangers to the safe and reliable operation of the power supply system and affecting the safe and punctual operation of high-speed trains.

[0003] The current 27.5kV multi-parallel cable metal sheath connection scheme for electrified railways has the following problems.

[0004] 1. The cable metal sheath connection scheme lacks a standard basis, posing safety risks during operation.

[0005] 2. Under this scheme, since the ends of the cable metal sheaths are interconnected to form a closed loop, there is mutual inductance between the loop and the cable conductor. Due to the small distance from the conductor, the mutual inductance between the loop and the cable conductor is large, and due to the electromagnetic induction phenomenon, circulating current will inevitably be generated in the cable metal sheath. Due to the influence of the circulating current, the current carrying capacity may be exceeded and the cable may be burned.

[0006] 3. The cable metal sheath connection solution lacks a suitable monitoring system, which makes it impossible to effectively monitor and analyze the current in the metal sheath, and it is also impossible to detect the problem of excessive return current in time. Utility Model Content

[0007] The utility model aims at the deficiencies of the existing technology, and provides a multi-parallel 27.5kV cable metal sheath grounding structure, which optimizes the number of sheath protectors and can effectively reduce the influence of the cable metal sheath current, ensuring the safe and reliable operation of the cable. At the same time, the current in each metal sheath and the grounding branch can be collected and monitored in real time, and the problem of excessive current in each loop can be discovered in time.

[0008] The utility model is realized by the following technical solutions:

[0009] A multi-parallel 27.5kV cable metal sheath grounding structure, comprising a busbar, an input side loop, an output side loop and a current detection device;

[0010] The busbar is connected with a plurality of input side loops and an output side loop;

[0011] Multiple same-phase power supply cables are arranged on each phase of the power supply line for parallel power supply;

[0012] The shielding layer and armoring layer of the metal conductor of each cable at one end of the same-phase power supply cable are respectively connected to different input side loops;

[0013] The shielding layers and armoring layers of the metal conductors of multiple cables at the other end of the same-phase power supply cable are respectively connected in parallel to different sheath protectors;

[0014] The sheath protector and the output side circuit are respectively connected to different grounding devices;

[0015] The input side circuit and the output side circuit are both equipped with current monitoring devices for collecting the current of each circuit.

[0016] Furthermore, the busbar is connected to the reserved input side loop.

[0017] Furthermore, the sheath protector is a lightning arrester.

[0018] Furthermore, the current monitoring device is communicatively connected to the substation integrated automation system or the online monitoring system.

[0019] Furthermore, the busbar, the input side loop, the output side loop and the current monitoring device installed in the input side loop and the output side loop are all installed in a junction box.

[0020] Furthermore, the cables are arranged in a horizontal cross-pattern using TFTFT, wherein T represents a plurality of power supply cables of the same phase connected in parallel, and F represents a plurality of return cables of the same phase connected in parallel.

[0021] Compared with the prior art, the utility model has the following beneficial effects:

[0022] 1. The utility model provides a multi-parallel 27.5kV cable metal sheath grounding design scheme, which standardizes the future cable metal sheath grounding design and improves the cable operation reliability.

[0023] 2. The utility model provides a multi-parallel 27.5kV cable metal sheath grounding design scheme. Through simulation and comparative analysis, the changing law of the circulating current in the cable metal sheath under different cable arrangements of the main electrified railways is analyzed, and a recommended scheme is given to reduce the impact of the circulating current in the cable metal sheath. This provides a theoretical basis for the implementation of the cable metal sheath design scheme in the future.

[0024] 3. The multi-parallel 27.5kV cable metal sheath grounding design provided by the utility model can collect and monitor the current of the cable metal sheath and the grounding branch in real time, and promptly discover problems such as excessive current in each loop. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the implementation of the utility model or the technical solution in the prior art, the following is a brief introduction to the drawings required for the implementation or the prior art description. Obviously, the drawings in the following description are only exemplary, and for ordinary technicians in this field, other implementation drawings can be derived from the provided drawings without creative work.

[0026] Figure 1 Schematic diagram of two traditional 27.5kV cable metal sheath wiring schemes;

[0027] Figure 2 A schematic diagram of the metal sheath grounding structure of multiple parallel 27.5kV cables provided by the utility model;

[0028] Figure 3 Schematic diagram of different cable arrangement structures;

[0029] Reference numerals in the figure: 1 - sheath protector, 2 - current monitoring device. DETAILED DESCRIPTION

[0030] The exemplary embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. Although exemplary embodiments of the present invention are shown in the accompanying drawings, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments described herein. On the contrary, these embodiments are provided in order to enable a more thorough understanding of the present invention and to fully convey the scope of the present invention to those skilled in the art. It should be noted that, in the absence of conflict, the embodiments of the present invention and the features described in the embodiments can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0031] The utility model provides an embodiment of a multi-parallel 27.5kV cable metal sheath grounding structure, such as Figure 2 shown.

[0032] A junction box is arranged beside the railway cable, in which a busbar, a plurality of input side loops, an output side loop and a current monitoring device 2 installed in each input side loop and output side loop are installed.

[0033] The busbar is connected to a plurality of input-side circuits and one output-side circuit.

[0034] A plurality of same-phase power supply cables are arranged in each phase of the power supply line for parallel power supply. The power supply line in this embodiment adopts three same-phase power supply cables.

[0035] Each input side loop is separately connected to the shielding layer and armor layer lead-out terminals of the metal conductor of each cable at one end of the same-phase power supply cable through connectors and conductors. At the same time, input side loops with unconnected cables are reserved on the busbar for use when the number of same-phase power supply cables is increased later; the shielding layers and armor layers of the metal conductors of the three cables at the other end of the same-phase power supply cable are separately connected in parallel to two sheath protectors 1, and each sheath protector 1 is separately connected to the grounding device R2.

[0036] The sheath protector 1 adopts a lightning arrester.

[0037] The output side loop is connected to the grounding device R1 through a connector and a conductor.

[0038] A current monitoring device 2 is installed on each input side circuit and output side circuit respectively to collect the current of each circuit; the current of each circuit collected by the current monitoring device 2 is uploaded to the substation integrated automation system or online monitoring system for real-time monitoring.

[0039] The cables are arranged horizontally in TFTFT format, where T represents multiple power supply cables of the same phase connected in parallel, and F represents multiple return cables of the same phase connected in parallel.

[0040] Combined with the characteristics of my country's electrified railway traction power supply system, the multi-parallel 27.5kV cable metal sheath wiring scheme provided by the utility model is compared with the existing technical scheme. With the help of electromagnetic transient analysis software PSCAD / EMTDC, a multi-parallel 27.5kV cable model is built. The cable layout, segment length, cable load current and other factors are simulated and analyzed. The simulation results are shown in Table 1.

[0041] At present, there are mainly the following ways to arrange 27.5kV Internet cables on domestic railways: Figure 3 The TTTFF shown in (a) is arranged vertically, as shown in Figure 3 The horizontal arrangement of TTTFF shown in (b) and Figure 3 The TFTFT shown in (c) is arranged horizontally in a cross pattern; in the figure, T1, T2, and T3 represent multiple power supply cables of the same phase connected in parallel; in the figure, F1 and F2 represent multiple return cables of the same phase connected in parallel; and D is the distance between the power supply cable and the return cable.

[0042] Table 1 Simulation results of current changes in the metal sheath of multiple parallel 27.5kV cables under different cable layouts

[0043]

[0044] The cable metal sheath in each scheme in Table 1 is divided into a cable shielding layer and an armoring layer.

[0045] According to the comparison results, the following conclusions can be drawn:

[0046] 1. Different cable layout methods have a great influence on the cable metal sheath current. Among them, the horizontal cross layout is the best, followed by the vertical up and down layout. The horizontal cable layout is poor and is not recommended in actual cable layout.

[0047] 2. The current in the metal sheath of multiple parallel 27.5kV cables has nothing to do with the length of the cable segment, but changes in direct proportion to the cable load current. The increase or decrease multiple of the cable metal sheath current is the same as the change in the cable load current.

[0048] 3. Under certain cable layout conditions, different wiring schemes for the metal sheaths of multiple parallel cables have a great influence on the current in the metal sheath. The circulating current of the cable metal sheath is too large under the centralized grounding scheme at the end of the cable metal sheath and the separate grounding scheme at the end of the cable metal sheath. Taking the recommended cable metal sheath wiring scheme as an example, the shielding layer current in the cable metal sheath is reduced by 69% and 61% respectively compared with the centralized grounding scheme at the end of the cable metal sheath and the separate grounding scheme at the end of the cable metal sheath; the armor layer current is reduced by 56% and 48% respectively compared with the centralized grounding scheme at the end of the cable metal sheath and the separate grounding scheme at the end of the cable metal sheath. The proportion of the cable metal sheath circulating current to the cable load current is controlled below 10% to meet the standard requirements. Based on the current data of each loop collected by the current monitoring device, combined with artificial intelligence technology, the operation of the return system is automatically learned and judged through the current data, and alarm information and suggestions are actively provided to the operation and maintenance personnel as needed to realize the intelligent operation and maintenance of the return system.

[0049] It should be noted that in the description of the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected" and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a direct connection, or an indirect connection through an intermediate medium, or it can be the internal communication of two components. For those skilled in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

Claims

1. A multi-parallel 27.5kV cable metal sheath grounding structure, characterized in that: It includes a busbar, an input side circuit, an output side circuit and a current detection device; The busbar is connected with a plurality of input side loops and an output side loop; Multiple same-phase power supply cables are arranged on each phase of the power supply line for parallel power supply; The shielding layer and armoring layer of the metal conductor of each cable at one end of the same-phase power supply cable are respectively connected to different input side loops; The shielding layers and armoring layers of the metal conductors of multiple cables at the other end of the same-phase power supply cable are respectively connected in parallel to different sheath protectors; The sheath protector and the output side circuit are respectively connected to different grounding devices; The input side circuit and the output side circuit are both equipped with current monitoring devices for collecting the current of each circuit.

2. According to claim 1, a multi-parallel 27.5kV cable metal sheath grounding structure is characterized in that: The busbar is connected to the reserved input side loop.

3. According to claim 1, a multi-parallel 27.5kV cable metal sheath grounding structure is characterized in that: The sheath protector is a lightning arrester.

4. A multi-parallel 27.5kV cable metal sheath grounding structure according to claim 1, characterized in that: The current monitoring device is communicatively connected to the substation integrated automation system or the online monitoring system.

5. A multi-parallel 27.5kV cable metal sheath grounding structure according to claim 1, characterized in that: The busbar, the input side loop, the output side loop and the current monitoring device installed in the input side loop and the output side loop are all installed in the junction box.

6. A multi-parallel 27.5kV cable metal sheath grounding structure according to claim 1, characterized in that: The cables are arranged in a horizontal cross-pattern using TFTFT, where T represents multiple power supply cables of the same phase connected in parallel, and F represents multiple return cables of the same phase connected in parallel.

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