Online monitoring system for expansion joint status

1. Preface

State Grid Corporation of China stated in 12.2.1.3 of the 2018 version of the anti accident measures that "GIS manufacturers should provide engineering expansion joint configuration plans during equipment bidding, data confirmation, and other stages, and should be included in the review content of the Engineering Design Joint Committee. The plan includes adjustment parameters such as the type, quantity, and location of expansion joints, as well as a detailed table corresponding to the "expansion joint (state) expansion amount - environmental temperature" for each expansion joint. Expansion joint scales should be set up for outdoor installations across different foundations and indoor installations across expansion joint locations.

At present, GIL/GIS equipment mainly consists of switches, current transformers, isolation switches, pipeline busbars, outlet sleeves, expansion joints and other equipment. Among them, the pipeline busbar is an important component of GIL/GIS, and its length is generally several hundred meters. The expansion joint of GIL/GIS equipment, as an accessory device of pipeline busbar, is mainly used for length adjustment compensation during installation of GIL/GIS equipment and compensation for the expansion and contraction of pipeline busbar tube with seasonal and environmental temperature changes after operation. The length of GIS pipeline busbar will vary with the change of environmental temperature. If the expansion joint of GIL/GIS cannot adjust and compensate for the expansion amount due to installation or manufacturing process problems, it may cause deformation and leakage of the connection part of the GIL/GIS equipment due to expansion stress, and seriously lead to insulation breakdown of the equipment. Currently, the vast majority of expansion joints are in an unmonitored state, which poses many safety hazards. The displacement monitoring of busbar tube expansion joints is achieved through manual observation and recording, which has the weaknesses of heavy manual workload, high labor cost, poor real-time performance, and low data accuracy. So, online monitoring of the status of expansion joints is an important project for the daily operation and maintenance of GIL/GIS equipment.

IIOnline monitoring system for expansion joint statusmain architecture

2.1 System Topology

2.2 System Description

The system adopts low-power Internet of Things technology and edge computing technology, supports battery or DC power supply, transmits to the intelligent collection network through wireless LORA or wired RS485 for shutdown, realizes real-time collection, high-speed processing and reliable transmission of monitoring data, and ensures accurate measurement of deformation. By optimizing the human-computer interaction interface, improving system operability, upgrading intelligent algorithms, and achieving fault warning and diagnosis. The sensor sends data to the management platform for analysis and display through an intelligent collection gateway, achieving unmanned inspection and improving the quality and efficiency of operation and inspection. The system improves the efficiency of GIS equipment operation and fault investigation. Including local monitoring, remote monitoring, and abnormal linkage, further standardizing construction work and improving the operation and maintenance level of urban power grids.

IIIOnline monitoring system for expansion joint statusEquipment Introduction

3.1 Intelligent collection host

The intelligent collection host is an on-site monitoring host that integrates the monitoring of the working status of displacement sensors, on-site temperature display (optional), alarm prompts and remote transmission, event recording and data recording. It can also modify the alarm threshold and other parameters of wireless displacement sensors on site. It can support communication such as IEC61850, 104, Modbus, MQTT, etc., meeting various requirements for communication with backend software in various application scenarios.

·Configuration instructions: Each region is equipped with an intelligent collection network shutdown.

3.2.1 Technical Parameters

3.2 Displacement Sensor

The displacement monitoring sensor of the expansion joint adopts a low-power design, supports battery or DC power supply, and is transmitted to the Internet of Things network for shutdown through wireless LORA or wired RS485. The sensor has high linear accuracy, smooth micro linear characteristics, and micrometer level repeatability accuracy. It adopts advanced resistance material processing technology, multi contact precious metal brushes, special sliding brush support and resistance substrate material selection, and a sturdy shell to enhance the durability of the product. The structure is compact and beautiful, and the service life can reach billions of reciprocating movements. It is easy to install and disassemble.

·Configuration instructions: Each expansion joint is equipped with 1-4 displacement sensors, with a recommended configuration of 4 sensors that can measure both lateral and longitudinal displacements.

3.2.1 Technical Parameters

4、 Equipment installation

4.1 Installation of displacement sensor

① As shown in the figure, first install the matching fixture customized according to the size of the expansion joint. Use fixtures to fix displacement sensors. Be careful to avoid the position of the expansion joint flat iron and bolts to ensure they are secure.

② After the fixture is fixed, install the displacement sensor device first. After the fixing is completed, pull the rope or rod out to the reserved hole of the fixture at the other end of the expansion joint for fixation. During the installation process, pay attention to keeping the two ends of the sensor level and avoid tilting or misalignment to avoid affecting measurement accuracy.

Schematic diagram of displacement installation position

③ Install 1-4 displacement sensors on each expansion joint. After installing the wireless displacement sensor, the signal antenna needs to be adjusted to point towards the corresponding area network shutdown position to ensure signal stability. The power supply and communication lines of the wired displacement sensor are laid to the shutdown point of the intelligent acquisition network, and the cables are protected by metal software. Wireless displacement sensors do not require wiring.

Schematic diagram of wireless displacement installation completion

Schematic diagram of wired displacement installation completion

4.2 Installation of intelligent collection network shutdown

Adopting an outdoor wall mounted intelligent collection network shutdown, it is fixed to a pole or wall near the power box with a clamp. The rack mounted host group screen is located in the corresponding local cabinet area. Take AC220V power from the power box, and the internal network communication method requires laying network cables or optical fibers in the nearest control cabinet and entering the local area network inside the station.

Installation diagram of gateway machine

4.3 Access to Management Platform

Main station platform: installed in the main control room, used for analyzing, browsing, storing, viewing data, and pushing alarms.

Installation diagram of backend system