Shougang flue gas desulfurization project cable and switch cabinet optical fiber temperature measurement project

Chemical plants, power plants and other large industrial enterprises lay a large number of power cables and control cables, connected with a variety of high-voltage equipment, these cables are distributed in the cable shaft, cable tunnel, cable bridge, cable sandwich.

Cable fire accounted for 15.6% of industrial fire accidents, the accident is mainly caused by the fault of the cable itself and the external environment, of which the fault of the cable itself accounted for about 25%.

Most of the fire accidents are caused by high temperature, so it is particularly important to timely and accurately monitor the change of cable temperature and issue an early warning before the fire occurs, so that users have sufficient time to take appropriate measures to avoid accidents or fires.

Cable and switch cabinet fire causes and characteristics

According to statistical analysis, there are two main causes of cable trench, cable bridge and tunnel fire:

(1) Internal cause: fire failure caused by the cable itself. There are many reasons for the failure of power cables, which can be summarized as follows:

a, the quality of cable products;

b, the cable running time is long, resulting in aging;

c, the cable long-term overload operation or in a harsh environment;

d, cable construction quality or joint production technology level is low;

e, man-made damage to the cable.

(2) External causes: combustible gases (such as gas, natural gas, biogas, etc.) string into the cable trench, tunnel, because the cable trench, tunnel is relatively dense when the open fire (artificial or cable discharge, etc.) will immediately cause the entire cable explosion fire.

Distributed optical fiber temperature measurement system DTS is an internationally advanced temperature measurement technology, which can realize the distributed temperature measurement of the entire cable bridge and cable trench, find the cable hot spot in time, and prevent the problem from "burning", which is of great significance to ensure the safe operation of large industrial and mining enterprises.

This scheme adopts a distributed optical fiber temperature measuring system DTS and a fiber grating temperature demodulation instrument, which can realize real-time temperature measurement at any position of 6 sintering machines and temperature monitoring at key positions of 23 high and low voltage switchgear, so as to achieve prevention. Once it is found that the measured environmental temperature value or temperature rise rate exceeds the set threshold, the system automatically alarms, and sends the real-time alarm signal to the monitoring room through Ethernet or relay, which is convenient for the on-duty personnel to deal with.

In this scheme, the temperature of the cable in the cable trench is measured by the distributed optical fiber sensing system and the key area of the switch cabinet is measured by the optical fiber grating demodulation instrument. Then the data of the two are integrated and uploaded to the server side for information summary, and finally a set of integrated cable trench-switch cabinet monitoring system is formed.

Each detection cable is connected to the DTS measuring host through the pigtail (pigtail is provided with the host when delivery), and one end of the pigtail is the measurement

For cable channels, the detection cable is usually laid along the cable line or sine wave shape. For this project, in order to increase the cable hot spot response, multiple detection optical cables (linear laying) are buried in the cable trough; The upper surface of the cable can be laid in a sine shape.

Distributed DTS optical fiber temperature sensor is used to monitor cable tray in power plant cable trench

Significance of power plant temperature monitoring:

◆ Timely detection of hot spots (especially cable joints with potential accidents) and other environmental anomalies;

◆ Change from manual inspection to automatic real-time monitoring of process status;

◆ Postponing investment costs such as routine maintenance;

◆ Safely increase loop carrying capacity;

◆ Periodic emergency assessment can be achieved.

Design objectives of integrated monitoring for distributed power plants:

Real-time online temperature monitoring;

Provide early detection of fire hazards;

Clear indication of fire hazard locations;

The alarm signal is transmitted to the monitoring room for the staff on duty to deal with or the fire alarm control system for emergency and linkage control.

Simple and convenient wiring, high performance reliability

With the rapid development of urban construction and power grid, the rate of power grid cabling is getting higher and higher, and the task of operation management is also increasing. According to incomplete statistics, in the past ten years, more than 100 major accidents have occurred due to cable fire and spread into disaster, burning more than 320,000 meters of cable, restoration and reconstruction work is costly and time-consuming, and only the loss of less power supply has reached more than 10 billion yuan. Cable fire accidents have their own special hazards, that is

It is the failure of the control loop that causes the expansion of the accident and even damages the main equipment, and it is difficult to repair and cannot resume production for a long time. In addition to the overheating and fire accident of the cable itself, external factors such as tunnel water, small animal invasion, flammable gas and toxic gas leakage around the cable, and illegal theft also pose a major threat to the safe operation of the cable, and directly increase the difficulty and danger of manual inspection.

Construction of cable tunnel comprehensive monitoring system can effectively reduce the work intensity and safety risks of inspectors, reasonable arrangement of state maintenance, greatly reduce the accident rate of transmission cables, avoid adverse social effects, reduce the loss of electricity sales, but also effectively reduce the theft of tunnel ancillary facilities

◆ Causes of cable tunnel fire:

◆ Cable intermediate joint production process quality is not up to standard, joint connection loose

◆ The cable is bent or considered damaged

◆ Cable contact resistance increases, long-term operation leads to temperature rise, joint burst insulation layer breakdown

Through the detection cable laid on the cable surface, the temperature measuring host monitors the temperature information of the cable in the tunnel in real time, finds the hot spot in time, accurately locates it, and gives a timely warning.

At the cable junction, the detection optical cable is fixed at the cable terminal and cable junction by winding in a double ring mode to ensure that the temperature measuring optical cable is in close contact with the cable terminal or cable connector.

The working principle and installation method of DTS-detector of Wuxi Brillouin distributed optical fiber temperature measurement system The recoverable differential temperature sensor cable of the detector is composed of an inner conductor (two core non-polarity), an insulation layer and a braided shield layer (see Figure 1). The insulating material of the insulating layer is a special heat-sensitive material, so the resistance between the two inner conductors has a negative temperature characteristic.

The negative temperature coefficient is characterized as a logarithmic function, that is, the resistance value of the detector at normal temperature will be much larger than that at abnormal temperature. In order to ensure that the system can accurately sense the temperature change, the detector must be connected with a special interface module and pass reasonable module parameters

Cable bridge, cable tunnel, cable trench, cable sandwich and other cable fire area installation methods

For the fire detection in the cable area, the linear thermal fire detector can be laid by sine wave contact or linear suspension. This method has a good effect on fire detection, but in engineering applications, in order to replace the detector for convenience, the detector is installed overhead. This works just as well for fire detection. Note: When the detector is installed overhead, it should be arranged in the center of the power cable trailer. When the width of the trailer is more than 600mm, two detectors should be installed. For specific installation, see Figure 5-1: The temperature-sensing cable is soft. For example, if it is installed in a coal pipeline where heavy foreign objects are likely to fall, steel wires should be added for protection to prevent heavy objects from breaking the temperature-sensing cable when the equipment is working. At the same time, when the coal pipeline is used, attention should be paid to waterproof to avoid the cable getting wet for a long time.

An independent fiber optic distributed temperature monitoring system is used in the cable tunnel of the passenger station for different environments

Overall design scheme

In this engineering solution, an independent optical fiber distributed temperature monitoring system is adopted for the cable tunnel of the newly built passenger station. The optical fiber temperature monitoring system can monitor the temperature under different environments respectively, so as to detect the hidden trouble earlier and reduce the loss. At the same time, a large number of online monitoring data are provided to provide reliable basis for operators to fully understand the use of electrical equipment.

The optical fiber temperature sensing system shall be a distributed linear differential constant temperature optical fiber temperature sensing fire detector, which is composed of optical fiber temperature measuring host (controller), temperature sensing optical fiber, alarm output unit, monitoring management software, upper monitoring computer, monitoring cabinet and corresponding auxiliary equipment required. The whole monitoring system can communicate with the main fire alarm controller through the communication interface or dry contact relay terminal of the host through temperature measurement.

System layout scheme

According to the design specification, two sets (4km,2 channels) distributed temperature sensing optical fiber systems are used to monitor the temperature and fire online in the cable tunnel of the newly built railway passenger station.

One set (4km,2 channels) distributed temperature sensing optical fiber system controller is set in the fire control room of the west station building, and the other set is set in the fire control room of the East station building. One end of the detection cable in each channel is fused with the pigtail and connected to the optical fiber interface of the controller respectively. The other end of the detection cable is led into the cable tunnel along the cable channel and laid in a straight line on the top of the tunnel. The detection cable is fixed on the top of the cable tunnel through a Z-shaped bracket or hook every 1-2 meters.

Detecting cable cabling requirements

(1) At least 10 meters shall be reserved for the cable traction to one end of the DTS host control cabinet for the welding of the cable and pigtail.

(2) At both ends of the cable junction (or break point) in the tunnel, at least 10 meters of cable should be reserved for normal welding of the cable on the ground.

(3) The reserved optical cable ring should be coiled and fixed.

(4) The bending radius of the cable is not allowed to be less than 150mm.

(5) Before installing the cable, the length of the cable should be checked, and the cable should be selected according to the length of the cable and the distance of the connection. Optical cables or their connectors avoid traffic arteries and other obstacles.

(6) Before and after laying optical cables, the appearance of optical fibers should be checked; The cable should be intact.

(7) The cable connection box must be fixed.

(8) Unload the cable from the car. Use a forklift or hoist to gently place the cable from the car on the ground.

When the optical cable is unloaded from the car, it is appropriate to use a straight plank placed between the car platform and the ground, forming a slope less than 45º, with a rope through the middle hole of the optical cable disc, the person in the car to pull both ends of the rope, so that the optical cable disc down the slope of the wooden plate at a constant speed. When unloading the cable, it is strictly prohibited to stack, lay it flat, and directly roll the cable down from the height to prevent strong impact on the cable and cause damage.