Application of distributed optical fiber temperature warning for transmission belt in coal field

Distributed temperature anomaly warning and monitoring for power cables and substations in petrochemical energy-consuming enterprises

As the cable itself, no matter what causes the fire accident, they have to go through the following processes: insulation damage somewhere in the cable → intermittent or continuous discharge → local heating of the cable insulation is significantly decreased → explosion or arc occurs somewhere in the cable and bad gas is generated → the entire cable bridge and cable trench are on fire.

Cable fire characteristics:

(1) Fast spread and fierce fire. The cable itself is a kind of flammable material, because the number of cables in the cable tunnel is more and more, and the tunnel and overhead are densely laid, some are still in the environment of overlapping or staggered layout with high temperature hot pipes, the cable sandwich is covered with cobweb like cables, coupled with the height difference of the cable shaft to form natural ventilation, and the fault or fire of the cable can not immediately power off. Therefore, once these places are on fire, the fire is particularly fierce and harmful.

(2) Difficulty in emergency repair. Cable fire produces a lot of smoke and toxic gases, CO, CO2 content is very high, especially ordinary plastic cable is not only easy to catch fire, but also produce hydrogen chloride gas through the gap, the hole will diffuse to the electrical device room, forming a thin hydrochloric acid attached to the electrical device, and form a layer of conductive film, seriously reduce the insulation of the equipment and wiring circuit, so even if the fire is extinguished, Safe operation is still affected. This kind of disaster is called secondary hazard.

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 accidents 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 fire accidents are caused by high temperature, so timely and accurate monitoring of cable temperature changes before the fire occurs

This scheme adopts a 4km, 8-channel distributed optical fiber temperature measuring system DTS, which can realize real-time temperature measurement at any position of the transformer cable bridge in chemical enterprises, so as to achieve prevention. Once the measured ambient temperature or temperature rise rate is found on the cable bridge to exceed the set threshold, the system will automatically alarm, and send the real-time alarm signal to the monitoring room through Ethernet or relay, which is convenient for the on-duty officer to handle.

The measuring host is placed in the monitoring room, and the distributed optical fiber temperature measurement system can be connected to the monitoring room through routing or network cable. Used to display temperature distribution curve, visual interface and alarm information. Mainly used for instrument parameter setting and management, and display temperature and alarm information; The client software is installed on the user's PC and can remotely view real-time temperature data and alarm information

Detect the welding between the optical cable and the pigtail, and place the welding part in the optical cable splicing box for protection. Probe the cable from the measuring masterThe machine is laid close to the cable line, and the key parts can be fixed together with plastic cable ties.

Detecting the cable installation mode

Each detection cable is connected to the DTS measurement host through a pigtail. One end of the pigtail is connected to the measurement host, and the other end is fused with the detection cable through a connection box. This scheme adopts a 4km, 8-channel DTS. Cable bridge routing is divided into channels as shown in the figure, and channels are reserved

In this project, in order to increase the cable hot spot response, a number of detection cables are laid in the cable troughIn this project, in order to increase the cable hot spot response, a number of detection cables are linearly buried in the cable trough, and the detection cables are back and forth on each bridge

Distributed fiber optic temperature measurement DTS products are used in storage tank temperature monitoring systems

With the increase of chemical tank reserves, there are more and more storage tanks in domestic large chemical plants. The safety of chemical storage tank has always been an issue that departments and enterprises at all levels of chemical industry attach great importance to.

At present, the chemical storage tanks under construction in China mainly use floating roof tanks and spherical tanks. The top of the floating roof oil tank adopts the secondary sealing technology, but it is not completely sealed, and there is the possibility of a small amount of chemical liquid and gas leaking out from the sealing ring, and these leaking gases are prone to fire under natural conditions such as high solar temperature and lightning strikes. Article 8.6.2 of the national standard GB50737-2011 Design Code for Petroleum Reserve clearly stipulates that an automatic fire detection device should be set up on the oil tank, and the detection area of the fire detector should be divided according to the linkage control requirements of the fire extinguishing system. When the optical fiber type temperature detector is used, the optical fiber temperature detector should be set above the secondary sealing ring of the oil tank floating disk, and this requirement is also applicable to the chemical storage tank.

Distributed optical fiber temperature sensor DTS is a new generation of linear optical fiber temperature sensor or detector in the world, which has the advantages of intrinsic explosion-proof, anti-strong electromagnetic interference, anti-lightning strike, high measurement accuracy, light weight, small size and so on. In particular, the distributed optical fiber temperature sensor is a continuous distributed temperature fire detector, which can achieve temperature measurement at any point along the optical fiber, without measuring blind areas, and the optical fiber is both a transmission medium and a sensing element, without additional temperature sensor parts, simple installation, high reliability, and its performance is better than the traditional linear temperature detector. Suitable for chemical storage tank fire monitoring applications.

The new generation of distributed fiber optic sensor DTS is a continuous distributed no-power detection technology, which is mature and advanced, and can well overcome the drawbacks of the above fiber grating detector, as follows:

(1) The optical cable is a sensor, there is no fusion point in the middle, high reliability: the optical cable itself is a temperature sensor, the optical cable both plays the role of the temperature detector and acts as an important role in signal transmission, "transmission", "sense" integration; Because there is no need to install additional sensing elements, there is no fusion point in the middle of the sensing cable, and the reliability is high.

(2) Continuous distributed measurement, no measurement blind area: DTS is a continuous distributed measurement, which can obtain the temperature of each point along the sensing cable. At present, the distance between adjacent temperature points can reach 0.25m, and the temperature information is rich without measurement blind area. Based on continuous temperature analysis, the alarm mode of regional temperature difference can be realized.

Oil storage tank temperature measurement optical fiber construction method guidance

The detection cable is connected from the equipment through the connection box and buried to the bottom of the storage tank. When the optical cable is buried, it is necessary to dig a trench in the ground in advance, the depth of about 0.5m to 1m, the detection optical cable and the protection of galvanized steel pipe are laid in the dug trench, and the excavated soil is backfilled after the laying is completed. There is a firewall at the edge of the storage tank, and a cement road between the equipment and the storage tank, which has a certain influence on the laying of the detection cable, and the dug trench should be used during the laying.

After the cable is laid to the bottom of the storage tank, it is connected to the top of the storage tank through the galvanized steel pipe fixed on the side of the storage tank. The elbow is connected by an explosion-proof metal hose. The galvanized steel pipe on the side wall of the storage tank is fixed to the galvanized steel pipe.

For the temperature measuring cable at the top of the storage tank, the cable is laid along the line of the tank top sealing ring, and the existing screws on the sealing ring are used to fix the detection cable with iron clips on the sealing ring screws. As shown in the picture below: