Application of self-regulating electric heating cable to protect the subway line 2 of the Jinan Transit Railway from freezing.

Published on:

2023-03-29 10:30

Jinan Transit Line 2 with a total length of 36.4 km, including 34.8 km of underground lines and 1.6 km of overhead lines, will be opened on March 26, 2021. The average annual temperature in Jinan is 14.5 °C, and the extreme temperature is the lowest-19.7 °C. Fire and household water supply pipes for ventilation shafts, entrances and exits of metro stations, ends of sections, entrance and exit sections are extremely vulnerable to freezing, while traditional constant power heating cables generate constant heat and cannot intersect. Not suitable for shutdown, power will increase after shutdown, and there are certain shortcomings in cable burning and energy saving. After research, our self-regulating electrical insulation system was finally selected to protect subway pipelines from freezing.

The heat preservation by electric heating is to dissipate a certain amount of heat through the heat heater and supplement the heat loss of the heated pipe through direct or indirect heat exchange to meet normal operating requirements for temperature rise, heat preservation or antifreeze. The self-regulating electric heating cable is a core strip made of a layer of PTC material evenly extruded between two parallel metal wires. When the two wires at one end of the cable are connected to the power supply, the current flows to the side of the same wire. The layer of PTC material reaches another wire, and the PTC layer is a resistive heating element continuously connected in parallel between two wires, converting electrical energy into thermal energy. The resistivity of the heating cable gradually increases with the increase in temperature and can increase by several orders of magnitude at a certain temperature. This PTC effect can limit the flow of current and has the characteristics of temperature control. The self-regulating heat preservation system includes self-regulating heating cable, control cabinet, temperature control system, temperature measurement device, temperature sensor and external insulation of the pipeline. It consists of a protective layer, identification, etc. D. The main component of the system is self-regulating heating cable.

The temperature sensor is placed in the appropriate location of the pipeline, and the temperature control module is installed in the control unit. The heating power of the cable is highest at the moment of power on. As the temperature increases, the resistance of the easily accessible material in the cable gradually increases, and the internal working current and electrical heating power gradually decrease until the heating power initially compensates for the heat loss, so that the system is at a new temperature equilibrium. This compensation heating method is very energy efficient. This heating procedure is carried out repeatedly to ensure the normal operation of the pipeline system in winter.

For important public places at metro stations, the constant normal operation of the fire water supply system must be ensured. The self-regulating electric heat preservation system is a kind of heat preservation measure that is actively heated to compensate for heat loss. At present, it is the most effective application of freezing heat preservation measures, and it can effectively solve a large number of subway entrances, ducts and holes. Problems with non-freezing in winter of the pipes of the fire-fighting water supply system and some pipes of household water supply on the floor and layer of ground and above-ground stations.

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