Heat Tracing Methods of Electric Heating Cables
1. The core material of self-regulating electric heat tracing is PTC semi-conductive plastic, whose resistance increases with temperature rise. However, when the temperature rises to a certain value (this temperature value is the threshold temperature, which can actually be adjusted as needed), the resistance suddenly increases sharply, thereby blocking the current and stopping heating; when the temperature is below the threshold temperature, the resistance of the PTC material automatically decreases, allowing current to flow and continue heating. This maintains the system at a stable temperature. The basic self-regulating electric heat tracing cable (heating cable) consists of a PTC core strip and an insulating layer. The PTC material is extruded (or wrapped) uniformly and continuously onto parallel metal wire cores (also called bus wires) to form a flat strip, which is the PTC core strip. It is then covered with a polyethylene or PVC insulating layer. When the environment requires reinforcement or corrosion resistance, a braided layer or fluoropolymer jacket can be added. When the two conductive bus wires at one end of the core strip are connected to a power supply, current flows from one bus wire laterally through the parallel PTC material layer to the other bus wire, forming a parallel circuit. A core strip of a certain length has a certain resistance at a certain temperature and exhibits PTC characteristics. When current flows through the parallel PTC material layer, Joule heat is generated, causing the core strip to heat up. At the same time, the heat from the core strip is transferred through the cable insulation layer to the lower-temperature heated system, compensating for the heat dissipated by the system to the environment.2. Constant power electric heat tracing cables maintain a constant power output after being powered on, which does not change with the external environment, insulation material, or the material being traced. The power output or cutoff is usually controlled by a temperature sensor.
A: Parallel constant power electric heat tracing cables have resistance wires connected in parallel. They work by using the resistance wires to generate heat and heat the pipeline.
Principle: Two parallel nickel-plated copper stranded wires are wrapped in a fluoride insulation layer as power bus wires. A nickel-chromium alloy heating wire is wound around the inner insulation layer, and at fixed intervals, the heating wire is welded to form a continuous parallel resistor. When the power copper bus wires are energized, each parallel resistor generates heat, forming a continuously heating electric tracing cable that can be cut to any length.
B: Series constant power electric heat tracing cables have resistance wires connected in series. They work by using the resistance wires to generate heat and heat the pipeline.
Principle: Series electric heat tracing cables use insulated copper stranded wires as power bus wires, which also serve as the heating core wires. When current passes through the core wires with a certain internal resistance, Joule heat is generated (Joule-Lenz law Q=0.24I^2Rt), and the heat is proportional to the square of the current, the resistance of the core wire, and the time of current flow. Therefore, as the series electric heat tracing cable is energized over time, it continuously emits heat, resulting in uniform heating. Since the core wires of the series electric heat tracing cable have the same current and equal resistance, the entire cable heats uniformly from end to end, and its output power is constant, unaffected by ambient temperature or pipeline temperature.
3. Mineral insulated heating cable is a special heating cable that uses metal as the outer sheath, electric heating material as the heating element, and magnesium oxide powder as the insulation. The heat output of mineral insulated heating cable is related to the working voltage, the cross-section of the heating core, and the length of the cable.
Principle of Self-Regulating Heat Tracing Cable
The self-regulating electric heat tracing solution is mainly achieved through self-regulating heat tracing cables. The self-regulating heat tracing cable consists of conductive plastic, two parallel bus wires, an insulating layer, a metal shielding mesh, and an anti-corrosion outer jacket. The conductive plastic, made from plastic and conductive carbon particles through special processing, is the heating core. When the ambient temperature around the heat tracing cable is low, the conductive plastic undergoes micro-molecular contraction, causing the carbon particles to connect and form a circuit, allowing current to pass, and the cable begins to heat. When the temperature is high, the conductive plastic undergoes micro-molecular expansion, causing the carbon particles to separate, interrupting the circuit, increasing resistance, and automatically reducing the power output, thus lowering the heat output. When the ambient temperature drops again, the plastic returns to the micro-molecular contraction state, the carbon particles reconnect to form a circuit, and the heating power of the cable automatically increases. Since the entire temperature control process is automatically regulated by the material itself, the control temperature will neither be too high nor too low. Therefore, the excellent characteristics of electric heat tracing are unmatched by other heat tracing systems.
