Structure and Performance of Electric Heating Cable
The basic structure, classification and performance characteristics of constant power and self-control heating cables
The self-controlled temperature electric heating scheme is mainly completed by the self-controlled temperature electric heating cable. The temperature-controlled electric heating cable is composed of conductive plastic and 2 parallel bus bars with insulation layer, metal shielding net and anti-corrosion jacket. Among them, the conductive plastic, which is specially processed by plastic and conductive carbon particles, is the heating core. When the temperature around the heating wire is low, the conductive plastic produces micro-molecule shrinkage, the carbon particles are connected to form a circuit to allow current to pass, and the heating wire starts to generate heat; When the temperature is high, the conductive plastic produces micro-molecule expansion, and the carbon particles gradually separate, causing the circuit to be interrupted, the resistance rises, and the heating wire automatically reduces the power output and the heat generation decreases. When the surrounding temperature becomes cold, the plastic returns to the micromolecular contraction state, the carbon particles are connected to form a circuit, and the heating power of the heating cable automatically rises. Since the entire temperature control process is automatically adjusted by the province, the control temperature will not be too high or too low. Therefore, the good characteristics of electric heat tracing are unmatched by other heat tracing systems.
Two parallel insulated copper stranded wires are used as the power bus, and the heating wire with PTC characteristic is wound on the skeleton, and every other heating section length is alternately connected to the bus to form a continuous parallel resistance. A single-phase 220V power supply is connected to the bus bar, and the resistors connected in parallel generate heat.
1.2 Appearance of single-phase parallel constant power heating cable:
A-core wire
B-Core insulation layer fluoroplastic
C-structural layer
D－heating cable
E－Insulation sheath fluoroplastic
F－Metal shielding net
G-Outer sheath fluoroplastic
2.1 The internal structure of the three-phase parallel constant power heating cable:
Three parallel insulated copper stranded wires are used as the power bus, and every other heating section length is connected to the power bus a-b-c-a-b-c alternately and cyclically. A continuous parallel resistance is formed between every three phases, and the bus bar is connected to a three-phase 380V power supply, and each parallel resistance generates heat.
2.2 Three-phase parallel three-phase electric heating cable structure
A-core wire
B-Core insulation layer fluoroplastic
C-structural layer
D-heating wire
E－Insulation sheath fluoroplastic
F－Metal shielding net
G-Outer sheath fluoroplastic
3.1 Structure principle and appearance of series electric heating cable
Three parallel insulated copper stranded wires with the same cross-sectional area and a certain length are the power bus bar and the heating core wire, and one end of them is reliably short-circuited. A 380V power supply is connected to the other end to form a star load. According to Joule and Lenz's law: Q=0.24IRT electric energy is transformed into thermal energy. The star-shaped load continuously emits heat, forming a continuous and uniform heating cable. According to actual needs, the three-phase (single-phase) of the electric heating cable can be separated (split) or integrated into one.
1. Three constant power series electric heating cables
2. Double constant power series electric heating cable
3. Single constant power series electric heating cable
A- core
B- Insulation layer of busbar
C- Outer sheath
D- Metal shielding net
E- Reinforced (anti-) sheath
The self-control temperature heating cable can automatically limit the working temperature of the cable when it is heated;
The self-controlled temperature heating cable can automatically adjust the output power according to the temperature change of the heated system without additional equipment;
The cable can be shortened arbitrarily or used in a certain range, and the above-mentioned performance remains unchanged;
Allow cross-over-winding laying without worry of overheating and burning;
The temperature of the heating pipeline is uniform, will not overheat, and is safe and reliable;
Save electric energy; during intermittent operation, the temperature rise starts quickly;
Low installation and operating costs;
Easy to install, use and maintain;
Facilitate automated management;
No environmental pollution;
Features such as long service life.
Performance characteristics of constant power heating cable
The constant power parallel electric heating cable has a constant heat per unit length. The longer the heating tape used, the greater the total output power, and the pipeline maintains a high temperature. The heating tape can also be cut to the actual length at will on site. In addition, the heating tape can be easily attached to the surface of the pipe due to its softness. The metal shielding net of the outer layer of the heating belt can prevent the generation of static electricity and be safely grounded. It not only improves the overall strength of the heating belt, but also plays a role in heat transfer and heat dissipation.
According to the composition of polymer PTC materials, self-control heating cables are divided into two types: low temperature type and high temperature type.
Commonly used in the market are heating cables with a temperature rating of 65°C with polyolefin as the base material and 110°C and 150°C heating cables with a fluorine-containing material as the base material. The temperature class here is defined as the highest ambient temperature that the heating cable can effectively apply. It can also be understood that the cable can be used stably for a long time and produce the highest ambient temperature of effective heating power output, which exceeds the specified temperature level. On the one hand, due to the increased resistance, the output power of the cable itself is very small, and the actual heating efficiency is very low. On the other hand, long-term over-temperature use will degrade or attenuate cable performance such as PTC characteristics and heating power, which will reduce the service life and operational reliability of the cable. However, it is also possible to be exposed to a temperature environment exceeding the extreme temperature for a short period of time. Therefore, in addition to the above temperature level, there is another temperature level for the self-control heating wire. For example, for cables with a temperature class of 65°C, the temperature class is 85°C; For cables with a temperature class of 110°C, it is 130°C; For a 150°C cable, it is 230°C. However, the effective output power of the cable at this time is close to zero.
Due to the lack of relevant literature, many people have a wrong understanding of the temperature grade of the self-controlling heating cable, thinking that it refers to the highest surface temperature of the heating cable. Therefore, there are 45.65°C, 85°C and 105°C grades of polyolefin heating. In fact, because the output power of the cable is related to the ambient temperature. The surface temperature of the cable is closely related to the ambient temperature and heat preservation state during the test. Therefore, it is unscientific and inaccurate to use the surface temperature to define the temperature grade of the self-control heating cable. What we need to remember is that the maximum continuous use temperature of the heating cable with polyolefin as the base material should not exceed 65°C.
According to the power of heating output
The output power of the self-controlling temperature heating cable refers to the output power per unit length of the cable under the condition of an ambient temperature of 10 degrees Celsius. Classified by heating power output, there are three types of self-control heating cables: high, medium and low. Generally speaking, the heating power less than 35W/m is a low-power heating cable; The heating power is greater than 35W/m but less than 70W/m is a medium-power heating cable; The heating cable is higher than 65W/m.
Classified by the place where the heating cable is applied
General-purpose heating cable: refers to a heating cable composed of copper wires, polymer PTC materials and a single-layer flame-retardant sheath. Mainly used for heating or tracing of pipe network in general occasions. Explosion-proof reinforced heating cable:
A metal mesh is compounded on the outer layer of a general-purpose heating cable. This structure cable can effectively eliminate static electricity and resist external mechanical collisions. Mainly used in places with explosion-proof requirements.
Anti-corrosion and explosion-proof enhanced type: The heating cable of this structure is the outer layer of the metal mesh of the explosion-proof reinforced heating cable, and then a layer of fluorine-containing material is compounded. The heating cable with this structure can effectively prevent and resist static electricity, mechanical collision and various corrosive media. It is mainly used in places where the environment is harsh or there are flammable and explosive materials.
Super long heating cable: This is a five-core or six-core heating cable with a special structure. In addition to the two parallel wires wrapped by the polymer PTC material, there are also 3-4 metal wires with insulating sheaths in the same direction, plus metal armor. Used to transmit electrical energy. This special structure enables the longest continuous use length of the cable to exceed 1100 meters, so it can be applied to heat tracing in oil and gas pipelines and downhole heat in oil fields.
Safety heating cable: This is a three-core heating cable. In the cable, another monitoring wire is routed along the length in the flame-retardant sheath. The monitoring wire can transmit information about abnormal changes in output power, overcurrent conditions, and local damage along the line to the central control room at any time. It is convenient to know the heating situation along the line in time to ensure the safe and reliable operation of the cable.
Medium voltage type: It refers to the heating cable with the applicable voltage between 100-660V. The self-controlling temperature heating cable we generally refer to refers to this type of cable. In practical applications, 120 and 250V cables are interchangeable, but the maximum continuous use length of 120V heating cables is usually half of 240V. The continuous application length of this type of cable usually does not exceed 200 meters.
High-voltage cable: It refers to the heating cable with applicable voltage between 380-650V. They are mainly the aforementioned 5-6 core heating cables. The continuous application length is usually greater than 500 meters.
Explosion-proof power junction box: Used to protect the safety wiring of the heating cable. The quality of the connector is related to the safe use and service life of the heating cable system. The universal model is FDZ.
Explosion-proof intermediate junction box: Facilitate the connection of heating cables on complex pipelines. It can also be used as a power junction box under the premise that it does not exceed the maximum use length. Common models are FIH and FTH etc.
Junction box at the end: One section of the self-limiting heating cable is connected to the power supply, and the other section can be sealed with a terminal junction box, or a heat shrinkable tube can be used. Never connect the two sections of the heating cable, and do not connect the two parallel busbars FZH
Explosion-proof temperature controller: Use the thermocouple temperature control probe to sense the temperature of the heating cable, and manually control the temperature accurately. The PTC self-limiting heating cable can use heating wire for heating without installing a temperature controller. For example, the constant power electric heating must use a thermostat to limit the temperature, the general type is BJW.
Foil tape : Used to expand the heating area of the electric heating cable, increase the heat gathering and insulation range, and improve the heating efficiency
Thermal tape: Used to play a fixed role for the electric heating system. Generally, the heating tape is glued and fixed on the heating pipe or related equipment, and stainless steel cable ties are also used for fixing.
Warning label: After the construction is completed, paste it on the outer surface of the heat tracing pipeline as a sign and a power-on warning
Principle of self-controlling heating cable
The self-controlled temperature electric heating scheme is mainly completed by the self-controlled temperature electric heating cable. The temperature-controlled electric heating cable is composed of conductive plastic and 2 parallel bus bars with insulation layer, metal shielding net and anti-corrosion jacket. Among them, the conductive plastic, which is specially processed by plastic and conductive carbon particles, is the heating core. When the temperature around the heating wire is low, the conductive plastic produces micro-molecule shrinkage, the carbon particles are connected to form a circuit to allow current to pass, and the heating wire starts to generate heat; When the temperature is high, the conductive plastic produces micro-molecule expansion, and the carbon particles gradually separate, causing the circuit to be interrupted, the resistance rises, and the heating wire automatically reduces the power output and the heat generation decreases. When the surrounding temperature becomes cold, the plastic returns to the micromolecular contraction state, the carbon particles are connected to form a circuit, and the heating power of the heating cable automatically rises. Since the entire temperature control process is automatically adjusted by the province, the control temperature will not be too high or too low. Therefore, the good characteristics of electric heat tracing are unmatched by other heat tracing systems.Constant power heating cable structure
1.1 The internal structure of a single-phase parallel constant power electric heating cable:Two parallel insulated copper stranded wires are used as the power bus, and the heating wire with PTC characteristic is wound on the skeleton, and every other heating section length is alternately connected to the bus to form a continuous parallel resistance. A single-phase 220V power supply is connected to the bus bar, and the resistors connected in parallel generate heat.
1.2 Appearance of single-phase parallel constant power heating cable:
A-core wire
B-Core insulation layer fluoroplastic
C-structural layer
D－heating cable
E－Insulation sheath fluoroplastic
F－Metal shielding net
G-Outer sheath fluoroplastic
2.1 The internal structure of the three-phase parallel constant power heating cable:
Three parallel insulated copper stranded wires are used as the power bus, and every other heating section length is connected to the power bus a-b-c-a-b-c alternately and cyclically. A continuous parallel resistance is formed between every three phases, and the bus bar is connected to a three-phase 380V power supply, and each parallel resistance generates heat.
2.2 Three-phase parallel three-phase electric heating cable structure
A-core wire
B-Core insulation layer fluoroplastic
C-structural layer
D-heating wire
E－Insulation sheath fluoroplastic
F－Metal shielding net
G-Outer sheath fluoroplastic
3.1 Structure principle and appearance of series electric heating cable
Three parallel insulated copper stranded wires with the same cross-sectional area and a certain length are the power bus bar and the heating core wire, and one end of them is reliably short-circuited. A 380V power supply is connected to the other end to form a star load. According to Joule and Lenz's law: Q=0.24IRT electric energy is transformed into thermal energy. The star-shaped load continuously emits heat, forming a continuous and uniform heating cable. According to actual needs, the three-phase (single-phase) of the electric heating cable can be separated (split) or integrated into one.
1. Three constant power series electric heating cables
2. Double constant power series electric heating cable
3. Single constant power series electric heating cable
A- core
B- Insulation layer of busbar
C- Outer sheath
D- Metal shielding net
E- Reinforced (anti-) sheath
Performance and characteristics of heating cable
Performance characteristics of self-control temperature heating cableThe self-control temperature heating cable can automatically limit the working temperature of the cable when it is heated;
The self-controlled temperature heating cable can automatically adjust the output power according to the temperature change of the heated system without additional equipment;
The cable can be shortened arbitrarily or used in a certain range, and the above-mentioned performance remains unchanged;
Allow cross-over-winding laying without worry of overheating and burning;
The temperature of the heating pipeline is uniform, will not overheat, and is safe and reliable;
Save electric energy; during intermittent operation, the temperature rise starts quickly;
Low installation and operating costs;
Easy to install, use and maintain;
Facilitate automated management;
No environmental pollution;
Features such as long service life.
Performance characteristics of constant power heating cable
The constant power parallel electric heating cable has a constant heat per unit length. The longer the heating tape used, the greater the total output power, and the pipeline maintains a high temperature. The heating tape can also be cut to the actual length at will on site. In addition, the heating tape can be easily attached to the surface of the pipe due to its softness. The metal shielding net of the outer layer of the heating belt can prevent the generation of static electricity and be safely grounded. It not only improves the overall strength of the heating belt, but also plays a role in heat transfer and heat dissipation.
Basic structure and classification of self-controlling temperature cable
Temperature classificationAccording to the composition of polymer PTC materials, self-control heating cables are divided into two types: low temperature type and high temperature type.
Commonly used in the market are heating cables with a temperature rating of 65°C with polyolefin as the base material and 110°C and 150°C heating cables with a fluorine-containing material as the base material. The temperature class here is defined as the highest ambient temperature that the heating cable can effectively apply. It can also be understood that the cable can be used stably for a long time and produce the highest ambient temperature of effective heating power output, which exceeds the specified temperature level. On the one hand, due to the increased resistance, the output power of the cable itself is very small, and the actual heating efficiency is very low. On the other hand, long-term over-temperature use will degrade or attenuate cable performance such as PTC characteristics and heating power, which will reduce the service life and operational reliability of the cable. However, it is also possible to be exposed to a temperature environment exceeding the extreme temperature for a short period of time. Therefore, in addition to the above temperature level, there is another temperature level for the self-control heating wire. For example, for cables with a temperature class of 65°C, the temperature class is 85°C; For cables with a temperature class of 110°C, it is 130°C; For a 150°C cable, it is 230°C. However, the effective output power of the cable at this time is close to zero.
Due to the lack of relevant literature, many people have a wrong understanding of the temperature grade of the self-controlling heating cable, thinking that it refers to the highest surface temperature of the heating cable. Therefore, there are 45.65°C, 85°C and 105°C grades of polyolefin heating. In fact, because the output power of the cable is related to the ambient temperature. The surface temperature of the cable is closely related to the ambient temperature and heat preservation state during the test. Therefore, it is unscientific and inaccurate to use the surface temperature to define the temperature grade of the self-control heating cable. What we need to remember is that the maximum continuous use temperature of the heating cable with polyolefin as the base material should not exceed 65°C.
According to the power of heating output
The output power of the self-controlling temperature heating cable refers to the output power per unit length of the cable under the condition of an ambient temperature of 10 degrees Celsius. Classified by heating power output, there are three types of self-control heating cables: high, medium and low. Generally speaking, the heating power less than 35W/m is a low-power heating cable; The heating power is greater than 35W/m but less than 70W/m is a medium-power heating cable; The heating cable is higher than 65W/m.
Classified by the place where the heating cable is applied
General-purpose heating cable: refers to a heating cable composed of copper wires, polymer PTC materials and a single-layer flame-retardant sheath. Mainly used for heating or tracing of pipe network in general occasions. Explosion-proof reinforced heating cable:
A metal mesh is compounded on the outer layer of a general-purpose heating cable. This structure cable can effectively eliminate static electricity and resist external mechanical collisions. Mainly used in places with explosion-proof requirements.
Anti-corrosion and explosion-proof enhanced type: The heating cable of this structure is the outer layer of the metal mesh of the explosion-proof reinforced heating cable, and then a layer of fluorine-containing material is compounded. The heating cable with this structure can effectively prevent and resist static electricity, mechanical collision and various corrosive media. It is mainly used in places where the environment is harsh or there are flammable and explosive materials.
According to the purpose of heating cable classification
Ordinary heating cable: This is a heating cable with a two-core structure. It is composed of two parallel metal wires coated with polymer PTC material and flame-retardant sheath material or metal mesh and fluorine material sheath. Due to the influence of the conductor diameter and the voltage drop along the length, the connection length of this kind of cable generally does not exceed 200 meters.Super long heating cable: This is a five-core or six-core heating cable with a special structure. In addition to the two parallel wires wrapped by the polymer PTC material, there are also 3-4 metal wires with insulating sheaths in the same direction, plus metal armor. Used to transmit electrical energy. This special structure enables the longest continuous use length of the cable to exceed 1100 meters, so it can be applied to heat tracing in oil and gas pipelines and downhole heat in oil fields.
Safety heating cable: This is a three-core heating cable. In the cable, another monitoring wire is routed along the length in the flame-retardant sheath. The monitoring wire can transmit information about abnormal changes in output power, overcurrent conditions, and local damage along the line to the central control room at any time. It is convenient to know the heating situation along the line in time to ensure the safe and reliable operation of the cable.
According to the voltage classification of the heating cable
Low voltage type: It refers to the heating cable with the applicable voltage range between 12-36V. This type of cable generally has a low heating power, and the continuous use length does not exceed 10 meters. Strictly follow the voltage requirements when using it, otherwise, it may cause accidents such as cable fire. The scope of application is mainly civil health products and heated seats for vehicles and ships.Medium voltage type: It refers to the heating cable with the applicable voltage between 100-660V. The self-controlling temperature heating cable we generally refer to refers to this type of cable. In practical applications, 120 and 250V cables are interchangeable, but the maximum continuous use length of 120V heating cables is usually half of 240V. The continuous application length of this type of cable usually does not exceed 200 meters.
High-voltage cable: It refers to the heating cable with applicable voltage between 380-650V. They are mainly the aforementioned 5-6 core heating cables. The continuous application length is usually greater than 500 meters.
Compose the application system of heating cable
Any type and specification of heating cables, such as heating cables with self-limiting temperature, heating cables with constant power, etc.Explosion-proof power junction box: Used to protect the safety wiring of the heating cable. The quality of the connector is related to the safe use and service life of the heating cable system. The universal model is FDZ.
Explosion-proof intermediate junction box: Facilitate the connection of heating cables on complex pipelines. It can also be used as a power junction box under the premise that it does not exceed the maximum use length. Common models are FIH and FTH etc.
Junction box at the end: One section of the self-limiting heating cable is connected to the power supply, and the other section can be sealed with a terminal junction box, or a heat shrinkable tube can be used. Never connect the two sections of the heating cable, and do not connect the two parallel busbars FZH
Explosion-proof temperature controller: Use the thermocouple temperature control probe to sense the temperature of the heating cable, and manually control the temperature accurately. The PTC self-limiting heating cable can use heating wire for heating without installing a temperature controller. For example, the constant power electric heating must use a thermostat to limit the temperature, the general type is BJW.
Foil tape : Used to expand the heating area of the electric heating cable, increase the heat gathering and insulation range, and improve the heating efficiency
Thermal tape: Used to play a fixed role for the electric heating system. Generally, the heating tape is glued and fixed on the heating pipe or related equipment, and stainless steel cable ties are also used for fixing.
Warning label: After the construction is completed, paste it on the outer surface of the heat tracing pipeline as a sign and a power-on warning
