Working principle of self-regulating heating cable

Application in the national economy

To increase the temperature in the inner part of the fresh drinking water pipeline, compounds are used, the hygienic safety of which is confirmed by a special document. Such cables are installed by means of special glands and interact with drinking liquid. These are profile compounds approved by organizations that control environmental safety;

To protect against the formation of ice on flights of stairs, playgrounds, parking lots, devices for lifting wheelchairs in order to avoid various injuries to people, appropriate temperature increase systems are also used;

To protect the roof and its elements from the cold, to counteract the icing of systems for removing water from the roof. Installing a cable can prevent the formation of an ice crust and icicles. If these steps are not taken, the roof, water removal pipes, cable network may be damaged. From the fall of ice formations from the roof, damage can be done to both property and life or health of people;

In the gas, chemical and oil industries to increase the temperature inside pipes in a cold atmosphere (in order to prevent them from icing); to increase the temperature of pipes to increase the permeability of substances flowing through them (in order to prevent the appearance of very dense formations and narrowings that interfere with permeability);

To regulate the temperature of tanks with products of the oil industry (oil, bitumen, tar, etc.). The same is true for chemically active solutions, substances, etc. Security measures make it possible to prevent property damage;

In the food industry, they increase the temperature of the drainage pipes of refrigeration units, form evaporation in refrigeration units, warm the drainage trays from the compartments of refrigeration units, increase the temperature of the crankcases of piston types of pumps before they are activated in cold conditions. In addition, self-regulating cables perform temperature rise of individual food storage, fresh water and fire tanks;
To increase the temperature of the earth's surface in various agricultural buildings, including greenhouses and livestock buildings. Due to systems based on electrical connections capable of automatic regulation, it becomes possible, at low cost, to create comfortable conditions in such buildings during all seasons of the calendar year, which is well reflected in the agricultural industry as a whole.

General characteristics and differences of a self-regulating cable

Self-regulating heating cables is a whole line of heating cables and tapes developed thanks to semiconductor nanotechnologies, the distinguishing feature of which is an independent change in power in different parts of the same segment depending on the ambient temperature. They are popular when installing anti-icing systems, heating household pipes, as well as oil and gas pipelines.

Heating cables for anti-freeze systems must meet stringent criteria for reliability and service life. In practice, two types of electrical cables are most often used as such connections: resistive and self-regulating.

Resistive cables with constant power are a sealed copper core that has resistance to the entire circuit to direct current (the so-called ohmic resistance) and is covered with a special protective sheath. This core simultaneously plays the role of an incandescent element.Such connections have a specific length, and their ability to release thermal energy is in no way related to air temperature.

For self-regulating cables, a conductive matrix based on a carbon polymer acts as a heating element, capable of changing such a characteristic as conductivity depending on the ambient temperature. The cable allocates optimal heating power exactly where and when it is needed. As the ambient temperature drops, more heat is released. Conversely, as the temperature rises, less heat is released.

There are no disadvantages associated with an excessive increase in temperature or, conversely, with its lack. In addition, due to the presence of an automatic control device, great energy savings are created. In particular, anti-icing systems on resistive connections (constant in power) consume twice the amount of energy than the same structures on a self-regulating type of connections. In addition, self-adjusting heat tracing systems provide maximum safety, and for extreme and difficult conditions of use, special types of electrical connections are made according to the standards of the American Institute of Electrical and Electronics Engineers and the European Committee for Electrotechnical Standardization.

Such a heating system is much more perfect and safe than a resistive one and is capable of providing the most optimal heating mode even without additional automation. Its installation is more convenient since the cable can be cut at the installation site to exactly the length that is needed for specific purposes.

Principle of operation and design

Self-adjusting tapes and cables change power and heat generation according to the temperature of the atmosphere, i.e. they constantly feel temperature changes without any additional sensors. As a result, different cable connection points with a heated object may have a different temperature, and devices and mechanisms adjacent to the connection will increase their temperature to a different extent.

To supply voltage along the entire length of self-regulating tapes, without crossing, a pair of copper stranded conductors is built-in. They are supplied with a constant electrical voltage. Between the conductors of electricity is placed the key element of the cable - a specially made semiconductor carbon polymer matrix with the designation PTC (Positive Temperature Coefficient - Positive Temperature Coefficient). The meaning of the PTC effect is that the carbon nanomaterial that makes up the matrix, when the threshold value is reached, changes its resistance and releases less power. Each self-regulating cable manufacturer has its own unique secret technology or matrix production recipe (like every baker has a recipe for making bread). Moreover, the recipe for soot, from which the matrix is made, differs for different types of samreg in terms of power and purpose. During the production process, the soot undergoes a process of "crosslinking" by irradiation with an electron particle accelerator. This is necessary to help the matrix retain its PTC characteristics and polymer stability during repeated heating and cooling.

It is also known that in the matrix structure, in addition to graphite particles, small metal nanoparticles are added to conduct current within the entire structure. The heated matrix expands, the conductive metal-graphite bridges break. As a result, the resistance of the section increases, the current decreases, and heat generation decreases. During cooling, the reverse process occurs: the matrix shrinks, the number of communication channels between the conductive metal nanoparticles becomes larger, the resistance of the power unit decreases, and the power and heat generation increase.

Protective internal insulation made of Polyolefin or Fluoropolymer protects the matrix from wear and moisture, and an additional metal braid performs the function of mechanical protection and grounding at the same time. The outer sheath of the cable is also coated with Polyolefin or Fluoropolymer. If necessary, elements resistant to UV radiation are added to the sheath, if the cable is intended to be placed in the open sun.

When a self-regulating electrical cable is connected to the network, the matrix glows along its entire length. Then, depending on the amount of heating, an equilibrium occurs, i.e. different junctions will allocate a different value thermal energy capacity.

The principle of operation of a self-regulating cable

Prices for heating pipes in our catalog

Roof heating prices in our catalog

See also: How to choose a cable for pipe heating

The principle of operation of the self-regulating heating cable

Design of self-regulating heating cable

Self-regulating cables have been developed primarily for the purpose of heating water pipes, sewer pipes, as well as downpipes and gutters. The first self-regulating matrix heating cable was developed by Pentair Thermal Management over 30 years ago and has been marketed under the RayChem brand ever since.

The principle of operation of the self-regulating heating cable

A distinctive feature of a self-regulating heating cable is the property of internal thermal stabilization, due to which the temperature of the cable body is always constant (for example, 65, 120 or 190 ° C, depending on the type of cable), and the power is conditional. In fact, the conductive matrix of a self-regulating heating cable is a PTC (Positive Temperature Coefficient) thermistor - a resistor with a positive temperature coefficient, i.e. its resistance increases rapidly with increasing temperature.

The material of the self-regulating semiconductor matrix includes electrically conductive particles that are closer together at low temperature and thus form conduction paths between the strands. When the temperature rises, the particles separate from one another due to thermal expansion and the number of conduction paths decreases. As a result, the resistance between the conductors increases and, accordingly, the electrical power decreases. When the ambient temperature decreases, the opposite effect is achieved.

In other words, the heat output of a self-regulating cable varies with temperature. When the temperature of the object heated by it rises, the thermal power of the cable decreases, and vice versa. At a certain moment, when the thermal power of the cable becomes equal to the thermal losses of the heated object, thermodynamic balance sets in. If the ambient temperature changes, the cable will respond to it by maintaining a constant temperature of the heated object.

Thus, a self-regulating cable, unlike resistive types, never experiences local overheating and does not burn out. The second advantage of a self-regulating cable is that it can be cut to any length, from 0.5 to 150 meters.

Design of self-regulating heating cable

The heating part is made of two tinned copper conductors (A) filled with a special mixture of graphite and semiconductor polymers, which form a self-regulating semiconductor matrix (B). Copper conductors do not touch each other, but are closed through a matrix, which is the heating element. The heating part is insulated with fluoropolymer thermoplastic (C), which is an excellent protection against water. Next comes the tinned shield (D), for grounding and mechanical protection.The material of the outer sheath (E) has several types depending on the external corrosion-chemical operating conditions of the self-regulating heating cable model. When operating in simple conditions, a sheath made of polyolefin (P) plastic compound is used. In difficult operating conditions (condensate, acid vapors, corrosion, scale, ultraviolet), a fluoropolymer (F) is used. Radiation crosslinking technology is used to process the matrix and outer sheath of the self-regulating cable, which allows achieving the same level of heat shrinkage as that of cross-linked polyethylene.

Keywords: anti-icing, pipe heating, self-regulating cable, roof heating

Types and types of samregs

Domestic electrical heating systems mainly use low-temperature self-regulating cable, which can withstand heating up to 85 C. Medium-temperature and high-temperature cables have a significantly higher heat resistance and are usually used in the mining and manufacturing industries.

By purpose, self-regulating cables and tapes are classified:

For heating household pipes;
For anti-icing systems (heating of roofs, gutters, paths, platforms);
For industrial heating (heating of oil and gas pipelines, industrial tanks).

According to the presence of a shielding braid, cables are divided into:

Shielded - with a protective grounding screen;
Unshielded - without protective braid and grounding.

Due to the presence of the screen, the price of the cable increases by 2 times, therefore, in ordinary domestic heating places that are not subjected to mechanical stress and have little contact with a person, it is rational to purchase an unshielded version.

In terms of linear power (power per 1 linear meter), there are the following main types:

10 W/m - for heating inside pipes;
15 W/m - for heating inside and outside pipes;
24 W/m - heating of roofs, paths, outside the pipe;
30 W/m – heating of roofs, pipes and anti-icing systems;
40 W/m – heating of roofs, gutters, valleys, anti-icing systems.

There is also a classification according to the type of outer shell:

With a food casing - for heating inside water pipes and sewers;
With UV protection - for placement on rooftops and places where there is a lot of ultraviolet radiation emitted by the sun.

Mounting Features

The main part of the installation of a self-regulating cable is its coupling and connection to the power unit. For independent production of these works, it is enough to strictly follow the instructions that are included in the installation kits, and, most importantly, respect such an unsafe phenomenon as electricity.

To splice a self-regulating cable, you will need:

A set of heat shrinks and crimp terminals;
Pliers;
Building hair dryer (in extreme cases, you can get by with a lighter);
Stationery or sharply sharpened household knife, small in size;
Power wire (two-core - for a cable without a braid; three-core - for a cable with a braid).

First, you need to prepare a three-core (two-core) power cable, carefully removing a part of the outer insulation and removing a layer about 1 cm long from the insulator of each wire. The main insulation about 5 cm long is removed from the heating wire with a knife. the screen must be untwisted, and then twisted again into 1 core. It will be used for grounding.

Stepping back from the edge of the cable by 2 cm, we remove the double insulating layer, under which there is a self-regulating black matrix. It must also be cut out with a sharp knife, leaving only 2 copper wires running along it, about 1 - 1.5 cm long, cleaned.

On the three-core power cable, it is necessary to bend the yellow-green wire in the opposite direction, which will be used to connect the ground.Then the twisted braid of the ground wire is connected to the yellow-green wire and fixed with a larger diameter heat shrink tubing. To do this, a heating element is put on a cut-off small tube and this place is heated with a hair dryer until the structure shrinks completely.

The other two wires are connected to 2 copper conductors of the heating cable. The wires are connected in this way: we take the crimp sleeves from the installation kit and put these sleeves on the copper conductors of the heating cable on one side, and on the bare part of the power wire on the other, and then crimp them with pliers.

After the two main wires are securely fixed with insulated bushings, heat shrink tubing of a smaller diameter is put on the joint and heated with a hair dryer or lighter until reduced in volume. During heating, glue is released from the tube, which allows you to securely fix the wired connection.

The other end of the self-adjusting tape must also be insulated with the remaining heat shrink. To do this, you need to cut the cable in half lengthwise 0.5-1 cm, trying not to expose the copper wires along the cable. Then one of the resulting halves must be cut with a knife and the other left in this form. This is done in order to exclude the closure of the copper wires to each other. Next, heat shrink is put on the end of the cable and heated with a hairdryer. You can also crimp the tip with pliers for tight bonding.

The connection of the heating element is completed, and you can install it as the main element of the anti-icing system.

Selection Tips

When choosing a self-regulating cable, you do not always need to focus on price. You need to consider what you will use it for and in what conditions it will be operated. Here are some things to know before buying:

Cable power. To heat pipes from the outside, cables of 16-30 W / m.r.m. are usually used, if the cable heats the pipe from the inside, then 10-15 W of linear power is enough. For roofs and drains, samregs with a power of 30-40 W / m.r.m. are usually used;
UV protective shell. If the cable will lie in the open sun and it will be affected by UV radiation, then you need to buy a cable with UV protection;
Ground braid. Self-regulating cables are sold with or without a grounding braid (screen). The price of a cable without "ground" is about 1.5-2 times cheaper. It is advisable to use it for heating pipes that go into the ground, wells, on roofs. The most important thing is to splice this cable with a reliable adhesive seal to ensure protection against water ingress. A cable with a screen is safer, however, but much more expensive, which is not always justified, especially since they have the same self-regulating heating matrix. It determines the durability of the cable and in this regard, the same cable in terms of service life will seriously differ in price;

starting power. When any self-regulating cable is turned on, its power consumption is higher than the nominal one. For a good quality self-regulating wire, the power increases by 20-50%, for a low-grade samreg (usually made in China), the starting power can “fly up” at times. This indicates the instability of the matrix and its fragility. Also, a low-grade cable requires more powerful power machines;

air cavities. When buying, you need to squeeze the cable with your fingers and run them along its length. A low-quality cable is not made according to standards and air cavities will be felt inside it. There will be a feeling that the outer sheath lags behind the inner parts of the cable. And, on the contrary, if the production process is debugged, the technology is followed, then the outer sheath sits tightly on the cable, makes up a single whole with it;
Thickness. Self-regulating cable is usually about 1cm wide and 3-4mm thick.In the markets of Minsk and in the regions, sellers, trying to attract a buyer with a “red” price, slip a Chinese cable. It comes to the fact that its width is a little more than 0.5 cm. With such a thickness, the area of heat generated is much lower and such a samreg is much less effective. And if the matrix, which is 2 times smaller in size, emits similar heat, then its life is short-lived. In addition, there is a possibility that over time, the supply wires may close with each other due to the fact that in some places the heating matrix melts or collapses.

Advantages and disadvantages of self-regulating heating systems

Advantages:

No overheating. Self-regulating thermal cables can be overlapped without any risk of overheating. Their intersection with each other does no harm

This is of no small importance for regulating and locking mechanisms, for example, when it is necessary to wrap a valve on a pipe. It also happens that the heating cable in anti-icing systems is covered with dirt, leaves and other debris.

In this case, the usual resistor will burn out while the samregs will work reliably;

Ease of cutting. Such cables can be cut from a common bay to the required length immediately on the spot “in the field”. This gives additional flexibility when plans do not fit the "real life" situation on site. Such connections can be divided into pieces of the required length with a maximum length of up to 0.7 - 0.15 km (depending on the type of samreg). In contrast, resistive cables have a well-defined length;

Self-adjustment. During operation, it is not required to install complex multi-channel temperature controllers, because the cable abruptly reduces power after reaching a certain threshold temperature. This mode is ideal for anti-icing systems, where it is often very difficult to maintain the desired temperature along the entire length of the section. Samreg itself finds a suitable temperature for each zone;

Saving electricity. Due to the point heat release where it is required and the minimum heat release in places that do not require heating, a self-regulating cable is much more economical than a resistive one. In anti-icing systems, a resistive cable is usually connected to one temperature sensor and generates heat where the sensor is located and heating is required, and in places where it is not needed.

Flaws:

starting power. When installing, it must be borne in mind that the initial voltage can be a maximum of twice the operating rated voltage, and the supply network must cope with this. A similar situation develops with the selection of control equipment of suitable power;

Limited heat dissipation. It is impossible to raise the temperature in the room with this connection in a short time. When the room is heated, the power of the cable drops, and it ceases to heat the surrounding room just as intensively;
Relatively high cost. The price per 1 running meter of a self-regulating cable is 2-3 times higher than that of a constant power cable. This can immediately scare off a consumer who does not understand the issue. If we calculate the energy savings and other advantages, then such an excess of the price is quite justified;
Relatively small length of one section. Depending on the type of cable, the maximum length of a self-regulating cable cannot exceed 65-120 meters. Resistors are many times longer. This imposes the task of installing additional power points;
Limited service life. Such a cable, on average, lasts about 10-15 years. Further, its matrix begins to degrade and significantly reduce power down to 0.