A heating cable is an electrical device based on the principle of operation on the Joule-Lenz law and intended to maintain the temperature regime of a supervised facility. Owners of private houses install similar systems to protect the drain from freezing in the cold season.
The history of the creation of cable heating systems
There is so little information about the development of cable heating systems that you should dwell on this. Indeed, as sources say, the start was taken in the 30s of the 20th century. But the patent application was filed in 1929!The difference in the correct pronunciation: the idea of cable heating appeared in the 20s. And on December 17, 1929, an application was filed and filed with the patent office. This somehow protected the author from plundering the idea. Christian Backer Berg staked out something new for himself that would make a profit in the future.
The practice of filing varies by country. For example, in Canada, a special state institute is engaged in the reception of unfinished ideas, so that the author is able to get information about developments in the affected area in time. Of course, the details are known only to copyright holders.
After the application has been submitted, an expert committee is appointed to consider the crux of the matter. At the same time, the quality of the submitted documents and the novelty of the invention are assessed. The reason for refusal is multiple signs. For example, if the obviousness of a creative intention is recognized, or a repetition of already existing patents. In the course of consideration of the application, the commission needs explanations from the author. The US patent number US1857615 A was under examination for more than two years and, being filed on December 17, 1929, was approved only on May 10, 1932.In modern Russia, the review period is about 12 months.
According to this document, the public was presented something resembling a modern heating element. The electrical conductor is insulated with crystalline powder, the design was placed in a metal tube, as in a heating element of a washing machine or an iron. As conceived by the creator, the product was intended to represent the subject described in the title of the article. If necessary, the heating cable raised the temperature to the desired level. By the way, the inventor called his product tubular( TEN - tubular electric heater).This is how the idea is explained( novelty and applicability in production):
- The core of the high-resistance wire is coiled to increase the value of the heat output of the product( per unit length).
- Crystalline filler is needed to withstand high temperatures. Today, polymers that are impossible in the 30s of the 20th century are actively used in the construction of the heating cable.
- The metal sheath( in the original steel, today is often used and copper) is needed to transfer heat to the outside as best as possible. And today, the heating elements are constructed according to the specified scheme. Metal provides adequate strength.
- A specific manufacturing process involved placing a helix of crystalline magnesium in a metal tube, followed by steam treatment. Due to the described conditions, active formation of hydroxide proceeded. By volume, it turned out more than 2 times more than magnesium remained. The hydroxide powder served as an insulator. The remaining water was evaporated at a "relatively high temperature."Then there are technological details of the production process.
Curiously, specific values are not indicated. In modern chemistry, it is known that at a temperature of 350 degrees Celsius, magnesium hydroxide decomposes, losing water. What process did the inventor have in mind, perhaps just drying the steam used? The inventor did not disclose the secret as a guarantee that the secret of the patent will not be disclosed by a third party, even in the case of accidental or intentional transfer of information to third parties. In the course of the text, the inventor notes the fact of possible contact of a spiral under current with a metal sheath, which makes the electrical insulation of the product not high enough( for modern devices - 20 MΩ).To solve the problem, an additional spiral of slightly larger diameter is inserted, which reliably protects the voltage from the exit to the outside.
The above patent laid the foundation for the invention of the resistive cable. The further course of scientific thought stopped for years. The following original patent from Norway is declared on May 14, 1947.In the USA it is registered under the number US2494589 A. The patent has already claimed the design of a self-regulating heating cable. Two current-carrying separated by a layer of polymer matrix. The essence of the invention: with increasing temperature, plastic with disseminated metal powder expands, regularly increasing electrical resistance. As a result, the current decreases, the heat released by the Joule-Lenz law decreases. These processes lead to a decrease in temperature.
The result is a cooling. Then the matrix is compressed, the current increases again, the process returns to the starting point. This is repeated countless times, due to which the regime is maintained within the normal range. The invention is conveniently thought-out automatism, the formation of the desired design for heating objects. The self-regulating cable due to the present features is taken of any length( in practice, the maximum is limited by the total current throughput, which demonstrates the highest value near the power source and descending to the end).
Features of the heating cable
In everyday life, the heating cable is more often used as an anti-icing system for the edges of roofs, drains, porches, steps, paths. In this case, the task is to maintain the temperature around zero degrees. Other applications are called industrial. Sometimes the heating cable is used to heat the water in the pipe if the temperature is insufficient.
Constantly the product works in conjunction with a controller that performs control operations. Resistive heating cable needs a sensor, is not able to independently regulate its work. From the installation of the sensor and depends on the performance of the system. Practical applications where consumption is not regulated are extremely rare. In other cases, the supply voltage or other parameters vary. For self-regulating cables, such measures are unnecessary.
The use of the heating cable
The use of the heating cable in the industry is declared by the international standard IEEE 515. It is not available for free download in electronic form and is sold at a price of just over $ 100.The IEEE organization gives subscribers access to it( for money).Sometimes resources speculate on the interest of this document and even offer to download an executable file for installation. .. Fearing the deployment of Trojans and other evil spirits on a computer, avoid similar suggestions. A Russian type of pipe heating system is considered to be a translation in the GOST R IEC 62086-2 document, according to which the installation types are divided into classes:
- I - it is required to maintain the temperature above a certain point. Characteristic of anti-icing systems. Suppose a sharp increase in temperature, the accuracy of the sensors requires a small one.
- II - maintaining temperature in the middle and wide range. A mechanical thermal switch is suitable as a sensor.
- III - requires maintaining a temperature in a narrow range. As in refrigerators. Thermocouples are used as sensors.
Heating systems are( together with the types listed in the list) for the serviced object critical( C) or non-critical( NC).In the first case, the signaling of the failure of this part of the equipment is provided; the main line should be supplemented with a backup line( with separate power supply with electric current and automatic switching on by the controller command).In non-critical cable heating systems, the requirements for temperature are lowered; when the parameters go beyond the envisaged detrimental consequences, they will not occur.
Thermal insulation is required. For systems, underfloor heating is a substrate under the heating element with the expectation that the energy goes exclusively upwards. Such measures minimize the cost of electricity, in addition - change the operating conditions of load-bearing structures. Thus, the thickness of the heat insulation layer is selected according to the existing conditions. For example, in a typically panel house, the heating of the lower ceiling from the side of the apartment will decrease when the floor heating system is equipped with it. This means that the plate will freeze over the winter from the end, which can lead to a significant reduction in the life of the building structure.
Let us mention a simple fact: in connection with the ideology developed in the country, this requirement will only be considered by owners of private houses. In economic terms, the cost of losses going to the heating of the ceiling, sometimes turns out to be lower than the difference in price between different thicknesses. It is possible to try to save money in this regard and not harm the common cause. For example, the difference in price between Penofol A-05 and A-10 for a small room will be a couple of thousand rubles, which is similar to many kWh of energy. Therefore, it is necessary to calculate the losses through a layer of insulation - find out special computer programs - and compare the cost over the entire period of operation.
Obviously: the result depends on the floor covering material( the ratio of its resistance to heat transfer to that of Penofol).Compare with the calculated( according to the project of the house) heated floor from the atmosphere of the apartment. If the numbers are similar, they are not too different, and the economic feasibility of using a thinner layer of insulation is proven, it is more reasonable to use this option when laying the heating cable.
In the case of heating pipes on top of the insulation is protected by a rigid, usually metal, shell. From the overlap of the basement, the layer is separated by waterproofing to avoid getting wet. Moisture in the materials blocks their useful properties. This happens with mineral wool. The thermal insulation layer must withstand mechanical loads. For this purpose, it is possible to lay it under the crate or otherwise. A suitable case would be a laminate substrate, combining good resistance to mechanical loads and insulating properties.
As far as fire hazard is concerned, cable power is usually low, high temperatures should not be expected even in case of breakage. Another thing is a short circuit. Provide a circuit breaker for this case in the switchboard. Regarding the choice among the available varieties, a self-regulating cable becomes safe. A polymer matrix with graphite additives increases the resistance with increasing temperature, which naturally reduces heating. For example, on the areas under the furniture the consumption of electric current is reduced. All this does not relieve the need to purchase and install a circuit breaker.
Sometimes a heating cable is placed in the thickness of the screed. Such technologies are used by builders for drying concrete. The feeding ends are then cut off, and the cable remains in the thickness of the plate. It should be understood that the maintainability of the system in this case is sharply reduced, plus it is difficult to ensure the absence of moisture and equip the structure with the required thermal insulation.