RU2821850C1 - Power takeoff device and pipeline electric heating system containing such device - Google Patents

Abstract

FIELD: electric heating.

SUBSTANCE: disclosed group of inventions relates to electrical heating systems, as well as to secondary power sources, in particular to devices for power takeoff from a heating conductor. Power take-off device contains two current transformers with channels and secondary windings, to the output terminals of which a load is connected through the control unit. Conductor is laid through the channels of the current transformers, which is connected by means of connecting couplings to a heating conductor connected to an alternating current source. Current transformers are located in connection box or remote cabinet. In the version, the inductive-resistive heating conductor includes a central conductor, an inner insulating layer and a ferromagnetic outer conductor located coaxially above them. Connection box is made of a current-conducting material with magnetic properties and is connected to an external ferromagnetic conductor. Pipeline electric heating system comprises heating conductor connected to AC source and power takeoff device.

EFFECT: efficient power takeoff from heating conductor of various systems of electric heating of pipelines without local reduction of linear power of heating in zone of transformer installation, as well as essential modifications of electric heating system.

18 cl, 7 dwg

Description

Application area

The claimed group of inventions relates to electric heating systems, as well as to secondary power sources, in particular to devices for taking power from a heating conductor, based on the operating principle of a current transformer.

State of the art

Today, the use of resistive and induction-resistive electric heating systems is widely known for heating long-distance industrial pipelines.

A system for resistive electric heating of a pipeline over a considerable distance of up to 200 km without an accompanying network and with one power point is known from the patent for the invention RU 2727717 C1, publ. 07/27/2020 And the most effective inductive-resistive electric heating system at a distance of up to 25 km is an electric heating system using the “SKIN effect” [RU 2589553 C1, publ. July 10, 2016]. The system contains a central conductor, an internal insulating layer and a ferromagnetic outer conductor located coaxially on top of them, wherein the internal insulating layer is made of a polymer material, and the outer conductor is made in the form of a steel pipe with a wall thickness of less than three thicknesses of the SKIN layer at the operating frequency of the supply voltage.

Electric heating systems known from the prior art do not provide power to devices for monitoring, indicating and controlling the parameters of the electric heating system, located at a distance from the system's power source. Heating of pipeline shut-off valves is also not provided. Therefore, to connect devices and heat shut-off valves, additional power supply networks will be required, which will make the electrical heating system more complex and cost-effective; in addition, in some sections of the pipeline it may not be possible to place an accompanying network. To solve this problem, the following technical solution is known.

There is a known method for collecting electricity from the linear part of inductive-resistive, inductive and resistive electric heating systems [RU 2755647 C1, publ. 09/17/2021]. The method consists in installing two connecting elements on the heating conductor of the electric heating system at a certain distance from each other, in each of which the heating conductor is spliced through a branching connector, and an insulated electrical wire of the appropriate voltage class is connected to the branched end of the connector, through which the electrical potential and is introduced into the device for powering and controlling the heating element of the heat loss source or the actuator drive through the input corresponding to the installation area of the heat loss source or actuator, and the heating element of the heat loss source or the actuator drive is also connected to the power and control device. The used selection device and electrical heating system are adopted as a prototype.

The main disadvantage of the known method is that the power take-off will lead to underheating of the section of the pipeline from which the potential difference is supposed to be removed, so an increase in the linear power of the system is required to compensate for the voltage drop in the take-off section. But the increased power will be along the entire length of the system, and not just in the extraction section, which will lead to an increase in the power consumed by the system, as well as to its overheating. The disadvantages include the required high electrical safety measures when installing a branch coupling on a conductor, since the potential removed from it is much higher relative to the ground.

There is a known method of powering autonomous devices located along high-voltage overhead power lines by taking power from the phase conductor of the lines. For example, this method is disclosed in the following patent documents: RU120519U1, RU2496204C1, RU179239U1, RU2326479C1, RU2379742C1, US10958102B2, US10077861B2, US2021384854A1. The method involves the use of an inductor placed on a closed or open core and placed in the magnetic field of a high-voltage line, that is, a power take-off device is used consisting of a current transformer with a channel for the phase wire of the line and a secondary winding, equipped with various schemes for regulating and controlling output parameters.

Disclosure of the Invention

The objective of the stated group of technical solutions is to create a device for taking power from the heating conductor of an electric pipeline heating system, designed to power additional electronic equipment or a heating device that is free from the disadvantages of the prototype.

The technical result consists in the efficient extraction of power from the heating conductor of various pipeline electric heating systems without a local decrease in the linear heating power in the transformer installation area, as well as significant modifications to the electric heating system.

The claimed technical result is achieved through the use of the following set of features, namely: the power take-off device contains at least one current transformer with a channel and a secondary winding to the output terminals, to which a load is connected through the control unit, and a heating conductor is laid through the channel of the current transformer or a conductor connected by a set of connectors to a heating conductor connected to an alternating current source.

In particular embodiments, the heating conductor can be an induction-resistive conductor that is part of an electric heating system based on the skin effect or a resistive heating cable. The load can be an additional heating element, or a device for monitoring and controlling electrical heating parameters, including with wireless data transmission, or an electric drive for pipeline shut-off equipment, or a video monitoring and alarm device, or a data transmission device. The control unit may contain a voltage and current protection device, a current control relay, a voltage stabilizer, a voltage converter and a voltage control module. The additional heating element can be a self-regulating or resistive heating cable. The conductor passing through the transformer channel can be connected to the heating conductor using couplings. Current transformers can be located in a junction box or cabinet. The device can be made explosion-proof.

Also, the technical result is achieved due to the following set of features: an electric pipeline heating system contains an induction-resistive or resistive heating conductor connected to an alternating current source, and a power take-off device, including at least one current transformer containing a channel through which a heating conductor or conductor is laid, connected through a set of connectors to the heating conductor, and an additional heating element is connected to the output terminals of the secondary winding of the transformer, directly or through a control unit.

In private versions, the additional heating element is a self-regulating or resistive heating cable. The power take-off device may preferably comprise at least two current transformers, the secondary winding of which is connected in parallel or in series. Current transformers can be located in a junction box fixed to the pipeline, in particular under thermal insulation. The junction box can be equipped with couplings for the heating conductor and the secondary winding terminals of the current transformers. The junction box can be made of a conductive material with magnetic properties. Current transformers can be located in a remote cabinet. The system can be made explosion-proof.

Graphic materials

Graphic materials are presented that explain the essence of the stated technical solutions, where:

Fig. 1 - current transformer with heating conductor;

Fig. 2, 3 - power take-off device located in the junction box;

Fig. 4 - power take-off device located in a remote cabinet;

Fig. 5a is an experimental graph of the dependence of power on the active load of the secondary winding of one type of current transformer at given currents in the heating conductor;

Fig. 5b - experimental graph of the influence of load on the current of the secondary winding of the current transformer at given currents in the heating conductor;

Fig. 5c is an experimental graph of the effect of active load on the voltage of the secondary winding of one type of current transformer at given currents in the heating conductor.

Implementation of technical solution

The power take-off device from the heating conductor of the electric heating system is relevant for powering electronic equipment used to control and monitor the electric heating system of pipelines and additional heating elements for heating shut-off equipment, as well as auxiliary drives, without building additional power networks. It is proposed to use a current transformer mounted on a heating conductor as a power take-off source. To power additional electronic equipment and an additional heating element, the energy removed from the secondary winding of such a transformer is used.

The principle of operation of the transformer is as follows. The operating current in the heating conductor creates a magnetic flux in the magnetic core of the transformer, inducing an EMF in the secondary winding, which causes the appearance of current. Power take-off using current transformers is the most effective, since it does not lead to a local decrease in the linear heating power of pipelines in the area where the transformers are installed and does not require significant modifications to the electrical heating system.

It is worth noting that there is no local reduction in power in the CT installation area, but after the power take-off point the linear heating power of the pipeline decreases. The extent of this reduction is negligible if the level of power taken is low. It is desirable that the level of power taken does not exceed 0.5% of the total power of the pipeline heating system.

As shown in FIG. 1-4, the power take-off device includes a current transformer 1 with a channel 2 through which a heating conductor 3 or a conductor 4 passes, connected through a set of connectors to a heating conductor connected to an alternating current source. A load is connected to the output terminals 5 of the secondary winding of the transformer through the control unit.

The load can be a device for monitoring and controlling electrical heating parameters, including with wireless data transmission, or an electric drive for pipeline shut-off equipment, or a video monitoring and alarm device, or a data transmission device. Since these electronic devices have different supply voltages, for their proper functioning the control unit contains a voltage and current protection device, a current control relay, a voltage stabilizer, a voltage converter and a voltage control module.

Devices for controlling and monitoring the parameters of the electric heating system ensure energy-efficient and safe operation of the system. These devices monitor the parameters of the heated object, namely the temperature regime of the object, the temperature of the ambient air, the heating conductor, and also control the electrical parameters, namely current, voltage and circuit integrity.

The power of the heating system is regulated by thermostatic equipment depending on the set heating temperature and the ambient temperature. In the absence of current in the heating conductor, power take-off is impossible, and the consumer can be powered by an uninterruptible power supply, for example, in the form of a battery located in the control unit, which makes the power take-off device multifunctional and efficient.

Depending on the type of pipeline electric heating system, the heating conductor can be a resistive heating cable or an induction-resistive conductor (IRC), which is part of an induction-resistive heating system (IRSN) based on the skin effect.

Serially produced current transformers are usually not detachable; therefore, it is possible to pass the heating conductor through their channel only when installing an electric heating system on the pipeline. To install transformers on an already installed system, cut the heating cable and connect it using a set of connectors 6 with a conductor passing through the transformer channels. To avoid overheating, the cross-sectional area of conductor 4 passing through transformer 1 and connected to heating conductor 3 must be greater than or equal to the cross-sectional area of the heating conductor. Cable sleeves can be used as connectors 6. Insulators 7 can be installed in the junction box for attaching cable joints to them, which will facilitate installation and increase electrical safety. Consequently, the power take-off device can be installed on an already installed electric heating system and in any place without significant changes or modifications to the system.

The parameters of transformers and their number are determined depending on the required power taken. If there are a significant number of transformers, they can be arranged in several rows, and to prevent kinks and ensure an allowable bending radius of the conductor when passing it through channels, and as is known, a heating cable has an allowable bending radius, the use of special rollers 8, as well as tension mechanisms 9, will be required.

Current transformers are placed in a junction box 10, located directly on the pipeline 11 or in a remote cabinet 12. The CT can be secured in the junction box or cabinet using studs and/or a fixing strip 13.

On pipelines used, for example, for transporting hydrocarbons, there is a danger of the formation of an explosive atmosphere and to ensure safety, the junction box and remote cabinet can be made explosion-proof, which makes the power take-off device and electrical heating system explosion-proof.

The skin effect electric heating system includes a heating conductor consisting of a central conductor, an inner insulating layer and a ferromagnetic outer conductor located coaxially on top of them. In a heating cable connected to an AC source, an electrically insulated center conductor carries alternating current through one branch of the circuit, and in the opposite direction, alternating current passes through a ferromagnetic outer conductor, forming the return branch of the circuit, resulting in heat generation. When such a heating conductor is used in a power take-off device, a center conductor or a conductor connecting its parts is passed through the transformer channel. And the junction box in which the transformers are located is connected through couplings to an external ferromagnetic conductor through which reverse current flows. Therefore, to ensure the integrity of the return branch of the circuit, a box made of conductive material with magnetic properties is used. Thus, power take-off can be carried out from various electrical heating systems, which makes the power take-off device efficient and versatile.

In the case when the current transformers are located in a remote cabinet, an installation box 14 is installed on the pipeline, in which the conductor passing through the transformer channels is connected to the heating conductor through couplings. When used as part of an induction-resistive heating system, the mounting box 14 must also be made of a conductive material with magnetic properties.

In resistive electric heating systems, a resistive heating cable or conductor is passed through the channel of the current transformer, connecting its parts.

The power take-off device is effective for heating pipeline fittings (filters, valves, gate valves, etc.). In this case, the additional heating element can be connected to the connected current transformers directly without using a control unit, which simplifies the design of the power take-off device, and the additional heating element can be a resistive or self-regulating cable.

When constructing a power take-off system, both series and parallel connection of current transformers is allowed. When the secondary windings of transformers with the same transformation ratio are connected in series, the current strength is the same as when only one of the transformers is connected to the circuit, while the load is distributed equally among the two, i.e. the output voltages of the secondary windings are summed.

When current transformers are connected in parallel, the current in the load is equal to the sum of the currents in the secondary windings of each transformer, and the voltage across the load corresponds to one transformer. Typically, this circuit is used to obtain non-standard transformation ratios.

The general calculation procedure using the example of a power take-off system on current transformers from the heating conductor of an induction-resistive heating system explains the essence of the claimed invention.

Standard factory documentation does not contain load characteristics of manufactured current transformers, since it is focused on their use as current meters for loads close to a short circuit. Therefore, for the transformers used in the power take-off system, the load characteristics of the transformers should be obtained experimentally.

These load characteristics include a series of dependences of the secondary winding currents and the voltages at the output of the secondary winding for a wide range of active loads in the range of operating currents of the heating conductor.

Based on the obtained characteristics, a set of experimental graphs, shown in Fig. 5a-c, was constructed of the influence of the load on the ability of the CT to take power from the IRSN in the expected range of heating conductor currents.

The main parameters when constructing a power take-off system using a CT from an IRS are the amount of power taken, the current in the IRS and the load characteristics of the used CT. In one selection system, the use of CTs with different load characteristics is not allowed.

The current in the IRP and the linear heating power of the required pipeline are known from the calculation of the IRP. The amount of power taken is determined depending on the purpose of its use.

When using the extracted power, for example, to heat the valves of a heated pipeline, a thermal calculation must be performed, taking into account the dimensions of the valve, the required temperature of the valve, its operating conditions, the presence of insulation, its thickness and properties.

An estimate of the required power for heating a valve, insulated similarly to the heated pipeline, can be obtained using a table of norms for added power depending on the diameter of the pipeline.

∅ pipe, mm d89 d108 d159 d209 d273 d325 d377 d426 d530 d630 d830 d1020 CD 1.1 1.4 2.1 2.8 3.4 4.1 4.5 5.1 6.4 7.7 10 12.3

Then P _oz =P _tr *Kd, where P _oz is the heating power of the valve, P _tr is the linear heating power of the pipeline, K _d is the added power coefficient. For example, if heating the d159 pipeline requires an IRSN with linear power P _tr = 14 W/m, then heating the valve installed on it may require up to P _oz = 14 * 2.1 = 29.4 W.

Let us assume that the current in the IRP I _irp = 100 A and the required heating power of the valve on a pipeline with a diameter of d159 R _oz = 29.4 W. To build the power take-off system, current transformers TSHL-0.66-III-1-10-0.5-300/5 were used.

From a set of graphs of the influence of the load on the ability of a CT to take power from the IRSN, a graph is selected for I _irp = 100 A. Using this graph, the maximum power that can be taken from the IRSN is determined using one transformer TShL-0.66-III-1-10- 0.5-300/5, from where we get R ₂ =7.5 W with a load R ₂ =2.9 Ohm.

Thus, in order to provide the required heating power of the valve P _oz = 29.5 W, N≥P _oz /P ₂ will be required, i.e. N=4 current transformers. Based on two other load characteristics, we determine I ₂ = 1.6 A and U ₂ = 4.7 V.

If, when building a power take-off system, the current transformers are connected in series, then to heat the valve, a heater with a resistance of R _n = R ₂ * 4 = 11.6 Ohm will be required. The current through the heater will be I _n =I ₂ =1.6 A, and the voltage drop U _n = U ₂ *4 = 18.8 V.

If, when building a power take-off system, current transformers are connected in parallel, then to heat the valve, current I _n = I ₂ * 4 = 6.4 A must pass through the heater, the voltage drop across the heater will be U _n = U ₂ = 4.7 V , and the heater must have a resistance R _n = R ₂ /4 = 0.725 Ohm.

The choice of CT connection diagram depends on the choice of heating cable design and its length, taking into account the dimensions of the heated valve.

The selection of a heating cable should begin by determining its possible length for the selected valve. The minimum and maximum length of the heating cable that can be wound around the selected valve. For example, to heat a valve on pipelines with a diameter of d159, from L _min = 1.2 m to L _max = 1.8 m of cable is required.

If a circuit with a series connection of CTs is selected for power take-off, then for heating the valve you should select heating cables with linear resistance from R _min = R _n / L _max = 11.6/1.8 = 6.44 Ohm/m to R _max = R _n /L _min =11.6/1.2=9.67 Ohm/m.

The heating cables correspond to this resistance range:

- with a nichrome core with a diameter of 0.4 mm, having a resistance of 8.75 Ohm/m;

- with a fechral core with a diameter of 0.3 mm, having a resistance of 7.09 Ohm/m;

- with a core of 3×0.25 ns, having a resistance of 7.33 Ohm/m.

Let's take a heating cable of a 3×0.25 ns design with a stainless steel core. In this case, to heat the valve, it is necessary to make a section of length L = 11.6/7.33 = 1.58 m from this cable.

If a circuit with a parallel connection of CTs is selected for power take-off, then for heating the valve you should select heating cables with linear resistance from R _min =R _n /L _max =0.725/1.8=0.4 Ohm/m to R _max =R _n /L _min =0.725/1.2=0.6 Ohm/m.

The heating cables correspond to this resistance range:

- with a copper core with a diameter of 0.21 mm, having a resistance of 0.505 Ohm/m;

- with a conductor 4×0.5 constantan, having a resistance of 0.59 Ohm/m;

- with core 3×0.3 CuNi6, having a resistance of 0.47 Ohm/m.

Let's take a heating cable of the design 3×0.3 CuNi6. In this case, to heat the valve, it is necessary to make a section of length L=0.725/0.47=1.54 m from this cable.

Calculations are carried out in a similar way for power take-off from the heating conductor of a resistive electric heating system.

Thus, the proposed group of inventions ensures efficient and safe power take-off from the heating conductor of extended electrical heating systems of pipelines of various types in the required location to power additional electronic equipment or a heating element without building an additional network and without local reduction of the linear heating power in the area where the power take-off device is installed.

Claims (18)

1. A power take-off device containing at least two current transformers with channels and secondary windings, to the output terminals of which a load is connected through a control unit, and a conductor is laid through the channels of the current transformers, connected by means of couplings to a heating conductor connected to the source AC, and the current transformers are located in a junction box or remote cabinet. 2. The device according to claim 1, characterized in that the heating conductor is an induction-resistive conductor that is part of an electric heating system based on the skin effect or a resistive heating cable. 3. Device according to any one of paragraphs. 1 or 2, characterized in that the load is an additional heating element. 4. The device according to claim 3, characterized in that the additional heating element is a self-regulating or resistive cable. 5. Device according to any one of paragraphs. 1 or 2, characterized in that the load is a device for monitoring and controlling electrical heating parameters, including with wireless data transmission, or an electric drive for pipeline shut-off equipment, or a video monitoring and alarm device, or a data transmission device. 6. Device according to any one of paragraphs. 1-5, characterized in that the control unit contains a voltage and current protection device, a current control relay, a voltage stabilizer, a voltage converter, a voltage control module and an uninterruptible power supply. 7. Device according to any one of paragraphs. 1-6, characterized in that the secondary windings of the current transformers are connected in parallel. 8. Device according to any one of paragraphs. 1-6, characterized in that the secondary windings of the current transformers are connected in series. 9. Device according to any one of paragraphs. 1-8, characterized in that the junction box or remote cabinet is explosion-proof. 10. A device for taking power from an induction-resistive heating conductor, including a central conductor, an internal insulating layer and a ferromagnetic outer conductor located coaxially on top of them, connected to an alternating current source, containing at least one current transformer with a channel and a secondary winding, to output terminals of which the load is connected, and a central conductor or a conductor connected through a set of connectors to the central conductor is laid through the channel of the current transformer, and the current transformer is located in a junction box made of conductive material with magnetic properties and connected to an external ferromagnetic conductor. 11. An electrical pipeline heating system containing a heating conductor connected to an alternating current source and a power take-off device, in which a conductor is laid through the channels of at least two current transformers having channels and secondary windings, connected by means of couplings to the heating conductor , connected to an alternating current source, with the current transformers located in a junction box or remote cabinet, and an additional heating element is connected to the output terminals of the secondary winding of the transformer directly or through a control unit. 12. The system according to claim 11, characterized in that the additional heating element is a self-regulating or resistive heating cable. 13. The system according to any one of paragraphs. 11 or 12, characterized in that the secondary windings of the current transformers are connected in parallel. 14. The system according to any one of paragraphs. 11 or 12, characterized in that the secondary windings of the current transformers are connected in series. 15. The system according to any one of paragraphs. 11-14, characterized in that the junction box is fixed to the pipeline. 16. The system according to claim 15, characterized in that the junction box is located under the thermal insulation of the pipeline. 17. The system according to any one of paragraphs. 11-16, characterized in that the junction box is made of conductive material with magnetic properties. 18. The system according to any one of paragraphs. 11-17, characterized in that the junction box or remote cabinet is explosion-proof.