JPH0129312B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a skin current heating tube having multiple sections. More specifically, the circuit of an induced skin current heating tube (hereinafter referred to as "skin current heating") consists of multiple sections in which the secondary induction circuits do not make metallic contact with each other and are insulated or nearly insulated, and are connected in series to a single power source. This invention relates to a system in which an abnormality in current due to a short circuit accident (including insulation failure) in any of the heating tube circuits can be easily detected in the vicinity of the power source in a tube circuit (simply referred to as a heating tube circuit).

To explain the skin current heating tube here, the skin current heating tube consists of a ferromagnetic tube and an insulated wire passed through it. It has a circuit in which alternating current flows in a concentrated manner near the inner surface of the ferromagnetic tube. There are roughly two types of circuits that such a skin current heating tube has.
The first one is the ferromagnetic tube and the insulated wire passed through it, each one end of which is electrically connected to an AC power source, and each other end of which is electrically connected to each other,
It is called a series skin current heating tube. An example of a skin current heating tube having such a circuit is described in Japanese Patent Publication No. 40-12128 (Japanese Patent No. 460224).
In the second type, both ends of the insulated wire are electrically connected to an AC power source to form a closed circuit, and both ends of the ferromagnetic tube are electrically connected to each other so that the impedance is as low as possible. It forms a closed circuit (secondary induction circuit). An example of a skin current heating tube with such a circuit is published in
It is described in the specification of No. 588 (Japanese Patent No. 612750) and is called an induced skin current heating tube. However, in the skin current heating tube referred to in the patent specification, certain limitations are placed on the thickness so that the current does not substantially flow out to the outside of the ferromagnetic tube, but in this specification, such limitations are not applied. A general term that includes things that exist and things that don't. There are other means to prevent current from flowing outside the ferromagnetic tube. For example, as disclosed in JP-A-56-130551, even if the parallel ferromagnetic tubes have thin walls, they can be made relatively short and arranged closely together.

In any type of skin current heating tube, the cross-sectional shape of the ferromagnetic tube is not limited to circular, but may be triangular or crescent-shaped, for example. A portion of the wall of the ferromagnetic tube may be formed of a wall of a transport tube for the ferromagnetic material to be heated. The ferromagnetic tube may be cut in the middle, and adjacent ends formed in this shape may be electrically connected to each other. Further, the cross-sectional shape of the ferromagnetic tube may not be completely closed, but may have a small gap. An example of this is a ferromagnetic tube with a circular cross section, in which a cut is made in the length direction (this reduces the amount of heat generated in the portion of the ferromagnetic tube corresponding to the length of the cut). There are things that can be done. Another example is to place a ferromagnetic material member with an L-shaped or arc-shaped cross section on a ferromagnetic material transport pipe so that its recess faces the transport pipe, and place a ferromagnetic material member with a ferromagnetic material member having an L-shaped or arc-shaped cross section on the transport pipe. There is a ferromagnetic tube constructed by staggered welding between two ends and the transport tube.

The heat-generating tube circuit to which the present invention is applied is a relatively long heat-generating tube circuit mainly used for pipelines for heavy oil or certain types of crude oil that require temperature maintenance, snow melting for railway rails, etc. is economical for such long-distance electric heating elements.

For example, in the pipeline, part of the route is on land and the other part is underground on the ocean floor.
There are many cases where the conditions such as ambient temperature are different, or where the seabed part is electrolytically protected, but the land part does not need to be protected against electrolytic corrosion. In such a case, it may be necessary to change the heat output of the heating element in each of the above parts, or to prevent corrosion protection current from flowing to parts that do not require corrosion protection, resulting in wasted power. It becomes necessary to divide the pipeline into necessary sections and insulate them from each other. In this case, as a matter of course, it is necessary to take precautions such as dividing the electric heating element attached thereto and insulating them from each other so that the electric heating element attached thereto does not short-circuit the divided insulation.

Furthermore, on railway rails, electric heating elements are often installed along the rails and used for freezing, melting snow, etc. near the rails. Railway rails are also insulated to prevent signal current from flowing to other rail sections, but in order to prevent this insulation from short-circuiting at the heating element, consideration must be given to dividing the heating element and insulating it from each other. It becomes necessary.

Examples of things that take this kind of consideration into consideration are Patent No. 570099 (Special Publication No. 44-25672) ``Method of feeding power to a heating element consisting of multiple compartments'' for pipelines, and for railway rails. ,
There is a patent No. 872268 (Special Publication No. 52-1525) ``Electric heating rail.'' In these examples, as described above, the heating tube circuit is divided into a plurality of sections, which are insulated and connected in series with each other, and a single power supply is common to one set of the plurality of sections.

An overview of the above-mentioned known invention will be explained with reference to FIG.

As an example, FIG. 1 shows a case where there are two sets of upper and lower series skin current heating tubes. In this figure, the heating tube circuit consists of a first section having a ferromagnetic heating tube 1 that shares a power transformer 3, and a second section having a ferromagnetic heating tube 1' connected in series with this heating tube circuit. , the upper group is created in the first and second sections,
The lower set consists of a first section heat generating circuit having a ferromagnetic heat generating tube 101 that shares a power transformer 103, and a second section heat generating circuit having a ferromagnetic heat generating tube 101' in series with this heat generating circuit. . Hereinafter, the ferromagnetic heating tube (equivalent to the ferromagnetic tube in the skin current heating tube) will be simply referred to as a "heating tube."

In the figure, 2 and 102 are heating tubes 1 and 1, respectively.
01, 2' and 102' are insulated wires passed through heating tubes 1' and 101', respectively.
are transformers that insulate each section, 5, 6,
5' and 6' are connections for the heating tube circuits of the first and second sections of the upper set, and the same connection 10 is used for the lower set.
5, 106, 105', 106'.

The object to be heated, for example, a pipeline,
Although not shown in the figure, it is electrically integrated with the installed heating pipe over its entire length, and the insulation of this pipeline is an insulating flange, but the insulator 7
shall be represented by.

Although the groundings 8, 8', 108, 108', etc. are each shown at one location in FIG. 1, they may normally be distributed along their entire length. There is an insulator 7 between the two heating tubes 1 and 1', and although they are not connected metallically, the resistance value of the ground 8 and 8' is within several ohms to several tens of ohms. They are usually installed every 50 to 100 meters, so they are not completely insulated, but close to it.

The circuit of the heating tubes 101, 101' is also the heating tube 1,
It is the same as circuit 1', and the upper and lower sets may be used to heat the same pipeline, or separate pipelines (perhaps in this case, these pipelines are not too far apart) You can think of them as parallel).

Under normal operating conditions, the heating tube circuit of the first section of the upper group receives a current i ₁ , that of the second section receives a current i ₁ ', and the heating tube circuit of the first section of the lower group receives a current. Assume that current i _{2 '} is flowing in the second section.

In such a circuit, if an insulation failure occurs in either wire 2 or 102 of the heating tube circuit in the first section of the upper or lower group, the problem is simple: the current i ₁ or i ₂ differs from the steady value. The differential relay 10 operates from this point, and although not shown, it becomes possible to issue an alarm or shut off the power.

With the wiring connection as shown in Figure 1, even if an insulation failure occurs in the heating tube circuit of the second section, which is the load circuit of the isolation transformer 4 or 104, for example at 11 in the figure, the current i ₁ ' in this circuit will change. can influence i ₁ via the isolation transformer 4 to operate the differential relay 10, and can prevent the spread of accidents due to poor insulation.

This method can detect even a minute current change, for example a current change of about 2%, in either one of the two sets of upper and lower circuits. 1. The resistance of electric wires 2, etc. changes depending on the temperature, and therefore the current changes, so if two circuits heat and keep separate pipelines warm, it is difficult to detect even temperature abnormalities in each pipeline. It is possible.

In Figure 1, an isolation transformer 4 is used as a power transformer 3.
1 unit, power transformer 103, isolation transformer 1
Although the case where one 04 is supported is shown, the number of isolation transformers is not limited to one, but if necessary, the number of isolation transformers 4
It is also possible to provide another isolation transformer on the load side to create a third section heating tube circuit, but the operation of the differential relay 10 is the same as described above.

Next, Figure 2 shows an example of the circuit disclosed in the above-mentioned Japanese Patent Publication No. 52-1525 "Electrical Heating Rail", in which 12 is a power transformer, 13 is a heating tube circuit in the first section, and a heating tube circuit in the second section.
Although the compartment's heating tube circuit is electrically insulated,
It is an isolation transformer for magnetically coupling and supplying power. The other numbers may be considered to have the same meanings as in FIG.

Then, in such a circuit, the differential relay indicated by 10 will operate if there is poor insulation in the electric wire 2 or 102 placed in the first section, but if the differential relay is in the second section, for example 1 in the figure.
The differential relay 10 does not operate in response to an insulation failure indicated by 1.

The known circuits explained above in Figures 1 and 2 not only require an expensive isolation transformer, but also the circuit shown in Figure 2 requires insulation on the second section side, which is isolated from the power transformer side. The differential relay 10 cannot be operated in response to a defect.

In the present invention, a single common power source is used without placing an isolation transformer between the heating tube circuits in multiple sections that are mutually insulated, and the heating tubes in sections other than the first heating tube circuit section are provided with relays. The aim is to enable the detection of fault currents caused by poor insulation of electric wires in circuits as well.

The present invention provides a secondary circuit of each skin current heating tube (hereinafter referred to as a "heating tube secondary circuit") in an induced skin current heating tube having a single common power supply and a common primary circuit and having multiple sections connected in series. ) are insulated from each other, or something close to it, and a differential relay is installed near the power supply to detect abnormal current when a short circuit occurs in each heating tube circuit, and each heating tube secondary circuit is When a short-circuit accident occurs in a section other than the section closest to the power source among the skin current heating tubes in the plurality of sections, the impedance connects that section and the section closer to the power source. The gist of this invention is a multi-section skin current heating tube through which a current of 1 to 1000 mA flows.

The present invention will be explained with reference to FIG. In Fig. 3, the numbers not specified have the same meanings as in Fig. 1, but 12 is a power transformer, and the heating tube circuit of the first section formed by heating tubes 1 and 101 near the power source is not shown. , the undersea pipeline is heated and kept warm, and since this portion of the pipeline requires electrical corrosion protection, a corrosion protection power source 15 is installed. Although not shown, the heating tube circuit of the second section formed by the heating tubes 1' and 101', which is far from the power source, heats and keeps the land pipeline connected to the submarine pipeline, and this part is electrically connected. Since corrosion protection is not required, the pipeline is connected with an insulating flange so that the corrosion-protective current from the seabed does not flow to the land and cause a loss, and the secondary circuit of the heating tube is also divided into the above sections. Therefore, insulation 7 is required.

On the other hand, the insulated wires 2, 2', 102, 102' that pass through the heating tubes 1, 1', 101, 101' are themselves coated with insulation, so they short-circuit the insulated flanges of the pipelines on the sea floor and on land. There's nothing to do.

Now, in such a circuit, if we do not take into account the presence of the ground 8, 8' and the impedance 14 that is specially planned, then the electric wire 2 or 10 of the first section
2 and the heating tube 1 or 101, the differential relay 10 (an overcurrent relay may also be used) is activated.
Insulation failure in wire 02', for example insulation failure in wire 2'11
It goes without saying that the differential relay 10 does not operate even if .

However, in actual pipelines, the insulation between the pipeline and the earth is not perfect, and although grounding 8 on the seabed is undesirable, it can exist, and grounding 8' on land is necessary when the pipeline passes petroleum. It may be necessary to remove static electricity.

Therefore, the grounding 8, 8' short-circuits the insulation 7, although imperfectly, sometimes by several ohms, and for this reason, the ground fault current generated in the insulation defect 11 operates the differential relay 10 through this short-circuit. I might let it happen.

In the present invention, an impedance 14 is provided to avoid such uncertainties caused by the grounding 8, 8'.

The value of this impedance 14 is such that the ground 8,
8'. The type of impedance may be a reactor, a resistance, a capacitor, or a combination thereof. For example, it may be desirable to use a material that does not allow corrosion-protective current (direct current) to pass through it as much as possible. For this purpose a differential current relay 1
It is desirable to have a capacitor that allows zero operating current (alternating current) to pass through, but does not allow corrosion protection current (direct current) to pass through. Therefore, a capacitor is ideal.

However, although the corrosion protection voltage of capacitors is as low as a few volts DC,
The AC voltage applied to the capacitor varies depending on the degree of change, so it must be able to withstand this.

Although the case of pipelines has been described above, the present invention can be similarly applied to the case of railway rails as described above.

In FIG. 3, the case where the heating tube circuit has two sections and therefore one impedance 14 has been explained, but even if there are three or more sections, the impedance 14
If the connections are made, insulation defects in any section can be detected. As the number of impedances 14 increases, they are connected in series with each other, so the insulation in the heating tube circuit of the section where the sum of these impedances is the largest, that is, the section farthest from the differential relay 10 Of course, it is necessary to select an impedance value that allows the differential relay 10 to operate even in the event of a failure.

In Fig. 3, the differential relay 10 connects the center of the secondary winding of the power transformer and the connection 5 of the first section heating tube circuit.
As shown in Fig. 1, in Fig. 3 the electric wires 2 and 10 are
Alternatively, a current transformer may be inserted into each of 2 and connected to take the difference in current. This may be more common.

In the above explanation, the insulated wires 2, 102,
2', 102' and heating tubes 1, 101, 1', 1
Although I did not mention the material, dimensions, etc. of 01' etc.,
Of course, the present invention is applicable not only when these are equal but also when they are unequal.

[Brief explanation of drawings]

1 and 2 are diagrams of a known multi-section heat generating circuit, and FIG. 3 is a diagram of a multi-section heat generating tube circuit of the present invention. In these figures, the numbers are common to each figure and represent the following: 1,101, 1', 101' are ferromagnetic heating tubes, 2,102, 2', 102' are insulated wires passed through the ferromagnetic tubes, 3,103 and 12
is a power transformer, 4, 104, 13 is an isolation transformer,
5, 6, 105, 106, 5', 6', 105',
106' is a connection for connecting electric wires to each other or to the heat generating tubes; 7 is an insulating flange for insulating each heat generating section;
Insulators such as sockets, 8, 8', 108, 10
8' is the grounding of the heating tube or a pipe or rail electrically connected to it, 9 and 109 are current transformers, 10 is a differential relay, 11 is poor insulation of the electric wire,
14 is the impedance connecting each heat generating section, 1
5 is an electric corrosion protection power source.

Claims (1)

[Claims] 1. In an induction-type skin current heating tube having a single common power source and a common primary circuit and having multiple sections connected in series, two of the skin current heating tubes of each of said skin current heating tubes are
The secondary circuits are insulated from each other or nearly so, and a differential relay is installed near the power source to detect abnormal current when a short circuit occurs in each heating tube circuit, and the secondary circuits of each heating tube are isolated from each other. When a short-circuit accident occurs in a section other than the section closest to the power source among the plurality of skin current heating tubes, the impedance is the impedance that connects that section and the section closer to the power source. A skin current heating tube having multiple sections, characterized in that it allows a current of 1 to 1000 mA to flow therethrough.