JPS6310540B2 - - Google Patents

Description

Detailed Description of the Invention (Industrial Application Field) The present invention is a method for controlling the temperature of a pipeline when a long object to be heated, for example, an object that solidifies at room temperature, is heated and transported as a fluid through a pipeline. Concerning a heating element for retention.

(Prior art) Induced skin current heating tubes (hereinafter sometimes referred to as "prototype") are well known, and are described in, for example, the 1978 edition of "Electrical Engineering Handbook" edited by the Institute of Electrical Engineers of Japan, and are widely used in the field of surface heating. However, the "simple induced current heating tube" (hereinafter sometimes referred to as the "simple type") was developed to facilitate the manufacturing and construction of this heating tube.
(Special Publication No. 58-16104) is also known.

(Problems to be Solved by the Invention) The above-mentioned simple type is easier to manufacture than the previous skin current heating tube (prototype), but it requires the conductive ferromagnetic heating tubes to be placed in close contact with each other. Therefore, special tools and techniques are required when bending the ferromagnetic heating tube, for example.

The present invention is intended to eliminate these difficulties and enable construction using the same tools and techniques as conduit pipe work for general electrical wiring.

(Means for solving the problem) In the simple type, the wall thickness of the conductive ferromagnetic tube is made thinner to facilitate processing and deformation, but this causes some leakage magnetic flux, and this leakage magnetic flux As a result, a small leakage voltage was generated on the outer surface of the tube.

This leakage voltage increases depending on the distance between the tubes, the length of the tubes, and the difference in primary and secondary currents. Therefore, the simple type was characterized by reducing the length and the distance between the tubes in order to lower the leakage voltage, but in the present invention, instead of reducing the distance between the tubes,
Next, the insulated wires forming the circuit are successively intersected at adjacent points of each set of tubes whose ends are electrically connected, so that the leakage voltage of each set is According to the length direction, in the case of a single phase, two sets of adjacent pairs cancel each other as much as possible, and in the case of three phases, between three pairs, so that there is no practically dangerous voltage on the heated object. Prevented from occurring.

(Example) First, before explaining the present invention using an example, a conventional technique will be explained with reference to the drawings.

FIG. 1 is a schematic cross-sectional view of an induced skin current heating tube. 1 is an AC power source, and in this case, conductive ferromagnetic tubes such as steel tubes 3 and 4 are electrically connected at both ends with 5 and 6.
It consists of two sets: one set consisting of conductive ferromagnetic tubes 3' and 4' whose ends are electrically connected at 7 and 8, and inside each of these two sets The electric wire 2 is passed through the heating tubes (conductive ferromagnetic tubes) 3, 3', 4', and 4, and is connected to the terminal of the single-phase power supply 1, forming a primary circuit. Current i ₁ flows. and heating tubes 3, 3' and 4',
Each set of 4 forms a secondary circuit, and the secondary current
i ₂ is playing.

In the prototype induced skin current heating tube shown in the above-mentioned Electrical Engineering Handbook, the tube thickness t is set to be more than twice the skin depth S of the alternating current, so t≧2S and i ₁ = i _{2 .} = i ₂ ′ (1) Therefore, there was practically no leakage magnetic flux or voltage outside the heating tube, and it could be used as a safe heating tube.

Next, in the simple induced current heating tube, as mentioned above, t was set to 0.5S≦t<2S (2), that is, the thickness of the tube was made thin, so equation (1) does not necessarily hold, and i ₁ − i ₂ or i ₁ −i ₂ ′ exists,
Extra-tube leakage magnetic flux, or leakage electric field, occurred. This leakage electric field e ₂ is proportional to each magnetic field H ₂ created by the leakage magnetic flux, and H ₂ is, for example, between the tubes 3 and 4, where g is H ₂ = {g, (i ₁ − i ₂ )} (3 ), there is a functional relationship with g and (i ₁ − i ₂ ), and the smaller g and i ₁ − i ₂ are, the more
H ₂ , or e ₂ , has become smaller.

Therefore, in the simple type, the tubes 3 and 4 are brought close together so that g approaches zero.

The above explanation will be easier to understand by looking at Figures 2 and 3. In these figures, the primary current i ₁ flowing through the electric wire 2 can hardly be considered to be due to the skin effect, but since the heating tubes 3 and 4 are ferromagnetic tubes, the relationship in equation (2) also shows that 2
The secondary current i ₂ does not flow uniformly across the radial cross section of the tube as shown, and the relationship in equation (1) does not necessarily hold; an external magnetic field H ₂ exists, and an accompanying electric field e ₂ is generated. . Then, assuming that the length of the tube 3 or 4 is l, a voltage of v ₂ =e ₂ l (4) will be measured between both ends 5 and 6. However, even if the length l of the tube is sufficiently long compared to its diameter d, the value of the external magnetic field _H2 changes in the circumferential direction of the tube, so of course
e ₂ also changes, and v ₂ in equation (4) is 5 of the voltmeter lead wire,
Even if the connection point on 6 is constant, it changes depending on the position through which the lead wire passes, and even if the distance g is zero, a small amount of voltage v ₂ remains. Therefore, in the simple type, the maximum length of the pipe set was set to 1 km.

The above is an overview of the prototype and simple induced current heating tubes, and the present invention will be explained below.

FIG. 4 shows a schematic cross-sectional view of a part of a set of conductive ferromagnetic tubes when the power source of the present invention is single-phase, and FIG. 5 corresponds to FIG. 1 when the power source is three-phase. .

First, in Figure 4, 3, 4; 3', 4', etc.
Corresponds to the ferromagnetic tube with each number in the figure, 5',
6' is a joint box or bull box for ordinary electrical wiring, and the connections 5, 6, and
It also holds 7th and 8th mag.

And the electric wire 2 in Fig. 1 is 2 in Fig. 4.
Each set of ferromagnetic tubes is crossed, such as 1, 22, 23 or 23', 22', 21'. In this way, most of the leakage magnetic flux for each set is almost perpendicular to the plane of the paper, but the direction is upward and downward of the plane for each adjacent set as shown in the figure.
If the length of each set is equal, the sum of the voltages in the length direction of the heat generating tube between both ends of the two sets will be almost zero. If the number of pairs is even, the sum of the voltages across the entire length will be almost zero.

In actual case, the lengths of each set may not be equal and the number of sets may not be even, but the voltage across the entire length will not be higher than the voltage across the set with the maximum value of l.

To illustrate this with a numerical example, in Figure 1 or Figure 4, the diameter of the heat generating tubes 3 and 4 is d (m), and the distance between them is g.
(m), the inductance L (H) per meter of heat generating tube due to the magnetic flux outside the tube is approximately L≒2ln2(g+d)/d×10 ^-7 (H/m) (5), so for example g = 0.1 m, d = 0.015 m, when the pipe length is 100 m, L = 5.5 × 10 ^-5 (H) (6) Therefore, if the frequency of alternating current is = 50 Hz, v ₂ in equation (4) becomes (3 ), assuming that i ₁ − i ₂ = 10A, v ₂ = 2πL (i ₁ − i ₂ ), v ₂ = 0.17V (7), and such a low voltage is not only harmless to humans and animals, but also corrosion-resistant. The voltage is not high enough to have a negative effect on the voltage.

Moreover, this v ₂ is the highest voltage along the tube 3 or 4, and since the direction of the electric field is opposite on the surface of the tube 3 or 4, the terminals of the voltmeter lead wire for voltage measurement are connected to the boxes 5' and 6. Even if it is connected to a fixed point of ′,
It varies in the range of 0 to 0.17V depending on the position of the lead wire.

Furthermore, for example, if there are 10 sets of heat generating tubes, each set has an equal length of 100 m, and the total length is 1 km.
The maximum voltage along 1 km is 0.17 V per set, but since it is the sum of (+0.17 V) and (-0.17 V) at both ends of 1 km, it can be considered almost zero V.

The above is just an example of calculation; in actual cases, there are objects to be heated nearby, and these also have an effect, so v ₂
Although the value of v 2 changes considerably from that obtained by equation (7), it is desirable that the maximum value of v ₂ be 1V or less.

(Function) As described in detail in the examples, according to the cross-type induced current heating tube of the present invention, the ferromagnetic tubes are not placed in close contact with each other as in the simple type, but the space between the ferromagnetic tubes is Even if it is considerably larger than the diameter of the tube, it is easy to keep the maximum voltage that can be measured outside the tube to 1V or less.

In the embodiment, a case has been described in which a single phase and a set of two heat generating tubes are used, but the operation is the same in the case of a three phase system and three heat generating tubes as shown in FIG.

In FIG. 5, the electric wire 100 is inserted as 101 in the next set, and then as 102 in the next set, the electric wire 110 is inserted as 111, 112, the electric wire 120 is inserted as 121,
122 is inserted. And the heating tube is 13
The set 0,131,132 and 140,141,14
Two cases of 2 are shown. Furthermore, the fourth
As shown in Fig. 5, the leftmost terminal in the figure is the terminal of the power supply 1', 1'', and the rightmost terminal is connected to the electric wires. In the case of Fig. 5, it is a three-phase star connection. .

In the case of Fig. 5, each box 105, 10
It is generally best to have the wires cross each other in each box, but in some cases it is also possible to have only two wires cross each other alternately, creating a so-called triple braid. .

(Effects of the Invention) As described above, the cross-type induction current heating tube of the present invention has a thinner tube wall thickness than the original induction skin current heating tube, making it easier to process, so it does not have complicated curves. Close contact with the object to be heated is facilitated, facilitating heat transfer.

Furthermore, unlike simple induced current heating tubes, there is no need to place the tubes in close contact with each other, making processing easier.
The pipe can be processed using normal conduit piping techniques and tools.

Furthermore, if the object to be heated is a pipeline,
The pipe diameter of the transportation main pipe is several times to several tens of times thicker than the heat generating pipe, so in order to distribute the heat as evenly as possible on the surface of this thick main pipe, the heat generating pipes are separated from each other and distributed over the main pipe. This is one method, and the present invention also makes such a method possible.

As mentioned above, the cross-type induced current heating tube of the present invention not only has the same effect as the original induction skin current heating tube, but also has easier processing and heat transfer than the original or simple induction current heating tube. enhance the effect,
Enables uniform temperature of the heated object.

[Brief explanation of the drawing]

Figure 1 is a schematic cross-sectional view of a single-phase induced skin current heating tube (prototype) with two sets (two each) of heating tubes, and Figure 2 shows the thickness of the heating tube compared to the skin depth of alternating current. FIG. 3 is a schematic diagram for explaining the current and magnetic flux distribution near the cross section of the heat generating tube when the heat generating tube is not sufficiently thick. Figures 4 and 5 are schematic cross-sectional views of the cross-type induced current heating tube of the present invention, with Figure 4 showing an example of a single-phase case, and Figure 5 showing an example of a three-phase case. . In Figs. 1 to 3, 1 is an AC power source, 2 is an insulated wire passing through the heating tubes 3, 4, 3', 4', 5 and 6 are a set of tubes 3 and 4, 7 and 8 are tubes 3', 4' is an electrical connection that shorts the pair at each end. In Fig. 4, 5' and 6' are the connections 5 and 6 in Fig. 1,
Boxes with meanings such as 7, 8, etc., 21, 22,
23, 21', 22', 23' are heating tubes 3,
The insulated wires are passed through the sets of 4, 3', 4' and are crossed in the boxes 5', 6'. These wires correspond to the wire 2 in FIG. 1 and are connected to the single-phase power supply 1', but are numbered separately for ease of explanation. Figure 5 has been numbered with the same consideration as Figure 4.
In the figure 100, 101, 102, 110, 1
11, 112, 120, 121, 122 are heat generating tubes 130, 131, 132, 14 in series, respectively.
Insulated wire passing through 0, 141, 142 etc., 10
5, 106, 107 are connections 5,
6, 7, 8, etc., the wires are crossed in the boxes.

Claims (1)

[Claims] 1 Two rows of insulated wires when single-phase alternating current is used as the power supply, and three rows of insulated wires when three-phase alternating current is used, one end of which is electrically connected to each other, and the other end of which is electrically connected to each other. Two wires (in the case of a single phase) or three wires (in the case of a three phase) of substantially the same length each connected to each phase terminal of the AC power source and each row of these electric wires. ) consisting of a plurality of sets of conductive ferromagnetic tubes, each set having a configuration in which each set is electrically connected to each other at both ends, and a common set consisting of the insulated wire. This is an induced current heating tube in which an independent secondary circuit is formed for each set in relation to the primary circuit, and the wall thickness (t) of the ferromagnetic tube is the skin of the alternating current flowing through the tube. 0.5S≦t＜2S for depth (S)
A cross-type induced current heating tube characterized in that the insulated wires are successively crossed at adjacent points of each set of tubes to form a primary circuit.