JPH0157477B2 - - Google Patents

Description

Detailed Description of the Invention [Industrial Field of Application] The present invention is concerned with controlling the temperature of a pipeline when a relatively long object to be heated, for example, an object that solidifies at room temperature, is heated and transported as a fluid through a pipeline. The present invention relates to an electric heating element used for snow retention, snow melting in road ditches, anti-freezing, snow melting along railway rails, etc.

[Conventional technology]

A similar technology that precedes the present invention is the "induced skin current heating tube" (hereinafter sometimes referred to as the prototype), which was described in the 1978 edition of "Electrical Engineering Handbook" edited by the Institute of Electrical Engineers of Japan, and was widely used for surface heating. It is used in the field of In addition, Japanese Patent Publication No. 16104/1983 (hereinafter referred to as a "simplified type") for facilitating the manufacture and construction of this heating tube is also known.

[Problem that the invention is trying to solve]

The above-mentioned simple type was easier to manufacture and install than the previous skin current heating tube (prototype), but since the conductive ferromagnetic tubes (heating tubes) that made up this type needed to be closely connected to each other, for example, Special tools, techniques, and considerations were still required when attempting to bend the ferromagnetic tube.

The present invention has been made in order to eliminate these difficulties and to enable construction using the same tools and techniques as conduit pipe construction for general electrical wiring.

[Means to solve the problem]

In the simple model, the wall thickness of the ferromagnetic tube was made thinner than the original model in order to facilitate processing and deformation, but this caused some leakage magnetic flux, and this leakage magnetic flux caused a small amount of damage to the outer surface of the tube. However, leakage voltage occurred.

This leakage voltage varies depending on the distance between the tubes, the length of the tubes, and the difference between the primary current i ₁ flowing through the insulated wire passing through the tubes and the secondary current i ₂ flowing through the secondary induction circuit.

Therefore, in order to lower this leakage voltage, the simple type is characterized by limiting the length of the tubes to 1 km or less, and by making the tubes close together.

In the present invention, the tubes are separated from each other without being brought into close contact with each other, and the distance g between the tubes and the difference in primary and secondary current (i ₁ -
i ₂ ), the pipe length l should be set so that the maximum value of the leakage voltage determined in relation to the pipe outer diameter d and length l is 2.5V or less.
The distance was selected to be 100m or less.

〔Example〕

First, FIG. 1 shows a schematic cross-sectional view of an induced current heating tube. In this figure, reference numeral 1 denotes a single-phase AC power supply, and reference numeral 2 denotes a single-phase AC power supply connected to the AC power supply 1 through two conductive ferromagnetic pipes, such as steel pipes 3 and 4, whose ends are short-circuited by electrical connections 5 and 6. A primary current _i1 is passed through the insulated wire, and the ferromagnetic tubes 3 and 4 form a secondary circuit to carry the current.
It becomes a heat generating tube by pouring _i2 .

Now, the wall thickness of the ferromagnetic heating tube is t (cm), the length is l (cm), the outer diameter is d (cm), and the depth of the skin of the alternating current flowing through this ferromagnetic heating tube is s (cm). ), when
First, s is expressed as s=5030√ _r (1) where μ _r is the relative magnetic permeability of the ferromagnetic heating tube, ρ is the resistivity (Ωcm), and f is the power frequency (Hz), but d>s , l > d and t > 2s (2), even if the outer surface of the ferromagnetic heating tube is short-circuited with a good conductor such as copper wire, the alternating current i ₂ will not flow into the copper wire and will generate heat safely. The prototype was an induced skin current heating tube that could be used as a tube.

In the simplified version, the relationship in equation (2) was set to 0.5s<t<2s (3), and instead the ferromagnetic heating tubes were brought into close contact with each other.

This is illustrated in Figure 3, which shows a schematic cross-sectional view similar to Figure 1.
To explain with reference to Fig. 4, if there is a gap g (cm) between the tubes 3 and 4 in Fig. 3, then under the condition (3), i ₁ ≠ i ₂ (4), and for this reason, the leakage magnetic field H ₂ creates an electric field e ₂ . In other words, there is a functional relationship between g and (i ₁ −i 2 ) as e _{2 ∝H 2} = f{g, (i ₁ − i ₂ )} (5), and g and (i ₁ −i ₂ ) increases, e ₂ increases. Therefore, as shown in FIG. 4, by bringing the ferromagnetic heating tubes 3 and 4 closer together to bring g closer to zero, it was possible to bring e ₂ closer to zero. However, e ₂ is close to zero only near the close contact point,
A small amount of e ₂ exists on the heating tube away from the close contact point, and a voltage such as v ₂ = e ₂ l (6) appears on the heating tube surface, so a restriction was placed on the length l to be 1 km or less.

It is difficult to calculate the voltage v ₂ appearing on the surface of the heating tubes, but if g≫d (7), then the extra-tube inductance L of the heating tubes 3 and 4 is
(H/cm) is per 1 cm of the length of the heating tube L≒2ln2 (g+d)/d×10 ^-9 (H/cm) (8) Therefore, if g=10cm, d=1.5cm, l=
At 10000 cm, the total inductance L _t is L _t =5.5×10 ^-5 (H) (9). Therefore, now if f = 50H ₂ and i ₁ - i ₂ = 10 A, the voltage v ₂ between both ends 5 and 6 of the heating tube 3 or 4 is v ₂ = 0.17 from v ₂ = 2πfL _t (i ₁ - i ₂ ). V (10). Such low voltages are harmless to humans and animals.

However, in reality, there is an object to be heated near the heating element, and this may be a ferromagnetic material, or some of the leakage magnetic flux from the heating tube may pass not only into the air but through the heating tube itself, causing actual leakage. Voltage v ₂ is often higher than equation (10).

Therefore, the present invention attempts to limit this _v2 to 2.5V or less.

The basis for this value of 2.5V is that it is a voltage that is safe even if the majority of the human body is underwater and comes in contact with it, as shown in the Japan Electric Association's Electrical Technical Guidelines: JEAG8101-1971, 104 Allowable Contact Voltage.

In the present invention, the heating tubes 3 and 4 shown in FIG.
However, as shown in the schematic cross-sectional view of FIG. 2, there is a set of ferromagnetic heating tubes 3 and 4 that are electrically connected at 5 and 6, and a set of heating tubes 3' and 4' that are electrically connected at 7 and 8. and two sets, two secondary circuits are formed, and even if connections 6 and 7 are not connected or connected, the voltage v ₂ between connections 5 and 8 should be 2.5 V or less It is characterized by

[Effect]

As detailed in the examples, the thin induced current heating tube of the present invention does not require the heating tubes to be brought into close contact with each other as in the simple type, and even if the gap between them is larger than the diameter of the heating tube, (3) Among the relationships in equations (6) and (6), the maximum leakage voltage is mainly limited by limiting the length l.
The voltage is 2.5 V or less, which is safe even if the human body comes into contact with water, and the maximum value of l is usually 100 m.

All of the above explanations were for single-phase AC power supplies, and the heating tubes were in two rows like 3 and 4, but in the case of three-phase AC power supplies, the heating tubes were in three rows, and they were connected in a three-phase star shape. There is no need to explain it.

〔Effect of the invention〕

As stated above, the length of the present invention is 100 m.
In the following, it is suitable as a heating element for a relatively bent object to be heated, and it is easier to process and install than a prototype induced skin current heating tube or a simple induced current heating tube.

[Brief explanation of drawings]

Figure 1 is a schematic cross-sectional view of an induced skin current heating tube in the case of a single phase, Figure 2 is a schematic cross-sectional view of two sets of heating tubes, and Figure 3 is a cross-sectional view of the thin induction heating tube of the present invention. A part is schematically shown along with the distribution of the primary current i ₁ and the secondary current i ₂ inside the ferromagnetic tube, the extra-tube magnetic field H ₂ and the accompanying electric field e ₂ . FIG. 4 shows the case of a simple induced current heating tube. In these figures, 1 is an AC power supply, 2 is an insulated wire (or cable) that becomes the primary circuit, 3, 4, 3', 4' are conductive ferromagnetic tubes (heating tubes), and 5 and 6 are ferromagnetic tubes. 3, 7 of 4,
8 is a connection between the ferromagnetic tubes 3' and 4'.

Claims (1)

[Claims] 1. Two rows of insulated wires when using single-phase alternating current as the power supply, and three rows of insulated wires when using three-phase alternating current, one end of which is electrically connected to each other, and the other end of which is electrically connected to the Two (in the case of single phase) or three (in the case of three phase) wires of substantially the same length that are connected to each phase terminal of the AC power supply and which are penetrated by each row of these wires, respectively. The conductive ferromagnetic tube is composed of at least one set of conductive ferromagnetic tubes that are electrically connected to each other at both ends, and when there is a plurality of sets, the insulated wire This is an induced current heating tube in which a secondary circuit is formed for each set with respect to a common primary circuit formed by the ferromagnetic tube. 0.5s≦t≦2s for current skin depth s
In the relationship, the tubes in each set are separated from each other, and the length of the tubes is 1.
A thin induced current heating tube characterized in that when a set is made, the length of the set is 100 m or less, and when there are multiple sets, the length of the entire set is 100 m or less.