JPH0145195B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is intended to prevent poor insulation, short circuits, disconnections, etc. of insulated wires used in long-distance skin current heating tubes, preferably several kilometers in length or more, which are powered by one AC power supply. The present invention relates to finding the location of a fault more easily and accurately than the location of an AC power source.

The skin current heating tube referred to here includes, in principle, two types of circuits. The first is a ferromagnetic heat-generating steel pipe 1 and an insulated wire or cable 2 as shown in Figure 1.
These are connected in series to an AC power source 4 through an electric wire 3.

The second method is to pass an insulated wire 2 through a ferromagnetic heat-generating steel tube 1 as shown in FIG. It is called an induced type skin current heating tube connected at 3'.

These ferromagnetic tubes 1 are designed such that the wall thickness of these tubes is 2 times the skin depth of the alternating current passing through them, so that the current i flows only on the inner surface and does not flow out to the outer surface of the tube.
It is more than twice as thick.

The first type of skin current heating tube was published in the 1970s.
No. 12128 (US Pat. No. 3,293,407), and a second type of skin current heating tube is disclosed in Japanese Patent Publication No. 46-588 (US Pat. No. 3,515,837).

Recently, such skin current heating tubes have been used to heat and insulate long-distance pipelines, and their lengths are several tens of meters long.
Km or more, and those reaching 100 Km or more have been implemented. However, the length of skin current heating tubes supplied by one AC power source is about 10 to 20 km, and land pipelines were the main method.

On the other hand, when a short circuit or disconnection 5 occurs in the insulated wire 2 in the skin current heating tube shown in FIG. 1 or FIG. .

However, this pulse radar method was applied for in 1983.
As stated in No. 213758 "Skin current heating tube with fault section detection circuit", since the heating steel tube 1 is made of ferromagnetic material, the voltage pulse attenuates quickly, making it difficult to detect the fault location 5 located several kilometers away from the power source. It was difficult.

The present invention is intended to make it possible to discover the fault location 5 up to 20 km or more without impairing the characteristics of the skin current heating tube.

FIG. 3 is a sectional view of the skin current heating tube of the present invention, which, unlike the known ferromagnetic heating steel tube 1 shown in FIGS. 1 and 2, has a non-magnetic metal conductor layer 6 on its inner surface.

In the known skin current heating tube shown in FIGS. 1 and 2, the amount of heat generated by the electric wire 2 is usually about 10 to 30% of the total, and the remainder is generated on the inner surface of the steel tube 1. It is desirable to generate as much heat as possible in the inner skin of the steel pipe 1. it is,
The heat generated in the wire 2 flows through the insulating layer 7 to the object to be heated 8, but since the insulation of the wire 2, which is usually plastic, is both an electrical insulator and a thermal insulator, the heat generated in the wire is reduced. The higher the ratio, the higher the temperature of the conductor 2. On the other hand, the heat generated in the inner skin of the steel pipe 1 flows to the object to be heated 8 through the weld 9, etc., but the thermal resistance of this part is extremely small, and therefore the temperature rise of the steel pipe 1 relative to the object to be heated 8 is less than 1°C. It only becomes. Therefore, the heat is generated by wire 2
It is more economical to design the inner skin portion of the steel pipe 1 to have as much as possible, since there is no need to use the highly heat-resistant insulator 7.
For this purpose, it is better to make the resistance of the inner skin of the steel pipe 2 larger than that of the wire 2, since the current flowing through the wire 2 in FIG. 1 or 2 flows through the steel pipe 2 with the same magnitude. In the skin current heating tube, a ferromagnetic steel tube is used not only to prevent the current i from flowing out of the tube, but also to increase the skin action and increase the resistance of this part.

However, in the unlikely event that a fault like that in 5 occurs in wire 2, even if you try to find the fault point using the pulse radar method, the width of the pulse, expressed in time, will be
Since it is on the order of microseconds, the equivalent resistance becomes large due to the skin effect, and the attenuation of the pulse in a skin current heating tube is extremely large compared to that in a non-magnetic tube. The distance is at most several kilometers.

The present invention was made to increase this measurable distance.

In the present invention, we focused on the fact that when used as a heating tube, the power frequency is in the range of 10 to 100 Hz, that is, a normal commercial frequency, whereas in the pulse radar method, it is on the order of MHz. Normally, the thickness (or depth) S (cm) of the skin, which indicates the range through which the current i flows in the heating tube 1, is expressed as ρ, the resistivity of the conductor (Ωcm),
When μ is the relative magnetic permeability and f is the frequency of the power supply (Hz) It is well known that in the case of steel pipes, S in equation (1) is _{S 1} ⁼ 0.087cm = _0.87mm ( 2) On the other hand, for example, in the case of zinc, a non-magnetic material, when μ=1, ρ ₂ =6×10 ^-6 and f=1MHz, S ₂ =0.0123cm=0.123mm (3) It is only about 14% of the case of equation (2).

Therefore, the present invention provides a non-magnetic conductor 6 on the inner surface of the ferromagnetic steel pipe 1 with a thickness of 1 to 1000 microns, preferably 3 to 500 microns.
The gist is to form an inner lining of about 10 to 300 microns, more preferably about 10 to 300 microns.

Examples of materials that can be used for the non-magnetic conductor 6 include aluminum, copper, brass, austenitic stainless steel, bronze, etc. in addition to zinc.

The inner surface width in the circumferential direction of the steel pipe due to this lining 1
cm, the decrease in resistance per 1 cm of steel pipe length can _{be calculated using equation (2), where the resistance without lining is r 1 =} ρ/S ₁ = 18×10 ^-6 /0.087 = 2.069 ×10 ^-4 Ω (4) On the other hand, the resistance r ₂ of the lining can be calculated using equation (3): r ₂ = ρ ₂ /S ₂ = 6 × 10 ^-6 /0.0123 = 4.88 × 10 ^-4 Ω (5), so the combined resistance r is r=r ₁ r ₂ /r ₁ +r ₂ =1.453×10 ^-4 Ω (6), which is reduced to about 70% of the case without lining.

Therefore, in the above case, when there is no lining, if the heat generation of electric wire 2 is 20% and the heat generation of heating tube 1 is 80%, then the heat generation due to the lining is 20 + 80 × 0.7 = 76 (assuming that the current i is constant) %), which would decrease to 76%, making it uneconomical in this respect. However, at the same time, the voltage per unit length of the heating tube is as low as 76% when the current i is constant, and when the wire rating or power supply voltage is constant,
There is an advantage that the power supply distance by a single power supply becomes correspondingly longer. In order to make it easier to understand, the above explanation ignores the influence of the presence of a lining on the depth of the skin of the steel pipe, but the approximate trend is correct.

As explained above, the presence of the lining affects the economic efficiency of the tube as a heat generating tube to some extent, but the non-magnetic lining such as zinc allows the distance at which a pulse radar can detect a failure point to be dramatically increased to 20 to 40 km. It was confirmed through calculations and experiments that the

For example, if a 25A steel pipe is used as a heat-generating steel pipe, its inner diameter is 27.6mm, so if the lining thickness is 0.123mm, the effective inner diameter is 27.354mm.
This does not mean that the inner diameter has become smaller in practical terms.

As has already been confirmed in power cables, coaxial cables, etc. that use non-magnetic conductors such as copper and aluminum, the distance over which fault points can be found using the pulse radar method increases by an order of magnitude.

In addition, in order to prevent as much as possible the above-mentioned decline in economical efficiency of the heating tube, consideration must be given to changing the thickness of the lining along the length of the heating tube powered by a single power source.

Further, the number of nonmagnetic metal conductor layers forming the lining is not limited to one type, and may be two or more layers.
For example, if there is a requirement for corrosion resistance, it is possible to use two layers, one layer being a zinc layer and the other being a brass layer.

In Fig. 3, 9 means welding or heat transfer cement to fix the heat generating tube 1 and the heated object 8 and to improve heat transfer. If the material melts, a part of it may be damaged, but since welding is usually done intermittently and the heating time for welding is short, the damage is only a partial part, and this is not the case in the above book. It does not reach the extent that it affects the effectiveness of the invention.

[Brief explanation of drawings]

Fig. 1 is a schematic vertical cross-sectional view of a known series-type skin current heating tube, and Fig. 2 is a schematic vertical cross-sectional view of a known induction type skin current heating tube, where 1 is a ferromagnetic heating steel tube, and 2 is an insulated wire or cable passed through 1. , 3 is a connecting wire, 3' is a low impedance conductor connecting both ends of the ferromagnetic heat generating steel pipe, 4 is a power source, and 5 is a failure point. FIG. 3 is a cross section of a skin current heating tube improved according to the present invention, where 6 is the lining of the steel pipe 1, and 7 is the electric wire 2.
The insulating layer 8 indicates an object to be heated, for example, a part of the pipe wall of a pipeline main pipe that requires heating. Reference numeral 9 indicates welding, heat transfer cement, or the like for fixing the heat generating steel pipe 1 and the object to be heated 8 and further improving heat transfer.

Claims (1)

[Claims] 1. Pass an insulated wire through a ferromagnetic steel pipe, connect the insulated wire and the steel pipe in series with an AC power supply, or use the insulated wire as a primary circuit,
In a so-called skin current heating tube configured such that a steel pipe serves as a secondary circuit, and the wall thickness of the steel pipe is approximately twice or more the depth of the skin of an alternating current flowing through the steel pipe, the insulated wire is The inner surface of the steel pipe is lined with at least a thick non-magnetic metal conductor layer that enables detection from a predetermined position to the failure point by the radar pulse method in the event of a failure such as a disconnection or dielectric breakdown. A long-distance skin current heating tube with an inner lining, which is characterized by having a long distance. 2. The long-distance skin current heating tube with a lining as claimed in claim 1, wherein the non-magnetic metal conductor layer serving as the lining has a thickness of 1 to 1000 microns. 3. The long-distance skin current heating tube with a lining as claimed in claim 2, wherein the non-magnetic metal conductor layer serving as the lining has a thickness of 5 to 500 microns. 4 The thickness of the non-magnetic metal conductor layer that is the lining is
The long-distance skin current heating tube with lining as claimed in claim 3, characterized in that the lining is 10 to 300 microns. 5 The non-magnetic metal conductor layer serving as the lining is made of zinc,
6. The lined long-distance skin current heating tube according to any one of items 1 to 5, characterized in that it is made of at least one of aluminum, copper, lead, brass, austenitic stainless steel, and bronze.