JPS614192A - Lined long distance skin current heating tube - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is designed to prevent poor connections, short circuits, disconnections, etc. of insulated wires used in long-distance skin current heating tubes that are powered by one AC power supply and preferably have a length of several tens or more. 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 basically includes two types of circuits.The first is a ferromagnetic heating steel tube 1 as shown in FIG. These are connected in series by electric wires 3.

The second method is to pass an insulated wire 2 through a ferromagnetic heat-generating steel tube 1 as shown in FIG.
This is called an induced skin current heating tube in which both ends of the tube 1 are connected with an impedance 3' as small as possible so as to form a secondary circuit.

These ferromagnetic tubes 1 carry a current of 1 only on their inner surfaces.
The wall thickness of these pipes is so that the flow does not flow out onto the outside surface of the pipe.
It has a thickness more than twice the depth of the epidermis of the alternating current passing through it.

-The first type of skin current heating tube was published in 1977-121.
A second type of skin current heating tube is disclosed in US Pat.

Recently, such skin current heating tubes have been used to heat and insulate long-distance pipelines, and their lengths are several 10- or more.
Some have been implemented that reach over 0 km. But 1
The length of the skin current heating tube supplied from two AC power sources is 1
The range ranges from 0 to 20b, and land pipelines are the main ones.

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
As stated in No. 58 "Skin current heating tube 1 with fault section detection circuit, since the heating complex and tube 1 are ferromagnetic,
The attenuation of the voltage pulse was fast, and it was difficult to find the fault location 50 more than a few feet away from the power source.

The present invention does not impair the characteristics of the skin current heating tube,
It is intended to make it possible to discover fault positions 5 up to 20 points or more.

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

In the known skin current heating tube shown in FIGS. 1 and 2, the amount of heat generated by the electric wire 20 is usually 10 to 30 in the total culm, and the remainder is generated on the inner surface of the steel tube 1.

It is desirable that as much heat as possible be generated in the inner skin of the steel pipe 1.

This is because the heat generated in the wire 2 flows through the insulating layer 7 to the heated object 8, but the insulation of the wire 2, which is usually plastic, is both an electrical insulator and a thermal insulator. The higher the rate of heat generation, 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 welding 9, etc., but the thermal resistance in this part is extremely small, so the temperature 1'r of the steel pipe 1 relative to the object to be heated 8 is It has no choice but to be below IC. Therefore, if the design is designed so that as much heat is generated as possible in the inner skin portion of the steel pipe 1 than in the electric wire 2, there is no need to use the highly heat-resistant insulator 7, and the economical efficiency becomes higher. For that purpose, it is better to make the resistance of the inner skin part of the steel pipe 2 larger than that of the electric wire 2, since the current flowing through the electric 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 the one 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 is on the order of microseconds when expressed in time, so the skin effect cannot be detected. The equivalent resistance increases because of
In the case of a skin current heating tube, the attenuation of the pulse is extremely large compared to the case of a non-magnetic tube, and the distance from the pulse generation point, that is, the measurement point, to the failure point is at most a few meters.

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 of the skin (skin thickness or depth) that indicates the range through which the current i of the heating tube 1 flows) S (crn), ρ is the resistivity of the conductor (Ωcrn), μ is the relative permeability, and f is the frequency of the power source ( It is well known that when H7, ), in the case of steel pipes P, =
18 x IQ-'Qtrn, μ=1000.
When f = 60Hz, 8 in equation (1) is -8, = 0.087crn = 0.87mm
(2)-, whereas, for example, in the case of zinc, which is a non-magnetic material, μ=ρ4=6xto-', f-IM
When set to Hz, S2 - 0.0123cm = 0.123m (3) and (2
) is only about 1t% of the case of formula.

Therefore, the gist of the present invention is to line the inner surface of the ferromagnetic steel pipe 1 with a non-magnetic conductor 6 to a thickness of 1 to 1000 microns, preferably 3 to 500 microns, and more preferably 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 reduction in resistance per circumferential inner surface width 1α of the steel pipe and steel pipe length IQ due to this lining can be calculated by using equation (2), where the resistance without lining is rI, and then r+ ” P+ / 8+ = 18 X 10-'1
0.087 = 2.069 x 10-'Ω, whereas the resistance r of the lining is calculated using equation (3) as rz = Pt/St = 6 x '0-'0.0123
= 4.88 x 10-'Ω, so the combined resistance r is reduced to about 70% of the case without lining.

Therefore, in the above case, when there is no lining, if the heat generated by the wire 20 is 20 and the heat generated by the heating tube 10 is 80, then the heat generated by the lining is 20+80 , 76 inches, which makes it less economical. However, at the same time, if the current i is constant, the voltage per unit length of the heating tube is as low as 76 cm, and if the wire rating or power supply voltage is constant, the power supply distance with a single power supply becomes correspondingly longer. be. 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 economic efficiency of the heat generating tube is somewhat affected by the presence of the lining, but the non-magnetic lining such as zinc dramatically increases the distance over which a pulse radar can detect a failure point by 20 to 40 mm. This was confirmed through calculations and experiments.

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

And, as has already been confirmed in electric 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.

Furthermore, 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.

Furthermore, the number of nonmagnetic metal conductor layers forming the inner lining does not need to be 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 object to be heated 8 and to improve heat transfer. Some parts of it may be damaged by things that dissolve in it, but
Since welding is normally performed intermittently and the heating time for welding is short, the damage is only local and does not reach the extent that it affects the effects of the present 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 column connecting both ends of the ferromagnetic heat generating steel pipe, 4 is a power supply, and 5Gi failure point. FIG. 3 is a cross-sectional view of a skin current-generating tube improved according to the present invention, where 6 shows the lining of the steel pipe 1, and 7 shows a part of the pipe wall of the pipeline main pipe that requires electricity. 9 indicates welding, heat transfer cement, etc. for fixing the heat generating steel pipe 1 and the heated object 8 and further improving heat transfer.

Claims (5)

[Claims] (1) Pass an insulated wire through a ferromagnetic steel pipe and connect the insulated wire and steel pipe in series with an AC power supply, or use the insulated wire as the primary circuit and the steel pipe as the secondary circuit. In a so-called skin current heating tube, which is constructed as shown in FIG. A lining characterized in that the inner surface of the steel pipe has at least one thick non-magnetic metal conductor layer as a lining, which enables detection from a predetermined position to the failure point by a radar pulse method when a failure occurs. Long distance skin current heating tube. (2) The thickness of the non-magnetic metal conductor layer that is the lining is 1 to 1.
A long-distance skin current heating tube with a lining as claimed in claim (1), characterized in that the lining is 1000 microns. (3) The thickness of the non-magnetic metal conductor layer that is the lining is 5 or more.
A long-distance skin current heating tube with a lining according to claim 2, characterized in that the lining is 500 microns. (4) The thickness of the non-magnetic metal conductor layer that is the lining is 10
A long-distance skin current heating tube with a lining according to claim 3, characterized in that the lining is 300 microns. (5) Items (1) to (5) characterized in that the non-magnetic metal conductor layer serving as the lining is made of at least one of zinc, aluminum, copper, lead, brass, austenitic stainless steel, and bronze. A long-distance skin current heating tube with a lining as described in any of paragraphs.