US3755650A

US3755650A - Elongated heat-generating apparatus providing for a reduction in the highest voltage to be applied

Info

Publication number: US3755650A
Authority: US
Inventors: M Ando
Original assignee: Chisso Corp
Current assignee: JNC Corp
Priority date: 1970-11-20
Filing date: 1971-11-16
Publication date: 1973-08-28
Anticipated expiration: 1990-08-28
Also published as: AU463831B2; AU3568671A; JPS5027225B1; DE2157530C3; DE2157530B2; GB1366690A; DE2157530A1

Abstract

An elongated heat-generating apparatus is divided into at least two sections and a transformer is provided at each division between adjacent sections of said at least two sections and linked with the electrical circuits of the adjacent sections. The output voltage of the transformer is as near as possible to the highest voltage allowed for the section, the resistance of which is adjusted in relation to the definite voltage to meet the required quantity of heat in that section.

Description

limited States Patent [1 1 Ando 1 Aug. 28, 1973 [54] ELONGATED HEAT-GENERATING 3,293,407 12/1966 Ando 219/301 APPARATUS PROVIDING FOR A 3,575,581 4/1971 Ando 219/301 REDUCTION IN THE HIGHEST VOLTAGE TO BE APPLIED Masao Ando, Kahokuku, Kanagawa, Japan Inventor:

Chisso Corporation, Osaka, Japan Nov. 16, 1971 11.8. CI 219/301, 219/1049, 219/300, 219/477, 307/83, 323/44 R, 338/295 int. C1. H051) 3/00 Field of Search 219/300, 301, 10.49, 219/1051, 535, 477;-307/54, 69, 83; 323/44 R; 338/295 References Cited UNITED STATES PATENTS 8/1970 Ando 219/300 8/1971 Ando 219/300 Primary Examiner-A. Bartis Attorney-Fred C. Philpitt 5 Claims, 7 Drawing Figures PATENTEflmza ms FIG. l

PRIOR ART FIG. 7

FIG; 5 FIG. 6

ELONGATED HEAT-GENERATING APPARATUS PROVIDING FOR A REDUCTION IN THE HIGHEST VOLTAGE TO BE APPLIED BACKGROUND OF THE INVENTION The present invention relates to an elongated electrically heat-generating apparatus to be used as a heat source for, e.g. a pipeline which requires heating or temperature-maintenance such as a long-distance pipeline for transporting heavy fuel oil, in which apparatus the highest voltage of its circuit is limited to as a value as possible, and the electric power necessary therefor is provided from one electric source.

Although the present invention can be applied to any heat-generating apparatus in which an elongated, electrically resistant body is used as a heat-generating body, it will be herein illustrated in reference to a heatgenerating apparatus utilizing skin effect current which is applicable particularly advantageously in the present invention.

The heat-generating apparatus utilizing skin effect current referred to herein comprises a ferromagnetic pipe and an insulated electric wire passing through the inside of the pipe, one end of said insulated wire being connected to one end of said ferromagnetic pipe remote from an a.c. source, the other ends of said insulated wire and said ferromagnetic pipe being both connected to the a.c. source, and the wall thickness of said ferromagnetic pipe being greater than twice the depth of skin of the a.c. flowing therethrough. Such a heatgenerating apparatus utilizing skin effect current is described in my US. Pat. No. 3,293,407 which is assigned to the assignee of the present application.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention along with its background will be illustrated referring to the accompanying drawings for the better understanding.

FIG. ll shows a cross-sectional view of a known heatgenerating pipe utilizing skin effect current to which the present invention can be applied; FIG. 2, a schematic view of circuit for illustrating the principle of the heat-generating apparatus of the present invention; FIG. .3, a schematic view of the voltage distribution of the heat-generating apparatus of the present invention; FIG. 4, a cross-sectional schematic view of a pipeline to which the heat-generating apparatus of the present invention is applied for heating it; and FIGS. 5, '6 and 7, cross-sectional views of heat-generating pipes utilizing skin effect current to which the present invention is applied.

DETAILED DESCRIPTION OF THE PRIOR ART In FIG. I, which illustrates the prior art pipe heating systems, a ferromagnetic pipe 1, e.g. a steel pipe, is shown and 2 shows an insulated electric wire passing through the inside of said ferromagnetic pipe, one end of said wire being connected to one terminal of an a.c. source 3, and the other end thereof being connected to one end 6 of said ferromagnetic pipe remote from the a.c. source. The other end 5 of said ferromagnetic pipe I near to the a.c. source is connected to the other terminal of the a.c. source 3 by means of an electric wire 4. Thus, alternating

currents

7 and 7 flow. Numeral 9 shows a power transmission line to the a.c. source 3.

Further, if necessary, a short-circuit electric wire 8 for shorting the inside of the pipe can be used, through which an alternating current 7" flows. The effectiveness of such a short-circuit electric wire 8 is described in my detail in US. Pat. No. 3575581, also assigned to the assignee of this application.

The point of the effectiveness of the short-circuit electric wire 8 in the present invention is that the quantity of heat to be generated in the whole of the heatgenerating apparatus utilizing skin effect current, can be thereby adjusted.

Now, in the circuit of FIG. 1, if the resistivity of the ferromagnetic pipe is p(Q cm), the specific permeabilit y is u, and the frequency of the power source is f (Hz), the so-called depth of skin, S (cm)is cit-- pressed as follows: I

$55030 P/ (if) With this S, if the wall thickness of the abovementioned ferromagnetic pipe 1 is t( cm), the length is l(cm), and the inner diameter is d (cm), and further if there is the following relationship between them,

then the current 7' flowing through the ferromagnetic pipe 1 flows concentratedly only through the inner skin portion of the ferromagnetic pipe 1, and substantially no voltage appears on the outer surface of the ferromagnetic pipe. Accordingly, even if the outer surface of the ferromagnetic pipe is shorted by a low impedance conductor, substantially no current flows therethrough, and also even if a conductive substance to be heated is contacted with the outer surface, substantially no flow of current to the substance is observed. Due to such safety, the ferromagnetic pipe can be utilized as a heat-generating pipe.

In such a heat-generating apparatus, the heat generated along the inner skin portion of the heat-generating pipe amounts to 80 90 percent of the total heat, and the remainder is generated in the insulated electric wire 2. Accordingly, if both the

ends

5 and 6 of the heatgenerating pipe 1 are short-circuitted by a short-circuit electric wire 8, passing through the inside of the pipe as seen in FIG. 1, then a part of the current 7 (shown in 7") flows through the short-circuit electric wire to reduce the apparent resistance of the heat-generating pipe. Thus, if the'current 7 is maintained at the same value, the heat to be generated is reduced. The voltage necessary for such a heat-generating pipe utilizing skin effect current, is 300 700 V if an alternating current of 50 60 Hz is used for the electric source, a steel pipe having an inner diameter of l 3 cm is used as the ferromagnetic pipe, and an a.c. of I00 200A is passed through the insulated electric wire. Thus, if the length of the heat-generating apparatus as shown in FIG. 1 is 40 km, at least 12 KV is necessary for the voltage of the electric source 3. However, it is practically very difficult to use an insulated electric wire to which a voltage of 12 RV is applied, in the inside of such a heat- SUMMARY OF THE INVENTION The object of the present invention is to provide an apparatus in which a much lower voltage than 12 KV is utilized, for the insulated electric wire, in the abovementioned case.

The present invention resides in an elongated heatgenerating apparatus which comprises an elongated electrically heat-generating body, and conductors connecting both the terminals of said body to an electric source, said body and said conductors being both divided into at least two sections and a transformer being inserted at each divided point thereof, the input side of said transformer being connected to a section near to said source, while the output side being connected to an adjacent section remote from said source, the output voltage of said transformer being as near as possible to the highest voltage allowed for the section on the output side, the capacity of said transformer corresponding to the loads obtained by substracting, from the total load of all the sections, the sum of the loads of all the preceding sections nearer to said source, and the resistance of each section corresponding to the quantity of heat required to generate in each section.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Now, the present invention will be illustrated referring to FIG. 2 and following drawings.

In FIG. 2, a heat-generating pipe (a ferromagnetic pipe) and an insulated electric wire as seen in FIG. 1, are both divided into four sections, 10 l4; l1 I5; 12- 16; and 13 17. It is now assumed for easy understanding that the length of the heat-generating pipe is divided into four equal sections and the resistance of the heat-generating pipe in each section is uniform in the longitudinal direction of the pipe although such equal length and such uniformity of resistance are not always necessary, and in some cases, unequal length and non-uniformity of resistance would be preferable.

The heat-generating body in FIG. 2 can be considered to correspond to the heat-generating pipe 1 in FIG. 1; the electric wire 14, to the electric wire 2; the transformer 18, to the electric source 3; and the current 22, to the current 7. It is assumed that the value of the current 22 is i; the output voltage of the transformer 18 is V and also this V'is the highest allowable value; and in this case, the short-circuit electric wireof FIG. 1 is omitted. In such an apparatus, the potential difference between the insulated electric wire 14 and the heat-generating'pipe, as shown by the straight line 30 in FIG. 3, is V on the output side of the transformer 18, while it is zero at the point remotest from the transformer 18, that is, at the right end of the heatgenerating pipe 10. In this case, since the circuit current is i, the output capacity of the transformer 18 is Vi.

Next, the circuit of the section on the input side of the transformer 18 will be illustrated. In this circuit, too, the voltage on the output side, of the transformer 19 is assumed to be the highest one V allowed for the insulated electric wire 15. In order to make the quantity of heat to be generated in the heat-generating pipe 11 equal to that at the heat-generating pipe 10, the current 23 must be 2 1, since the lengths of the heatgenerating pipes 10 and 11 are equal as mentioned above, and the voltage on the input side, of the transformer 18 must be V/2. Thus, the output capacity of the transformer 19 is 2 Vi which is twice the capacity of the transformer 18. If this consideration is further applied to the circuits relative to the sections on the input side of the transformers l9 and 20, the voltages and currents on the input and output sides, of the

transformers

18, 19, and 21, and the output capacities I thereof are as shown in the following table. The differences between the output capacities of the adjacent transformers are all vi.

In this table, the voltage and current on the input side, of the transformer 21 and not shown since they are dependent on the voltage of the transmission line 26 and this has nothing to do with the present invention.

The potential difference between the insulated electric wire 15 and the heat-generating pipe 11 is shown by the straight line 29 in FIG. 3; the potential difference between the insulated electric wire 16 and the heat-generating pipe 12, by the straight line 28; and the potential difference between the insulated electric wire 17 and the heat-generating pipe 13, by the straight line 27. As seen from the table, the current 24 must be 3i and the current 25 must be 4i.

The dotted line in FIG. 3 shows the potential difference distribution between the insulated electric wire and the heat-generating pipe in case where the abovementioned division is not carried out. As apparent from this figure, if the division is not carried out, the voltage of the source is 4 V which is four times that in the case of the division into four sections.

Now, in order to equalize heat-generation per unit length of each four section when the respective voltages and currents on the output side are given as above, there must exist the following relationships among each resistance per unit length, of the heat-generating circuit in each section:

wherein R is the resistance per unit length, of the heat-generating circuit in the section on the output side of the transformer 18; R is that in the section between the transformers 19 and 18;R, is that in the section between the transforrners 20 and 19; and R is that in the section between the

transformers

21 and 20.

As for the method for holding such relationships in the heat-generating apparatus utilizing skin efiect current, adjustment of R R and R (if R is fixed in the above-mentioned formula (3)) by means of a shortcircuit electric wire as shown as numeral 8 in FIG. 1, or the like, and/or adjustment by varying the diameter or material of the ferromagnetic pipe, can be exemplified.

Various modifications corresponding to the shortcircuit electric wire 8 are illustrated in FIGS. 5, 6 and 7.

According to the method of FIG. 5, an electric wire 35 coated by an insulating layer 36, corresponding to the electric wire 2 in FIG. I, is passed through the inside of a ferromagnetic pipe 37 as mentioned above, and further, a short-circuit electric wire 38 corresponding to the short-circuit wire 8 in FIG. 1 is passed through the clearance part 39 inside the ferromagnetic pipe 37. In this case, the short-circuit electric wire 38 is not necessary to be insulated.

In FIG. 6, an electric wire 40 coated by an insulating layer 41, corresponding to the electric wire 2 in FIG. 1, is passed through the inside of a ferromagnetic pipe 43, but the insulated electric wire has further on its surface, a metallic tape shield 42 for preventing corona discharge which corresponds to the short-circuit electric wire 8 in FIG. 1. If the metallic tape is insufficient for adjusting the resistance, a means corresponding to the short-circuit electric wire 38 in FIG. 5 can be added.

In FIG. 7, an electric wire 44 coated by an insulating layer 45, corresponding to the electric wire 2 in FIG. 1 is passed through the inside of a ferromagnetic pipe 46, and further an electrically conductive metal 47 such as metallic sodium, is melt-filled (that is, filled through melting the metal) in the clearance part inside the ferromagnetic pipe, which metal has properties of melting at a relatively low temperature and not corroding the insulating layer 45 when it is filled in the clearance part, (in other words, melting at such an extent of temperature that the insulation of the insulated electric wire is not broken at the temperature), and corresponds to the short-circuit electric wire 8 in FIG/1.

In FIG. 4 showing a laterally cross-sectional view of a pipeline to which a heat-generating apparatus as mentioned above is applied for heating it or maintaining the temperature, numeral 31 shows a transporting main pipe; numeral 33, a ferromagnetic pipe corresponding to the pipe 1 in FIG. 1; numeral 32, an insulated wire corresponding to the wire 2 in FIG. 1; and numeral 34, an insulating layer. The explanation as to the mutual relationship among the elements constituting the heatgenerating apparatus of FIG. 4 will be unnecessary.

The present invention relative to an elongated heatgenerating apparatus limiting the highest voltage as described above referring to the heat-generating apparatus utilizing skin effect current, can be also applied to an elongated electrically heat-generating body e.g. an inorganic-insulated metal sheath cable (referred to usually as Ml cable), other than the heat-generating apparatus utilizing skin efi'ect current, but the case applied to the heat-generating apparatus utilizing skin effect current is most economical.

The above-mentioned equal division is not always necessary, but, in most cases, it is most economical.

The present invention has an advantage in that the voltage applied to the insulated electric wire is much reduced by the division as seen in FIG. 3, but has disadvantages in that transformers are required at each divided point; an insulated electric wire having a large capacity of current must be used in the heat-generating pipes excluding the final section; and means are needed to satisfy the above-mentioned formula (3) in order to prevent the increase of heat generation per unit length of each section except the final one, accompanied by the increase in the current. However, in the provision of transformers at each divided point which is most problematical among the above-mentioned countermeasures, single-layer winding transformers can be used as apparent from FIG. 2, and hence the provision is not so much an economical burden. In the case of the above-mentioned heat-generating apparatus laid over a distance of 40 km, the present apparatus was more economical as compared with the case where a transmission line is provided along a long pipeline and feeding transformers are provided at each divided point.

In the above-mentioned consideration, the power factor of the circuit in the heat-generating pipe is assumed to be I, but the above-mentioned consideration is not changed even when the power factor is a little worse.

What is claimed is:

1. Elongate electrical heat generating apparatus comprising:

an elongate electrically conductive heat generating body which is divided into at least two sections,

a transformer for each of said sections,

a source of alternating electric power,

circuit means including the secondary of each said transformer and also the associated section of said conductive body for passing an electric current along the length of said section,

said circuit means further including the primary of the transformer for the next said section more remote from said source for energizing said primary with the current passing through the associated section,

each said transformer providing across its secondary winding substantially the same predetermined voltage,

said transformer secondaries further providing different respective current amplitudes with each such secondary for a section of said conductive body nearer said source providing a current amplitude greater than that provided for the next more re mote section,

and means for providing different electrical resistances for the respective said circuit means associated with said transformer secondaries to provide a predetermined heat output per unit length for each said section.

2. The heat generating apparatus of claim 1 wherein each said section of said conductive body comprises a section of ferromagnetic pipe,

said circuit means including an insulated electric wire passing through the inside of the respective associated pipe section,

the end of said wire nearer said source being connected through the secondary of the transformer associated with the respective section to the end of the pipe nearer said source and the other end of said wire being connected through the primary of the transformer associated with the next more remote section to the other end of said pipe,

the wall thickness of said pipe being greater than twice the skin depth of the alternating current.

3. A heat-generating apparatus according to claim 2, wherein the ferromagnetic pipe, in at least one section other than the section remotest from said a.c. source, is short circuited by a conductor passing through the inside of said ferromagnetic pipe and connected to the opposite ends of said pipe to provide thereby said means providing different electrical resistance for said sections.

4. A- heat-generating apparatus according to claim 3, wherein the insulated wire passing through the inside of the ferromagnetic pipe in at least one section has a me- 8 said ferromagnetic pipe, said metal having a melting temperature at which the insulation of the insulated electric wire passing through the inside of the ferromagnetic pipe is not damaged.

=0: a: a: a:

Claims

1. Elongate electrical heat generating apparatus comprising: an elongate electrically conductive heat generating body which is divided into at least two sections, a transformer for each of said sections, a source of alternating electric power, circuit means including the secondary of each said transformer and also the associated section of said conductive body for passing an electric current along the length of said section, said circuit means further including the primary of the transformer for the next said section more remote from said source for energizing said primary with the current passing through the associated section, each said transformer providing across its secondary winding substantially the same predetermined voltage, said transformer secondaries further providing different respective current amplitudes with each such secondary for a section of said conductive body nearer said source providing a current amplitude greater than that provided for the next more remote section, and means for providing different electrical resistances for the respective said circuit means associated with said transformer secondaries to provide a predetermined heat output per unit length for each said section.

2. The heat generating apparatus of claim 1 wherein each said section of said conDuctive body comprises a section of ferromagnetic pipe, said circuit means including an insulated electric wire passing through the inside of the respective associated pipe section, the end of said wire nearer said source being connected through the secondary of the transformer associated with the respective section to the end of the pipe nearer said source and the other end of said wire being connected through the primary of the transformer associated with the next more remote section to the other end of said pipe, the wall thickness of said pipe being greater than twice the skin depth of the alternating current.

4. A heat-generating apparatus according to claim 3, wherein the insulated wire passing through the inside of the ferromagnetic pipe in at least one section has a metallic tape shield thereon and the metallic tape shield is utilized as the short circuiting conductor.

5. A heat-generating apparatus according to claim 3, wherein the short circuiting conductor comprises an electrically conductive metal which is melt-filled inside said ferromagnetic pipe, said metal having a melting temperature at which the insulation of the insulated electric wire passing through the inside of the ferromagnetic pipe is not damaged.