JPS6316701B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a novel method for detecting a short circuit in an insulated pipe such as a hot water supply pipe, particularly in a conductor-coated insulated pipe whose outer periphery is coaxially coated with a conductive jacket material. It is something to do.

In general, hot water pipes are installed indoors where they are difficult to see, such as under the floor, so when installing the interior of the room after piping, the nails used for this are often driven into the hot water pipes by mistake. Even if this happens, we do not notice it, so after completing the interior work, we detect whether or not there is any damage to the hot water pipe due to the nailing, and the location of the damage and repair it, thereby preventing a hot water pipe leakage accident. It is necessary to prevent it. Therefore, the 8th
It has been proposed to use a conductive coated heat insulated pipe (hereinafter abbreviated as heat insulated pipe) 1 as shown in the figure as a hot water supply pipe. This heat-insulating pipe 1 is made by covering a core pipe 2 made of a copper pipe with a conductive jacket material 4 such as carbon-based rubber through an insulating heat-insulating material 3 such as a polyurethane foam material. If a DC voltage is applied between the core tube 2 and the outer covering material 4, if the core tube 2 and the outer covering material 4 are short-circuited by the nail 5 due to the above-mentioned nailing, a current will flow; During this time, no current flows due to the insulation resistance, which makes it easy to determine whether or not a nail has been driven. In addition, by measuring the DC resistance of the insulated pipe 4 and calculating the distance to the nailing point where the short circuit occurred from the measured resistance value, it is possible to know the distance from the measurement point to the nailing point. This makes it easier to find and repair nailing points. However, in reality, the resistance value of the jacket material 4 is not constant and varies, and the resistance value is not constant at the joint part of the piping path of the insulated pipe 1. There was a problem in that it was difficult to calculate the distance to the point accurately. Furthermore, when there are two or more short-circuit points in the piping route due to nailing, or when the piping route is branched, the distance calculated from the measured resistance value has no meaning at all. In other words, even if the heat insulating pipe 1 is used, the conventional method can only determine the presence or absence of a short circuit, and is still ineffective in searching for the location of the short circuit.

The present invention makes it possible to search for the location of such a short circuit.

The inventor of the present invention first focused on applying a method for detecting short circuits in electric wires, etc. This is because when a ground fault occurs in a wire, an intermittent current is passed through the wire, and a detector that detects this intermittent current is moved along the wire, so that the detector no longer detects the intermittent current. This is a method of detecting ground faults by determining the However, even when this method was applied to the above-mentioned heat-insulating pipe 1, it had no effect at all.
This is because even though the above method is effective for overhead distribution lines, single-wire wiring, or parallel electric wires, the above-mentioned insulated pipe 1 in which the core pipe 1 and the jacket material 3 are arranged coaxially becomes a coaxial cable, and the core This is thought to be because the magnetic fluxes emitted by the tube 1 and the jacket material 3 cancel each other out. However, if we look at the electrical structure of the conductor-covered heat-insulating pipe 1, we will see that in the case of a coaxial cable, the resistance between the inner conductor and the outer conductor is set to be negligible, whereas the heat-insulating pipe 1 In this case, the resistance of the core tube 2 made of copper tube is negligibly small, while the outer sheath material 4 is a perfect resistor with a resistance of 2KΩ/
m, the capacitance is 0.345PF/m, and the insulation resistance between the core tube 2 and the jacket material 4 is 200MΩ/m or more, and if expressed as a lumped constant circuit, the insulation resistance is compared to the contact resistance in a nailing accident. Since the contact resistance is extremely large, if the contact resistance is ignored, the result will be as shown in FIG. 9, which is not a perfect coaxial cable. Therefore, we thought that a leakage electric field and a leakage magnetic field were generated in this insulated pipe 1, and after repeated trial and error to find a method to detect the short circuit using this leakage electric field and leakage magnetic field, we found that the core tube 2 is grounded, the leakage electric field and leakage magnetic field disappear at the short circuit point, and the short circuit point can be detected by detecting this vanishing point by electric field induction and magnetic field induction.

To explain this with reference to FIG. 1, in the insulated pipe 1 where a short-circuit accident has occurred at point A, the core pipe 2 is grounded 6, and an audible frequency AC 7 is applied across the jacket material 4 and the core pipe 2. On the other hand, an electric field induction detector 8 having a well-known structure for picking up leakage electric fields, which is wired so that its output is inputted to a speaker 10 via an amplifier 9, is placed close to the adiabatic pipe 1 and When the tube 1 is moved from the end B toward the short-circuit point A, the speaker 10 continues to emit a sound, and as the detection path 8 approaches the short-circuit point A, the volume decreases and the speaker 10 passes through the short-circuit point. When I did that, the sound stopped. This means that a leakage electric field is generated in the insulation tube 1 from the end B of the insulation tube 1 to the short circuit point A, an electric field induced voltage is generated in the detector 9, and the leakage electric field disappears at the short circuit point A. . This was the same even when the electric field induction detector 8 was replaced with an electric induction detector to detect the leakage magnetic field linked to the leakage electric field.

Although it is not yet clear why such a phenomenon occurs due to the earth 6, the present invention will be proven below using experimental data.

A conductor-coated heat-insulated tube 1 with a length of 7 m in which the Γ core tube 2 is a copper tube with an outer diameter of 15.8 cm, and the jacket material 4 is a carbon rubber tube with an outer diameter of 23.3 cm. The above-mentioned heat-insulating pipe 1 has a resistance of 75 to 93%, a resistance of the jacket material 4 of 2KΩ/m, a capacitance of 0.345PF/m, and an insulation resistance between the core pipe 2 and the jacket material 4 of 200MΩ/m.
100V, by the method shown in Figure 1.
When an alternating current of 1000 Hz was applied and the core tube 2 was grounded, short circuit locations were determined using the electric field induction detector 8, and experimental data as shown in FIGS. 2 to 4 was obtained. a and b in Fig. 2 are when the short circuit point A is set at 2 m from the end B of the heat insulating pipe 1, a and b in Fig. 3 are when the short circuit point A is set at 4 m from the end B of the insulated pipe 1, and a and b in Fig. 4 are b shows the data when set at a distance of 6 m, and each a of Figs. b is detector 8
The data shows the data when detected from a distance of 30 cm. As shown in the graphs of FIGS. 2 to 4, the output voltage of the detector 8 rapidly attenuates when it reaches the short-circuit point and disappears when it almost coincides with the short-circuit point. It has been proven that short circuits can be detected accurately. Similar results were obtained when an experiment was conducted on an actually installed 50 m long insulated pipe.

In the above experiment, the core pipe 2 and the jacket material 4 of the insulated pipe 1 were short-circuited by a nail. There may be cases where the short circuit does not occur. For example, when the insulation pipe 1 has a crack in the jacket material 4 due to bending during piping, and a nail 5 is driven into the crack,
Even though the nail 5 is stuck into the core tube 2, the nail 5 does not come into contact with the jacket material 4, so that no short circuit occurs. However, even at this time, if water leaks from the nailed point of the insulated pipe 1, and the nail 5 and the outer sheathing material 4 are short-circuited due to water leakage, I wonder if the nailed point can be found by the method of the present invention. , conducted the following experiment. In other words, when the core tube 2 and the jacket material 4 are directly short-circuited by the nail 5, the contact resistance at that part is 10
It is extremely small, ranging from 20Ω. On the other hand, if there is an indirect short circuit due to water leakage, the contact resistance of the part is
It is about 10KΩ to 30KΩ. Therefore, as shown in FIG. 5, a hole 11 is made in the jacket material 4 of the insulated pipe 1, and a nail 5 is driven into the core pipe 2 through the hole 11, and water is replaced between the nail 5 and the jacket material 4. Variable resistor 12
When we tried the detection method of the present invention by intervening the variable resistor 12 and changing its resistance value, we found that although it differs depending on the voltage applied to the core tube 2 and the outer sheath material 4, according to experiments, The changed resistance value is 3MΩ to
Even if the resistance is 10 MΩ, if water leaks due to the above nailing and the outer sheathing material 4 and the core pipe 2 are short-circuited by the water leakage and the nail 5, the nailing point can be detected. I understand. Therefore, since it is customary to test for water leakage by applying a pressure of 10 kg/cm ² to the insulated pipe 1 during the completion inspection after construction of a building, it is preferable to use the method of the present invention after the water leakage test. Furthermore, when the applied voltage necessary for the detection was varied, sufficient detection could be achieved with a voltage as low as 24 V, which is safe for the human body.

Furthermore, in the method of the present invention, the voltage applied to the core tube 2 and the jacket material 4 is an alternating current (including a sine wave, other pulse waves, rectangular waves, and triangular waves) and a pulsating current (a full-wave rectified wave, a half-wave rectified wave, and a half-wave rectified wave). A periodic voltage (including rectified waves, other pulsating currents, and pulse waves) is used, but the following differences arise by selectively using alternating current and pulsating current. When the switch 13 in FIG. 1 is closed and a sinusoidal AC voltage is applied, a displacement current flows through the capacitance c of the circuit shown in FIG. For example, the leakage electric field is detected and the speaker 10 emits a sound regardless of the presence or absence of a short circuit. However, if the switch 13 is opened and a half-wave rectified voltage (or a full-wave rectified wave passed through a bridge circuit) is applied through the diode 14, the current will be Therefore, even if the leakage electric field detector 8 is brought close, no leakage electric field is detected and the speaker 10 does not make a sound, but when there is a short circuit, current flows and the speaker 10 makes a sound. Therefore,
When using pulsating flow, it is possible to determine whether there is a short circuit.
It also has the function of the DC resistance method mentioned at the beginning, and only when it is determined that there is a short circuit, it is necessary to perform the work of detecting the short circuit.

Conversely, when using alternating current as the applied voltage, use the direct current resistance method to determine the presence or absence of a short circuit before applying this alternating voltage, and then apply alternating voltage only to those that have a short circuit to detect the short circuit. Just keep doing it.

In addition, Earth 6 includes counterpoises that use electrostatic capacitance with the earth, and these include those that use an insulated wire running along the ground, and those that use a conductor wire connected to aluminum foil approximately 60 cm x 90 cm. It is also conceivable that the case of the circuit shown in FIG. 6, which will be described later, be made of metal.

Next, an embodiment of the circuit used in the method of the present invention will be explained with reference to FIGS. 6 and 7. Figure 6 shows a voltage application device, a tuning fork oscillator (trade name Microfork) 15
An oscillation stage 17 including an amplifier 16 which is a dedicated IC for this, an output amplifier 19 whose oscillation output is inputted via a variable resistor 18 for adjusting oscillation output, and an output amplifier 19 that boosts the output of the output amplifier 19 and matches impedance. It is equipped with a transformer 20, a changeover switch 13 and a diode 14 shown in FIG.
The voltage is applied to the core tube 2 and the jacket material 4 from the source.

FIG. 7 shows a short circuit detection device, which includes a jack 24 to which the electric field induction detector (or magnetic field induction detector) 8 shown in FIG. Impedance matching means 25 to be used, a preamplifier 26, and a McTave filter (using an operational amplifier is exemplified) 2 for amplifying the output of the preamplifier 26.
7. An output amplifier 29 into which the output of the McTave filter 27 is input via the voltage adjustment variable resistor 28, a speaker 30 driven by the output of the output amplifier 29, and the McTave filter 2.
It has a DC ammeter 32 into which the output of No. 7 is inputted via an amplifier 31. Furthermore, a resistance measuring section 37 is configured, which includes measurement terminals 33 and 34 that are in contact with the core tube 2 and the jacket material 4, an amplifier 35, and an oscillator 36. A switch 4 that selectively switches between the output terminal 38 and the output terminal 39 of the variable resistor 28
0 is set.

In the circuit of FIG. 7, first, the changeover switch 40 is switched to the output terminal 38 of the resistance measuring section 37 as shown by the solid line, and the resistance measuring section 37 is connected to the output amplifier 29. DC power +B is applied to the heat insulated pipe 1 by bringing it into contact with the core pipe 2 and jacket material 4 of the heat insulated pipe 1. If there is no short circuit, there is no input voltage to the amplifier 35 due to the insulation resistance between the core tube 2 and the jacket material 4, but if there is a short circuit, a voltage corresponding to the resistance up to the short circuit enters the amplifier 35. The oscillator 36 is operated by the amplified output, and the oscillation output is inputted from the changeover switch 40 to the output amplifier 29, so that the speaker 30 sounds.
Therefore, the presence or absence of a short circuit is determined by the presence or absence of sound from the speaker 30, so when the speaker 30 sounds, connect the changeover switch 40 to the output terminal 39 of the variable resistor 28 as shown by the broken line, and then An oscillation output is applied to the core tube 2 and the jacket material 4 by the voltage application device shown in FIG. go. When this electric field induction detector (or magnetic field induction detector) 8 picks up a leakage electric field (or leakage magnetic field), the induced current flows through the preamplifier 2.
6, McTave filter 27, variable resistor 28,
Then, the signal passes through the output amplifier 29 and enters the speaker 30 to emit a sound, while the strength of the leakage electric field (or leakage magnetic field) is displayed on the meter by the DC ammeter 32 after passing through the amplifier 31. When the electric field induction detector (or magnetic field induction detector 8) reaches a short circuit and the leakage electric field (or leakage magnetic field) disappears,
The speaker 30 stops sounding, and the DC ammeter 32 indicates the vicinity of point O, thereby allowing the short circuit location to be detected.

Note that the voltage applied to the conductor-coated heat-insulating tube 1 may be a low frequency, a high frequency, a high frequency modulated at an audio frequency, or the like.

As described above, the present invention provides electric field induction that captures leakage electric field changes in the insulated tube from a state in which the core tube of the conductor-coated insulated tube is grounded and a periodic voltage is applied across the jacket material and the core tube. A detector or a magnetic field induction detector that detects changes in the leakage magnetic field is moved along the insulated tube to detect the short circuit from the vanishing point of the leakage electric field or leakage magnetic field, so the resistance of the conductor-coated insulated tube is It has the advantage of being able to accurately detect short-circuit points without affecting variations in resistance or resistance changes at the joints of the piping, and even if there is a short-circuit in the piping due to nailing in two or more places, it can be detected from the voltage application end of the insulated pipe. By moving the detector and finding each short-circuit point one by one, and removing the nail each time, you can detect all the short-circuit points. By moving the electric field induction detector or magnetic field induction detector, the short circuit location can be easily detected.

In addition, when the voltage applied to the conductor-coated insulated tube is a pulsating current, if there is no short circuit in the insulated tube, no current will flow after the charging current flows, so an electric field induction detector or magnetic field induction detector Since a leakage electric field or a leakage magnetic field is not spread even if the conductor-covered heat-insulating tube is brought close, there is an advantage that the presence or absence of a short-circuit point in the conductor-coated heat-insulated tube can be determined before detecting the short-circuit point.

Furthermore, when the voltage applied to the conductor-coated heat-insulating tube is alternating current, the presence or absence of a short-circuit point in the heat-insulating tube can be simplified by determining the presence or absence of a short-circuit point by a DC resistance method prior to applying this voltage.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram showing the method of the present invention, Figs. 2 to 4 are graphs showing experimental data, Fig. 5 is a diagram showing the water leakage test method, and Fig. 6 shows an embodiment of the present invention. Figure 7 is a circuit diagram of the voltage application device, Figure 7 is a circuit diagram of the short-circuit detection device, Figure 8 is a cross-sectional view of a conductor-covered heat-insulated pipe to which the present invention is applied, and Figure 9 is a lumped constant of the heat-insulated pipe shown in Figure 8. It is a circuit. 1... conductor coated heat insulated tube, 2... conductive core tube,
3... Insulating heat-insulating pipe, 4... Conductive outer covering material, 6...
...Earth, 8...Electric field induction detector or magnetic field induction detector.

Claims (1)

[Scope of Claims] 1. In a conductor-coated heat-insulated tube formed by covering the outer periphery of a conductive core tube with a conductive jacket material via an insulating heat-insulating material, the core tube is grounded, and the jacket material and the core are connected to each other. A short-circuit point between the jacket material and the core tube is detected by an electric field induction detector that applies a periodic voltage across the tube to detect changes in the leakage electric field of the insulated tube or a magnetic field induction detector that detects changes in the leakage magnetic field. A method for detecting short circuits in conductor-coated heat-insulating pipes. 2 Claim 1 in which the periodic voltage is alternating current
Method for detecting short circuits in conductor-coated heat-insulated pipes as described in Section 1. 3 Claim 1 in which the periodic voltage is a pulsating current
Method for detecting short circuits in conductor-coated heat-insulated pipes as described in Section 1. 4 Prior to the application of a periodic voltage, a DC voltage is applied across the outer cover material and core tube of the conductor-coated insulated pipe, and the presence or absence of a short circuit between the outer cover material and the core tube is determined based on the DC resistance. A method for detecting a short circuit in a conductor-coated heat-insulating pipe according to claim 1, which includes the method.