JP2782078B2 - How to measure cable fault points - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring a distance from an end of a cable to an accident point, and particularly to a method useful for measuring an accident point in a multi-branch line.

[Prior Art] Conventionally, a pulse radar method is generally used as a method for measuring a distance from an end of a cable to an accident point and detecting the accident point. The main pulse radar methods are the transmission pulse radar method and the accident discharge detection pulse radar method.

The transmitting pulse radar method transmits a pulse from one end of an accident cable to the cable, receives a reflected pulse reflected at the cable accident point, that is, a point where the characteristic impedance changes, and returns to the pulse transmission end of the cable again. , The distance from the reflection time of the reflection pulse to the accident point is calculated. On the other hand, in the self-discharge detection pulse radar method, a high voltage is applied to an accident cable to cause a discharge at the accident point, and the discharge pulse at this time is a direct wave that returns directly to the measurement end of the cable, and a far end of the cable Utilizing the fact that it is reflected once and reflected waves returning to the measurement end,
The distance to the accident point is calculated from the time difference between the direct wave and the reflected wave reaching the measuring end.

[Problem to be Solved by the Invention] The above-described pulse radar method is an extremely effective method when the cable line is composed of one cable, but many branch lines are connected to the cable. In such a multi-branch line, its reliability is significantly reduced. The pulse radar method is a method of finding an accident point using a pulse propagating in a cable.However, in a multi-branch line, since the cable branch part is small but a characteristic impedance change point, the pulse This is because the part is reflected and the pulse necessary for the measurement is distorted. This pulse distortion causes an error when measuring the fault point. Also, the greater the number of branches in the cable line, the more pronounced the pulse distortion. For this reason, the pulse radar method described above cannot be applied to fault point measurement in a multi-branch cable line, and no other effective method has been found.

Therefore, an object of the present invention is to provide a cable fault point measuring method capable of accurately measuring a fault point even in a multi-branch cable line.

[Means for Solving the Problems] The cable fault point measuring method according to the present invention comprises: applying a power to a faulty phase cable via a power supply capacitor to generate a discharge at the fault point; Circulates through the shielding layer to return to the power receiving end, measures a discharge current that attenuates and oscillates due to the resonance action of the power supply capacitor and the inherent inductance of the cable, and based on the oscillation frequency of the discharge current, determines the fault phase cable. Calculate the inductance from the charged end to the fault point, and detect the fault point by calculating the distance from the charged end to the fault point from the calculated inductance and the inductance of the entire length of the cable that is known in advance. It is characterized by the following.

Alternatively, power is applied to the faulty phase cable via a power supply capacitor to cause a discharge at the faulty point, and the discharge circulates through a shielding layer that is short-circuited with the cable conductor at the faulty point, returns to the power receiving end, and The discharge current that attenuates and oscillates due to the resonance action of the capacitor and the inherent inductance of the cable is measured, and the cycle t of the discharge current is calculated based on the oscillation frequency of the discharge current. The distance from the power receiving end to the fault point is calculated from the cycle T of the damped oscillating current in the entire cable length, and the fault point is detected.

In the above-described method for measuring the fault point of the cable, the calculation of the inductance from the charged end of the faulty phase cable to the fault point or the calculation of the cycle t is performed based on the discharge electromagnetic wave radiated by the discharge current. Is also good.

[Operation] When a discharge is generated at the accident point, the conductor of the cable and the shielding layer are short-circuited by an arc, and a discharge current circulates through the conductor and the shielding layer. Strictly speaking, the line constant at this time has a distributed capacitance between the conductor and the shielding layer and a round-trip inductance from the power application end to the fault point. Since the capacitance is sufficiently smaller than the capacitance of the power supply, the line constant can be considered to be only the inductance. Thus, the discharge current is
Attenuated vibration occurs at a frequency determined by the inductance and the capacitance of the capacitor of the power supply device. Here, the inductance changes in proportion to the distance from the receiving end to the fault point. Therefore, if the attenuation oscillation frequency of the discharge current is measured and the inductance of the line is determined, the distance from the receiving end to the fault point is determined. Will be detected.

In addition, the electromagnetic wave generated by the discharge current also has the property of attenuating and oscillating at a frequency determined by the inductance of the line and the capacitance of the power supply capacitor in the same manner as described above. Accident points can be detected.

EXAMPLES The present invention will be described in detail below based on examples shown in the drawings.

FIG. 1 is a schematic diagram showing an example of a method for measuring a fault point of a cable according to the present invention. In the drawing, reference numeral 1 denotes a test cable, and it is assumed that an accident point 4 due to a ground fault, a short circuit accident, or the like exists at an arbitrary position of the cable 1. Reference numeral 2 denotes a power supply unit connected to one end of the cable 1 for applying a voltage to the cable 1 and causing a discharge at an accident point 4; a DC power supply Hv, a power supply capacitor C for charging, and a blocking resistor R
b, and a resistor R for suppressing the discharge current of the power supply capacitor C. Reference numeral 3 denotes a current detector having current waveform observation means connected to both ends of the shunt resistor Rs of the power supply device 2.

In the above configuration, when a high voltage is applied to the cable 1 by the power supply device 2 and a discharge occurs at the fault point 4, the conductor 10 and the shielding layer 11 of the cable 1 are short-circuited by the discharge arc. As indicated by the chain line, the discharge current i circulates through the conductor 10 and the shielding layer 11 and returns to the power receiving end of the cable 1. At this time, the line constant of the line through which the discharge current flows is only the reciprocating inductance from the power application end of the cable 1 to the fault point and the capacitance of the power supply capacitor C of the power supply device 2 as described above. Due to the resonance action between the inductance and the capacitance, the vibration is attenuated.

This discharge current and its waveform are observed by a current detector 3 such as an oscilloscope, and the cycle t of the oscillation damping frequency f of the discharge current is obtained to calculate the frequency f from a relational expression of f = 1 / t. , Is calculated from the relational expression. Since the capacitance of the power supply capacitor C of the power supply device 2 is constant, only the inductance varies depending on the position of the fault point 4 of the cable 1, that is, the cable length between the power application end and the fault point 4. If the inductance of the cable 1 is known in advance, the distance L from the power receiving end of the cable 1 to the fault point 4 can be calculated.

If the total length of the cable 1 is known, the distance L from the power-carrying end of the cable 1 to the fault point 4 can be obtained by the following method. That is, first, when the cable 1 is healthy, the conductor 10 and the shielding layer 11 are short-circuited at the far end thereof, power is applied to the cable 1 by the power supply device 2, and the period T of the damped oscillation current in the entire length D of the cable 1 is obtained. Next, in the same manner as above, the discharge current when the fault point 4 exists in the cable 1 is detected, and the cycle t of the damped oscillation is obtained. By comparing the period T of the damped oscillating current with respect to the total length D of the cable 1 and the period t of the damped oscillating current with respect to the distance L from the power application end to the fault point 4, the distance L is obtained by the following equation. Can be.

L = (t / T) ² · D In the embodiment shown in FIG. 1, since the shunt resistor Rs is used for detecting the discharge current, the detected voltage includes a DC component. If the current transformer is used for discharge current detection, the DC component can be excluded,
When observing a current waveform with an oscilloscope or the like, measurement of a time interval at a zero-crossing point can be easily performed, and the intervention of an error is reduced. Furthermore, this method takes the square of the ratio of the period T of the damped oscillating current to the total length D of the cable 1 and the period t of the damped oscillating current to the distance L to the fault point 4,
Since the value after the decimal point becomes smaller by squaring,
As a result, the error of the period time measurement of the damped oscillating current can be reduced by the so-called square effect.

FIG. 2 is a schematic view showing another embodiment of the present invention,
The difference from the above embodiment is that the fault point is measured by receiving the electromagnetic wave e generated by the discharge current flowing due to the discharge at the fault point 4 by the receiving device 5 installed near the power application end of the cable 1. . That is, the discharge current i accompanying the discharge at the fault point 4 is an extremely large current, and the discharge current i forms a leakage electromagnetic field around the cable 1 and the power supply device 2. Although this leakage electromagnetic field is the electromagnetic wave e shown in the figure, the electromagnetic wave e naturally has the same characteristics as the discharge current that attenuates and oscillates. By receiving this electromagnetic wave e and obtaining the attenuation oscillation period of the electromagnetic wave e, The distance L to the accident point 4 can be obtained in the same manner as in the above embodiment.

As the receiving device 5 used in this embodiment, for example, a receiving device having a configuration as shown in FIG. 3 can be used. The receiving device 5 includes an antenna 51 such as a search coil for capturing a magnetic field of the electromagnetic wave e, and a tuning amplifier 52 for tuning a signal received by the antenna 51 to a resonance frequency and amplifying the signal. Note that the resonance frequency is determined by a sweep signal generator.
The tuning amplifier 52 sweeps the signal and supplies it to the tuning amplifier 52. The tuning amplifier 52 performs tuning amplification for each resonance frequency given while sweeping and outputs the result. This output signal is input to the selection circuit 54, and the maximum value is selected and output from the amplification values obtained at each resonance frequency, and the display device 55 displays a signal waveform based on the maximum signal value. Have been.

The electromagnetic wave e has a center frequency, which is the frequency component having the strongest electromagnetic field intensity. Therefore, it is important to perform the measurement based on the center frequency in order to efficiently perform the fault point measurement without error. Note that the center frequency varies depending on the distance L from the power receiving end of the cable 1 to the fault point 4.

The operation when such a receiving device 5 is used will be described. The electromagnetic wave e is received by the antenna 51, and the received signal is input to the tuning amplifier 52. In the tuning amplifier 52, the received signal is tuned to the resonance frequency that is transmitted while being swept by the sweep signal generator 53 in a range of, for example, several kHz to several tens of kHz (the center frequency of the electromagnetic wave e is generally in this range). To amplify. As a result, the discharge electromagnetic wave is amplified for each frequency component in the sweep range. Next, the amplification values for each frequency component of these discharge electromagnetic waves are sent to the selection circuit 54. The selection circuit 54 selects the center value of the discharge electromagnetic wave generated by the discharge at the fault point 4 by selecting the maximum value from the plurality of amplification values. Then, only the amplification value of the center frequency is transmitted to the display device 55, and the received waveform of the center frequency is displayed. Thus, the period t of the damped oscillation of the electromagnetic wave e is obtained from this waveform,
The distance L to the accident point 4 is obtained in the same manner as in the above embodiment.

FIG. 4 is a schematic diagram showing a case where the present invention is applied to the measurement of fault points in a multi-branch cable line. In the figure, it is assumed that a large number of branch cables 110 are connected to a trunk cable 100, and one of the branch cables 110 has an accident point 40. 101 indicates a conductor of the trunk cable 100, 102 indicates a shielding layer thereof, 111 indicates a conductor of a branch cable, and 112 indicates a shielding layer thereof. The power supply device 2 and the current detector 3 as shown in FIG. 1 described above are connected to one end of such a multi-branch cable line.

In such a configuration, when a high voltage is applied to the multi-branch cable line by the power supply device 2 to cause a discharge at the fault point 40, the conductor 101 of the trunk cable 100 and the fault point 40 are present as shown by a dashed line in the figure. Conductor 11 of branch cable 110
1.Shielding layer 11 of branch cable 110 short-circuited by discharge arc
2, and a discharge current i circulating through the shielding layer 102 of the trunk cable 100 and returning to the power receiving end flows. At this time, the discharge current i
Flows only in the above-mentioned route, and the line constant of the line through which the discharge current i flows is determined by the round-trip inductance between the trunk cable 100 and the fault point 40 of the branch cable 110 and the power supply device. This is only the capacitance of the power supply capacitor, and the discharge current i is attenuated and vibrated by the inductance and the capacitance. Thus, in the same manner as in the above embodiment, the distance from the charging end to the accident point 40 may be calculated from the damping oscillation frequency of the discharge current i. Of course, it is also possible to receive the electromagnetic wave generated by the discharge current i and determine the distance to the accident point 40 from the damped oscillation frequency of the electromagnetic wave. In the case of such a multi-branch cable line, even if the distance to the accident point can be calculated by measuring only from the power receiving end, points at the same distance exist at a plurality of locations on the trunk cable and the branch cable. It is possible. In this case, the same measurement is performed by moving the power-carrying end to the terminal side of the branch cable, and a point where the distance calculated by these measurements matches is searched to determine whether the accident point is on the main cable or the branch cable. You can find out if it is above.

In the pulse radar method that measures the rising of a traveling wave pulse in detail and obtains a time difference, the pulse is partially reflected at a connection point between the main cable 100 and the branch cable 110, and the pulse is distorted. However, it was not suitable for measuring the fault point of a multi-branch cable line. On the other hand, in the present method, the fault point is obtained from the damped oscillation frequency of the discharge current i circulating through the conductor and the shielding layer of the cable which is brought into a conductive state by discharge without using the traveling wave pulse. There is no influence of the branch point between the branch cable 100 and the branch cable 110.

In each of the above embodiments, the discharge current i or the electromagnetic wave e
The damped oscillation frequency must be measured while the discharge continues at the accident point. Therefore, it is preferable that the discharge time is long. To realize this, the power supply capacitor C of the power supply device 2 is used.
Should be increased (about 2.5 μF). Further, in order to eliminate the influence of the distributed capacitance between the cable conductor and the shielding layer, it is necessary to increase the capacitance of the power supply capacitor C. As a result, the decay oscillation frequency of the discharge current i decreases, and the traveling wave pulse superimposed on the discharge current i can be easily separated by a filter when detecting the waveform of the discharge current i. Note that the resistor R for suppressing the discharge current of the power supply capacitor C does not usually need to be inserted, and may be inserted as needed.

[Effects] As described above, according to the method for measuring a fault point of a cable according to the present invention, discharge which circulates through a conductor and a shielding layer of a cable without using a traveling wave pulse unlike a conventional pulse radar method. This method is to determine the distance to the fault point from the damped oscillation frequency determined by the round trip inductance of the current from the charged end of the cable to the fault point and the capacitance of the power supply unit. Even if there is a branch point, the measurement can be performed without being affected by the branch point. Therefore, the fault point measurement of the multi-branch cable line, which has a large error intervention in the pulse radar method or the like, can be accurately performed.

[Brief description of the drawings]

FIG. 1 is a schematic view showing one embodiment of a method for measuring a fault point of a cable according to the present invention, FIG. 2 is a schematic view showing another embodiment, and FIG.
FIG. 4 is a block diagram showing one row of a receiving device used in the present invention, and FIG. 4 is a schematic diagram showing an application example of the present invention in a multi-branch cable line. DESCRIPTION OF SYMBOLS 1 ... Cable, 10 ... Conductor, 11 ... Shielding layer, 2 ... Power supply device, 3 ... Current detector, 4 ... Fault point, 5 ... Receiving device, C ... Power supply capacitor, i ... Discharge current, e ...
Electromagnetic waves

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kunihiko Sanada 1008 Shinbori, Kumagaya-shi, Saitama Mitsubishi Cable Industry Co., Ltd. Kumagaya Works (72) Inventor Takao Sanada 3-4-1 Marunouchi, Chiyoda-ku, Tokyo Mitsubishi Cable Examiner Nobuhiko Egasa in the Tokyo Office of Industrial Co., Ltd. (58) Field surveyed (Int. Cl. ⁶ , DB name) G01R 31/08

Claims (3)

(57) [Claims] 1. A power supply is applied to a faulty phase cable via a power supply capacitor to generate a discharge at a faulty point. The discharge circulates through a shielding layer which is short-circuited with a cable conductor at the faulty point and returns to a power receiving end. Measuring a discharge current that attenuates and oscillates due to a resonance action between the power supply capacitor and an inductance inherent to the cable, and calculates an inductance from a power application end of the faulty phase cable to a fault point based on a vibration frequency of the discharge current, A method for measuring a fault point of a cable, comprising calculating a distance from a power receiving end to a fault point based on the calculated inductance and a previously known inductance of the entire length of the cable to detect the fault point. 2. A power supply is applied to the faulty phase cable via a power supply capacitor to generate a discharge at the faulty point. The discharge circulates through a shielding layer which is short-circuited with the cable conductor at the faulty point, and returns to the power receiving end. Measuring a discharge current that attenuates and oscillates due to a resonance action between the power supply capacitor and an inherent inductance of a cable, calculates a cycle t of the discharge current based on an oscillation frequency of the discharge current, A method for measuring a fault point of a cable, comprising calculating a distance from a power receiving end to a fault point based on the cycle T of the damped oscillating current in the entire length of the cable and detecting the fault point. 3. The method according to claim 1, wherein the calculation of the inductance from the power-carrying end of the faulty phase cable to the faulty point or the calculation of the cycle t is performed by a discharge electromagnetic wave radiated by a discharge current. A method for measuring a fault point of a cable, characterized in that the method is carried out based on the following.