JP3035865B2 - Fault location method for multi-branch cable - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for locating a fault point of a three-phase cable including a branch line.

[Conventional technology]

In the event of a ground fault, disconnection, or phase-to-phase short-circuit occurring in a cable, locating the point at an early stage is a very important technique for shortening the cable recovery work period. However, until now, there has been no method for straightening the fault point of a multi-branch cable obtained by arbitrarily branching and connecting a three-phase cable in a state where the branch lines are connected. Therefore, the multi-branch cable is opened once at each branch point to make a cable section without any branch that is divided every branch, and a cable section where an accident has occurred is found by conducting a continuity test etc. on each cable section. Then, for the cable section including the accident, for example, the pulse radar method was applied to locate the accident point.

The pulse radar method is a method in which a steep pulse voltage is applied between a faulty phase conductor and a grounding sheath covering this phase at one end of a three-phase cable having no branch, and a voltage waveform generated at the voltage application end is obtained. . When there is a fault point of ground fault or disconnection, the input pulse voltage is reflected at this fault point and returns to the voltage application terminal again. Therefore, at the voltage application terminal, the time difference t between the input waveform and the reflected waveform of the pulse voltage is reflected. Ask for. The time difference t is determined by a constant (inductance L _m of the conductor per unit length of the cable and a capacitance C _m of the ground to the conductor) determined by the structure of the cable and a distance x _m from the voltage application point to the fault point, It is possible to obtain the x _m from the relationship.

[Problems to be solved by the invention]

However, such a method requires a very troublesome operation of first finding out the cable section where the accident has occurred while sequentially opening the branch points of the multi-branch cable at the time of the accident, which requires a great deal of time. And had been a bottleneck for cable restoration work.

An object of the present invention is to provide a method for locating an accident point of a multi-branch cable in a state where branch lines are connected.

[Means for solving the problem]

According to the present invention, a multi-branch cable obtained by arbitrarily branching and connecting a three-phase cable covered with a grounding sheath for each phase and connecting it at an arbitrary location is provided. A method for locating the point of an accident when an accident has occurred. A voltage application end is provided between a conductor in an accident phase at one end of a multi-branch cable and a grounding sheath, and a voltage waveform rises sharply at this voltage application end. One of a DC power supply for outputting a DC voltage and an AC power supply for outputting an AC voltage and changing its frequency is connected, and when the output voltage of this power supply is applied, it is connected to the voltage application terminal. A plurality of resonance frequencies of the generated voltage are measured, and on the other hand, the multi-branch cable is regarded as a combination of the cable sections divided for each branch connected in series and in parallel. Assuming the cable section where the accident occurred, the length from the branch point to the accident point is unknown x for the cable section, and its terminal impedance is ground fault resistance when a ground fault occurs, and infinite when a disconnection occurs, The cable impedance when viewing the multi-branch cable side from the voltage application end is expressed as a function of x, and the sum of this cable impedance and the power supply impedance when viewing the power supply side from the voltage application end is set to zero. A calculation formula for calculating the value of x is derived from the calculation formula, a plurality of x values are obtained for each of the plurality of resonance frequencies from the calculation formula, and a cable section where the obtained values of x match each other is an accident point. Judge. Or a method of locating an accident point in a case where a multi-branch cable obtained by arbitrarily branching and connecting a three-phase cable in which a grounding sheath is not interposed between phases causes an inter-phase short-circuit accident at any one place, The voltage between the short-circuited conductors at one end of the multi-branch cable is defined as a voltage application end, and a DC power supply that outputs a DC voltage whose voltage waveform rises sharply at this voltage application end, or an AC voltage is output and the frequency can be changed. One of the AC power supplies is connected, and when the output voltage of this power supply is applied, a plurality of resonance frequencies of the voltage generated at the voltage application terminal are measured, while the multi-branch cable is divided for each branch. It is considered that each of the cable sections connected is connected in series and in parallel, and the cable section in which the accident occurred is assumed. The length from the branch point to the fault point is an unknown number x, the terminal impedance of which is zero, and the cable impedance when viewing the multi-branch cable side from the voltage application end is expressed as a function of x. A calculation formula for calculating the value of x is derived by setting the sum of the power supply impedance when the power supply side is viewed from the voltage application end to zero, and a plurality of calculation formulas are obtained from the calculation formula for each of the plurality of resonance frequencies. An x value is obtained, and a cable section in which the obtained x values match each other is determined to be an accident point.

[Action]

According to the method of the present invention, in a multi-branch cable obtained by arbitrarily branching a three-phase cable covered with a grounding sheath for each phase, the multi-branch cable is connected to the multi-branch cable when a ground fault or disconnection accident occurs. A plurality of resonance frequencies of a voltage generated at this voltage application terminal are measured by applying a steeply rising DC voltage or an AC voltage having a changing frequency to one end of the multi-branch cable. Each section is considered to be connected in series connection and parallel connection, and the cable section in which the accident has occurred is assumed. For the cable section, the length from the branch point to the accident point is defined as unknown x. The terminating impedance is set to ground fault resistance when there is a ground fault, and to infinity when there is a break, and the cable impedance when the multi-branch cable side is viewed from the voltage application end. By expressing the impedance as a function of x and setting the sum of the cable impedance and the power supply impedance when viewing the power supply side from the voltage application terminal to zero, the voltage resonance condition at the voltage application terminal can be obtained. A calculation formula for calculating the value of x under the resonance condition is derived, and a plurality of values of x are obtained by substituting the plurality of measured resonance frequencies into the calculation formula. The same calculation is performed as described above, again assuming that the cable section has caused an accident, and the calculation is repeatedly performed for each cable section until the obtained values of x match each other. It is determined that a cable section where the values of x match each other is an accident point.

Also, in a multi-branch cable obtained by arbitrarily branching and connecting a three-phase cable in which a grounding sheath is not interposed, when a multi-branch cable causes a short circuit accident, the multi-branch cable has a steep connection between one end conductors. A plurality of resonance frequencies of a voltage generated at the voltage application terminal are measured by applying a rising DC voltage or an AC voltage having a changing frequency, while each of the multi-branch cables is connected in series with each of the divided cable sections. It is assumed that the cable section is connected and connected in parallel, and the cable section where the accident has occurred is assumed.The length of the cable section from the branch point to the accident point is unknown x, and the impedance at the end of the cable section is assumed to be zero. The cable impedance when the multi-branch cable side is viewed from the voltage application end is expressed as a function of x. Since the resonance condition of the voltage at the voltage application terminal is obtained by setting the sum of the dance and the power supply impedance when the power supply side is viewed from the voltage application terminal to be zero, a calculation formula for obtaining the value of x under this resonance condition Is calculated, and a plurality of values of x are obtained by substituting the plurality of measured resonance frequencies into the calculation formula. If the values of x are different from each other, it is considered that another cable section has caused an accident. Assuming the above, the same calculation as described above is performed, and the calculation is repeatedly performed for each cable section until the obtained plural values of x match each other. Judge as the accident point.

〔Example〕

 Hereinafter, the present invention will be described based on examples.

FIG. 1 is a circuit connection diagram illustrating a method for locating an accident point of a multi-branch cable according to an embodiment of the present invention. The multi-branch cable has a trunk line AB and branch lines P ₁ C branched from branch points P ₁ and P _2. , P
It is constituted by a ₂ D, which is one end of a multi-branch cable A
A DC power supply 1 and a voltage waveform analyzer 2 are connected to the points. The multi-branch cable is covered by a grounding sheath (not shown), all ends B, C, and D are left open, and five cable sections AP ₁ , CP ₁ , and P ₁ are divided for each branch.
The lengths of P ₂ , P ₂ D, and P ₂ B are defined as l ₁ , l ₂ , l ₃ , l ₄ , and l ₅ , respectively. On the other hand, the DC power supply 1 has a charging capacitor C ₁ charged with DC charge, a closing switch S, a series resistor R ₀ , a parallel capacitor C ₂ ,
Is composed of series reactor L _0, the DC voltage rises sharply by closing the start switch S is output between the ground and the point A. The voltage waveform analysis device 2 captures a voltage waveform generated between the point A and the ground, and obtains and outputs voltage components of each frequency by performing Fourier analysis. The resonance frequency can be obtained by this device. .

In general, the impedance Z _S when viewed from one end of a cable section covered with a grounding sheath and having no branch point on the cable side.
Is It can be expressed as. Where: l: Cable section length Z _G : Termination impedance at the other end Where R is the conductor resistance per unit length of the cable, L is the inductance of the conductor, C is the capacitance of the conductor to ground, G is the conductance of the conductor to ground, and ω is the angular frequency of the applied voltage (= 2π). ).

Looking at the cable of the distributed constant from one end that its impedance is Z _S means that the cable is equivalent to the impedance element having a concentration impedance Z _S. Therefore, in the case of a cable connected in series, the impedance of the cable connected to the subsequent stage is set to Z _S1, and Z _S1 is substituted for Z _G in the equation (1) to obtain the total of the cables connected in series. The impedance can be determined. In the case of parallel-connected cable, the impedance viewed respective cable from the connection point to Z _1, Z _2, of which the total impedance of the parallel connected cable parallel value Z ₁ · Z ₂
/ (Z ₁ + Z ₂ ). The terminating impedance Z _G when the end of the cable is not a branch point but is open is assumed to be infinite. By doing so, the impedance when the cable side is viewed from one end of the multi-branch cable configured by arbitrarily branching the cable is regarded as the impedance of each cable section being connected in series and in parallel, respectively. Can be easily obtained by

In addition, the impedance of the cable section where the accident has occurred can also use (1). In equation (1), the cable section length 1 is the length x from the branch point to the accident point, and the terminal impedance Z _G is the ground fault. In the case of, the ground fault resistance value is used, and in the case of disconnection, the value is infinite.

The procedure for locating the fault point in the multi-branch cable of FIG. 1 will be described below.

First, the closing switch S of the DC power supply 1 is closed to apply a steeply rising DC voltage to the point A, and the resonance frequency _i (i =
1, 2,...) Are obtained by the voltage waveform analyzer 2.

Next, it is assumed that a ground fault has occurred at an arbitrary section of the multi-branch cable, for example, at a point X (distance x from the branch point P ₂ ) in the cable section P ₂ D. The side looking impedance Z _A is determined according to the method described above, and Z _A is represented as a function of the unknown x.

On the other hand, the power supply impedance Z ₀ when the power supply side is viewed from the point A is obtained. In the configuration of FIG. 1, if C ₁ = C ₂ = 1 (μF) R ₀ = 10 (Ω) L ₀ = 100 (μH), a simple equation is obtained for a high frequency of the order of kilohertz or more, Z ₀ = jωL ₀ (4)

Next, assuming that the output voltage when the DC power supply 1 is not loaded is V ₀ , the voltage V _A generated at the point _A is Therefore, the denominator of equation (5) is zero, that is, S ₀ + Z _A = 0 (6) is the resonance condition. For example, when the impedance Z _A of the multi-branch cable in FIG. 1 is obtained and the value of x is obtained from the equations (4) and (6), x = β ⁻¹ tan ⁻¹ [｛K tan (βl ₃ ) −1 ｝ / {K tan (βl ₃ ) tan (βl ₅ ) −tan (βl ₅ ) −tan (βl ₃ ) −K} (7) where K = tan (βl ₂ ) + ｛ωL ₀ tan (βl ₁ ) −Z｝ / {ωL ₀ + Ztan (βl ₁ )} (8) where γ and Z have the same constant for all cable sections in equations (2) and (3), and R = 0.
(Ω), G = 0 (1 / Ω), and γ = jω (LC) ^1/2 = j
β, Z = (L / C) ^1/2 . The ground fault resistance at the point X is set to 0 (Ω).

Resonance frequency measured at ω (= 2π) in equation (7)
_{When i} is substituted, i x values (x _i , i = 1, 2,...) are obtained. If the x _i values match each other, the cable section can be determined as an accident point.

In this case, if the obtained values of x _i are different from each other, it is assumed that another cable section has caused an accident, and the same calculation as described above is performed, and the obtained values of x match each other. The calculation is repeated for each cable section up to and including.

In the circuit connection diagram of FIG. 1, the multi-branch cable is a 6.6 kVCVT cable having a conductor cross-sectional area of 60 mm ² , the ground fault point is assumed to be the X point in the cable section P ₂ D, and the switch S of the DC power supply 1 is turned on. In this case, it was examined whether or not the fault point X can be located from the resonance frequency obtained by analytically calculating the voltage waveform generated at the point A by a computer.

The numerical values used for the calculation are as follows. The cable section lengths l ₁ to l ₅ are as shown in FIG.
(M), and the ground fault resistance was 0 (Ω). The constants of the CVT cable were as follows: R = 0 (Ω) G = 0 (1 / Ω) C = 0.37 × 10 ⁻⁹ (F / m) L = 1.74 × 10 ⁻⁷ (H / m)

FIG. 2 is a frequency characteristic diagram of a voltage component generated at the point A in FIG. 1. The voltage waveform at the point A is calculated by a computer, and the horizontal axis represents the frequency, and the vertical axis represents the frequency spectrum including the voltage component. Things. When the point X was an accident point, four resonance frequencies _i occurred as shown in the figure.

In the actual accident point location, since the cable section where the ground fault occurred is unknown, it is assumed that a ground fault has occurred in each cable section, and x _i corresponding to each cable section
The value is calculated from the _i value in FIG.

Table 1 is a characteristic table showing the value of x _i calculated assuming that a ground fault has occurred in each cable section. Since the resonance frequency _i is actually a measured value, it always involves a measurement error. error delta _i showed orientation error range of the assumed fault point x and there is a range of ± 0.05KHz respect _i. In Table 1, In some cases, x becomes negative or exceeds the total length of the cable section. In this case, since the estimated width of _i is large and the error is large, the accident point is determined from other _i values.

From the results of Table 1, the cable section excluding the cable section P ₂ -D is without the range of x _i overlap each other, has a mixed range together. Cable section P ₂ -D is x _i
Are overlapped with each other. Although _i has poor estimation accuracy, the range of x is estimated to be 47 to 127 (m) from the values of ₂ , ₃ , and ₄ , which is almost equal to the assumed position of the accident point, x = 100 m. accidents cable sections with matches is found to be between P ₂ -D.

The above embodiment shows the case where the ground fault, by a terminating impedance to infinity in the X point of the cable section P ₂ -D in the case of accidental disconnection, as well as position location in the case of earth fault It can be performed. Furthermore, even when a multi-branch cable with a three-phase cable in which the grounding sheath is not interposed between the phases causes a short-circuit accident, by considering one conductor of the short-circuiting phase as a substitute for the grounding sheath, each of the above-mentioned phases is reduced. The fault point can be located in exactly the same way as the fault point location method of the three-phase cable covered with the grounding sheath.

Further, as a power supply applied to the voltage application point, an AC power supply with variable frequency can be used. That is, the resonance frequency _i can be known by changing the frequency of the applied voltage and obtaining the voltage generated at the voltage application point.
The impedance Z ₀ of the power supply side can be determined by replacing an equivalent circuit composed of the inductance and capacitance.

Further, in the method according to the present invention, although the calculation formula of the value of x is very complicated like the example of the formula (7), the calculation of the formula of this degree can be easily executed by a commercially available personal computer.
The calculation result can be obtained immediately by programming the repetition calculation in advance.

〔The invention's effect〕

As described above, the present invention provides a DC power supply or a frequency-variable AC power supply that rises steeply at one end of a multi-branch cable when a multi-branch cable including a three-phase cable having a grounding sheath causes a ground fault or a disconnection accident. To measure a plurality of resonance frequencies, while assuming a cable section in which an accident has occurred, its position x is unknown, and the values of x obtained for a plurality of resonance frequencies from the resonance condition of the circuit match each other. Since the cable section was determined to be an accident point, it was possible to locate the accident point in the case of the conventional multi-branch cable. Can be provided.

Therefore, according to the method of the present invention, since the entire multi-branched cable arbitrarily branched can be located at a time, there is an advantage that the time required for the orientation is reduced and the cable recovery time can be shortened.

Further, even when a short-circuit accident of a three-phase cable in which the grounding sheath is not interposed between the phases occurs, one conductor of the short-circuiting phase is connected to the grounding sheath of the three-phase cable fault point locating method including the grounding sheath. There is also an advantage that the accident point can be similarly located by substituting.

[Brief description of the drawings]

FIG. 1 is an open-circuit connection diagram illustrating a method for locating an accident point of a multi-branch cable according to an embodiment of the present invention, and FIG. 2 is a frequency characteristic diagram of a voltage component generated at a point A in FIG. 1: DC power supply, 2: Voltage waveform analyzer, A, B, C, D: end of the cable, P _1, P _2: the branch point of the cable, l ₁ to l _5: cable section length, ₁ to _5: the resonant frequency, C _1: the charge capacitor, C _2: parallel capacitor, L _0: series reactor, R _0: series resistance, S: start switch, X: earth絡点.

Continued on the front page (72) Inventor Morihiko Iwagami 1-1-1, Tanabe-shinden, Kawasaki-ku, Kawasaki-shi, Kanagawa Prefecture Inside Fuji Electric Co., Ltd. (72) Inventor Katsuya Nagayama 2-4-1, Nishi-Atsujigaoka, Nishifutsu-shi, Tokyo Tokyo Electric Power Company Technical Research Institute (72) Inventor Tatsuyoshi Matsuura 2-4-1 Nishi-Atsujigaoka, Chofu City, Tokyo Tokyo Electric Power Company Technical Research Institute (56) References JP-A-52-45034 (JP, A) ) Shokai Sho 59-152473 (JP, U)

Claims (2)

(57) [Claims] 1. A multi-branch cable obtained by arbitrarily branching and connecting a three-phase cable covered with a grounding sheath for each phase and causing a ground fault or disconnection accident at an arbitrary point. A DC power supply that outputs a DC voltage at which a voltage waveform rises sharply at a voltage application terminal between the conductor in the accident phase at one end of the multi-branch cable and the grounding sheath, or at the voltage application terminal, or Connects any one of the AC power supplies that can output an AC voltage and change its frequency, and adjusts a plurality of resonance frequencies of a voltage generated at the voltage application terminal when an output voltage of the power supply is applied. On the other hand, the multi-branch cable is regarded as a combination of the cable sections divided for each branch connected in series and in parallel, and the cable section in which the accident has occurred is considered. For the cable section, the length from the branch point to the fault point is an unknown number x, and its terminal impedance is ground resistance when there is a ground fault, infinite when it is broken, and the multi-branch cable side from the voltage application end. Is expressed as a function of x, and a calculation formula for obtaining the value of x is obtained by setting the sum of the cable impedance and the power supply impedance when viewing the power supply side from the voltage application end to zero. And calculating a plurality of x values for each of the plurality of resonance frequencies from the calculation formula, and determining that a cable section in which the obtained x values coincide with each other is an accident point. Method for locating the accident point of a branch cable. 2. A method for locating an accidental short-circuit at an arbitrary point in a multi-branch cable obtained by arbitrarily branching and connecting a three-phase cable in which a grounding sheath is not interposed between phases. The voltage application terminal is formed between the conductors of the short-circuit phase at one end of the multi-branch cable, and a DC power supply that outputs a DC voltage whose voltage waveform rises steeply at this voltage application terminal, or outputs an AC voltage and changes its frequency One of the AC power supplies that can be connected to the power supply is connected, and when the output voltage of this power supply is applied, a plurality of resonance frequencies of a voltage generated at the voltage application terminal are measured, while the multi-branch cable is connected. Each of the cable sections divided for each branch is considered to be connected in series and in parallel and combined, and the cable section in which an accident has occurred is assumed. The length from the branch point to the accident point is an unknown number x, the terminal impedance of which is zero, and the cable impedance when viewing the multi-branch cable side from the voltage application end is expressed as a function of x. A calculation formula for obtaining the value of x is derived by setting the sum of the power supply impedance when the power supply side is viewed from the voltage application end to zero, and a plurality of calculation formulas are obtained for each of the plurality of resonance frequencies from the calculation formula. A method for locating a fault in a multi-branch cable, comprising determining an x value and determining that a cable section in which the obtained values of x match each other is a fault point.