JPS6262299B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a cable fault point measuring method that includes a novel method for detecting traveling wave pulses when detecting fault points in power cables using traveling wave pulses.

In the event of an unexpected accident with the power cable,
Several methods are known for determining the distance from the cable terminal to the accident point. These are represented by the Murray loop method and the Murray Fisher method, and include the bridge method, which determines and measures the equilibrium condition based on the conductor resistance ratio of the line, and the pulse radar method, which measures by detecting the arrival time difference of traveling wave pulses. It is broadly divided into The pulse radar method further includes a method that uses only a fault phase wire and a method that uses a healthy phase wire together, and the latter method is often used because the pulse waveform appears relatively clearly compared to the former method.

The pulse radar method, which uses a healthy phase line as well as a faulty phase line, short-circuits the far end A of the faulty phase line X and the far end B of the healthy phase line Y, as shown in FIG. 1, for example.
A high DC voltage E is applied from the near end C of the fault phase line X to its core wire.
is gradually applied to cause a discharge at the fault point F, and the first traveling wave pulse _P1 returns along the fault phase line X and arrives at the near end C, and from the fault point F of the fault phase line , the position of the fault point F is known based on the arrival time difference between the far end B of the sound phase line Y and the second traveling wave pulse P ₂ passing through the sound phase line Y and arriving at the near end D. That is, if the cable length is L, the distance from the accident point F to the far end A is l, and the pulse propagation velocity within the cable is v, then the time difference T between the first and second traveling wave pulses P ₁ and P ₂ is It is expressed as T=(L+l)/v-(L-l)/v, and the position l of the accident point is determined as l=v/2·T (v is known). Traveling wave pulse in this case
P ₁ and P ₂ are generally obtained as waveforms as shown in FIG. 2 A and B, and the two-phenomenon synchroscope 1 allows the time difference to be visually observed relatively easily.

However, there is a limit to the accuracy of measurement using the synchroscope 1, and even more accurate measurements can be made to reduce the time difference T.
In order to measure this, digital measurement using a clock pulse counting method is suitable. For example, as shown by the dotted line in FIG.
The pulses shown in Figure 2 C and D are connected respectively.
Generates a square wave synchronized with the rising positions of P ₁ and P ₂ . These square waves are input to a gate circuit 4 consisting of a flip-flop circuit, etc., and the gate is activated as shown in E, and the output pulse from the clock pulse generation circuit 5, which generates the output shown in F, is guided to a counting circuit 6. Count the number of pulses corresponding to the input clock pulses shown above. As is clear from FIG. 2, this count value corresponds to the time difference T to be sought, and its resolution is determined by the frequency of the clock pulse, and the accuracy is greatly improved compared to visual measurement using a synchroscope.

In practice, this digital measurement has a few technical problems. First, the accident phase line
Since the normal phase line Y and the normal phase line Y are usually twisted together, the induced noise P _o shown in Fig. 2B appears from the first traveling wave pulse _P1 due to the fault phase line X to the healthy phase line Y. , which makes the operation of the square wave generating circuit 3 unstable. In order to prevent the square wave generation circuit 3 from operating due to this noise sound P _o , the trigger level e _t of the circuit 3 should be set higher than the peak value of the noise sound P _o as shown in Fig. 3. However, because the rise of the second traveling wave pulse P ₂ is inclined due to the equivalent time constant of the cable, the time t ₁ is originally
Where a square wave should be generated from circuit 3,
A square wave will occur at time t ₂ , and t ₂ − _{t 1} =
The time difference T will be measured longer by Δt.
This will not be a problem if Δt is always constant, but the rising slope of pulse P ₂ , that is, the equivalent time constant of the cable, depends on the type and length of the cable.
Since it naturally differs depending on the position of the accident point F, Δt becomes an error factor and requires some kind of solution. Furthermore, an appropriate value should be determined for the trigger level e _t , and depending on its magnitude, there are problems such as affecting measurement accuracy.

The present invention solves the above-mentioned problems and digitally accurately generates the first and second traveling wave pulses P ₁ and P ₂
The purpose is to provide a cable fault point measurement method that can accurately locate the fault point F by measuring the time difference T of the cable line. The phase line is short-circuited at the far end, voltage is applied to the fault phase line to cause a discharge at the fault point, and based on the discharge, a first traveling wave pulse arrives at the near end of the fault phase line. , in a method of measuring the position of a fault point by the arrival time difference of the second traveling wave pulse arriving at the near end of a sound phase line, the first and second traveling wave pulses are used to determine the position of the fault point, etc. They are integrated by an integrating circuit with a large time constant so that the rising slope is constant regardless of the phase line, and the voltage is proportional to the voltage applied to the line in order to remove the noise of the first traveling wave pulse induced in the healthy phase line. The outputs of the integration circuits are level-discriminated based on the trigger level potential, the clock pulse gate circuit is opened by the level discrimination output based on the first traveling wave pulse, and the level discrimination output is based on the second traveling wave pulse. The method is characterized in that the gate circuit is closed and the arrival time difference between the first and second traveling wave pulses is measured by counting the clock pulses generated during the opening operation of the gate circuit.

The method according to the present invention will be explained in detail based on the embodiment shown in FIG. 4 and below.

In FIG. 4, the conditions for the fault phase line X and the healthy phase line Y are the same as those in FIG _. The voltage is divided by a pulse voltage divider circuit 10 using a capacitor voltage divider, and the DC component is voltage divided by a DC voltage divider circuit 11 using a resistor voltage divider. This is because these partial voltages are too high if the potential obtained at the near end D is used as it is, and will cause trouble in the next processing circuit. The pulse voltage divided by the pulse voltage dividing circuit 10 is sent to the integrating circuit 12, where it is subjected to integration processing. What is especially important is that this integration circuit 1
2, and the integrator circuit 1 shown in FIG.
The time constant τ ₀ of 2 is expressed as τ ₀ = R・C,
The purpose is to make this time constant τ ₀ larger than the equivalent time constant τ of the cable. As a result, the second traveling wave pulse _P2 , which is the output of the pulse voltage dividing circuit 10 shown in FIG. 6A, is integrated by the integrating circuit 12 as shown in FIG. It is determined by the time constant τ ₀ of 12 and is almost unaffected by the rising slope of the pulse P ₂ which changes as the pulse propagates in the cable. Equivalent number of points in the cable τ
As mentioned above, is determined by the type of cable, length, etc., and can be expressed as a function of length Z as τ=f(Z). In the example, the cable has the maximum time constant when the fault point F is near the near end C of the fault phase line X, and the length of the cable is
This is when it becomes 2L. Therefore, in the embodiment, it is necessary to set the number of time points τ ₀ of the integrating circuit 12 to τ ₀ >τ=f(2L), and it is necessary to set the number of time points τ ₀ to a sufficiently large value in terms of the circuit. , or it may be manually adjustable. The output of the integrating circuit 12 is superimposed on the output of the DC voltage dividing circuit 11 in a combining circuit 13, and is sent to an AC/DC separating circuit 15 via a lead wire 14.
Here, it is separated into the DC component and the integral waveform component of pulse _P2 . The integrated waveform is input to the level discrimination circuit 17 via the limiter circuit 16 that cuts the upper limit of the voltage, so that the waveform shown in FIG. 6C is input to the level discrimination circuit 17. on the other hand,
The DC component is input to the level discrimination circuit 17 via the DC generation circuit 18, and this signal determines the potential of the trigger level e _t shown in FIG. 6C. Therefore, when the level discrimination circuit 17 receives an input from the limiter circuit 16 that is equal to or higher than the trigger level e _t , the level discrimination circuit 17 outputs a signal, and this signal is used as a gate closing signal to the gate circuit 4.

The first traveling wave pulse _P1 of the fault phase line X arriving at the near end C is processed in exactly the same way,
The circuits 10 to 117 correspond to the circuits 10 to 17 for the healthy phase line Y. The time constant of the integrating circuit 112 is the same as the time constant τ ₀ of the integrating circuit 12, and the output of the DC generating circuit 118 is also the same as the output of the DC generating circuit 18.
The trigger levels e _t are set to the same potential. The counting method using the gate circuit 4, clock pulse generation circuit 5, and counting circuit 6 is the same as that explained in FIG. It will be sent to circuit 4.

Therefore, according to the measuring method according to the present invention, as shown in FIG. 4, the far ends A and B of the fault phase line If a high voltage E is gradually applied to cause a discharge at the fault point F, two traveling wave pulses are generated based on this discharge, and at the near end C there is a fault phase line X as shown in Fig. 7A. The first traveling wave pulse P ₁ returns to the near end D, and the far ends A, B,
The second traveling wave pulse P ₂ passing through the healthy phase line Y arrives, and furthermore, the induced noise P _o of the first traveling wave pulse P ₁ is also obtained at the near end D prior to the pulse P ₂ . These traveling wave pulses P ₁ , P ₂ and the noise wave P _o are subjected to integration processing as shown in C and D, respectively, by integrating circuits 112 and 12. The time constant τ ₀ of the integrating circuits 112, 12 is the maximum time constant τ = f of the cable.
(2L), so that the rising slopes of the integral waveforms of the traveling wave pulses P ₁ and P ₂ have almost the same magnitude. Therefore, the trigger level e _t input to the level discrimination circuits 117, 17
If the potentials of are the same, the level discrimination circuit 117,
The time delays for the traveling wave pulses P ₁ and P ₂ of the output of 17 are both the same value Δt, and the pulses P 1 and P ₂ are exactly the same.
The gate circuit 4 can be activated by the time difference T between the rises of _P2 . The trigger level e _t is originally
This is to remove the induced noise P _o , and if it is made larger than necessary, it may contain some errors due to slight differences in the integral waveforms of the pulses P ₁ and P ₂ , so the signal It is made to be proportional to the magnitude of the DC component, that is, the peak value of the induced noise wave P _o . It is clear from the example shown in FIG. 1 that as long as the gate circuit 4 operates for a precise time difference T, accurate measurement can be carried out by counting clock pulses using the counting circuit 6.

In reality, the circuit group 20 within the dashed-dotted line frame in FIG.
114, it is connected to a circuit group 21, which is grouped within a dashed-dotted line frame and includes level discrimination circuits 17, 117, and the like. The combining circuits 13, 113 and the AC/DC separating circuits 15, 115 are provided in order to connect both circuit groups 20, 21 with two lead wires 14, 114, thereby reducing the number of connections to the terminals. . Therefore, if you do not mind connecting the lead wires, it is possible to further increase the number of lead wires, omit the combining circuits 13, 113, etc., and transmit the traveling wave pulse signal and the DC voltage signal separately. Furthermore, the DC voltage for adjusting the trigger level e _t does not have to be detected from both the near ends C and D, but can be extracted from either one to adjust the trigger level e _t
may be determined and input to the level discrimination circuits 17 and 117. Furthermore, when using shock wave voltage as the power source applied to the fault phase line X, it is necessary to obtain the DC voltage for the trigger level e _t from the charging voltage of the power source capacitor.

The advantages of the cable fault point measuring method according to the present invention explained above are summarized as follows.

(1) Since the first and second traveling wave pulses are made to have the same rising slope by the integrating circuit, the interference of errors in time difference measurement is reduced.

(2) Since the trigger level is adjusted according to the discharge voltage at the fault point, the influence of induced noise waves can be removed, and the time delay in level discrimination can be minimized, reducing the interference of errors.

(3) By passing the traveling wave pulse through an integrating circuit,
Small reflected pulses at intermediate connection points that are troublesome to measurements can be removed.

[Brief explanation of the drawing]

Figure 1 is a block circuit diagram of the conventional pulse radar method, Figure 2 is a time chart to explain its measurement principle, and Figure 3 is a time chart to explain the detection operation of the second traveling wave pulse. Figure, 4th
The following figures show one embodiment of the method according to the present invention. FIG. 4 is a block circuit diagram thereof, FIG. 5 is a circuit diagram of an integrating circuit, and FIG. 6 is for explaining the operation of the integrating circuit, etc. FIG. 7 is a time chart for explaining the principle of the measuring method of the present invention. Symbol X is the fault phase line, Y is the healthy phase line, A and B are the far ends, C and D are the near ends, P ₁ is the first traveling wave pulse, P ₂
is the second traveling wave pulse, P _o is the induced noise wave, e _t is the trigger level potential, 4 is the gate circuit, 5 is the clock pulse generation circuit, 6 is the counting circuit, 10, 110
11, 111 are DC voltage dividing circuits, 12, 112 are integrating circuits, 14, 114 are lead wires, and 17, 117 are level discrimination circuits.

Claims (1)

[Claims] 1. In measuring fault points on cable lines,
The fault phase line and the sound phase line are short-circuited at the far end, voltage is applied to the fault phase line to cause a discharge at the fault point, and based on the discharge, the first In the method of measuring the position of the fault point by the arrival time difference between the traveling wave pulse and the second traveling wave pulse arriving at the near end of the healthy phase line, the first and second traveling wave pulses are , in order to eliminate the noise of the first traveling wave pulse induced in the healthy phase line by integrating each with an integrating circuit having a large time constant so that the rising slope is constant regardless of the position of the fault point, etc. The outputs of the integrating circuits are level-discriminated by a trigger level potential proportional to the voltage applied to the line, and the gate circuit of the clock pulse is opened by the level discrimination output based on the first traveling wave pulse. The gate circuit is closed by a level discrimination output based on pulses, and the arrival time difference between the first and second traveling wave pulses is measured by counting the clock pulses generated during the opening operation of the gate circuit. How to measure cable fault points. 2. The cable failure point measuring method according to claim 1, wherein the traveling wave pulse component and the DC component that determines the trigger level potential are transmitted through the same signal line, thereby reducing the number of terminal connections.