JPS6313372B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for locating faults in group-based two-wire wired transmission lines including bidirectional common repeater amplifiers often used in submarine cables.

Figure 1 shows a group-based two-wire wired transmission line including N repeaters, 1-1, 1-2,..., 1
-(N+1) are cables, 2-1, 2- respectively
2, . 4 is a terminal station (hereinafter referred to as station B) which transmits the high group signal 6 and receives the low group signal 5. Each repeater includes one repeater amplifier 7, two low-pass wavers 8, and two high-pass wavers 9, as shown in FIG.
It is designed so that a low group signal 5 and a high group signal 6 transmitted in opposite directions shown by 5 and 6 can be amplified by one relay amplifier 7.

It is a well-known fact that, as shown in Figure 3, if a cable failure occurs at point F of the above transmission line and signal transmission becomes impossible, station A 3 will transmit a burst-like low signal as shown in 1 in Figure 4. Group signal m ₀ (hereinafter referred to as original signal)
The relays 2-1, 2-2,
Since the harmonics of the original signal generated by the non-linear characteristics of ..., 2-M fall into the high group frequency band, the harmonics generated at each repeater become a continuous burst signal as shown in 2 in Figure 4. m ₁ , m ₂ , ..., m _M are sent back to station A 3, and the number of incoming burst signals that are sent back is the number M of repeaters existing between station A 3 and the failure point F. There is a method of detecting the location of a fault by using facts that match. This method is generally called the distortion folding method. In this case, _each of the repeaters _2-1 , _2-2 ,..., 2
- Original signal sent from station A 3 to identify M
The burst length t _a of m ₀ is t _a <2l ₀ /c seconds (l ₀ : distance between repeaters, c : propagation speed of signal traveling in the cable)
It is said that According to this method, there is no point of failure between station A 3 and repeater 2-M immediately before failure point F, and the point of failure is at cable 1-(M+1) or repeater 2-(M+1). Although it is possible to determine that there is a cable 1-(M+1) or repeater 2-(M
+1) cannot be precisely determined.

As a method for determining where the fault point is located on cable 1-(M+1), there is the following method (hereinafter referred to as the second fault location detection method), which is an improved version of the distortion folding method. (See Paper No. 1728 "A Method for Detecting the Location of Submarine Cable Faults" presented at the National Conference of the Institute of Electronics and Communication Engineers in 1981 and Patent Application No. 1976-76062). In this method, the distortion factor of a repeater generally changes by changing the terminal impedance of the repeater, and the impedance when looking from the repeater 2-M closest to the fault point in Figure 3 to the fault point side of the cable is calculated using the formula As shown by (1), it changes periodically with respect to changes in frequency, and the period is c/2l ₁ Hz, which depends on the distance l ₁ from repeater 2-M to fault point F. It takes advantage of this fact.

Z _i =1−m ²・e ^-4 〓 ^l −j・2m・e ^-2 〓 ^l sin(2βl)/1
+m ²・e ^-4 〓 ^l −2m・e ^-2 〓 ^l cos(2βl)Z ₀ (1) where Z ₀ : Cable characteristic impedance m : Signal reflection coefficient at failure point α+jβ : Cable propagation constant β :2π・/c: Signal frequency c: Signal propagation speed In other words, in this method, the burst signal _m0 shown in FIGS. 4 and 1 is sent from station A 3,
Observing the harmonic signals generated at 2-2, ..., 2-N and sent back at station A 3 is the same as the distortion folding method described above, but the burst-like signal m sent from station A 3 Making the fundamental frequency of ₀ variable,
Also, limit the harmonic signals observed at Station A 3 to only the harmonic signals generated at repeater 2-M, and pay attention to how the amplitude of the received signal changes with respect to changes in the frequency of the transmitted signal. is different from the distortion folding method described above. In other words, in the distortion folding method described above, if the frequency of the burst signal (original signal) m ₀ sent by station A 3 is continuously changed,
A burst harmonic signal m ₁ generated by a repeater other than 2-M shown in FIGS. 4 and 2 and sent back,
While the amplitudes of m ₂ ,..., m _M-1 are almost constant, the amplitude of the harmonic signal m _M generated at repeater 2-M and sent back is equal to the frequency of the original signal m ₀ . It changes periodically with a period of Δ=c/2l ₁ (Hz). Therefore, the harmonic signal sent back from repeater 2-M while changing the frequency of the original signal _m0 is
If we know the period Δ of the amplitude change of m _M , we can reversely
l ₁ can be found.

However, the second fault location detection method described above also has the following drawbacks. The reason why the impedance viewed from the repeater 2-M toward the fault point changes periodically with respect to frequency changes is that the signal to be sent from the repeater 2-M toward the fault point and the fault point F in FIG.
This is because the signals reflected and sent back mutually interfere at the output point 0 of the repeater 2-M, and until the reflected wave from the F point reaches the 0 point, the terminal impedance of the repeater 2-M is equal to the characteristic impedance of the cable like that of other repeaters, and it is not until the reflected wave from point F reaches point 0 that repeater 2-M
The terminal impedance of the cable is different from the characteristic impedance of the cable. Therefore, for a while after the original signal m ₀ sent by station A 3 reaches the repeater 2-M, the amplitude of the harmonic signal is the same as in the case where no disturbance occurs, and the original signal m ₀ is F
The amplitude of the harmonic signal changes only after it is reflected at a point and reaches the zero point again. That is, the amplitude waveform of the harmonic signal generated by the repeater 2-M consists of two parts 3-1 and 3-2, as shown in 3 of FIG. 4 with the time axis enlarged. 3-1 is the harmonic signal before the original signal is reflected at point F and reaches point 0 again,
The part 3-2 is a harmonic signal after the reflection of the original signal reaches the 0 point. The burst length of the original signal
If t _a and the distance from repeater 2-M to the failure point is l ₁ , the time lengths t _b and t _c of 3-1 and 3-2 are t _b = 2l ₁ /c seconds, t _c = t, respectively. _a −2l ₁ /c seconds.

In the second fault location method, repeater 2-M
Part 3-2 is effective in knowing the distance from the point to the point of failure. In actual submarine cable relay systems, it is often necessary to make some relay sections, such as the relay section where an ocean section equalizer is inserted, considerably shorter than the general relay section l ₀ , and also In order to separate the harmonic burst signals sent back from the repeater, the burst length t _a of the original signal is
needs to be much shorter than 2l ₀ /c seconds. In this case, "3-2 which is an effective signal for fault location detection"
_In order _for the portion _of There is a theoretical restriction that "limited to the section near the repeater."
When considering the feasibility of the measuring device, it goes without saying that the range in which fault positions can be detected becomes narrower.
The above are the drawbacks of the second fault location detection method.

The present invention, similar to the second fault location detection method described above, has the advantage that the distortion factor of the repeater depends on the value of the terminal impedance, and that the fault point side of the cable is viewed from the repeater 2-M closest to the fault point. This method is based on a cable fault location detection method that utilizes the fact that impedance changes periodically in response to changes in frequency. This is what we provide.

The present invention will be explained in detail below.

In the present invention, similarly to the second fault location detection method described above, a burst original signal whose fundamental frequency is in the low group frequency band is sent from station A 3, and the repeater 2
The harmonic burst signal generated at −M is received at station A 3, but one feature is that the burst length of the original signal sent from station A 3 is 2 (l ₀ + l ₁ )/c seconds or longer. shall be. In the following, an example will be explained in which the burst length of the original signal is longer than the time required for the signal to travel the distance from station A 3 to failure point F, 2 (M·l ₀ +l ₁ )/c seconds.

Figure 5 shows the original signal 1 sent from station A, the harmonic burst signal 2 sent back from each repeater to station A,
It also shows the relative time relationship of the amplitude waveform 3 of the composite wave of harmonic burst signals sent back from each repeater. The original signal 1 is a burst signal whose fundamental frequency belongs to the low group frequency band, and its burst length T is longer than 2(M·l ₀ +l ₁ )/c seconds. When the original signal 1 is amplified by the first repeater 2-1, the original signal is amplified at a level such that a burst signal whose frequency component is a harmonic of the original signal is generated due to the nonlinearity of the repeater amplifier. If the burst signal generated at this time has a frequency component in the high group frequency band, this component will be transmitted in the direction of station A 3, opposite to the transmission direction of the original signal, and station A 3 will transmit the original signal. It reaches station A 3 after a time of 2l ₀ /c seconds has elapsed since it was sent. Repeaters 2-2, 2 other than 2-1
-3,...,2-M also generate the above-mentioned harmonic burst signals one after another during amplification of the original signal and are sent back to station A 3, but the time when these arrive at station A 3 A delay of 2l ₀ /c seconds occurs in each case. In other words, as shown in 2 in FIG. 5, the harmonic burst signal m ₁ generated at the first repeater 2-1 is generated after 2l ₀ /c seconds have elapsed since the time τ _B when station A 3 started transmitting the original signal. The signal then arrives at station A 3 and continues for the same time T as the burst length of the original signal. The harmonic burst signal m ₂ generated in the second repeater 2-2 is generated after 4l ₀ /c seconds have elapsed since τ _B , that is, the harmonic burst signal m 2 generated in the second repeater 2-2 is further 2l ₀ than the harmonic burst signal from the first repeater 2-1. Arrives at station A 3 with a delay of /c seconds and continues for T. The harmonic burst signals generated by other repeaters are also
It arrives at station A 3 with a delay of 2l ₀ /c seconds. The harmonic burst signal that finally arrives at station A 3 is generated at the repeater 2-M closest to the fault point, and since the original signal does not reach the repeater far from the fault point, it is transmitted from that repeater. There is no possibility that harmonic burst signals will be sent back.

The harmonic burst signal generated at 2-M is from τ _B
After 2M·l ₀ /c seconds have elapsed, it begins to arrive at station A 3. The intensity of this harmonic burst signal is shown in FIG.
As shown in m _M , the apparent termination impedance of the repeater is the same as the characteristic impedance of the cable during the first 2l ₁ /c seconds, so the distortion when the repeater is terminated with the characteristic impedance of the cable is However, after only 2l ₁ /c seconds have elapsed, the terminal impedance of the repeater becomes the value given by Equation 1, which is different from before. Become.

Since the harmonic burst signals sent back from each repeater mentioned above all have the same frequency components, station A3 cannot separate them, and receives a composite of these signals. I will do it. That is, the amplitude of the signal received by station A 3 has a waveform that changes over time, obtained by combining the two signals, as shown in 3 in FIG. What should be noted here is that the signal received by station A 3 is a composite wave of harmonic burst signals sent back from multiple repeaters, but of these, station A 3 stops transmitting the original signal. During the period of 2l ₀ /c seconds starting from the time τ _E when 2(M-1)l ₀ /c seconds have elapsed, only the harmonic signal from repeater 2-M is received, and this In the received signal during the time period, there is an invalid signal that is not affected by the signal reflection at the fault point F (m First part shown in _M
2l ₁ /c seconds), and the entire received signal during this time period is affected by the signal reflection at the failure point F.

Therefore, if the signal in this time period is extracted by some method, the fault location can be detected in exactly the same manner as the second fault location detection method described above.

That is, the basic configuration of the fault position detector according to the present invention is as shown in 10 of FIG. In FIG. 6, numeral 11 is a transmitter having a function of generating a burst original signal, and transmits a burst signal having a fundamental frequency _A and a burst length T to a submarine cable through a hybrid 12. Here, the frequency _A needs to be variable, and the burst length T needs to be longer than 2(l ₀ +l ₁ )/c seconds. When the original signal is sent from the transmitter 11, a composite wave of burst signals with a fundamental frequency of 2 _A generated by many repeaters along the cable is sent back, and this is received by the receiver via the hybrid 12. do. The receiving section includes, for example, a gate circuit 13 and a CRT terminal 14 for waveform observation. In the receiving section, the gate circuit 13 uses the _gate circuit 13 to transmit the signal for only 2l 0 /c seconds from the time when 2(M-1)l ₀ /c seconds have elapsed to the time when 2Ml ₀ /c seconds have elapsed, as measured from the transmission end time _τ E of the original signal. The gate is opened, a signal only for this time period is taken out, and the signal strength is measured by the CRT terminal 14.
Included in the extracted signal is repeater 2-M
As mentioned above, it is only the harmonic signals generated from the . At this time, when the fundamental frequency _A of the original signal sent from the transmitter 11 is continuously changed, the strength of the received signal changes periodically, so the period of change is read. If this period is ΔHz, it can be seen that the distance l ₁ from the repeater 2-M to the failure point F is l ₁ =c/2Δ.

The above explanation took the equipment used at Station A as an example, so the fundamental frequency of the original signal sent from the landing station belonged to the low group frequency band, and the received signal belonged to the high group frequency band. . However, when the present invention is used at station B, at least two high group signals with different frequencies are simultaneously sent from the fault location detector according to the present invention, and the mixture of these signals generated at the repeater near the fault point is eliminated. By receiving the low frequency band component of the modulated wave at the receiving section of the detector, it is possible to know the location of the fault in exactly the same way as in the device for station A described in detail above.

As described in detail above, the present invention is a cable fault location detection method based on a similar operating principle to the second fault location detection method already described as publicly known. This has the advantage that it is possible to detect the position regardless of the distance between them.

[Brief explanation of the drawing]

Figure 1 is a block diagram of a two-wire wired transmission line by group, Figure 2 is a diagram showing the circuit configuration of a repeater with a bidirectional common amplifier included in Figure 1, and Figure 3 is a diagram of a group with a failure point in the middle of the cable. A block diagram of another two-wire wired transmission line, FIG. 4 is a diagram for explaining the relationship between transmitted signals and received signals by a known fault location detection method, and FIG. 5 is a diagram for explaining the relationship between transmitted signals and received signals by the fault location detection method according to the present invention. FIG. 6, which is a diagram for explaining the relationship between signals, is a block diagram showing a specific example of a detector used in the present invention. 1-1, 1-2,..., 1-(N+1), 1-(M
+1)...Cable, 2-1, 2-2...2-N,
2-M...Repeater, 3, 4...Terminal station, 5...Low group signal, 6...High group signal, 7...Relay amplifier, 8...
...Low pass wave generator, 9...High pass wave generator, 10
... Fault position detector, 11 ... Transmission section, 12 ...
Hybrid, 13... Gate circuit, 14...
CRT terminal, F...point of failure, O...repeater 2-M
output point.

Claims (1)

[Claims] 1 A burst signal having at least one fundamental frequency component is sent to the transmission line from one end of a grouped two-wire wired transmission line, and at least the burst signal is amplified by a relay amplifier near the cable fault point. phenomenon in which newly generated frequency components due to the nonlinearity of the relay amplifier are sent back to the end of the transmission line when
Furthermore, by utilizing the phenomenon that when the fundamental frequency of the burst signal is changed, the intensity of the frequency component newly generated in the relay amplifier near the failure point changes, the frequency component between the relay amplifier and the failure point is changed. In the fault location detection method, the burst length of the burst signal sent from the end of the transmission line is determined by the distance between two adjacent repeaters and between the fault point and the nearest relay to the fault point. It is set to be equal to or longer than the time required for a signal to propagate over twice the sum of the distances between the transmitter and the transmitter, and furthermore, the burst signal is A signal that arrives at the end of the transmission line after the time when twice the time required for an electrical signal to propagate between the end of the transmission line and the second repeater from the failure point has elapsed from the transmission stop time. A method for detecting a cable fault location, comprising extracting the fault point and measuring the distance between the fault point and a repeater closest to the fault point.