JPS6313614B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for locating faults in grouped two-wire wired transmission lines having bidirectional common repeater amplifiers, which are often used in submarine cables.

Figure 1 shows _the configuration _of a group-based two-wire wired transmission line including N repeaters.
…, 1 _(N+1) are cables, 2 ₍₁₎ , 2 ₍₂₎ , …,
2 _(N) are repeaters, and 3 is an end that sends out a low group frequency band signal 5 (hereinafter referred to as "low group signal") and receives a high group frequency band signal 6 (hereinafter referred to as "high group signal"). station (hereinafter referred to as "station A"), 4 is a terminal station (hereinafter referred to as "station B") that transmits the high group signal 6 and receives the low group signal 5. Each repeater 2 ₍₁₎ , 2 _(2
) ,...,2 _(N) each include one repeater amplifier 7, two low-pass wavers 8, and two high-pass wavers 9, as shown in Fig. 2, and transmit in opposite directions. The low group signal 5 and the high group signal 6 to be transmitted can be simultaneously amplified by one relay amplifier 7.

One of the methods for detecting the position of a fault occurring in such a submarine cable transmission line is a known method called a distortion return test (hereinafter referred to as a "simple distortion return test") shown in FIG. As shown in the figure, when station A 3 sends out a burst signal m ₀ whose carrier frequency belongs to the low frequency band, nonlinear distorted waves are generated from each repeater due to the nonlinearity of the amplification characteristics of the repeater amplifier 7. A part of it falls into the high group frequency band, and a continuous burst signal m ₁ , m 2 , ... m _M corresponding to the repeaters 2 ₍₁₎ , 2 _{(2) ,} ..., 2 _(M) is generated. It is then sent back to station A 3. By using the fact that the number M of reversely transmitted burst signals matches the number M of repeaters existing between station A 3 and the point of failure (hereinafter referred to as the point of failure) F, the point of failure can be found. Cable 1 _(M+1)
It is determined that the Fault point cable 1 _(M+1)
The following method (hereinafter referred to as the "conventional frequency scanning distortion aliasing test") is an improved method of the simple distortion aliasing method as a method for detecting where the strain is located. (See paper 1728 “A method for detecting the location of submarine cable faults” and patent application No. 76062-1983) presented at the general national conference of the academic society.

FIG. 4 is an example of a method for detecting fault location using a conventional frequency scanning distortion valve test. This method is based on the fact that the distortion factor of the repeater changes depending on the change in the terminal impedance, and that the impedance when looking from repeater 2 _(M) nearest the fault point F in Figure 4 to the fault point F side of the cable is calculated using the formula (1), and this impedance is expressed by the repeater 2 on the frequency axis.
_(M) to the fault point F at a frequency interval of c/2l ₁ (Hz) (where c is the signal propagation speed in the cable) depending on the distance l ₁ (hereinafter referred to as "fault point distance"). It takes advantage of periodic changes.

Z _i =1−m ²・e ^-4dl −j・2m・e ^-2dl sin(2β
l)/1+m ²・e ^-4dl −2m・e ^2dl cos (2βl) Z ₀ (1) where Z ₀ : Characteristic impedance of cable (Ω) m : Reflection coefficient of signal at failure point α + jβ : Propagation constant of cable α: Attenuation constant β: 2π・/c: Phase constant: Signal frequency (Hz) c: Signal propagation _velocity in the cable (m/s) The non-linear distorted wave m _M sent out from station 3, generated at repeater 2 _(M) nearest to the failure point F, and sent back is received at station A 3. At this time, the sent out burst-like signal m ₀ The carrier frequency of M is changed, and the amplitude change period Δ of the received distorted wave m _M on the frequency axis is investigated. Since the amplitude change period Δ (Hz) of the nonlinear distorted wave m _M generated at repeater 2 _(M ) and the fault point distance l ₁ (m) are related by equation (2),
If the amplitude change period Δ is known, l ₁ can be obtained by substituting it into equation (2).

l ₁ = c/2Δ (2) where c is the signal propagation speed in the cable (m/
s) However, the fault location detection by conventional frequency scanning distortion folding test has the following drawbacks. Repeater 2 _(M)
In Fig. 4, the distorted wave amplitude from the repeater 2 changes periodically according to the frequency change of the transmitted signal.
Signal 10 trying to be sent from _(M) toward failure point F and signal 1 reflected at failure point F and sent back
0' interfere with each other at the output point O of the repeater 2 _(M) closest to the fault point F, so that the terminal impedance of the repeater, that is, the input impedance of the faulty cable, becomes frequency dependent as shown in equation (1). This is because the operating level of the signal inside the repeater changes accordingly. Therefore, until the reflected wave 10' from the failure point F reaches point O, the terminal impedance of repeater 2 _(M) is equal to the characteristic impedance of the infinitely long cable and has almost no frequency dependence. The terminal impedance of the repeater 2 _(M) becomes different from the characteristic impedance of the cable only after the reflected wave 10' from the failure point F reaches the O point. Therefore, for a while after the signal M ₀ sent out by station A 3 reaches repeater 2 _(M) , the amplitude of the nonlinear distorted wave is the same as in the case without interference, and the sent signal m ₀ is reflected at the failure point F and reaches the output point O again, and the amplitude of the nonlinear distorted wave shows frequency dependence. That is, the amplitude waveform of the nonlinear distorted wave generated at repeater 2 _(M) consists of two parts, and as shown enlarged as m' _M in FIG. The transmitted signal is reflected at the failure point F and returns to the output point O.
is the nonlinear distorted waveform before reaching the output point O, and is the nonlinear distorted waveform after the reflected wave 10' of the transmitted signal reaches the output point O. Let t ₀ be the burst length of the outgoing signal m ₀ , and let the distance from repeater 2 _(M) to the fault point F be
When l ₁ , the time lengths ta and t _b of and are t _a =2l ₁ /c _{and t b =} t ₀ -2l ₁ /c, respectively.

It is the part that is effective in determining the distance to the failure point F using equation (2). In actual submarine cable relay systems, it is often necessary to make some relay sections, such as the relay section where an equalizer is inserted, shorter than the general relay section _l0 , and also In order to separate the burst-shaped distorted waves sent back from each other on the time axis, the burst length t ₀ of the transmitted signal needs to be much shorter than 2l ₀ /c. In this case, the part of the signal that is effective for fault location detection is the distorted wave m _M emitted from repeater 2 _(M).
In order for the fault to exist in the relay, the condition l ₁ <c・t ₀ /2 must be satisfied, so the detectable fault position range is within c・t ₀ /2 from repeater 2 _(M). There is a theoretical restriction that the distance is limited to .

The present invention provides a method for locating cable faults that can overcome the above-mentioned drawbacks of conventional frequency scanning distortion folding tests.

The present invention will be explained in detail below with reference to the drawings.

In the present invention, as in the conventional frequency scanning distortion aliasing test, a signal is sent from station A 3 at one end of the transmission line, and a nonlinear distorted wave generated at repeater 2 _(M) closest to the fault point F is received. and measure its amplitude. However _, in the present invention, as shown in _FIG .
and a continuous wave (second signal) 12 which also belongs to the low group frequency band but has a frequency ₂ different from the carrier wave. At this time, repeaters 2 ₍₁₎ , 2 ₍₂₎ ,...
2 _(M) , when the two sending signals 11 and 12 are applied simultaneously, intermodulation distorted waves m ₁ , m ₂ ,..., m _M having a frequency of ( ₁ + ₂ ) are generated, and these distorted waves are Both have the same burst length t ₀ as the transmission signal 11. By appropriately selecting frequencies ₁ and ₂ of the sending signals, the distorted wave frequency ( ₁ + ₂ ) becomes a frequency in the high group band, and the distorted wave burst from each repeater is sent back to station A3.

In this case, the continuous wave 12 of frequency ₂ is relayed by a cable and a repeater and is constantly transmitted to the failure point F, where it is reflected and reaches the repeater group 2 _(M) again. Therefore, repeater 2 _(M) and fault cable 1 _(M+1)
At the connection point O, the continuous wave 12 directly propagates the wave 12' and the reflected wave 1 from the failure point F.
2″ will always interfere with each other, so
The input impedance of cable 1 _(M+1) for continuous wave 12 always takes the value expressed by the above equation (1) and fluctuates at a frequency interval of c/2l ₁ determined by the fault point distance l ₁ . becomes. Accordingly, the signal operation level inside the repeater 2 _(M) for the continuous wave 12 also has frequency dependence of the same period. Therefore, the amplitude of the intermodulation distortion wave m _M generated in repeater 2 _(M) by signals 11 and 12 transmitted from station A 3 also changes periodically as the frequency of signal 12 changes. I will do it.

In other words, if you change the frequency of the continuous wave signal (second signal) 12 while keeping the carrier frequency of the burst-like first signal 11 fixed among the two signals sent from station A, the frequency of the continuous wave signal (second signal ₎ 12 is changed. Generated cross-modulation wave m _M
Unlike the case of the conventional distortion aliasing test, the amplitude of the received wave burst changes periodically at frequency intervals of c/2l ₁ (Hz) for all time periods from the rise to the end. At station A 3, the cross modulation wave corresponding to the change in frequency ₂ of the continuous wave signal 12
By detecting the fluctuation period of m _M and substituting it into equation (2), the fault point distance l ₁ can be determined.

FIG. 6 shows an embodiment of the present invention. In the figure, 13 indicates a continuous wave signal 12 and a burst signal 11.
It is a transmitter that has the function of simultaneously generating
The frequency ₂ of the signal 12 is variable, and the carrier frequency ₁ of the signal 11 is fixed. When signals 11 and 12 are sent from 13, a burst-like cross-modulation wave with a carrier frequency of ( ₁ + ₂ ) is generated at M repeaters in the middle of the cable, and the string is It is then sent back to station A 3. This is received via the hybrid 14 by a receiving section comprising, for example, a switch circuit 15 and a level meter 16. The switch circuit 15 is for extracting only the distorted wave m _M emitted from the repeater 2 (M) nearest to the failure point F from the received burst sequence, and the level meter 16 is for extracting the distorted wave m M emitted from the repeater 2 _(M) nearest to the failure point F. It is used to measure the amplitude of the wave m _M. The fault point distance can be calculated by measuring the amplitude of the extracted distorted wave while changing the frequency of the sending signal 12, finding its fluctuation period Δ, and substituting it into equation (2) for processing.

In the above explanation, the device used at station A 3 is taken as an example, and the frequency or carrier frequency of the signal sent from the terminal station both belong to the low group frequency band, and the carrier wave of the received distorted wave belongs to the high group frequency band. It was a case in point. When the present invention is used in station O 4, frequency ₂ of the continuous wave signal and carrier frequency ₁ of the burst signal are both selected to belong to the high group frequency band as transmission signals, and these are simultaneously transmitted from station O. , among the intermodulation waves generated by these signals at the repeater closest to the point of failure, the frequency components of ( ₁ - ₂ ) or ( ₂ - ₁ ) belonging to the low group frequency band are received by the receiving section of Station B. By doing so, the distance to the point of failure can be detected in exactly the same way as the device for station A detailed above.

Furthermore, in the above explanation, for convenience, it was assumed that the transmission signal applied from one end of the transmission line consists of a continuous wave signal having a unique frequency component and a burst signal having a unique carrier frequency component. second signal) and burst signal (first signal)
Either or both of them have multiple frequency components or carrier frequency components, and by changing the frequency of one frequency component in the continuous wave signal, the frequency of other frequency components in the continuous wave signal and all of the burst signals can be changed. By fixing the frequency of the carrier frequency component of these signals and measuring the fluctuation period of the burst-like cross-modulation wave that is sent back to the terminal station that sent the signal among the cross-modulation waves of these signals, it is possible to Similarly, it is possible to detect the distance to the fault point.

Next, other embodiments of the present invention will be described. Instead of the continuous wave (second signal) in the above explanation, the time required for the signal to propagate back and forth through one repeater section length l ₀ is 2l ₀ /
A second burst signal having a burst length longer than burst signal 11 by at least the length of burst signal 11 is
Even if it is used as a signal, it is possible to detect the fault position in exactly the same way. That is, as shown in FIG. 7, from station A 3, a burst signal (second signal) 12a having a bust signal longer than the time required for the signal to propagate back and forth through one relay section length _l0 , and a signal The time required for round trip propagation through one relay section length l ₀
A burst signal (first signal) 11 having a burst length shorter than 2l ₀ /c is transmitted. However, in this case, the transmission start time of signal 11 is
The failure point distance l ₁ from the transmission start time of a is the signal 12a.
It is necessary that the signal 12a be delayed by the time required for round-trip propagation, 2l ₁ /c or more, and must be before the transmission stop time of the signal 12a. This causes the signal 12a
If the signal 11 and the signal 12a are simultaneously applied to the repeater during the time when the reflected wave 12a'' from the fault point F reaches the repeater 2 _(M) closest to the fault point, the repeater A cross-modulated wave of both signals is generated.The amplitude of this cross-modulated wave m _M fluctuates periodically at fixed frequency intervals according to the frequency change of the sending signal 12a, as in the case of using the continuous wave described above. becomes.
Note that the shortest time length of the burst signal 11 is determined depending on the time required to detect the cross-modulation wave.

Next, an example of the configuration of the cable fault position detection device according to the present invention shown in FIG. 8 will be described. In this embodiment, switch circuits 17, 17 are provided at the outputs of the oscillators 13, 13.
, 17, the burst length and transmission timing of the transmission signal can be arbitrarily adjusted. Repeat cycle setting circuit 19, sending signal 11
The operation timings of the delay time setting circuit 20, the burst length setting circuit 21 for the sending signal, the delay time setting circuit 22 for extracting received burst waves, and the extraction time width setting circuit 23 are determined by the clock pulse 24 generated by the clock pulse generating circuit 18. Determined as a standard.

The repetition period setting circuit 19 issues a transmission start signal every set repetition period. This signal is applied to the burst length setting circuit 21 and makes the switch circuit 17 conductive for only the set time length. This converts the continuous wave from the oscillator 13 into the transmission signal 12 having a desired burst length.
On the other hand, the transmission start signal generated by the repetition period setting circuit 19 is applied to the switch circuit 17 via the delay time setting circuit 20 and the burst length setting circuit 21. The conduction is initiated with a delay of time, and the conduction is continued for the desired length of time. Thereby, the continuous wave from the oscillator 13 is converted into the transmission signal 11 having the desired delay time and desired burst length. These sending signals 11,
12 is sent to the submarine cable system via the hybrid 14. The distorted waves generated in each relay amplifier 2 by this sending signal are transmitted in the opposite direction and reach the switch circuit 15 via the hybrid 14.

Furthermore, the switch circuit 15 extracts only the distorted wave m _M from the relay amplifier 2 _(M) closest to the point of failure, and the level meter 16 indicates the level of the distorted wave. Note that the switch circuit 15 starts conduction with a delay of the time set by the delay time setting circuit 22 for extracting the received burst wave than the transmission start signal generated by the repetition period setting circuit 19, and sets the extraction time width of the received burst wave. The conduction continues for the set time of the setting circuit 23.

Furthermore, in this embodiment, the switch circuit 17
It is obvious that the fault position can be detected in the same manner as in FIGS. 5 and 6 described above by controlling the circuit so that it is always in a conductive state.

The repetition period setting circuit 19 used in FIG. 8 includes, for example, as shown in FIG. 9a, a counter 19-1 that counts the clock pulses 24, and a register 19-1 that stores a desired value in advance.
3. The count value of counter 19-1 is stored in register 19-
It is composed of a comparator 19-2 that outputs a pulse when the content of 3 matches. Counter 19-
The count value of 1 is reset by the output pulse of comparator 19-2.

Further, the delay time setting circuits 20 and 22 are shown in FIG.
This is realized by a circuit configuration similar to that shown in FIG. 9b. In this case, the start signal resets the contents of the counter 201 and starts counting.

Furthermore, the burst length setting circuits 21 and 23
As shown in FIG. 9C, a flip-flop 21-4 is added to the circuit of FIG. 9B. The flip-flop 21-4 is set by the start signal and reset by the output pulse of the comparator 21-2, and a burst length setting signal is obtained at its output.

As mentioned above, conventional frequency scanning distortion aliasing tests have the drawback of limiting the detectable fault distance, but one way to overcome this drawback is to use signals with relatively long burst lengths. A method has been proposed (IEICE Communication Systems Study Group Material CS80-118 "Fault location search method using load resistance dependence of submarine repeater nonlinear distortion")
(Refer to August 22, 1980 or Japanese Patent Application No. 54-37644).
This is a method based on the premise that nonlinear distortion waves do not occur beyond the point of failure, and it is a method that assumes that nonlinear distortion waves do not occur beyond the point of failure. It may not be possible to detect the fault position for a fault in a half-broken state, such as when only the outer conductor of the cable is cut, where the linear strain is folded back. This method also had the disadvantage that faulty relay sections could not be identified using the same method as the simple distortion loopback test shown in FIG.

In contrast, in the present invention, a composite signal of a continuous wave signal (second signal) and a burst signal (first signal) is used as the transmission signal, and the continuous wave signal is used to transmit signals to the repeater near the point of failure. While the signal operating level within the repeater is always subject to the influence of reflected waves from the point of failure, on the other hand, the desired cross-modulation distortion wave is generated only when a burst-like signal is applied to the same repeater. Therefore, it is considered that the intermodulation distorted wave bursts from each repeater do not overlap each other on the time axis, and that the distorted waves from the repeater closest to the point of failure fluctuate at frequency intervals corresponding to the distance to the point of failure. . That is, in the present invention, by setting the burst length of the burst-like transmission signal to be shorter than the time required for the signal to propagate round-trip through one repeater section, the distorted waves from each repeater do not overlap with each other. This method has the following advantages over known methods because it is possible to detect the distance to a fault point.

A single test device can simultaneously identify the fault occurrence section using a simple distortion aliasing test and measure the fault point distance using a frequency scanning distortion aliasing test.

It is also possible to measure the distance to a fault point for a fault in which a nonlinear distorted wave from the fault point itself or a nonlinear distorted wave from a repeater located beyond the fault point is returned.

Since the burst length of the transmitted burst signal can be fixed to a constant value regardless of the distance to the fault point, the test equipment and operation can be simplified.

Furthermore, although the above advantages have been explained assuming that the burst length of the transmitted signal is fixed, for example, by making the burst length of the transmitted signal arbitrarily adjustable using the switch circuits 17, 17 shown in FIG.
It is possible to provide one strain folding tester with the following multiple functions.

(1) A simple distortion folding test is possible by adjusting the burst length of the transmitted signal 12a to be shorter than the time required for the signal to propagate back and forth through one relay section.

(2) Conventional frequency scanning distortion folding tests are possible by adjusting the burst lengths of both outgoing signals 12a and 11 to be longer than the time required for the signals to propagate back and forth one repeater length.

(3) Adjust the burst length of the outgoing signal 11 to be shorter than the time required for the signal to propagate back and forth through one repeater section length, and make the outgoing signal 12a a continuous wave (equivalent to Figures 5 and 6) or a sufficiently long burst length. By using a burst wave with a burst length, a frequency scanning distortion folding test according to the present invention is possible.

[Brief explanation of the drawing]

Figure 1 is a system diagram showing the configuration of two-wire bidirectional transmission lines by group, Figure 2 is a block diagram showing the main circuit configuration of a repeater with a bidirectional common amplifier included in Figure 1, and Figure 3. 4 is a system diagram for explaining a fault location detection method using a known simple distortion aliasing test, FIG. 4 is a system diagram for explaining a fault location detection method using a known conventional frequency scanning distortion aliasing test, and FIGS. FIG. 6 is a system diagram for explaining the fault location detection method according to the present invention and a block diagram showing one embodiment of the present invention, FIG. 7 is a system diagram showing another embodiment of the present invention, and FIG. A block diagram showing an example of the configuration of a terminal device used in the present invention. FIGS. 9a, b, and c are block diagrams showing a specific example of a circuit used in the terminal device shown in FIG. 8. 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 device, 9...High-pass wave device,
10...Signal sent from the repeater closest to the point of failure, 10'...Signal reflected at the point of failure, 11
... Burst-shaped transmission signal, 12... Continuous wave transmission signal, 12a... Burst-shaped transmission signal used instead of continuous wave, 13... Transmission section used in the present invention, 14... Hybrid, 15... Switch circuit for receiving burst extraction, 16...Level meter, 17...Switch circuit for sending burst waveform formation, 18...Clock pulse generation circuit, 19...Repetition cycle setting circuit, 19-
1...Counter, 19-2...Comparator, 19-
3...Register, 20...Delay time setting circuit for sending signal 11, 20-1...Counter, 20-2...Comparator, 20-3...Register, 21...Sending signal burst length setting circuit, 21-1...Counter, 21-
2...Comparator, 21-3...Register, 21-
4...Flip-flop, 22...Delay time setting circuit for receiving burst wave extraction, 23...Receiving burst wave extraction time width setting circuit.

Claims (1)

[Claims] 1. When a cable failure occurs in a grouped two-wire bidirectional wired transmission line that includes at least one bidirectional common relay amplifier and forms multiple relay sections, the transmission line is sent from one end of the transmission line to the transmission line. When the transmitted signal passes through a relay amplifier near the point of occurrence of the fault, the intensity of the nonlinear distorted wave newly generated due to the nonlinear amplification characteristics of the relay amplifier and sent back to the end of the transmission line increases. Using a phenomenon that changes periodically according to the frequency change of the transmitted signal, detecting the cable length between the relay amplifier closest to the point of occurrence of the fault and the point of occurrence of the fault based on the period of variation in the distorted wave intensity. In the method, the transmission signal to the transmission path has at least one first carrier frequency component and has a time length shorter than the time required for the signal to propagate round-trip through one of the plurality of relay sections. a burst-like first signal having at least one second frequency component different from the first carrier frequency and having a time length longer than the time required for the signal to propagate back and forth through the repeater section; 2, and transmits the first signal to the repeater during the time when the reflected wave of the second signal from the point of occurrence of the fault arrives at the repeater closest to the point of occurrence of the fault. The time relationship between the first signal and the second signal is determined such that the second signal is applied simultaneously, and the second signal is included in the second signal as a frequency change of the transmitted signal. A cable fault location detection method characterized in that only the carrier frequency of the cable is changed.