JPH02259477A - Detection of fault position for submarine optical fiber cable - Google Patents

Abstract

PURPOSE: To detect the position of the failure of a repeating communication cable containing the surge protective device of a repeater by measuring the resistance of the cable by setting the protective device in a conducting state in a lowresistance state by eliminating normal power supply from the end of the cable. CONSTITUTION: The resistance of a repeating communication cable is measured at the terminal of an electrical conductor in the cable by effectively setting the surge protective device of a repeater in a conducting state in a low- resistance state by eliminating normal power supply from the end of the cable and impressing a current modulated to the electrical conductor at a terminal having a polarity and amplitude sufficient to reduce the effect of the polarity when a failure occurs. Therefore, the position of the failure of the cable including the surge protective device can be detected.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for locating faults in relayed submarine communication cables, particularly cables incorporating optical fibers as information transmission media.

Shallow Water 1 For example, submarine cables in the ocean on the continental shelf are damaged by fishing trawlers, ship anchors, etc. In the case of optical fiber relayed cables, it is not possible to use reflectometer techniques to locate fiber faults that exist beyond the first repeater.

At least for non-optical terrestrial cables, developed techniques include so-called "loopback" devices in repeaters that allow electrical resistance measurements to be made in a continuous section of the cable. However, while optical loopbacks performed electrically with regenerators are used for monitoring purposes, fault location loopbacks are
Not used in submarine fiber optic systems.

The cable is normally energized with a short circuit to the sea, so that if the fiber is buried, the fault can be detected by repeater optical monitoring methods, especially if the cable is buried. can be positioned closer to the
It is important to avoid repairing more than one cable in the same section, which is required when reflectometer methods are used to locate faults within a section. If, as sometimes happens, the cable has a shunt fault but the optical fiber remains unbroken, mere low frequency methods such as "electrode" and quasi-DC resistance methods can locate the fault: a good resistance measurement can save valuable ship time on "electrodeization".

Repeaters for submarine cables commonly incorporate surge protection devices, typically semiconductor diodes that conduct in response to power surges, thus allowing power surges to bypass the repeater circuitry.

According to the present invention, the repeater includes a surge protector to protect the power supply and signal repeater circuits from power surges, and a method for detecting the fault location of a relay communication cable, wherein the repeater disconnects the normal power supply from the end of the cable. removing and applying a modulated current to the electrical conductor at the terminals of sufficient polarity and amplitude to effectively conduct the repeater's surge protector in a low resistance state and at the same time reduce polarity effects in the event of a fault. , a method is provided that includes making a resistance measurement at a terminal of an electrical conductor within a cable.

Applying a current of appropriate amplitude and polarity to forward bias the semiconductor diodes of the embodiment submarine repeater improves conduction. Since the diode is normally in avalanche mode,
In the forward direction, normal repeater circuits do not work. Typically, a current of 100mA or more turns the surge protection diode needle "on" and provides an effective DC path through the repeater. A very low frequency modulation is applied to the 100mA current. The modulation is below 30Hz and is typically only 1/2-1H2. At this low level of modulation, it is possible to make DC resistance measurements of the cable from terminals that include an effective DC bus passing through the repeater as part of the cable. The measured resistance is the slope of the voltage/current curve over a range that distributes stable direct current, so low current effects (eg polarization effects) are avoided. The DC resistance of the electrical conductor of a submarine optical fiber cable is approximately 1 ohm/
It should be k. The DC resistance of the bus through the repeater should be low compared to the resistance of the cable.

When performing DC resistance measurements, for example using an Owen Bridge, it should be noted that failures in submarine cables are usually not short circuits or circuits. In fact, the intrusion of seawater into a damaged cable causes a resistive state due to conduction of seawater, etc.

This must be taken into account when calculating the location of the fault from DC resistance measurements. However, at the high values of DC allowed by this method, the fault resistance is reduced to a minimum.

The input impedance of the short circuit cable is: R + j X - Zo tanh7d S where Zo - characteristic impedance γ - propagation constant d - short circuit length.

At very low frequencies, γ is small, which allows us to expand Zotanhγd in a power series:

R + j [R and C are known exactly, but is inaccurate. ] Using the above identity, paying attention to R+ J W L = Z oγ, we obtain the following equation: R, + jx, −(R+jwL) d[1i/3
(R+JwL)jwcd2+ /15[(R+jwL
)jwc] 2d' ・] Focusing on the real part of this equation,
If we find R8 and ignore the count term, we get the following.

+215(w2 LC) s' ] At sufficiently low frequencies (i.e., sufficiently short lengths), the and C terms become:
With a small modification, even after some calculations, the equation for d measured Rs can be solved. The magnitude of the correction term affects the accuracy of the measurement. For example, at a frequency of 1/2 Hz, R-0,658 ohm/- C = 0.192 μF/Noodle L-411H/& d-7001 - 2/15 (14cR) d--5,04x1
0-32/3 (w2LC)d2-2.48x10-3
215 (w2LC) 2d' - The negligible total modification is then -2,56X 10' or 0.26%. However, since C and R are known exactly and the term contains only them, they are small anyway, so they do not introduce inaccuracies.

But here we have about 20% inaccuracy or 5X10'
The revised value of becomes uncertain. At 700 touches, this is 0
．． This corresponds to a distance error of 35-. This is highly uncertain. (Roughly, since ×8 is also measured, it can be solved by separating the imaginary term in the above equation and giving two connected equations to solve d and L.)

At some low frequency, the return current has a very small impedance (very well filtered) in the circuit connected to ground.
The cable extends over a very large distance.

Owen Bridge (Figure 1) appears to be the most convenient for measurements. The generator should provide direct current modulated by alternating current. This bridge should isolate either the generator or the detector (preferably the former) from ground, and has a small capacitance to ground compared to the cable capacitance, but removes direct current from the sensing terminals.

At equilibrium: R5-RbCb/Ca L, -R, RbC.

Note: Arrangement to eliminate floating by knee-second equilibration, etc. (not shown).

A suitable value should be Ca convex C6-20 μF. The next Rb is approximately the same as the cable resistance.

For very long lengths of cable, the short circuit reactance has a capacitance that can be solved by including an inductance in series with the cable and performing -order balancing or by using a shearing bridge (FIG. 2). Due to the difference in impedance values, a high gain detector is required; however, this is feasible as the bandwidth can be made very small.

For accuracy, a replacement method is inferred. That is, R8
includes a variable standard resistance. -The next equilibrium is the sending end (Rb and R
a) made of short-circuited cables, cables included, and other balances (at R, and Ra).

Decreasing the value of R5 is the fault resistance: R8 should initially be even more than the fault resistance.

[Brief explanation of drawings]

Figure 1 is a diagram showing the Owen Bridge, and Figure 2 is a diagram showing the Schering Bridge. C...Capacitance, L...Inductance, R
...Cable resistance. Patent applicant St.C. BLC Engraving of drawings (no change in content) 〜・2・6゜Procedural amendment for drawings subject to amendment (method) % formula %

Claims (1)

[Claims] 1. A method for detecting a fault location in a relay communication cable, the relay including a surge protector to protect the power supply and signal repeater circuits from power surges, the method comprising: A modulated current in the electrical conductor at the terminals of sufficient polarity and amplitude to remove the power supply and effectively conduct the surge protector of the repeater in a low resistance state and at the same time reduce polarity effects in the event of a fault. and making a resistance measurement at the terminals of an electrical conductor within the cable. 2. The method of claim 1, wherein the current is modulated at a frequency of 30 Hz or less. 3. The method of claim 2, wherein the current is modulated at a frequency of 0.5 to 1 Hz. 4. The method of claim 2, wherein said resistance measurement is made via an Owen bridge. 5. The method of claim 3, wherein said resistance measurement is made via an Owen bridge.