EA008653B1

EA008653B1 - Communication cable and method for controlling sheath integrity thereof

Info

Publication number: EA008653B1
Application number: EA200501606A
Authority: EA
Inventors: Вадим Юрьевич Гужвин; Александр Иванович Васильев
Original assignee: Тоо Казцентрэлектропровод
Priority date: 2005-11-11
Filing date: 2005-11-11
Publication date: 2007-06-29
Also published as: EA200501606A1

Abstract

The invention relates to cable engineering, in particular, to communication cables for use in telephone communication lines for determining and detecting location of cable sheath damage. For detecting the location of cable sheath damage there proposed to use coaxial conductors embedded into the cable sheath isolated therebetween by the sheath material or a special insulation layer, one of them is earthed and the second is under high constant voltage relative to the other. There are several embodiments to use the device. The leakage current between the coaxial conductors is measured for controlling sheath integrity. In case of sound cable sheath, the current in conductors is stipulated by the insulation current leakage between them and is 1 mkA. When the cable sheath of the inner insulation layer is damaged, there happened an electric breakdown of an air gap between the conductors forming a conducting path on the insulation surface, the current appears in the chain, exceeding hundred times the current leakage signaling the cable damage. The resistance between points A, B, C, D is measured for detecting the location of the cable damage when the conductors are closed (fig.1). By the formulathe relation of the cable length from its ends to the damage location is determined independently from a contact resistance in a closure location. The electrical capacities are measured between the points A, B, C, D for detecting the cable damage with breakdown of one or both more conductors by the formula:the relation of the cable pieces length from its end to the damage location (drw.4).

Description

The invention relates to cable technology, namely to the wires of communication and is used on telephone lines.

During the operation of cable lines there are frequent cases of damage to the cable sheaths. To control the integrity of the sheaths, there is a way to put cables under excess air pressure, which in practice does not allow to quickly determine the resulting integrity violation of the cable sheath, since the pressure change due to air leakage propagates along the line at a speed not exceeding 1 km per day, and damage site is generally impossible. The authors of the present invention do not know the analogs that allow promptly and with high accuracy to determine the occurrence of damage and its location.

To detect damage to the cable sheath, it is proposed to use coaxial conductors embedded in the cable sheath, insulated between them by a sheath material or a special insulation layer, one of which is grounded, and the second is at a high constant voltage relative to the other.

There are several ways to use the device.

To control the integrity of the shell measure the leakage current between the coaxial conductors. When the cable sheath is intact, the current in the conductors is caused by the leakage current of the insulation between them and is no more than 1 μA. When the cable sheath is damaged in the inner insulating layer, an electrical breakdown of the air gap between the conductors occurs with the formation of an electrically conductive track on the insulation surface, while a circuit produces a current exceeding the leakage current hundreds of times that will signal cable damage.

To detect the damage of the cable when the conductors are closed (Fig. 1), resistances between points A, B, C, are measured. According to the formula

AB ⁺ AC ⁺ & CP ⁺ ^ BP / 1 \ & AB ~ ^ AC ⁺ & CP ⁺ BP determine the relationship of the cable length from its ends to damage, regardless of the contact resistance at the circuit.

To detect cable damage when one or both of the conductors are broken (Fig. 2), capacitances between points A, B, C, Ό are measured. According to the formula

(Fig. 4) is the determination of the ratio of the lengths of the cable segments from its ends to damage.

A possible example of the practical implementation of the proposed device is shown in FIG. 3, where 1 is the polyethylene cable sheath, 2 is the outer coaxial conductor, 3 is the inner extruded polyethylene layers, 4 is the middle, 5 is the inner coaxial conductor, 6 is the waist insulation of the core, 7 is the shield wire, 8 is the cable core. Coaxial conductors are made of alumopolymer film. For electrical safety purposes, the inner and outer conductors have zero ground potential. A high DC voltage is applied to the middle conductor.

The proposed method of using the device with a device for monitoring the integrity of the cable sheath and detecting the place of its damage is shown in FIG. 4. The central controller controls the P1C controllers with switches, which, depending on the operating mode, connect to the monitored layers of the capacitance measuring blocks (blocks C), the electrical resistance meter (blocks K), and the high voltage block. The signals from the blocks enter the processor directly or through P1C controllers. The controller processes the signals from the blocks and outputs the results and an alarm to the indicator block.

In the protection mode, the electrical resistance of the outer alumina polymer layer is measured and the leakage current in the middle alumina polymer layer is measured against the effects of high voltage (4000 V). When changing any of the values, the controller issues an alarm signal to the indicator, switches off the high voltage unit with the switch and switches to the fault location mode. In the mode of determining the location of damage, the processor alternately through the switch makes connection to the line of blocks K and C, receives measurement results from them, calculates the nature of the damage and the distance to the damage. The processor then provides information on the nature of the damage and the distance to the damage site to the indicator. After the elimination of cable damage, the device is transferred to the protection mode.

Claims

CLAIM

1. Communication cable containing core, insulation and sheath, characterized in that tubular conductors coaxial with respect to the core and relatively to each other are mounted in its sheath, with the specified conductors being insulated from each other by a sheath material or a special insulation layer and are under high constant voltage relative to each other.

2. The method of monitoring the integrity of the cable sheath according to claim 1, containing the following steps:

- 1 008653 supplies high voltage to coaxial conductors and measures the leakage current between these conductors.

3. The method according to claim 2, which consists in the fact that in the case of insulation breakdown between coaxial conductors, according to the results of measuring leakage currents, calculate the distance to the place of damage.

4. The method according to claim 2, which consists in the fact that when one or both coaxial conductors are broken, electrical capacitances are measured between the conductor connection points and the distance to the fault is calculated.