RU2110075C1 - Process of location of fault in cable line - Google Patents

Abstract

FIELD: electrical engineering. SUBSTANCE: distinguished feature of proposed process consists in formation of magnetic field of invariable polarity by electrostatic machine in cable. This field is traced along route and disappearance of magnetic field above point of fault is registered by device measuring magnetic values, for instance, by ferroprobe tesla meter. EFFECT: increased accuracy, reduced consumption of materials, diminished time of search for location of fault, simplified process of search. 2 dwg

Description

 The invention relates to the electric power industry and can be used for topographic determination of the location of damage to cable lines.

 There are various methods (methods) for determining the location of damage in electrical networks and communication cables, which are divided into two groups: relative, allowing you to approximately determine the distance from the measurement location to the location of damage (pulsed, vibrational discharge, wave, loop, capacitive, high-frequency), and absolute, indicating the place of damage directly on the track (acoustic, induction, induction-switching, contact, etc.).

 At the same time, at least two methods must be used: relative and absolute, since the first ensures the speed of determining the damage zone where the operator should go, and the second specifies the excavation site on the highway [1, p. 8-9].

Common disadvantages of the known methods for determining the location of damage are:
- the dependence of search results on the experience and qualifications of the operator;
- the complexity and high cost of the applied equipment and methods for determining the location of damage;
- significant time (3-5 h) for troubleshooting;
- the need to burn the insulation of the cable cores to a transition resistance of less than 100 Ohms, which reduces the service life of cable lines.

 The most universal is the acoustic method, but it cannot be applied on cables that do not have holes in the sheath at the place of damage, if the cable lies at a depth of one and a half or more meters, if there is a sound-absorbing medium in the ground above the place of damage, if there is a strong metal bridge at the place of damage, as well as with high insulation of dangling conductors and with a small capacity discharged to a damaged cable.

The disadvantages of the methods of the overhead frame and induction-switching are the requirements:
- a large amount of earthwork for excavating pits;
- the presence of a metal circuit between the core and the cable sheath;
- complex preparation for measurements, etc.

 The pulse-induction method is complex, inaccurate, imperfect; contact (potential) methods are unreliable, acceptable only for an opened cable, therefore both of them did not get distribution.

 The closest technical solution for determining the location of damage to cable lines to the claimed (prototype) is an induction method based on the principle of capturing changes in the magnetic field above the cable, through which current is passed from the sound frequency generator. In this case, an alternating magnetic field is formed around the cable, the intensity of which is proportional to the current in the cable. On the surface of the earth above the cable with the help of an induction frame, an amplifier and a telephone, you can trace the field that propagates along the current path through the cable [2, p. 247-266].

The method adopted for the prototype, characterized by all of the above disadvantages. In addition, for its application certain conditions are required:
- firstly, it is necessary to have two broken wires so that the sound of the audio frequency goes through one core to the point of breakdown and returns to the source (generator) along the second core of the cable;
- secondly, to have a small (on the order of 0.2-0.3 Ohms) transition resistance at the breakdown site.

 But to achieve such a transition resistance by burning through the insulation, a lot of time is required and it is not always possible to achieve it (for example, when the cable is very wet). In this case, the current will go only partially through the breakdown location and will spread far behind the damage in the form of a capacitive current. Therefore, the signal will not abruptly break off at the point of breakdown, but will be tapped with a gradual attenuation [3, p. twenty].

 Thus, the induction method gives positive results only when the circuit between the conductors, and the most common type of damage (97-98%) is the closure of the core to the shell [1, p. 6].

 Therefore, determining the location of damage to cable lines remains a complex technical problem.

The aim of the invention are:
- increase the cable resource by eliminating the auxiliary operation of burning when determining the location of damage;
- reduction of time to search for a place of damage;
- improving the accuracy of measurements;
- simplification of the applied search techniques and equipment;
- reduction of material costs for determining the location of damage and restoration of energy supply to consumers.

 The goal is achieved by significantly simplifying the pattern of current spreading at the site of damage by eliminating the capacitive current behind the site of damage when using a high-voltage DC generator.

 The essence of the invention lies in the fact that when a damaged cable core is connected to an electrostatic machine of sufficient power, the current flowing through the cable creates a magnetic field, which is captured along the track using an induction sensor or other device for measuring magnetic quantities, and the place of damage is determined by the disappearance of the magnetic field as for multiphase and single-phase damage.

 A patent search showed the absence of methods for determining the location of cable damage with the proposed set of features.

 Thus, in this case, the known operations and elements are combined with new sequential connections, are used for a new purpose and give the proposed method new properties, manifested in positive effects, as a result of which the solution can be recognized as having significant differences.

 In FIG. 1 shows a circuit diagram of a magnetic field in a cable during single-phase damage; in FIG. 2 is a circuit diagram of a magnetic field in a cable during multiphase damage.

 As seen in FIG. 1, when searching for single-phase damage, a single-wire magnetic field is caused by the flow of current from an electrostatic machine (ESM), which is concentrated in the damaged conductor to the place of damage (MP), and after the damage becomes even not distributed, but scattered. Since the magnetic field strength is proportional to the current in the cable behind the damage site due to the change in its strictly concentrated character to scattered due to spreading in all directions, the magnetic field is no longer traced by a device for measuring magnetic quantities (for example, an induction frame), which has a finite sensitivity.

 In principle, it doesn’t matter whether we encode the current of the electrostatic machine at an audio frequency or we listen to breakdown discharges through the place of damage. This is important only for changing (increasing) the sensitivity of devices recording changes in the magnetic field strength above the cable, in the place of damage and behind it.

 As is known [2, p. 255], the field strength created by a single current is many times (30-100) higher than the field strength of a pair of currents. Consequently, the guaranteed reception of the field disappearance signal behind the damage site can be provided either by a multiple of a smaller power of the electrostatic machine, or by a significantly lower amplification of the signal perceived by the device for measuring magnetic quantities over the cable.

 The electrostatic machine is not only a source of high voltage, ensuring the flow of current through the place of damage at any transition resistance without burning insulation, but also an adjustable source that allows you to choose the most effective search modes.

 Thus, in contrast to the prototype, where with a single-phase short circuit, the magnetic field behind the damage site does not disappear, but decreases linearly, following the Biot-Savart law [1, p. 50, 51], with a single-wire power supply to the damaged core from an electrostatic machine, the place of damage can be clearly fixed by the disappearance of the magnetic field.

 In this case, the time to search for the damage site will be determined only by the time the operator moves along the highway from the connection point of the electrostatic machine to the damage site, even if it is not possible to use relative methods for determining the location of damage, and there is no need for expensive bulky and fire hazardous equipment for burning insulation.

 It should be borne in mind that when using the proposed method, it is possible in principle to double-check the search results (without changing the cable connection diagram) using a stethoscope (due to the presence of the accompanying acoustic effect of a high-voltage discharge at the site of damage) and electromagnetic pulse sensors of any design with light or sound indication.

 As for the search for multiphase damage (Fig. 2), the circuit for switching on the electrostatic machine, in principle, may not differ from the circuit for switching on the sound frequency generator [1, p. 48], used in the prototype, but the need for the preparatory operation of burning insulation, of course, disappears, ie also more rational.

 The above applies to any cable lines, including communication lines.

Sources of information:
1. V.S. Dementiev, V.K. Spiridonov, G.M.Shalyt "Determining the location of damage to power cable lines." Gosenergoizdat, Moscow-Leningrad, 1962

 2. G.M.Shalyt "Determination of places of damage in electrical networks." Energy Publishing House, Moscow, 1982

 3. I. Chilovsky "Development of the induction method of finding the place of cable damage." Power Engineer N 2, 1962

Claims (1)

 A method for determining the place of damage of cable lines, according to which a current is passed through the cable, the magnetic field of this current is captured along the cable path using a device for measuring magnetic quantities, and the place of damage is determined by the disappearance of the magnetic field, characterized in that the current in the cable is created by connecting it to a damaged one veins to an electrostatic machine.

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