EA026530B1 - Device for cable fault localization by an acoustic method - Google Patents

Abstract

The invention is related to electric engineering, in particular, to devices for producing high-voltage current pulses for electric cable fault localization by an acoustic method. A device for cable fault localization by an acoustic method comprises a high-voltage DC source with a capacitor connected in parallel to its output, and a discharger connected in series between the capacitor and the defective cable conductor, and further includes an inductance coil connected in series to the discharger, and a resistor connected between the defective cable conductor and the cable sheath. The technical result of the invention is protection of the capacitor against overvoltage and against overcurrents during discharge, two-fold voltage increase at the place of the cable breakdown, lower acoustic oscillations along the cable route and in the zone of serviceable cable couplers, and stabilization of the preset current pulses repetition rate.

Description

The invention relates to electrical engineering, in particular to devices for creating high-voltage current pulses for finding the place of damage to an electric cable by an acoustic method.

A device is known for determining places of cable damage by an acoustic method, containing a high-voltage DC source with a capacitor connected in parallel with its output and connected in series between a capacitor and a faulty residential cable, a spark gap to create high-voltage current pulses (Handbook for setting up electrical equipment of industrial enterprises. Ed. M G.G. Zimenkov, G.V. Rosenberg, E.M. Feskova, M, Energoatomizdat, 1983, p. 83).

The disadvantages of the known device include the occurrence of dangerously large amounts of current in the capacitor when it is discharged, especially when the distance to the place of cable damage is several meters, which in some cases leads to failure of the capacitor. In addition, with increasing electrical strength (swimming) of the defective cable location, residual voltage from the previous discharge appears on its core, which leads to an unpredictable increase in the voltage across the capacitor for the next discharge. This can lead to a breakdown of the capacitor or require the use of a more bulky and expensive capacitor. An increase in the electric strength of a defective cable location (swimming) disrupts the rhythm of following the capacitor discharges, which also makes it difficult to find the place of damage. The usual rhythm (pace) of the discharges is one discharge for every 2-5 s. The disadvantages also include the occurrence at the ends of the cable sheath of a large value of pulsed high-frequency voltage (units - tens of kilovolts), accompanied by current pulses with a power of hundreds to thousands of amperes. In other words, the cable sheath at the time of discharge of the capacitor for a short time (tens to hundreds of microseconds) turns into a powerful generator (tens to hundreds of megavolt amperes) of high frequency. Since the ends of the defective cable sheath are metal-bonded to the sheaths of low-voltage cables under operating voltage, part of the capacitor discharge power from the sheath of the defective cable is transferred under certain conditions to the sheaths of low-voltage cables, creating large voltage drops on them (units - tens of kilovolts), accompanied by the passage of current into hundreds of amperes. In turn, the sheath of the low-voltage working cable is connected to the zero working core in a three-phase network with a dullly grounded neutral, through which consumers are fed and the appearance of a high-voltage pulse voltage on the sheath of the cable causes insulation breakdowns, which turn into short circuits in low-voltage equipment, which is accompanied by its damage.

The disadvantages of the known device include the appearance of false sound vibrations along the cable path above serviceable couplings, and due to the large voltage drop across the cable sheath at the time of the capacitor discharge from the cable sheath, spark discharges occur on closely spaced (fractions-millimeters) metal structures accompanied by sound vibrations falsely mistaken for the place of damage.

The objective of the present invention is to limit the discharge current of the capacitor to a value that is acceptable for the capacitor used and to optimize it in order to significantly reduce false acoustic sound signals over the cable path when searching for the place of its damage.

The aim of the invention is also the stabilization of the rhythm of following the discharges of the capacitor and its protection from an unacceptable voltage level when the cable is “swimming”.

Another objective of the present invention is to protect low-voltage consumers of a three-phase network with a 0.4 kV deadly grounded neutral by significantly reducing the level of the pulse voltage at the ends of the cable sheaths, which eliminates emergency situations and failure of consumer equipment when using the acoustic method of finding the place of cable damage.

The technical result of the invention is to protect the capacitor from overvoltage and from overcurrents when it is discharged, a significant reduction in the voltage drop across the cable sheath, an increase in voltage to a twofold value at the point of cable breakdown, a decrease in the level of sound vibrations along the cable path and in the area of serviceable couplings, as well as stabilization given rate of current pulses.

The goals and the technical result are achieved by the fact that the device for determining the cable damage points in an acoustic way, containing a high-voltage DC source with a capacitor and a spark gap connected in parallel to its output, connected in series between the capacitor and the defective core cable, additionally includes: inductance in series with the spark gap , and between the defective core and the cable sheath is a resistor.

The drawing shows a schematic diagram of a device for determining the location of cable damage by the acoustic method in accordance with the present invention.

The device for determining the cable damage points by the acoustic current method comprises a high-voltage direct current source 1, a capacitor 2 connected in parallel to its output, a spark gap 4 and an inductance 5 connected in series between the capacitor and the defective cable 3, and a resistor 6 connected between the cable and its sheath .

The device for determining the places of cable damage in an acoustic manner works as follows: 1 026530. A DC high voltage source 1 charges a capacitor 2, which is periodically discharged into a defective cable core through a spark gap 4, and electrical discharges occur at the cable defect site, which excite acoustic signals captured by the acoustic detector above the cable damage site. In this case, the inductance 5 limits the discharge current of the capacitor to an acceptable value, and the resistor 6 provides the discharge of the defective core of the cable by the time of the arrival of the next pulse from the generator.

Inductance 5 is selected in accordance with the maximum allowable discharge current of the capacitor. Its presence in the discharge circuit also makes it possible to increase the voltage in the defective place of the cable to a factor of two from the value of the discharge voltage of the capacitor in the case of swimming of the breakdown place of the cable.

In addition, the inductance 5 can significantly reduce the voltage drop across the cable sheath at the time of discharge of the capacitor. This voltage is so many times less than the discharge voltage of the capacitor, how many times the inductance 5 is greater than the inductance of the cable sheath. This significantly reduces the risk of an emergency in a functioning three-phase 0.4 kV network with a dull earthed neutral.

The value of the resistor 6 is selected from the condition that in case of increasing the electrical strength of the defective place of insulation (swimming), the cable core is completely discharged by the arrival of the next current pulse.

A significant reduction in the magnitude of the drop in the pulse voltage on the cable sheath reduces the likelihood of electrical discharges from the cable sheath to closely spaced metal structures and thereby eliminates acoustic signals that are falsely mistaken for damage.

Claims (1)

CLAIM A device for locating cable damage acoustically, containing a high voltage source of direct current with a capacitor connected in parallel to its outputs, a discharger, to the input of which a capacitor is connected, and an inductance selected in series in order to reduce the voltage drop on the cable sheath at the moment capacitor discharge, and a resistor connected to the inductance output parallel to the high voltage source outputs and selected so as to ensure be defective discharge cables to the time of arrival of the next pulse from the high voltage source.