SU1644288A1 - Device for protection of communication lines against atmospheric overvoltage - Google Patents

Abstract

The invention relates to telecommunications. The purpose of the invention is to provide protection against breakdown of insulation between cable metal sheets formed by armor and sheath while protecting armored cable lines from direct lightning strikes to armor and preventing cable leakage. The primary winding of the transformer is included in the cable metal cable breakdown. Between the conductors and metal sheets of the cable, on the incoming side of the surge wave, gaps are inserted, in the control circuits of which the secondary winding of the specified transformer is switched on. 1 з.п f-ly, 1 silt

Description

The invention relates to telecommunications and can be used to protect sections of cable lines, such as river cable crossings, or to be used as a first stage of protection of wired terminal equipment.

The aim of the invention is to provide protection against breakdown between cable metal sheets formed by the armor and the sheath while protecting armored cable lines from direct lightning strikes to the armor and preventing cable leakage.

The drawing schematically shows the proposed device.

The arresters 1 are connected between the conductors of the line, namely, the conductors 2 and the combined brooms, cable glands, formed by armor 3 and sheath 4 at point 5. At the same point 5, grounding terminal 6, the secondary winding 7 of the step-up transformer, is connected, which through current-limiting resistors 8 connected to the clamping gaps of the controlled protective gaps 1, as well as the first terminal 9 of the transformer primary winding 10, the second terminal 11, which is connected to the joint metal coatings of the cable at point 12 from the protected part of the cable l

The device works as follows.

The lightning current wave incident on the metal-covering of the cable at point 5 is divided into three currents: AND, 2, C. The current li flows to the earthing switch 6, the current 2 flows through the primary winding 10 of the transformer and further along the metal sheets of the cable; the current s flows through the secondary winding 7 of the transformer, the current-limiting resistors 8, the interelectrode capacitances of the arresters 1 through the conductors 2 Due to the fact that the impedances of the circuits, where the currents h and h flow, are much greater than the resistance of the earthing,

H iz; And s

Therefore, the amount of current in the metal ducts of the cable in the protected area of the cable will be in

Qs

J

N5

00

Z3 / (Z3 + Zi + ZB)

times less than in the absence of a ground voltage b, where Z3 is the impulse resistance of the earth conductor b, Z4 is the reactance of the primary winding of the transformer; ZB is the characteristic impedance of the cable-to-ground circuit. This leads to protection from the current wave of lightning.

The current 2 flowing through the primary winding 10 of the transformer energizes the secondary winding 7 voltage U, which is applied to the ignition electrodes of the arresters 1. The transformer transformation ratio is chosen so that when a current of dangerous magnitude appears in the metal cables, the voltage U is sufficiently large for the breakdown of the intervals between the ignition electrodes of the arresters.

The ionization of the internal space of the arresters leads to a more than tenfold decrease in the voltage of the triggering between the main electrodes of the arresters and they operate almost simultaneously from the voltage wave propagating in the core-sheath circuit. This ensures the elimination of overvoltages in the core-sheath circuit. Combining the armor and the shell in the places of their ruptures and installing a grounding conductor prevents insulating breakdown between the shell and the armor and prevents the cable from leaking. Simultaneous triggering of arresters prevents the occurrence of overvoltages between cable cores.

During repair work, when the cable insulation is tested with a constant voltage less than the threshold (static breakdown voltage) of the arresters, the arrays do not work and do not interfere with the measurement. This eliminates the need to shut off dischargers for the duration of the repair and reduces the labor intensity of the repairs.

Claims (2)

1. A device for protecting lines from atmospheric overvoltages, containing a step-up transformer, the primary winding of which is included in the discontinuity of the conductor of a line exposed to atmospheric overvoltages, and the secondary winding of which is connected to the firing spark gap of a controlled protective discharge connected between the forward and reverse conductors of the line section located from the side of the atmospheric wave overvoltages the place where the transformer primary winding is connected, characterized in that, in order to provide protection against isolation between cable metal sheets formed by armor and sheath, while protecting armored cable lines from direct lightning strikes to armor and preventing cable depressurization, the sheath of the protected the cable is also made with a gap at the point of breaking the armor cable, cable envelope areas before and after breaking are connected to the corresponding cable armor sections at the connection points to the armor terminals of the primary winding of the specified transformer, to the common armor point and the casing from the side of the armor area exposed to atmospheric overvoltages, an additional earthing switch is connected The reactance of the primary winding of the transformer is selected by a large characteristic impedance between the metal-clad cable and ground. 2. The device according to claim 1, of which is in order to reduce the labor intensity repair work during cable insulation tests, the static breakdown voltage of the protective armature is chosen greater than the electrical strength of the cable insulation,