8.3 Types of damage and determination of their nature

Causes of violation of signal transmission over communication lines (if we talk about linear devices) can be either changes in the parameters of the lines themselves, or distortion of signals due to the effects of neighboring communication circuits, or interference due to extraneous influences (from power lines, electrified railways, radio stations, atmospheric discharges, etc.)

In this chapter, only damages to the lines themselves are considered: an open circuit, a decrease in insulation resistance between the wires or between the wire and ground, incorrect connection of the wires (interchange of the wires in cable circuits), the occurrence of a significant DC asymmetry of the circuit (for example, junction of wires). The nature of the damage to the linear wires is determined by agreement with the neighboring station on the establishment of a short circuit mode of this circuit (to check whether there is an open circuit) or idling mode (to check the insulation condition)

In the case of satisfactory values ​​of Rкз and Rхх (the latter both between the wires, and for each wire relative to the ground), the value of ohmic asymmetry is checked by the previous scheme. Incorrect connection of wires in the intermediate point can lead to a sharp change in the values ​​of Rкз and Rхх and to the appearance of significant mutual influences between the pairs.

Depending on the equipment available, the distance to the fault can be determined by measurements on direct current, alternating current and pulse method. In many cases, the damage site is determined first, and then the location of the damage is ascertained from the end of this site. For measurement using DC, a variety of bridge circuits are used. The methods using alternating current and the impulse method are based on fixing the time it takes for the electromagnetic wave to reach the point of damage, i.e., the heterogeneity of the circuit.