Causes of damage to cable and overhead power lines

Damage to cable and overhead power lines is one of the most common causes of emergency situations in electrical installations. Very often, an accident of the power line becomes the cause of more serious damage - an accident of the distribution equipment of the substation. Consider the main causes of damage to cable and overhead power lines.

Relay protection devices designed to protect equipment, including power lines, from damage as a result of emergency situations: short circuit, overload, ground fault. If for one reason or another the protective device does not work, in the absence of redundant protection, the equipment of the switchgear or the outgoing cable (overhead line) is damaged. That is, the first cause of power line failure can be identified — failure of relay protection devices.

The above reason may also be due to a malfunction of the protection device, for example, due to a software failure of the microprocessor protection terminal, failure of one of the electromechanical protection relays, or due to an incorrect selection of the protection operation setting.

The next reason is a violation of the integrity of the insulation: insulators of overhead power lines, cables... The main reason is the natural aging of the insulation.

Damage to power lines due to insulation failure occurs mainly on equipment that has leaked. Another reason for breaking the integrity of the insulation is mechanical damage or long-term operation of the line in overload mode.

Here are some examples of power line damage due to the above reason.

The cable line can be damaged if it is accidentally caught by the tractor during digging. A cable that does not have a protective sheath can be damaged by rodents. On the overhead power lines, due to excessive contamination of the strings of the suspension insulators, a phase overlap to ground occurred, resulting in a line failure.

The next reason for the failure of power lines is exposure to aggressive environmental conditions, bad weather conditions... Aggressive environmental conditions include excessive decrease or increase in air temperature, increased pollution, exposure to chemicals, etc.

In terms of weather conditions, the main causes of power line damage are: strong wind, storm, snowfall, wire icing, lightning. For example, as a result of a strong wind, a tree fell on an overhead power line and broke the wires.

The cable is laid in a room where aggressive chemicals are stored openly, and their periodic impact on the cable leads to destruction of its insulation. As a result of the lightning strike and the destruction of the arresters, a surge occurred, which led to damage to the power lines.

In addition to lightning (external) overvoltages, there are switching (internal) overvoltages that occur due to sudden load spikes, with ferroresonance phenomena, when removing and applying voltage to the power line. If there is no surge protection in this section of the power line, for example, due to damage to surge arresters installed on this line, then if a surge occurs, the power line will be damaged.

Damage to the power line due to overvoltage is due to the fact that the insulation of this line is designed to work at a certain voltage value, and when the voltage increases significantly, the insulation breaks down, resulting in a short circuit and possible damage to the power line.

The next reason why cable or overhead line damage can occur is personnel errors during line installation, including the presence of defects in end fittings and connectors. There are also cases where power lines are damaged due to manufacturing defects.