Increasing availability of LV electrical networks

Faults and disturbances in low voltage networks

The short-circuit

Short-circuits are normally caused by accidental contact between two power or earth conductors. A phase-to-earth insulation fault is equivalent to a phase-to-neutral short-circuit in TN.S earthing systems.

The major fault categories are:

1. Short-circuits
2. Overloads
3. Insulation loss.

The major disturbance categories are:

1. Leakage currents
2. Surges
3. Harmonics.

Rodents can survive for a number of months, without water, feeding only on the electrical cables placed in busbar trunkings. Crawling animals, that are longer, can bring two live parts of an electrical installation into contact.

Routings of mobile cables such as those of travelling cranes, robots and automatic machines are frequently affected by short-circuits resulting from crushing or tearing or from ageing of the electrical conductor insulator. During earthwork, excavators and mechanical machinery can sever all types of electrical power supplies.

The overload

The causes of tripping of protection devices due to overloads in an electrical installation are many.

However two main causes can be identified:

1. The electrical installation changes over time and nominal current is exceeded when the number of loads increases. This is for example the case of an increase in machine installed base, number of workstations, terminals, amount of traffic, etc.

2. Loads consume more current than normal due to a malfunction, for example: clogged lifting pumps, obstructed ventilation systems, overloaded or incorrectly serviced traversers, improperly adjusted or maladjusted systems, deterioration over time of parameters leading to reduced efficiency generating increased power, etc.

AUTHOR: Schneider Electric experts