Main kinds of Electrical Disturbances

Spikes and Notches

Two types:

• Those produced by induction of atmospheric discharges (lightning) to airlines.
• Those produced by abrupt variations in the load current, connections-disconnections of inductive or capacitative loads.

Effect: When they pass the anticipated limits, they produce break-downs in the isolations and semi-conductors.

Dropouts

These are deep or total collapses, lasting a few milliseconds. There are two different causes:

• Short-circuits at the point of consumption, freed later by the corresponding protection.
• Interruptions in the supply produced by the commutation of lines and discharge of protective devices with automatic pickup.

Effect: In equipment with memory or logical functions, a power outage (even if it lasts just a short time) often cause functional failures. IT equipment in general is very sensitive to these disturbances, which can cause an incalculable loss of information.

Over Voltages: Temporary (Surges)/Long-Lasting

Short/long-term over voltages due to a load reductions on networks with mediocre regulation (high impedance).

Effect:

They cause several problems to all kinds of equipment and installations:

• In lighting installations, they reduce the life of the bulbs.
• In IT equipment, they produce failures in the power supply and monitors.

Sub-Voltages: Temporary (sags)/Long-Lasting

These are short-term voltage collapses due to momentary or permanent overloads on the network.

Effect:

• Motor-driven induction machines reduce their speed and increase consumption.
• The lighting installations with discharge lamps have dark spots.
• System stoppages upon entering the minimum voltage work station.

Gradual and prolonged sub voltages (Brownout)

A progressive collapse for various seconds, which often ends in a total supply failure. These are produced when there are strong disturbances in the exploitation of the networks and central energy producers. (Lack of power, loss of synchronism, etc.).

Efecto: same consequences as an outage or dropout.

Failed Power Supply (Blackout)

A total failure generally due to the untimely activations of a distribution network protection device.

Effect: The power outages inevitably stop the equipment unless they possess their own exterior independent energy system.

But when the stoppage is produced in an untimely way, dangerous situations can come about as far as the safety of people and things, or also the loss of very valuable information (as is the case of IT equipment).

Current and/or voltage harmonics

Certain receivers consume non-lineal loads, that is, harmonic currents. These currents produce harmonic voltage collapses which modify the sinusoidal voltage wave originally produced (in the power station alternators).

Highly frequent disturbances

These are high frequency signals that superimpose the power supply voltage. They may consist of any defined frequency or broad band signal; stationary, flashes or repetitive impulses.

They are the result of undesirable couplings to the commercial network lines with apparatus that use high frequency technology or commutation. According to the type of coupling, they can take on a common mode or differential mode form.

Effect: These disturbances can cause all kinds of equipment failures: from operational failures to permanent damage.

Frequency Variations

The interconnected continental commercial networks (as is the case with most of the European ones) supply an almost invariable frequency which is very close to nominal frequency. This is because it is controlled through a mega-system which includes a very large number of synchronized machines, with an enormous overall strength and an almost infinite inertia.

On the contrary, on many islands and in other isolated areas or at independent installations with small electrical stations (or electrogen groups) substantial frequency variations are often produced. The variations are practically inevitable when there are connections or disconnections of comparable strength to the total strength of the system.