Quality of the electrical supply on an electrical network

The electrical network must behave as an ideal source of voltage without any internal impedance, with sinusoidal output and constant voltage at all points of the power supply.

In practice, we see that these conditions do not always apply, basically due to two types of causes:

- Generators and the distribution system have a certain internal impedance which causes voltage collapses and losses in the distribution system.

- The loads absorb:

* transitory currents (start-ups and load connections)
* non-sinusoidal currents (non-lineal loads)

Sometimes the causes for the disturbances are external: atmospheric, all of which contribute negatively to the quality of the power supply.

This type of disturbance causes:

- An increase loss thus causing lower performance.
- Electromagnetic compatibility problems (EMC): poor operation or untimely stoppages to the system and cause significant efficiency losses to production systems.

Classification of network disturbances

The main parameters which may be altered by a disturbance include (as defined under standard EN 50.160):

- Frequency
- Amplitude: temporal, power surges, sub voltages, etc.
- Form of the Wave: harmonic
- Symmetry of the triphasic system

In the last few years, there has been great advances in the minimization of the effects of network disturbances on equipment supplied by them.

Especially in Europe, the required compliance with the European Community Electromagnetic Compatibility Directive, has meant a substantial improvement in the two aspects of disturbances:

• On the one hand, the limitation of the conducive and radiated transmitters from the disturbing apparatus, although those due to Telecommunication Transmitters, Atmospheric Discharges and the Exploitation of Commercial Networks continue to exist.

• On the other hand, the reduction in susceptibility of the equipment to the disturbances.

Despite the improvements, there will always be disturbances which cause failures and/or breakdown in equipment. What follows is a list of the most common effects.

Main kinds of Electrical Disturbances