INTRODUCTION TO POLLUTED NETWORKS

Technological advance, experienced in the last period, has incorporated to the market electronic elements with higher performances and smaller size. This reduction in the size of the devices has meant that the power supplies of these devices achieve power density ratios (measured in watts per cubic inch) unimaginable just a few years ago.

The mentioned devices use internally to operate, switching topologies and power semiconductors which work at high frequencies. These technologies allow handling large powers in very small sizes.

The great disadvantage of these devices is derived from using that such equipments are doing of power supply. Using semiconductors devices, both controlled (IGBT, MOSFET, TRIAC, etc.) and uncontrolled (diode rectifiers) causes a consumption of switched and non-linear loads, which views from the supply side generate high degree of electrical pollution.

We will denominate, therefore, electrical pollution the totally circumstances due to the high harmonic content on the sinusoid corresponding to the main frequency of electrical installation, without prejudice to other phenomenon comprehended by what is called power quality or power supply quality.

To illustrate the polluted phenomenon of low voltage electrical networks, the phase current waveforms in bus bar inside GLVB of a Hotel in Madrid are presented.

Although it may seem that the poor wave quality in an electrical system is determined by the quality of supply, in most cases this is not so, and pollution of the network produces the contrary, from the loads up to supply.

This is because a pure supply without disturbances, to undertake an inner low voltage electrical installation (in which receptors are formed by elements with non-linear loads, switched, or generative harmonics) causes a disturbed current regarding to a voltage sinusoid. Because the impedances of power supplies, this current causes disturbed voltage drops along whole route, from the distribution and transformation centers up to supply points, after in some cases, the disturbances are exported from the loads up to the distribution company and the rest of subscribers connected to TC.

Such as collected in the Standard UNE_EN-50160: 2011, “Voltage characteristics of electricity supplied by public distribution systems”, the source of pollution in the indoor facilities is clearly the behavior of the loads connected to the network. The standard cites literally:

Also, in the same standard, in relation with the quality of electricity supply, the mainly following disturbances are identified :

• Conducted disturbances.
• Flicker of different severity.
• Frequency drift.
• Harmonic voltage (up to the 40th harmonic).
• Total harmonic distortion of the supply voltage.
• Fast voltage range.
• Power interruption.
• Voltage dips.
• Transient overvoltage.
• Voltage fluctuations.
• Voltage unbalance.

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