Electrical energy is a product and, like any other product, should satisfy the proper quality requirements. If electrical equipment is to operate correctly, it requires electrical energy to be supplied at a voltage that is within a specified range around the rated value. A significant part of the equipment in use today, especially electronic and computer devices, requires good power quality (PQ). However, the same equipment often causes distortion of the voltage supply in the installation, because of its non-linear characteristics, i.e. it draws a non-sinusoidal current with a sinusoidal supply voltage (see Section 3.1 of this Guide). Thus, maintaining satisfactory PQ is a joint responsibility for the supplier and the electricity user. According to standard EN 50160  the supplier is the party who provides electricity via a public distribution system, and the user or customer is the purchaser of electricity from a supplier. The user is entitled to receive a suitable quality of power from the supplier. In practice the level of PQ is a compromise between user and supplier. Where the available PQ is not sufficient for the user’s needs, PQ improvement measures will be needed and will be the subject of a cost-benefit analysis (see Section 2.5 of this Guide). However, the cost of poor PQ usually exceeds the cost of measures required for improvement - it is estimated that losses caused by poor power quality cost EU industry and commerce about € 150 billion per annum.
However, electrical energy is a very specific product. The possibility for storing electricity in any significant quantity is very limited so it is consumed at the instant it is generated. Measurement and evaluation of the quality of the supplied power has to be made at the instant of its consumption. The measurement of PQ is complex, since the supplier and user, whose sensitive electrical equipment is also a source of disturbances, have different perspectives.
Standard IEC 038  distinguishes two different voltages in electrical networks and installations:
The main document dealing with requirements concerning the supplier’s side is standard EN 50160, which characterises voltage parameters of electrical energy in public distribution systems. This is a European standard but it is supplemented in some regions or countries by other supplemental standards, such as  in Germany, or  in Poland. Many regional codes, such as the German TAB  apply to an individual utility, but these are being unified as part of the liberalisation of the German electricity market. According to IEC 038, both standard EN 50160 and rules [3,4] concern the supply voltage, i.e. that measured at the point of common coupling.
On the user’s side, it is the quality of power available to the user’s equipment that is important. Correct equipment operation requires the level of electromagnetic influence on equipment to be maintained below certain limits. Equipment is influenced by disturbances on the supply and by other equipment in the installation, as well as itself influencing the supply. These problems are summarised in the EN 61000 series of EMC standards, in which limits of conducted disturbances are characterised. Equipment sensitivity to utility voltage quality, as well as mitigation measures, are presented in Section 3 (Harmonics) and Section 5 (Voltage Disturbances) of this Guide.
The subject of this section is a detailed presentation of standard EN 50160 and an analysis of its requirements according to the operation of chosen equipment. Methods of measuring supply voltage parameters are also presented.Log in to post comments