Grid Power Quality

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Power-quality problems, including such issues as voltage irregularities and harmonic disturbances, can cause problems with a facility’s equipment and operations. Standards have been developed to help address this issue by defining the voltage characteristics customers can expect from the electricity supplied by public utilities. Additionally, larger utility customers often have contractual agreements with their utilities that can further specify supplied-power requirements. Power quality instruments (PQIs) are great tools for verifying that these requirements are being met.

The European CENELEC Standard EN 50160, “Voltage Characteristics of Electricity Supplied by Public Distribution Systems,” and International Electrotechnical Commission (IEC) technical specification IEC/TS62749, “Assessment of Power Quality – Characteristics of Electricity Supplied by Public Networks,” define allowable tolerance ranges for a number of power characteristics. Compliance to these standards and any related contracts, can be ensured through the use of PQIs installed on both sides of the customer’s meter. Figure 1 illustrates such an installation.

Verification of compliance can be ensured only with well-defined measurement functions, providing matching or comparable results. IEC 61000-4-30 specifies a class A measurement method and a class S measurement method that read:

Class A: This class is used where precise measurements are necessary, for example, for contractual applications that may require resolving disputes, verifying compliance with standards, etc. Any measurements of a parameter carried out with two different instruments complying with the requirements of Class A, when measuring the same signals, will produce matching results within the specified uncertainty for that parameter.

Class S: This class is used for statistical applications such as surveys or power quality assessments, possibly with a limited subset of parameters. Although it uses equivalent intervals of measurement as Class A, the Class S processing requirements are much lower. Some surveys may assess power quality parameters of several measurement sites on a network; other surveys assess power quality parameters at a single site over a period of time, or at locations within a building or even within a single large piece of equipment.

System designers and specifiers also need to be aware of one complementary – and key – standard, IEC 62586-1, “Power Quality Measurement in Power Supply Systems – Part 1: Power Quality Instruments (PQI)” as well as IEC 62586-2, “Power Quality Measurement in Power Supply Systems – Part 2: Functional Tests and Uncertainty Requirements.”

This standard provides testing methods to ensure compliance of measurement functions to IEC 61000-4-30 specifications.

Additional standards and regulations that apply in grid power quality applications are shown in Table 1.

Table 1-Grid Power Quality Set of Standards

If you are looking for more details, you can check out the following documents:

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