Power quality is not a new issue, although in recent years, due to an increasingly technologically advanced and vulnerable world, it has become more and more of a focus.
The consideration and the limits of electrical phenomena are derived from the standardization of electromagnetic compatibility (EMC) of IEC 61000-x-x.
Figure 1 (source: EN 61000-2-2, Appendix A) Principle of electromagnetic compatibility. Consideration of limits for the emission of disturbances and immunity
Emission = emitted disturbance (A)
Immission = disturbance compatibility (B)
Since it is impossible either to prevent all disturbances of the power quality or to make all devices completely stable to these disturbances, limits for the emission of disturbances and for the stability are agreed. This is a principle established in the field of electromagnetic compatibility, which takes into account aspects of technical feasibility and cost-effectiveness.
Die EN 50160 definiert die Merkmale der Spannung in öffentlichen NS-, MS- und HS-Versorgungsnetzen (Messung am PCC). Die EN 50160 gilt bei normalen Betriebsbedingungen sowohl an der Übergabestelle zwischen öffentlichem Netz und Kunden als auch an der Übergabestelle von Energieerzeugungsanlagen zum öffentlichen Netz. Für Energieversorger und industrielle Netzbetreiber ist die Überwachung dieser Merkmale am Netzübergabepunkt und innerhalb des Netzes ein wichtiger Bestandteil der Betriebsführung. Wesentliche Kennwerte sind die Frequenz, die Spannungshöhe, die Kurvenform und die Symmetrie der Leiterspannungen.
Environment - compatibility levels for low-frequency conducted disturbances and signalling in public low-voltage power supply systems (measurement at the PCC - Point of Common Coupling)
Environment - compatibility levels for low-frequency conducted disturbances in industrial plants (for industrial and non-public 50 / 60 Hz LV and MV alternating current systems up to 35 kV) 3 environment classes (measurement at the PCC, internal connection points)
Environment - compatibility levels for low-frequency conducted disturbances and signalling in public medium-voltage power supply systems (measurement at the PCC)
Figure 2: Such statistical power quality evaluations prove required conformities or identify possible problems. However, one has to be careful. Such statistically averaged evaluations do not state that there were not any events during the respective period of time.
The industrial park has just been completed. All of the facilities and systems are modern and state-of-the-art. In planning and implementation, strict attention was paid to the fact that all devices and machines complied with EMC guidelines in relation to emission and immission. In addition, a statistical evaluation of the electrical grid parameters of the
EN 50160 standard confirms that all parameters stay in their specified ranges (example figure 2). Comprehensive energy monitoring acquires all of the consumption data.
The whole plant is working in an optimum fashion, energy efficient and breaks down twice a week.
This phenomenon is no isolated occurrence. Operators mostly face an enigma. Despite careful planning and compliance with all provisions, serious disturbances occur which cannot be identified by any of the measuring equipment used. The reason is to be found in the complexity of today‘s facilities. The addition of disturbance levels leads, in the worst case, to an impairment of the plant (see figure 1). As grid phenomena occur only occasionally, they do not affect the statistical overall evaluation which, in total, leads to a wrong assessment of plant reliability. At this point, potential problems can be quickly identified by targeted measurements and corresponding activities initiated.
Figure 3: Voltage dips
Excerpt from EN 50160
Figur 4: Fields of application power quality monitoring
The common standards determine the voltage quality at the transfer point (PCC) of the utility to the grid user. The measurement at the PCC is used to check and comply with standards
(e.g. EN 50160) and contracts between energy provider and energy consumers.
Due to the continuous monitoring, a deterioration of the power quality can be detected early on and causes can be sought. The effectiveness of measures taken can be checked directly.
The IEC TR 63191 technical report DSPQ describes the phases that are necessary for the creation of a consumer-side power quality measurement plan for buildings and industrial facilities.
Such a power quality measurement plan enables the optimization of energy availability and efficiency and improves the lifetime of plants. If power quality phenomena are already present, it facilitates the diagnosis and correction of these quality problems.
Figure 5: Detecting problems before they occur
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