• Gossen Metrawatt
  • Camille Bauer

Standards

Relevant standards when considering the power quality

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.

Principle of electromagnetic compatibility

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.

EN 50160: Voltage characteristics in public power supply systems

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.

IEC 61000-2: Evaluation of the quality of an electrical grid

IEC 61000-2-2

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)

IEC 61000-2-4

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)

IEC 61000-2-12

Environment - compatibility levels for low-frequency conducted disturbances and signalling in public medium-voltage power supply systems (measurement at the PCC)

Compilance report EN50160.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.

Measuring, recording and evaluating power quality

Test and measuring procedure – IEC 61000-4-X

  • IEC 61000-4-30 Ed. 3:
    Power quality measuring procedure.
    Acc. to chapter 5.9.1 „Measurement method“:
    Measurement up to the 50th harmonic (bandwidth of 2.5 kHz at 50 Hz,
    requires a minimum sampling rate of 5 kHz).
  • New items of IEC 61000-4-30 Ed. 3 as compared to IEC 61000-4-30 Ed. 2
    + Current measurement is obligatory for Class A devices
    + Recording of level, imbalance, harmonics and interharmonics of currents in the same interval as the pertaining voltage channels
    + Measuring procedure for rapid voltage changes (RVC) has been added
  • IEC 61000-4-30 Klasse
    Measuring instruments according to IEC 61000-4-30 Class A provide measured values comparable across measuring instruments and manufacturers. Measured values of Class S measuring instruments cannot be considered comparable anymore.
    • IEC 61000-4-7
      Guideline to measure harmonics / interharmonics
    • IEC 61000-4-15
      Flicker meter design specifi cations

Everything is OK - the plant breaks down

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.

Voltage dips

Figure 3: Voltage dips

Excerpt from EN 50160

  • At least 95 % (LV) or 99 % (MV) of all 10-minute average values of the supply voltage effective value must range within the limits stated
  • No 10-minute average value of the supply voltage effective value may range outside of the limit of +10 %/ -15 % Un (LV) or ±15 % Uc (MV)

Areas of application of power quality monitoring

Areas of application of power quality monitoring
Figur 4: Fields of application power quality monitoring


Normative power quality monitoring at the PCC

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.

Power quality measurement in the field or in the application

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.

 

Monitoring the power quality on the demand side
Figure 5: Detecting problems before they occur

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